Duramax diff fluid

Duramax diff fluid DEFAULT

2500HD diff fluid replacement

B&B;530232 said:

Front diff:

80W-90 or any GL5 rated gear oil. Upgrading to full synthetic isn't a bad idea if you dont mind the extra expense.

Rear diff:

75W-90 synthetic No additives necessary, G80 or not.

Transfer case:

Dexron III ATF is the factory called fluid. A better alternative is Royal Purples Syncro Max MTL fluid. Solves the problem that these T-cases have with vaporizing the ATF and expelling it from the vent hose.


Just because a truck is equipped with push button 4X4 doesn't make it "auto" equipped. The AutoTrac fluid is for the 1/2 tons equipped with the actual on demand AutoTrac T-cases.

Click to expand...

Not to seem dumb, but can I ask what GL5 stands for? I'm going to hit up the local parts store today to buy some supplies and get this done this week.

Also, I'm just curious as to why so many limited slips diffs need an additive and mine does not? Sorry to be so quick to respond, but I am just curious because I need this truck lasting a few more years for me and am pretty anal about things... If i don't know how it works, I try to figure out everything I can about it before touching it.

And about the GM BLUE fluid.... thanks alot for that tip! I guess it makes sence since the last truck I used that in was a 2000 S10 ZR2... Not as heavy duty...


Sours: https://www.plowsite.com/threads/2500hd-diff-fluid-replacement.59574/

TheDieselPage.com Forums > 2001 - Current Chevrolet & GMC 2500HD/3500 Light Trucks > 2500HD/3500 HD Trucks & Drivetrain > Rear Diff Service


View Full Version : Rear Diff Service

For those of you that have changed the rear differential lube, how much did it take? Also, the owners manual gives the GM recommendation but no mention of a friction modifier is given for the G80 locker. If I use the recommended GM fluid, do I need a modifier? Thanks.


12-20-2000, 11:17

no friction modifier is needed w/ the g-80

Also, make sure you replace the fluid w/ the synthetic it came with, I believe it is Mobil 1. Can't remember the weight though. It should be posted in the owners manual.



Thanks I do have the part number but was curious on the capacity. The owners manual does mention and the parts guy says he has no idea how much the new axle will take. At $20 wholesale per quart I would rather not spend more than I have to and have it sit around for a couple of years.


12-21-2000, 15:31

My dealer told me that GM has a contract with Mobil for all there OEM lubricants. I keep forgetting to bring that owners manual inside the house. But if you know the weight you can purchase Mobil 1 synthetic gear lube at an Autozone for about half of what the dealer quoted you. I do know I saw the rear diff capacity listed somewhere. I'll try to find it and let you know.




The Mobil 1 Synthetic Gear lube is 75w-90.. That's what the owners manual states to use..
Mobil 1 75W-90 (http://dallnd6.dal.mobil.com/GIS/MobilPDS.nsf/26b7c4b33367a4a086256665004e4266/951b10d046e0bafd852567ba0050ec5f?OpenDocument)

2001 2500HD 4x4 Crewcab Duramax 6600
Allison 1000 Series. Driving it!!
The Diesel Page #330
My pictures of the 2001 Chevrolet/GMC Heavy Duty Pickups (http://hometown.aol.com/sovercash1/myhomepage/photo.html)

[This message has been edited by SteveO (edited 12-22-2000).]

My rear locker diff with "carbon fiber plates" acts weird. On snow from a stop in 2wd, if the rear tires spin, sometimes the driverside wheel will "ratchet" with a shuddering start/stop rotation of THAT wheel that shakes the whole truck "bang bang bang bang..." The passenger side wheel turns smoothly. I am getting more and more sure I am going to spring for the extended warranty, because my truck has had some probs. The 4wd light would keep flashing, apparently wasn't totally engaging, dealer fixed it but sometimes in 4wd has more whinyrough gear sound than other times, like gears aren't meshing the same/properly every time...mileage down to 13.0 last tank, 1000 miles on it (first tank 14.2, 2nd 13.8, some 4x4 snow driving, mostly city).

2001 2500HD ExCab longbed 4x4 DMax/Allison, love it but where is the "19mpg" from some people/magazines?!? My 6.2 Banks turbodiesel got 16-17mpg under same conditions.

Johnny GMC

12-24-2000, 13:28


Where in the owners manual does it state to use "Mobil 1 75W-90"

Do you know how many quarts the the locking rear diff takes. I think I read somewhere that the diff has a drain plug, is that true?

Johnny GMC

Member #5654

2001*SIERRA*SLE*2500HD*4WD*CC*DURAMAX/ALLISON (http://member.aol.com/yunchyboy/gmc.jpg)

Johnny GMC,

The manual states SAE 75w-90 Synthetic Lubricant (GM Part No. 12378261) or equivalent meeting GM Specification 9986115

The dealer (Which I called) said the Synthetic 75w-90 number was Mobil 1 75w-90 Synthetic. It just had GM Part numbers..

I don't know what the capacity is.. I will be finding out soon and will let you know..

Yes, It has a drain plug at the very bottom of the rear end.. Very nice not having to remove the pan to drain.. Make sure you drive the truck around at least an hour before trying to change it... The hotter the better..

2001 2500HD 4x4 Crewcab Duramax 6600
Allison 1000 Series. Driving it!!
The Diesel Page #330
My pictures of the 2001 Chevrolet/GMC Heavy Duty Pickups (http://hometown.aol.com/sovercash1/myhomepage/photo.html)

Our local "Mills Fleet Farm" stores sell Mobil 1 75w90 for about 5.99 a quart, which is the cheapest I have ever found. I went through a lot of it in the Quick Change rear diff and transmission of my race truck (past-tense). Much better deal than $20 at the dealer!!

The dealer parts department told me that three quarts is enough. I said give me four just to be safe. Get the GM Synthetic 75W-90, it costs $27.00 a quart http://www.62-65-dieselpage.com/ubb/frown.gif Whatever the factory put in this rear is some funny looking stuff. It is sort of a milky grey color. Anyway the reason I am writing this is to let you know to buy five quarts. The quart containers come with a little spout, but you still cannot squeeze it all in. So you have to get as much in as you can, then dump the bottles together and put as much in from the last one as you can. I put four quarts in and it was not running out. It must take just a little over four. Maybe it needs only four, but I could not get enough out of the containers to fill it. I would appreciate any feedback from other people changing the rear fluid. You probably want to change it at 500 miles the first time. The plug on the bottom makes it real easy. By the way, the best I can tell the bottom plug is plastic...Have fun with it!

Driving My GMC 2500HD Sierra SLE SWB Ext. With 6.6 Duramax\Allison And All The Goodies. Awesome Truck!

Neil Holland

12-26-2000, 22:23

Forget about the spout, you need to go and purchase a screw on pump with tube attached to it at the local auto parts store - very inexpensive. They are normally located by the gear lube.

Do you only have to change the rear end fluid if you have the locking rear diff, or does the standard rear end need changed also. I did not see this in the manual?

Lube Dude

12-28-2000, 10:33

I'm looking in a Check Chart Lubrication Recommendations Guide. This is what it says:

C3500HD with Dana 11" use Synthetic 75w140 GL-5 GM part number 12346140.

2000 full size models ezecpt vans, 1999 Silverado and Sierra with 4.3L, 4.8L, 5.3L, 6.0L Engine, use Synthetic 75w90 GL-5 GM part number 12378261.

All other models, standard and locking, use 80w90 petroleum GL-5 GM part number is preferred, Use synthetic 75w90 GM part number 12345836 in fromt differential when excessive shift effort is required to shift into 4WD when operating below 10Deg F.

Capacity refill;
1991-2000 K10/1500, 20/2500 3.6 pints
1998-2000 K30/3500 3.9 pints.
1991 V;K;
10/1500, 20/2500 4.0 pints
30/3500 6.0 pints
American 8-1/2, 8-5/8 ring gear 4.2 pints
American 9-1/2 ring gear 5.5 pints
American 10-1/2 ring gear 6.5 pints
Dana 11 ring gear 8.2 pints.

If yours took about 4 quarts do you have a dana 11? If you do you should be using the synthetic 75w-140.

Sincerely, Kevin

As far as I know the 2500HD's have a new 11.5 inch ring gear rear. They are not found on any of the charts that I have seen. The dealer's parts department knows little about what to put in them. If you look in the diesel supplement that came with your truck it gives you the GM part number. It says to use synthetic 75w90 for this rear. Hope this helps, let me know if I am missing something. Thanks, Kevin

Driving My GMC 2500HD Sierra SLE SWB Ext. With 6.6 Duramax\Allison And All The Goodies. Awesome Truck!

turbo Al

01-02-2001, 15:15

Xwing: I had the almost identical problem with my 1993 limited slip rear end when it was new. Dealer claimed it was "NORMAL" so finally when I couldn't take it anymore I took it in to have them Service the rear end-(they had refused to look at it under warranty) so I was willing to pay for outrageous service bill to prove a point. Guess what--the clutch pack had disintegrated and the oil was full of pieces--warranty claim NO CHARGE. The dead giveaway besides the noise was my mileage kept going down down down.
Turbo AL

WARNING: I submit this only to offer more choices, not to promote Pennzoil or start the dreaded synthetic vs petroleum argument http://www.62-65-dieselpage.com/ubb/smile.gif For those interested in rear diff oil options other than GM or Mobil, I emailed the following to Pennzoil:

I own a 2001 Chevrolet Silverado 2500HD with the G-80 "Locker" differential. The owner's manual states that the differential requires "SAE 75W-90 Synthetic Axle lubricant (GM Part No. 12378261) or equivalent meeting GM Specification 99861165." Do any of your products meet this requirement?

A Pennzoil tech rep replied:

Thanks for your inquiry. Yes, we have products in both the Pennzoil & Quaker State brand that will replace GM part no. 12378261. They are as

Pennzoil Synthetic SAE 75W-90 GL-5 part no. 56077 (1qt.)
Quaker State Ultra Premium SAE 75W-90 GL-5 part no. 61538 (1qt.)
Quaker State FCI Synthetic SAE 75W-90 GL-5 part no. 37555 (1qt.)

You can go to Pennzoil.com and navigate the website to find the product description and chemical properties.

I am sure you can email the oil company of your choice and get their equivalent vice spending $20+ for GM, plus your warranty will remain in effect.

Neil Holland

01-04-2001, 17:36


Thanks for the information. I have printed it and added it to my Duramax file. The GM Synthetic cost is outrageous! I have found Mobile 1 75W-90 for $6.99 per quart. Time to go out and price the Penz. and Quaker.

Amsoil has two different 75w-90 Synthetic gear lubes that meet the GL-5 spec. One is the series 2000 at about $7.00 per quart, and the other is about $5.70 per quart or about $22.00 per gallon. Both are listed as suitable for limited slip differentials. The key is the GL-5 spec. While I'm looking, they have a universal synthetic AT fluid as well, which meets the Allison specs. If anyone needs any info, let me know. I've used amsoil for over 20 years with great results.


01-05-2001, 16:37

FYI. I measured ~4 quarts out of factory oil and used exactly 4 qts. to fill and top off at fill hole. Neither drain plug is plastic.

Duramax VIN 1GCHC23151F111460, 2500HD, LS, CrewCab, Long Box, 2WD, Pewter/Graphite


Thanks for the info
Great to here we have alternatives to the dealer..

Thanks also for the info..

Does the drain plug have a rubber/plastic gasket? I looked the other night and as you said it's not plastic but it looks to have a Big plastic/Rubber washer?

Saw the Penzoil 75W-90 100% synthetic gear lube at Wal-Mart yesterday for $6.50/qt.

2001 Silverado 2500 HD LT ext. cab, LB, Duramax/Allison


01-06-2001, 08:11

The drain plug appeared to have a tapered, metal-to-metal seal and an elastomer seal, like an o-ring, molded into a groove behind the taper. There were no "flat" washers making a seal. Maybe the part we see from the outside is a protective covering: paint/plastic? I did not look that close. The plug/seal just comes out as one piece.

What's up with this?

I drain about 3.5 qts out and it takes just under 5 qts, yes 5 qts! to refill where it started to come out of the hole on level ground. Does anyone have the Helm's service manuals yet, or have a published capacity? Anyone put more than 4 qts in?

One huge bonus, though. This has got to be the world's EASIEST rear diff to service with a drain plug on the very bottom and a fill plug on the pan and not hidden away like most diffs.

An extra note. I have owned two previous GM posi-traction rear diffs and the Helm's factory manuals direct you change the fluid at the first 500 miles and then continue with the standard service schedule. Since I don't have the manuals for the HD yet, and it is a locker with no clutch pack (I assume), I was cautious and changed it at 2000 miles. Anyone with another input?


Did you check the fluid before it was drained it? I checked mine just after I bought the truck and it was fine..

I talked to HELM about Service Manuals the other day.. They said Feburary.. Didn't give a day.

2001 2500HD 4x4 Crew Cab LT, LB7-Duramax Diesel/Allison 1000 Series, Autometer Boost/EGT Gauges, Husky Floor liners, Vent Shades, Driving it!!
2001 Z06 Corvette> I wish!
TDP member #330

I never checked it before drainage. The only way I know how much came out is I refilled the old 1-qt bottles with the old oil for disposal. I figure that since I filled the old bottles to the very top, and with a bit of spillage, about 3.75 qts came out. No big deal, it's full now with almost 5 qts.

Thanks for the input.

turbo Al

01-15-2001, 13:06

I got this from an article for new replacement gears:

1. Breaking in new gears--after driveing first 15 to 20 miles stop let diff cool--15 min.

2. Keep under 60 mph untill 500 miles--NO towing.

3. Change out oil at 500 miles.

4. During first 45 miles of towing stop every 15 miles and let diff cool for 15 mins each time.

For the full article go to www.off-road.com (http://www.off-road.com)
click on skip intro, click on 4x4 content, click on Chev/GMC, click on Projects/features, click on Project Potent Rodent then scroll down to 4.88 gears and click on.
Turbo AL

[This message has been edited by turbo Al (edited 01-16-2001).]

At what mileage are owners changing the rear end fluid for the first time in the HDs.


I just brought my Duramax in for its first oil change. My diff did not have a plate or sticker that said "synthetic." Did they just forget to put the plate on or is it not supposed to be there?



Your suppose to change the fluid after towing for 500 miles, since it's winter and I don't tow much during that period, I changed mine at 5000 miles..

There is no plate or tag that I'm aware of.. The HDs I'm for sure take Synthetic rear-end fluid.. It also say's in the owners manual..

2001 Chevrolet 2500HD 4x4 Crew Cab LT, LB7-Duramax Diesel/Allison 1000 Series, Autometer Boost/EGT Gauges, Husky Floor liners, Vent Shades, Driving it!!
2001 Z06 Corvette> I wish!
The Diesel Page member #330

Thanks for the reply on the tag. Also, thanks for this forum. When I went in for my first service today, the tech was amazed that I had better information than he had. I told him how great it was to have a forum like this to share information.


Changed my rear diff fluid last night, using Mobil1 Synthetic 75w-90, using just over 4 quarts. Was a little surpised by the amount of metal residue on the drain plug. Wish I had changed sooner than 5400 miles.

Joe Dawson

02-16-2001, 14:26

I called Mobile and asked about their synthetic 75W90 gear lube. They said that it isn't specifically formulated to meet the GM spec but that it would be OK to use. What do you guys think?

Joe Dawson

02-16-2001, 20:43

Here is a link to an answer from Eaton on diffeential oil

2001 2500 HD GMC D/A CC Long Bed

Diesel Cruiser

02-18-2001, 17:14

Changed mine yesterday at 2200 mi. Happy to report, not too many steel fuzzies on the magnet. However, it took almost 5 qts., and I used a flexible hose pushed over tip of Mobile 1 75/90, loosing about a drop. One of the easier diff. lube changes I've done.

For my use. I wish they offered about a 3.08 or 3.23 ratio. I might pull 8500# once a year, the rest of the time I'd like mileage.

2001 2500 HD Ext. Cab/2WD/DuraMax/Allison and 3.73.


84 Chevy K10

02-19-2001, 12:50

Then get taller tires!


02-19-2001, 20:59

Changed the oil in my rear end today and found some things that are different from what I had thought. The rear cover on my 2500 HD that was ordered with G80 locking diffential only has 1 drain plug about half way up on the cover.When I drained the oil I only got out a little over 3 quarts and it was gray in color from metal partitals.It took a little over 4 quarts to fill to the plug.Now to my questions,do I have a G80,if so why the one plug, maybe early model as I took delivery on 11/7 and last but not least why was the rear end 1 quart low.Anybody have a way to identify the G80.Thanks in advance for all help I have received on this site.


02-19-2001, 21:44

Look in the glove box for the option label. If you have it it will say G80. Your window sticker would also have it. Your dealer can get you a replacement window label if you want one.


05-06-2001, 18:46

Thinking about going ahead and changing my rear diff. fluid at 3200 miles haven't towed much so it should be ok.

forrest green crew cab,duramax/allison pics at Http://photos.yahoo.com/pullinpower01


05-06-2001, 19:07

Hey guys

I have seen a few companies state on there synthetic gear lube that they meet the new GL6 standard. My question is, with this work in my new 2500HD Duramax/Allison with the G80 ??? Or do I have to stick with a GL5 rated oil ????

You help is always appreciated !!!

01 GMC 2500HD SLT Duramax/Allison Ext Cab LWB
On order since 09/2000
TPW 03/26 now 04/16
Built 04/18
Almost Home !!!!
Alberta Plate "Duramax"

From all I've read, I still haven't seen what GM spec. 99861165 is. Does anyone know? I'm curious as to whether that's equivalent to the new GL-6 rating some of you have seen?
But then, why didn't GM say that?

E-mailed Mobil 1, Pennzoil/Quaker State, andf Amsoil this week reference whether they meet the GM spec. for differential fluid. Mobil 1 said they didn't. Amsoil days they do. No answer yet from Pennzoil/Quaker State.

Was there any mention of exactly why the Mobile 1 gear lube did not meet the GM spec? Does anyone have any idea what the GM spec is or where we could see a copy of it?


Let me see if I've got this right? The Eaton consultant mentioned earlier on in this thread, said that Mobil 1 was OK. Worse thing that could happen would be some gear clatter. Mobil 1 = $8.00/quart. GMC Magic Lube = $28/quart. I think I'll change now with Mobil 1 and change again later with whatever other product ends up comparable to GM stuff. Seems to me that it would be better to change now to get the metal gunk out of the rear end after the 500 mile tow than to wait. In large part this is based on the fact that I have the Mobil 1 sitting here in a box.

2001 Chevy 2500HD 4x4 D/A LS Regular Cab Una-Goose Hitch, Line-X, Westin CP/SS Nerf Bars, Rare Pewter color. Took delivery 12/8/00. Virginia DURAMAX plates.

Johnny R,

Look at a post on this thread from CCR91 and dated 01-04-01, it will tell you the answer I got from Pennzoil.


E-mailed Amsoil, Mobil 1, Pennzoil/Quaker State, and Royal Purple asking whether their synthetic 75W-90 differential fluids meet the new GM spec.
Amsoil says theirs does.
Mobil says their Mobil 1 does not.
No answer yet from Pennzoil/Quaker State or Royal Purple.

Guys, sorry for posting the message twice. Although at least I added Royal Purple to the list the second time around.
Larry M,
Mobil offered no explanation other than it didn't meet the GM spec.; said to go to GM. Comforting, huh!!!
Did see your post but decided to ask anyway. Thought if we got "yes" twice, would increase confidence level.

Turbo Al

05-30-2001, 09:37

OK now I am an expert http://www.62-65-dieselpage.com/ubb/biggrin.gif changed the rear diff oil yesterday @500 miles. The truck had just been driven 40 miles and it was hot. Checked level through the upper fill hole and didn't get any reading with my finger so it was low.
Drained about 3.2 quarts out and put in 4.3 -- I am NOT happy about this missing quart. There is a slight amount of leakage from the front seal which I cleaned off and will monitor.
GUYS do yourself and your truck a big favor and drain the diff SOONER not later. The colour and amount of metal in this oil is hard to believe and I have been real gentle on it so far (gentleness wears off at 1,500 miles).
If you know me then you know that I also removed the diff cover to check everything. I am glad to report there is no reason to do this -- draining the oil hot removed all the oil and metal filing from the rear end and the shape of the casting leaves nothing in there worth wiping.
There are no Spider gears in this rear end G-80.
Because the ones I saw looked like "Tarantulas" they are huge. I fully intend to change this oil again as soon as I get some towing miles on it and will report what I find.
Turbo AL

Turbo Al,

What brand lube did you use?

Turbo Al
Does the rear cover have a gasket? was told
by dealer that one was not used that they just use silcone gasket sealer on diff cover.



Turbo Al

05-30-2001, 10:40

Larry M: I didn't have much choice the auto parts store only had Castrol Syn 75-90wt my first choice would have been Penzoil but they were out of stock. 5 liters @ $65.00 CDN.
AZDMAX: I don't think this rear end cover would seal very well with just sealer. I would not be tempted to use just sealer because the contact area in some spots is quite small. It has a gasket which I did damage a little taking off (gasket stayed on housing). All the bolts were RED locktighted and I retorqued them to 20 ft lbs (my specs not GM's) -- 13mm bolts (socket size) and lots of them.
The cover itself is very well designed -- it has "ridges" that flatten out when it's torqued down.
Turbo AL

Tader Jack

05-31-2001, 06:43

Changed to Amsoil 75W-90 Gear Lube in my 2500 HD w/ rear locker @ 2500 miles. Using Amsoil 15W-40 engine oil also. Easy rear diff. change with plug at bottom. Takes almost 5 full quarts, it's a little slow to fill but, easy. Got a little dizzy doing the figure 8's in the parking lot after the rear diff change. The guy watching me thought I was nuts.

2001 Chevy Silverado, 2500HD, Crew Cab, Short Box
LT Trim, Black Onyx w/ Tan Leather
Beltronics 980 Radar, Blinker Laser Radar Jammer
Lund Interceptor Wind Deflector
J&J Stainles Steel Tube Grill
Putco Stainless Bed Rails
Access Roll-up Tonneau Cover
Pendaliner SR Bed Liner
K&N Air Filter
DTA Stainless Running Boards and Mud Flaps
Lucerix Remote Control X-Mount Camper Mirrors
Uniden PRO CB Radio, Wilson Antenna
Air-Lift Super Duty Ride Control w/ Dual Controller
Tekonsha Voyager-XP Trailer Brake Controller
Running Amsoil 15W-40 Synthetic Heavy Duty Diesel & Marine Engine Oil
Running Amsoil 75W-90 Synthetic Gear Lube (GL-5) in Rear Differential
S&S 8.5SC Slide-in Camper (soon to come - mid-June)
18.7 mpg @ 75 mph cruising unloaded when new
(haven't checked since 2,500 mile oil change to Amsoil)

I just picked up four quarts of GM synthetic 70w-90 gear lube for 17.94 each. Came to 71.76.

It's an awfull lot but I won't need to do it again for a long while. I feel better with what GM is calling for until there is something else GM approves of. I know it's a rip, but hey, it's grape!

2001 2500HD Duramax/Allison Summit White CC/SB Loaded
VentShades, Husky Mudflaps, 255/85-R16 (32-1/2")Dunlop Radial Rover RV's PICTURES (http://onramp.uscom.com/~hoot/cars/2001gmc/)
1994 K1500 Blazer 350 Loaded, Flowmaster duals

dmax, let us know if the 4 quarts fills it to the top. Mine seemed to want a little more than that.

I'm surprised and a little disappointed that no one has reported what makes the GM lube so special and why major lube brands are apparently not meeting the GM spec.

The Mobil 1 lube I put in mine now has about 5000 miles on it with no apparent problems. I will be starting some serious towing soon and want to change it once more. Might have to put in the GM magic goo just for peace of mind.


2001 2500HD, D/A, regular cab LS, 4x4
Wish it was a 6 sp!

[This message has been edited by LarryM (edited 07-16-2001).]

I'm gonna pick up another quart on the way home and change it tonight. I don't want to run low.

It's a joke that the parts or service dept. doesn't have any idea what to use and how much.

Guy says, go by your owners manual. I says, ok here's the owners manual. I need this stuff, how much should I get? He says... sorry we don't know that either. Why aren't the capacities listed in the owners manual. One service guy said it's probably because they really don't want you doing the service. That's bull, cause if I dropped it off and they don't know what goes in it and how much either, they'll just put regular gear oil in it till it overflows and be done with it.
I'm willing to guess they don't list the capacities cause with all the different rears, someone might misread and not put enough in. The overflow method is mistake proof. They may have had problems with this before.

2001 2500HD Duramax/Allison Summit White CC/SB Loaded
VentShades, Husky Mudflaps, 255/85-R16 (32-1/2")Dunlop Radial Rover RV's PICTURES (http://onramp.uscom.com/~hoot/cars/2001gmc/)
1994 K1500 Blazer 350 Loaded, Flowmaster duals

[This message has been edited by dmax (edited 07-17-2001).]

heavy load

07-17-2001, 11:34

Turbo Al:

Was there a magnet on the inside of the diff cover? If so was it full of metal as well? Did you reuse the gasket on your diff?

01 2500HD Silverado LS Ext Cab 4x4 6.0 Sunset Orange

The son of a guns at this local dealership couldn't give me a fifth quart for less than $22.00. The other dealer where I got the 4 quarts @ $17.91 each is higher volume. That is the key. The larger the dealer, the better prices they get and in turn can pass that savings on to you. You have to ask for the lowest price.

I think the magnet is on the drain plug.

2001 2500HD Duramax/Allison Summit White CC/SB Loaded
VentShades, Husky Mudflaps, 255/85-R16 (32-1/2")Dunlop Radial Rover RV's PICTURES (http://onramp.uscom.com/~hoot/cars/2001gmc/)
1994 K1500 Blazer 350 Loaded, Flowmaster duals


07-17-2001, 13:03

On mine, both the drain and fill plugs are magnetic. It took right at 5 qts. to fill to the "overflow" method on mine, both times. I made sure the rear end was hot just before I pulled the plug, and let it drain for about an hour. The oil is thick and takes some time to run from the hubs to the drain. The first change (700 miles) had a little metal and a lot of suspended material. The second change (10K) was much cleaner and had no metal. I used Amsoil synthetic 75w-90.

2001 GMC Sierra SLT 2500HD 4X4 Ext. SB -D/A- INDIGO BLUE - Delivered November 2000

1985 K Blazer 6.2L N/A 500K+ original miles on Engine/Tranny (2 transfer cases, 1 pump, and a few rear ends)
Synthetic Oil!!

Changed mine to pennzoil,75-90 synthenic.
Get it from a local fleet maintainance
company for .90 a quart.They buy 500 gallon
at a time,it all cost the same.Someone is
making some big bucks.

2001 Duramax,3500,Dually,
Allison,4 door,Victory
red,4x4. 30 Ft. gooseneck
trailer,hydraulic tilt
for antique tractors.

Turbo Al

07-17-2001, 15:08

Heavy Load: No magnet inside cover & yes I reused the damaged gasket but should have replaced it. I just carefully lined up the separated parts -- some on cover -- some on diff. & it was damaged well above the full level.

2001 Ext Cab LB 4x4 Duramax/Allision, Victory Red, K & N
1993 6.5 TD 4x4 reg cab LB, 5 speed
1972 Pontiac Lemans

[This message has been edited by Turbo Al (edited 07-17-2001).]

Turbo Al,

Why did you take off the rear cover. Are you anal or what? That's ok. It's not a bad idea.

I drained about 3-3/4 quarts of hot oil. I jacked both sides to empty the axles. It pretty much quit dripping so I closed the bottom.

I put a level on the axle and jacked it level since it was a little uneven. Took just over four quarts.

Old stuff had the silvery swirls in it. Two small chips on the magnets.

Done till next time.

OK, so what is the general consensus on the capacity? From the posts I am seeing any where from 3.5 qts to nearly five. My dealer has offered me 3 qts left over from a warranty job for 10$ a quart. Do I need to buy two more at 17$?

01 Chevy 2500HD ext cab SB D/A Indigo Blue 285's, AR-23 16X8 Alloys, Westin Bars, RhinoLiner, ARE Z series cap, Polished Billet grill
93 ext cab LB 6.5TD 176K flawless miles! Wanna Buy it?

The true capacity is 3.83 quarts. That's very close to what came out of mine. What everyone seems to be finding is the factory fill does not jive with the filling instructions. But, it's only a half a quart difference. I was able to get a little over 4 quarts in. The rear does get hot so the more the merrier. My opinion is to fill till it runs out the hole ON LEVEL GROUND.

4 quarts is minimum to get that to happen. If you decide to use a fifth quart, it'll only use about a cup of it.

2001 2500HD Duramax/Allison Summit White CC/SB Loaded
VentShades, Husky Mudflaps, 255/85-R16 (32-1/2")Dunlop Radial Rover RV's PICTURES (http://onramp.uscom.com/~hoot/cars/2001gmc/)
1994 K1500 Blazer 350 Loaded, Flowmaster duals

[This message has been edited by dmax (edited 07-20-2001).]

Feeling a little dumb asking this question but where is the fill plug? I found the drain plug and assumed that the fill would be right on top but did not see anything there. Is it the bolt on the back side of the case?

Yes, it's in the back cover.

2001 2500HD Duramax/Allison Summit White CC/SB Loaded
VentShades, Husky Mudflaps, 255/85-R16 (32-1/2")Dunlop Radial Rover RV's PICTURES (http://onramp.uscom.com/~hoot/cars/2001gmc/)
1994 K1500 Blazer 350 Loaded, Flowmaster duals

Turbo Al

07-20-2001, 09:08

D-max: Your killing me here http://www.62-65-dieselpage.com/ubb/tongue.gif & I know you are http://www.62-65-dieselpage.com/ubb/mad.gif that I took mine off before you http://www.62-65-dieselpage.com/ubb/tongue.gif

Just wanted to see the locker up close and personal and if there was anything left (oil etc) in the bottom of the diff. there wasn't. Now I can sleep at night http://www.62-65-dieselpage.com/ubb/wink.gif


2001 Ext Cab LB 4x4 Duramax/Allison, Victory Red, K & N
1993 6.5 TD 4x4 reg cab LB, 5 speed
1972 Pontiac Lemans

You could have just asked Al...

2001 2500HD Duramax/Allison Summit White CC/SB Loaded
VentShades, Husky Mudflaps, 255/85-R16 (32-1/2")Dunlop Radial Rover RV's PICTURES (http://onramp.uscom.com/~hoot/cars/2001gmc/)
1994 K1500 Blazer 350 Loaded, Flowmaster duals

Turbo Al

07-20-2001, 09:57

http://www.62-65-dieselpage.com/ubb/biggrin.gif but but it's not mine & it's defective!


07-26-2001, 12:53

I changed my Diff today with Amsoil 75-90W, it took 4qts and 12oz, I only took out 3 1/2 qts. Just a little low, I can see that the dealer never checked it. I'm going on a 2000 mi trip tonight and will let you know if there's any problems.

2001 GMC D/A Crew-Summitt White-ICI Tube Bars-Weather Tech Shields-X-liner-5th wheel louvered tailgate

Looks like GM is putting in the spec'd amount but telling the customer to put in up to the filler which is more. Maybe the filler is higher than originally designed? There's really not enough a difference for any concern. Remember, you don't get it all out.

2001 2500HD GMC Duramax/Allison Summit White CC/SB Loaded, Straight Piped,
VentShades, Husky Mudflaps, 255/85-R16 (32-1/2")Dunlop RV's PICTURES (http://onramp.uscom.com/~hoot/cars/2001gmc/)
1994 K1500 Blazer 350 Loaded, Flowmaster duals
Raised in Rockdale, Pa. Lenni Boy!

What's the story with the figure 8's after changing the oil?


11-27-2001, 00:23

The figure 8's get the new lubricant into the clutch plates in the locking differential.

They are not really necessary, but- if you do not do them, you can experience some unpleasant harshness from the locker when going around corners. It'd go away with time.

PICTURES (http://www.picturetrail.com/somndmax)

2001 Chevy 2500HD Duramax, Allison, Ext. Cab SB Forest Green,
285's and Centerline's put away till spring... Now equipped with Goodyear Workhorse Extra Grips, 265/75-16 on the PYO's
Autometer Boost and EGT gauges, Amsoil air filter, Access Tonneau, Luverne Stainless boards, JL Audio 12" sub, Phoenix Gold amp, Clarion door speakers...
4" Kennedy Diesel exhaust installed!!
Power Play Module from Kennedy Diesel (http://www.kennedydiesel.com)
Diesel Page member #6184

More posts than Alli-max....


11-27-2001, 12:40

I went with the gm stuf ordered it from www.gmpartsdirect.com (http://www.gmpartsdirect.com) for 15.60 a quart

suposedly the stuf is made by texaco but i could not find it anywhere

here is more info http://forums.pickuptruck.com/cgi-bin/ultimatebb.cgi?ubb=get_topic&f=11&t=008139

2001 2500HD 8.1/allison


11-27-2001, 14:52

The figure 8s work out all the gears and gizmos in the diff differentiating the different wheel speeds during the manuevers. It also sloshes the new lubricant into and out of the two axle tubes to lubricate and flush old lubricant out of the axle bearings. Two tasks in one shot and fun to boot!

Tom Ashley
2001 DuraMax/Allison
2500HD Silverado LT
Lt Pewter/Graphite Lthr
Ext Cab/Shrt Box/4x4
Line-X/Century Ultra Cap
Amsoil 2-Stage Aircleaner

Turbo Al

01-11-2002, 11:03

Back to top for Letsgo


01-11-2002, 16:40

OK guys, you've convinced me to change my rear dif fluid, just got some Mobil 1 Syn 75W-90, what kind of bolt plugs am I gonna find when I get home? size? shape?

Silverado 2500HD CrewCab 8.1/Allison; Auto; SB 4x4; Indigo w/ red striping; Z85 Graphics; StylEyes headlight covers; 4-lamp conversion; tinted windows; taillight guards; Rhino-lined; Extang Sabre Tonneau; Escort 7500; Uniden 538W,
Flowmaster#530504 exhaust

I have an 02 3500 with the Eaton locker. I changed the rear dif fluid last week and measured that 3.8 quarts came out. This was just after a 50 mile trip at 65 to 70 mph. I put in 4 full quarts and it was about 3/8" from the bottom of the filler hole. I had 2,000 mileson the truck with about 800 miles of towing a little 6x12 foot motorcycle trailer on the fluid. The magnet only had a small amount of metal filings on it. I am scheduled to pick-up my 36' fifth wheel toy hauler and plan to change it again after 500 or so miles of real towing with the 80w-140 oil from GM at that time.

2002 K3500 Silverado LT 4x4, crew cab, D-MAX, allison, forest green tan leather, back country RB, G80 locker, climate control, off rd skid plates
Autometer Boost Gauge Autometer Pyrometer Gauge
Retrax bed cover
Hidden Hitch 5th wheel hitch
Jordan brake cont.

[This message has been edited by MaxDMax (edited 02-21-2002).]

Turbo Al

01-03-2003, 17:05



I worked for PZL/QS for a number of years. I can tell you that no one is buying synthetic gear oil for $4 a gallon.

My guess is that the company where you got it also buys some mineral gear oil and got the price mixed up


they are selling you non synthetic lube thinking it is syn.

Side note: PZL synthetic doesn't come in bulk. It would have been transfered into their bulk tank from 55-gallon drums.


01-03-2003, 22:08

Changed rear diff oil today at 7900 miles. Have done no towing yet. Fluid was gray with a little fuzzy metal on the plug. Hope I didnt wait too long. More importantly I was debating what to synthetic to use. GM's product was unreasonably expensive as expected. Said they only had the diff fluid in bulk and could not sell it to me in quarts (??) Anyway filled it with Mobil 1 synthetic 75W90 - I know a few others have done this. But have heard it doesnt meet GM's spec. What exactly does this mean? The service guy at GM told me honestly he didnt think using Mobil 1, made any difference in terms of quality or that using a non GM synthetic would effect warranty, etc.


01-03-2003, 22:58

I changed my rearend fluid yesterday. I put mobil 1 in. Mobil 1 meets GL5 specs and is ok to use. The owners manual calls for a gl 5 spec lube and my dealer said that mobil 1 was good to use.

2K3 EC SB 4X4

I changed mine right at 500 and it also was grey with mush on the magnet. Didn't smell to good either. From other posts I read we need to change it again after towing for 500 miles.

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So I take my 09 Duramax in for its very first service job to a licensed, shop that I trust. Later that day I get a phone call from the service manager saying that they had to put 2.0 l. of gear oil in the rear differential. Now I am thinking that this sounds odd as it only holds 3.0 l of gear oil to begin with, so I send an email to the service manager at the dealership that I purchased the vehicle from looking for an explanation. He responds by sending me the following bulletin.

#05-04-20-001A: Rear Axle Fluid Level May Appear to be Lower Than Published Specification - (Apr 1, 2009)

Rear Axle Fluid Level May Appear To Be Lower Than Published Specification

2005-2009 Chevrolet Silverado 2500/3500 Series Pickups

2005-2009 GMC Sierra 2500/3500 Series Pickups

with Four-Wheel Drive (VIN K)

This bulletin is being revised to update model years and to reclassify the previous bulletin from Advanced Service Information to Information. Please discard Corporate Bulletin Number 05-04-20-001 (Section 04 - Driveline/Axle).


On full-size 2500 and 3500 Series Four Wheel Drive (K Series) Chevrolet and GMC Pickups equipped with the 11.5" ring gear rear axle assembly, the factory lubricant fill level may appear to be lower than the published specification. This unit can be identified by the location of the fill plug on the rear axle housing cover, instead of on the front of the axle housing.

All axle assemblies are filled by volume of fluid during production. They are not filled to reach a certain level. On the 11.5" rear axle, the fill quantity is 3.0 Liters plus or minus 0.1 Liter (3.18 Quarts plus or minus 0.1 Quart). Testing has shown fluid level readings as low as 35 mm (1.4 in) below the bottom of the fill plug opening are acceptable, even with the correct amount of fluid in the axle, compared to the currently published specification of 17-21 mm (0.6-0.8 in) below the fill plug opening, even when the correct amount of fluid was installed in the axle assembly during production.

It is NOT necessary to add axle fluid to the axle when the fluid level is at or above 35 mm (1.4 in) below the bottom of the fill plug.

When checking the fluid level on any rear axle, variations in the readings may be caused by factory fill differences between the minimum and maximum fluid volume. Also, if a vehicle has just been driven before checking the fluid level, it may appear lower than normal because fluid has travelled out along the axle tubes and has not drained back to the sump area. Therefore, a reading taken five minutes after the vehicle has been driven will appear to have a lower fluid level than a vehicle that has been stationary for an hour or two. Remember that the rear axle assembly must be supported to get a true reading.

Ok....so this means that the only real way to determine if i have the proper amount of oil in the rear differential is to drain it completely and then fill it with 3.1 litres of gear oil

The shop I took my vehicle to does get the service bulletins, but in this case they did not fill the rear differential to the proper level. I was assured that they would be paying greater attention to these bulletins.

Now I may not be the sharpest knife in the drawer, but what happened to the good old days when you filled the rear differential up to bottom of the fill plug opening??? Or is this just another way to stick it to the consumer??

I wonder how many 05,06,07,08,and 09 Duramax rear ends have been overfilled causing seals to blow, and or premature wear?
Sours: http://www.outdoorsmenforum.ca/showthread.php?t=54719
Duramax LML Rear Differential Fluid Change

Duramax Fluid Capacities

Fluid Capacity

  • Automatic Transmission Fluid
    Trans Mfr CD 1000/MW7 and 1000/M74 Drain and Refill
    Automatic Transmission Fluid

    All capacities are approximate. When adding, be sure to fill to the approximate level. Recheck the fluid level after filling.

  • Front Axle (1500 Series 4WD): SAE 80W-90 Gear Oil. Front Axle (1500, 2500 HD, and 3500 HD Series): SAE 75W-90 Synthetic Gear Oil.

  • Front Axle (1500 Series 4WD): SAE 80W-90 Gear Oil. Front Axle (1500, 2500 HD, and 3500 HD Series): SAE 75W-90 Synthetic Gear Oil.

  • Rear Axle (Steerable): Synthetic Gear Oil; use ONLY GM Part No.12378557. DO NOT add Friction Modifier.

  • Use engine oils that have one of these designations: CI 4 or CH 4 for DURAMAX diesel engines. When it is very cold, below 0 Deg. F (-18Deg. C), you should use SAE 5W-40 to improve cold starting. Do not use other viscosity such as SAE 10W-30, SAE 10W-40, or SAE 20W-50.

  • Use ONLY engine oils that have one of these designations: CI 4 or CH 4 for DURAMAX diesel engines. When it is very cold, below 0Deg. F (-18Deg. C), you should use SAE 5W-40 to improve cold starting. Do not use other viscosity such as SAE 10W-30, SAE 10W-40, or SAE 20W-50.

  • Follow the Manufacturer’s Instructions for the mixture ratio.

Featured Article:

“Evolution of the Duramax”

As with most pickups in the industry, the Duramax line of diesel engines has come a long way from its inception to modern day. From the introduction of the LB7 almost 20 years ago, the engine output has nearly doubled its torque from approx. 500 lb-ft, to the modern-day workhorse pushing towards 1000 lb-ft, in the L5P engine line.

Though all of the Marketing departments at the big three diesel manufacturers tout the best in trucks, Dan Zelten of Dan’s Service Center (Eagle River, WI) claims he sees the least amount of Chevy’s in the shop for engine repairs. “A lot of Ford’s, however, have provided a good amount of business for us.”

For GM, they set the trend, teaming with Japanese manufacturer Isuzu, making it to market with the first redesign of the current-style high pressure direct-injector diesel engines. Dodge Cummins and Ford Power Strokes soon followed to take advantage of the new common rail injection design.

Prior to the release of the newly designed LB7, the Duramax was delivering 400+ lb-ft of torque. The revised 6.6L V-8 turbo diesel motor came along at the turn of the century featuring aluminum heads and 32 valves. With their high-pressure, common-rail, direct fuel injection mounted under the valve covers.

Read more HERE!

Sours: https://www.hotshotsecret.com/diagnose/chevygmc-pickup/duramax-fluid-capacities/

Fluid duramax diff


Duramax LML Rear Differential Fluid Change


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