Just wanted to know if anyone has any info on the gm (chevy and GMC) G80 rear differential feeling like it is locking up on some turns, Sort of a shutter then it is ok for miles , mostly left turns with a load. This just started at 41000 miles , the gear lube was changed at 5k miles and again at 25k, and at 36k before a 4k towing trip out west - Mobile 1 75-90. I do a lot of towing . I understand there is no additive needed other then 75-90 in this Differential, is that correct?. Thanks in advance for any Help
You are correct that no special additives are needed. I used Mobile 1 75-90 in mine also and have not experienced any problems. Just changed it at 70000 for the first time and the old lube did not look/smell all that bad. We don't tow as much as you though, approx 20000 of the 70000 miles on the truck. When you changed the lube was there alot/any metal or clutch material in the old lube?
2003 Silverado 2500 HD EXT Cab 6.0L Reese 15K
2006 Thor Wild Thing 28SG-M5
1988 HD Electra Glide Sport
2002 Yamaha Roadstar
2002 Suzuki Telefonica GSXR
I have always used/recommended the additive. The G80 has a govenor that locks the differential when you have one wheel spin out, but there is a clutch pack in there that should be considered as well.
To the OP- The only truck I have had that displayed the shutter you describe was my old '89 K1500. As you say it would shutter during low speed left hand turns, and usually only when I was towing.
I didn't pay it much attention though. BTW, my '89 K1500 had the additive, and still shuttered. FWIW
I'v had a couple of trucks to that or they would hesitate for a split second and then jerk forward. But it only did it a couple of times, on left hand sharp turns...never had an problems though.
2007 GMC Sierra 1500 Crew Cab Z71 with VortecMAX 6.0 V8
Weighted centrifugal lever. Older tossed it in at approx 200RPM differential
between left and right. Newer (circa 1999 IIRC) changed it to 100RPM
due to too many nailing the throttle and too much torque when it
kicks in. So grenaded itself too often. Till that switch is tossed,
it is basically an open differential.
Clutches and again, no slippage because it is a locker, not limited slip
Something is wrong with yours, so have it checked. Not by a dealer, but
a shop that does lots of diff's. Like a speed shop or 4x4.
'Tow a lot' and hope you didn't tow before getting some decent miles
on it new so that it could break in. Also hope you flushed it often,
especially if you tow heavy.
A lot depends on the diff ratio and tire dia.
-Ben Picture of my rig
1996 GMC SLT Suburban 3/4 ton K3500/7.4L/4:1/+150Kmiles orig owner...
1980 Chevy Silverado C10/long bed/"BUILT" 5.7L/3:73/1 ton helper springs/+329Kmiles, bought it from dad...
1998 Mazda B2500 (1/2 ton) pickup, 2nd owner...
Praise Dyno Brake equiped and all have "nose bleed" braking!
Previous trucks/offroaders: 40's Jeep restored in mid 60's / 69 DuneBuggy (approx +1K lb: VW pan/200hpCorvair: eng, cam, dual carb'w velocity stacks'n 18" runners, 4spd transaxle) made myself from ground up / 1970 Toyota FJ40 / 1973 K5 Blazer (2dr Tahoe, 1 ton axles front/rear, +255K miles when sold it)...
Sold the boat (looking for another): Trophy with twin 150's...
51 cylinders in household, what's yours?...
Devocamper wrote: Just wanted to know if anyone has any info on the gm (chevy and GMC) G80 rear differential feeling like it is locking up on some turns, Sort of a shutter then it is ok for miles , mostly left turns with a load. This just started at 41000 miles , the gear lube was changed at 5k miles and again at 25k, and at 36k before a 4k towing trip out west - Mobile 1 75-90. I do a lot of towing . I understand there is no additive needed other then 75-90 in this Differential, is that correct?. Thanks in advance for any Help
You have the Eaton G80 locker and there is no need for the additive. Also if you check the recommendations you should have never changed the fluid, just leave it alone. Eaton and GM both say it never needs to be changed. We don't hear a lot of problems here from folks who tow with them. Serious off-roaders break them, but then again they break a lot of things. Towing would not harm it.
In the past I have read posts where folks changed the fluids and inadvertently got junk in them and that had a bad impact.
I really think you should get it checked out by a shop that specializes in drive trains and see what it is. If it just needs flushing then put the GM grape juice back in it and quite mucking with it.
Goodness knows we all from time to time think to hard,
Good luck
Ken
08 Ford F250 SuperCab Lariet LB 4x4 6.4L Powerstroke
04 299RLS Sprinter
07 Ultra Glide Harley
00 BMW 540I Maroon
Friend of Bill Wilson
The service information for your truck on GMDEALERWORLD makes no mention on the additive one way or the other. If it were my truck, I would not use it. The posi additive that I have sold for 36 years is for use with dino gear oil, not the newer and better synthetics in use today.
99 F250 PSD CC LB 3.73 4X4 7360 lbs, and it can sink in the mud FAST, 2004 Coachmen Catalina TT 297RKS 8200 lbs on the road.
I replied to this before, but it must not of went through. The g80 in the trucks is a locker not a limited slip. The additive is not needed or recommended by Eaton. I have an 03 2500HD that was doing the same thing and a tech from Eaton explained to me how to get rid of the shudder. Even though it is a locker there is still clutch plates in it and they are all metal. The tech said that the clutch plates get glazed and that is what causes the shudder. I asked about the additive and he said it will help so it doesn't shudder, but it does not fix the cause. He had me dtake the truch and get one wheel on asphalt and one in the dirt, get on the gas enough to make the diff. lock. He said repeat it ten to 15 times and then switch so the other wheel is in the dirt and repeat 10-15 more times. After doing this he said change the fluid with any good quality synthetic, but NO additive. My truck was still under warraty so he suggested using GM fluid until it was out of warranty so if anything ever went wrong there was no hassles. After warranty he said Mobile One or Amsoil would be fine. The tech said that the additive will make the shudder go away because it actually makes the clutches slip and can actually make the locker malfunction. Limited slips use it to help when turning corners and such. In either case I did what he recomended and the problem was gone and never returned. Why you ask did I fix it myself when it was under warranty ?? Because GM said it was normal and nothing was wrong !!! Seems those words are pretty common these days.
Bryan
2003 2500HD Ext. cab short box
6.0 liter 4.10 gears, Nelson performance PCM
98 K1500 4x4 heavy duty 1/2 ton
6,600lb GVWR 5,280lbs on the scale empty
14 bolt rear diff. 3:73 , Tranny and oil coolers
250,000 miles still purrin' like a kitten
Lockers do make some clunking and shuddering by nature and the GM Gov Lok is notorius for that, which is what the Eaton is based on. To be sure, have it checked at a driveline shop. The clutch glaze can be removed by sanding the surfaces too.
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