Question for GM Techs on Chevy Tahoe

[Gary H NC]

My 99 Tahoe 4WD has started to have a slight slip when taking off from a dead stop.
I had this problem back a few years ago while it was still under warranty and the dealer said the problem was in the rear differential.

They changed the gear oil and added some "special" additive to the rear end lube and problem solved.That was 80K miles ago.
I'm pretty sure it is the exact same problem again by the way it feels.
At take off it feels like it grabs a little then catches fully...strange feeling.

When i changed the oil last time i checked the rear end and it was low.
All i had in the shop was 75w-90 Mobile One gear lube so i added that.
After about 50 miles of driving is when this slip feeling started.

I want to completley drain the rear diff. and fill it with the correct stuff.

Anyone have any idea what the dealer may have used.
That particular dealer is no longer there.

 

[paultjohnson]

Re: Question for GM Techs on Chevy Tahoe

When my 01 Silverado started doing that, It was just low on tranny fluid.. Go thru the steps .. get it to opp temp. Stop the truck, go from park thru all the gears, stopping for 2-3 sec in every gear and then back to park same way. All at a dead stop. foot on break. Pull tranny dip stick. Wipe it off and put it back in for 3 seconds, then check level.. .[ with engine running , on level ground...

 

[Gary H NC]

Re: Question for GM Techs on Chevy Tahoe

Yes,Will check the tranny level again. It was full when i done the oil change a few weeks ago.Nice and pink too.No burnt smell.

 

[paultjohnson]

Re: Question for GM Techs on Chevy Tahoe

OK Back to the rear end then Do you have a OEM locking rear diff ? I never had the --slippy feel like you. I always had 1 wheel turning, but in slippery conditions [ we get that now and again in Mn. ] when I would lose traction and the diff went to lock up so had had em both turning in back It was HARSH Like a nuetral drop.. The dealer told me the clutches in the R end get glazed or gunked up[ not really sure] He said go into a parking lot. put it into reverse and drive around backwards doing a bunch of sharp turns, left to right. That was supposed to de[ whatever] the clutch pacs by putting reverse friction on em .. It worked No more ... crlunksh... Yeah thats a word...

 

[Gary H NC]

Re: Question for GM Techs on Chevy Tahoe

Yes,original locking rear diff.
I just finished pulling the cover and letting it drain.
For 113 K on the clock it looks really clean and no metal on the magnet.

I was reading on a Chevy truck forum that the hard core 4WD guys run the Royal Purple with the additive already in it.Or there is a limited slip-locking rear additive that is sold to add to the lube.

Off to the parts house for a new gasket and to see what they have for lube.

 

[Gary H NC]

Re: Question for GM Techs on Chevy Tahoe

Oh,I will do the driving in reverse thing too...

 

[Gary H NC]

Re: Question for GM Techs on Chevy Tahoe

Found out that it calls for 80W-90. So not sure if the 75W-90 that was in it could have caused any issues.
Job is finished and filled with 75W-90 Valvoline Synthetic lube.

That Royal Purple was 20 bucks a quart!

Will test drive later and see if any difference...

Thanks for the input Paul..

 

[DECK SWABBER 58]

Re: Question for GM Techs on Chevy Tahoe

Did you add the additive that cuts down on clutch chatter?

As far as I know this is required on all GM locking differentials.

 

[Gary H NC]

Re: Question for GM Techs on Chevy Tahoe

Reading the owners manual it states not to use a friction additive on the 4WD models,but it is needed on the 2WD models.
The gear lube i bought said it was for limited slip and posi rear ends.
Wondering if i still need the additive?
Kinda confusing......I would hate to have to drain it again and go buy the AC Delco lube the manual tells you to use.

 

[TilliamWe]

Re: Question for GM Techs on Chevy Tahoe

Reading the owners manual it states not to use a friction additive on the 4WD models,but it is needed on the 2WD models.
The gear lube i bought said it was for limited slip and posi rear ends.
Wondering if i still need the additive?
Kinda confusing......I would hate to have to drain it again and go buy the AC Delco lube the manual tells you to use.

Owner's manual makes no sense, as both the 4wd and 2wd can use the same rear ends.

Check your glove compartment for the list of 3 digit codes. Go to the "G"s and find G80. If it's there, you have a locking rear differential. (I'll bet you a quarter you do, as almost every 4wd GM product I have ever seen has the locking rear diff).

The gear lube you bought should be fine.

 

[Gary H NC]

Re: Question for GM Techs on Chevy Tahoe

Yes..It did have a G80 i believe and some other numbers on the diff cover.I will verify that in the glove box codes.It was the 10 bolt cover.
Thanks!

I know it does lock because it will not do the right wheel burn out...lol!
On wet pavement both back wheels spin.

 

[dolluper]

Re: Question for GM Techs on Chevy Tahoe

Gary 75w90 syn gear oil front and back dif's on selectable 4wd...... now if you have full time 4wd then 75w90 syn gear oil rear dif..... FRONT dif takes 80w90 GL-5 gear oil as said before clutch chatter additive for rear lockers does help them help

 

[metalwizard]

Re: Question for GM Techs on Chevy Tahoe

I'm a little confused. How does a differential SLIP going straight? (or starting from a stop)

the clutches ONLY are in use during a turn, going straight there is NO pressure on them. the clutches hold the left and right axle together as long as they can untill they HAVE to go different speeds to go around a corner.

I agree with the other poster. check you TRANS.. I was a heavy line technician for Chevrolet and Jeep until the mid 90's i have NEVER heard of them slipping going straight. NOW if it's in a turn.. different story. OR if the TIRES are losing traction. But the DIFF cannot loose traction. unless the gears are so worn out they are slipping. and that does not happen. they Growl, clunk grind and Burn up WAY before your gears wear that bad.

Oh if the differential is GRABBING then maybe but not SLIPPING going straight.

 

[dolluper]

Re: Question for GM Techs on Chevy Tahoe

U-joint slop

 

[Gary H NC]

Re: Question for GM Techs on Chevy Tahoe

Checked U-joints..no slop there.
I will get it out and drive it tomorrow.I left it in the garage all day today.

So i need to put in the additive?

Thanks for the help guys!

 

[Gary H NC]

Re: Question for GM Techs on Chevy Tahoe

Just found this on a GM forum,

from a GM service bulletin..

LOCKING DIFFERENTIAL LUBRICANT (SERVICE INFORMATION) #91-4-109
SUBJECT: LOCKING DIFFERENTIAL (G80) LUBRICANT - (SERVICE INFORMATION)
VEHICLES AFFECTED: ALL LIGHT TRUCKS EQUIPPED WITH G80 REAR AXLE ALL YEARS
Some light duty trucks equipped with locking rear axles (G80) may exhibit rear axle chatter, especially when turning a corner from a stop.
This condition of alternate engagement and disengagement of clutches in differential assembly is usually caused by contaminated axle lubricant.
To correct this condition, drain and refill the rear axle with SAE 80W-90 GL5 (P/N 10950849). The use of any additive in locking rear axles (G80) is not recommended. Rear axle additives are designed for use in limited slip differentials which are normally installed in cars. All light duty trucks equipped with RPO G80 make use of a locking differential and the use of additives will delay the engagement of the locking mechanism and may decrease axle life.
VEHICLES/COMPONENTS INVOLVED: ----------------------------- Some light duty trucks equipped with locking rear axles, RPO G80.
SERVICE PARTS INFORMATION:
Part Number Description ----------- ------------------ 10950849 Lubricant, Rear Axle (1 litre)
Parts are currently available through CANSPO.
WARRANTY INFORMATION:
As specified in Light Duty Truck Maintenance Schedules, locking rear axle fluid drain and refill is required owner maintenance at the first engine oil change. Failure to drain and refill the rear axle as specified may contribute to a later axle chatter condition. Refer to the appropriate Light Duty Truck Maintenance Schedule or service manual, section OB, for further details on change intervals.
General Motors bulletins are intended for use by professional technicians, not a "do-it-yourselfer". They are written to inform those technicians of conditions that may occur on some vehicles, or to provide information that could assist in the proper service of a vehicle. Properly trained technicians have the equipment, tools, safety instructions and know-how to do a job properly and safely. If a condition is described, do not assume that the bulletin applies to your vehicle, or that your vehicle will have that condition. See a General Motors dealer servicing your brand of General Motors vehicle for information on whether your vehicle may benefit from the information.
? Copyright General Motors Corporation. All Rights Reserved.


The lube i used was the correct weight but stated it was for limited slip or posi-traction and met GL-5 standards. No mention of locking rear diffs.

 

[sprintst]

Re: Question for GM Techs on Chevy Tahoe

My old Camaro had a posi rear end that clunked when turning and that Gm additive solved that straight away.

For your newer G80 rear end it's probably time to drain and refill...see what GM has in the synthetic products if it isn't already. 80K is a long time between fluid changes especially if you've submerged the rear end.

 

[avenger79]

Re: Question for GM Techs on Chevy Tahoe

i know you said that particular dealer closed but you have to have a GM dealer close. best thing to do is go to the dealer and tell them you are changing your rearend fluid. they will give you what you need the first time. take your VIN with you.

I know on my ford I had to add friction modifier to the rear end.

i do agree with above also I've never heard of a rearend "slipping" going straight.
sounds like you need to go through and do a fluid and filter change on a lot of components.
i would look at doing a filter and fluid change on the tranny as well. not a flush and fill. take the pan down and change the filter. it's almost as easy as changing oil.

 

[98Shabah]

Re: Question for GM Techs on Chevy Tahoe

Slip going straight from a stop has nothing to do with the differential unless you're mashing the gas and spinning one rear tire.. If there really is "slipping" this is a transmission issue.. Slippage would usually indicate a worn pump, bad seals not holding the pressure, or a valve body problem.. in any event, it'd be time for a rebuild.

If it's not just slipping but "slack" in the driveline, then it'd be ujoints or worn ring and pinion in the rear diff, or a combination of both.. Get it off the ground and check for slop in the unjoints and diff.

 

[642mx]

Re: Question for GM Techs on Chevy Tahoe

I know it does lock because it will not do the right wheel burn out...lol!

That's called a "one tire fire"...lol.

The slip from a dead stop is mostlikely the torque converter. At least that's what I've seen from GM's with 150K+ miles on them.