Rear End Locking Issue

[jdewolfe]

I have had this happen twice now. Every once in a while it seems as if my locking rear end stays locked. I only notice it once I start turning and it will eventually dis-engage. Only seems to happen after the tires had been spinning. Today I spun to tires trying to get across some traffic and it stayed locked for a little bit. Last time was me screwing around. Any ideas why it is doing this? I'm pretty sure I'm just out of my 12 month/12,000 mile warranty for the pre-owned thing.

 

Thanks,

Jeff

[hockeypro1411]

Happens to me all the time. If I spin the tires in the rain real good or something, sometimes the G80 doesn't want to let go right away. Driving straight for a quarter mile or so usually dis-engages it.

[dlstewart01]

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 75W-90 GL5 (P/N 12378261). 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 ----------- ------------------ 12678261 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.

[flhusa1]

do not use any gear oil synthetic or conventional which states it has limited slip additives. look for gear oil that is used for manual trannys in import [jap] cars. you wont find any at the auto parts stores that does not have those additives. also clean the assembly with brake parts cleaner real good.

[dlstewart01]

What The manufacturer of the G80 says.......

 

"From Mr. Ralph Holmquist of Eaton, the maker of the locking differential:

"The maintenance schedule for the rear axle was developed by American Axle &

Manufacturing and GM truck based on multiple tests. The Eaton locker does

not require additional maintenance nor does it add heat to the lube. The

lube will darken due to the carbon wear on the clutch surfaces, much the

same as a disc brake pad & rotor. This does not damage axle components such

as seals or bearings. However, a new axle can produce excessive

temperatures (plus 350 degrees F) due to the ring & pinion breaking in that

will break the lube additives down. Avoid high loads, trailer towing and

high speed extended driving during the initial break in of the vehicle.

After the break in period axle temps will level at a much lower figure.

Lube changes are a good idea because the additives are replenished and

contaminates such as casting sand are eliminated. The axle is filled at the

factory with a synthetic 75w90 GL5 rating made by Texaco under part # 2276.

The GM service # is 12378261. This is the only lube we have done extensive

testing with to insure locker compatibility. The only negative to using one

of these other lubes is an increased potential for clutch chatter. This

really doesn't hurt anything and can be corrected by changing the lube. I

noticed in the latest GM owners manual the term "or equivalent" when

referring to the lube specification. Look for a GL5 rating on the bottle to

make sure the ring & pinion, seals & bearings are protected. Limited slip

additive is not needed."The following information outlines the type of

rear axle lubrication utilized in GM Truck axles.

I. Fluid Type

II. The 1500, 2500 and 3500 GMT 800 Trucks utilize SAE 75W-90 Synthetic Axle Lubricant. The GM part number is 12378261 and the specification is 9986115.

[Z45]

The only negative to using one of these other lubes is an increased potential for clutch chatter. This really doesn't hurt anything and can be corrected by changing the lube.

 

Whats funny is just about every complaint about chatter involves the oem lube, the very one this person recommends. I think they should test another brand instead of the low bidder. There are service bulletins on this up the ying-yang on rear axle chatter going bavk for years, even on nearly new vehicles but GM is stubborn and continues to use the same lube year after year and has the same problems year after year. Yet the manf. of the gear says the only lube you should use is the one that gives nothing but problems.

 

I have owned many G80 equipped GM trucks, all had G80, 87,89,92,96,99,01,04,08,10 and every one got changed to AMSOIL severe gear before the hit 5,000 miles and NEVER have I noticed any chatter, clunking, or any other anomalies with my trucks nor I my CTS with the G80 LSD.

 

Btw-GM charges a lot of money for their synthetic gear lube, way to much money.

[jblakeney]

Change the fluid. Refill with GL5 Synthetic add a friction modifier. If you still have this problem add some marvel mystery oil. Warm the Marvel Mystery Oil up prior to poring it in, 1 pint or less. This will reduce noise and locking problems in a locking differential. BUT CHANGE THE OIL FIRST if it still has a problem then add the Marvel Mystery Oil.

 

Jbo

[dlstewart01]

Change the fluid. Refill with GL5 Synthetic add a friction modifier. If you still have this problem add some marvel mystery oil. Warm the Marvel Mystery Oil up prior to poring it in, 1 pint or less. This will reduce noise and locking problems in a locking differential. BUT CHANGE THE OIL FIRST if it still has a problem then add the Marvel Mystery Oil.

 

Jbo

 

What GM says about a friction modifier...

 

***Important: Installing any friction modifier causes the clutch pack in the locking differential to slip and miss engagement. A fluid flush can often remove debris that is a contributor to clutch chatter. Adding friction modifier additive can cause a loss of locking differential functionality***

 

And MMO will thin the gear oil out way too much in my opinion...

[Stevens03]

My 03 use to do that and I never had an issue. I also changed the fluid after the first 500 miles but that still didn't stop it from doing it occasionally.

[P71_CrownVic]

I have had this happen twice now. Every once in a while it seems as if my locking rear end stays locked. I only notice it once I start turning and it will eventually dis-engage. Only seems to happen after the tires had been spinning. Today I spun to tires trying to get across some traffic and it stayed locked for a little bit. Last time was me screwing around. Any ideas why it is doing this? I'm pretty sure I'm just out of my 12 month/12,000 mile warranty for the pre-owned thing.

 

Thanks,

Jeff

That had happened to me as well. I don't think it's an issue...just the operation of the G80. It should unlock automatically at 25MPH or more...

[jdewolfe]

Thanks guys for all of the replies. I'm going to leave it for now, but will end up changing out the fluid at some point in time. If something changes, I'll be here to let you guys know.

 

Thanks again!!

[jblakeney]

What GM says about a friction modifier...

 

***Important: Installing any friction modifier causes the clutch pack in the locking differential to slip and miss engagement. A fluid flush can often remove debris that is a contributor to clutch chatter. Adding friction modifier additive can cause a loss of locking differential functionality***

 

And MMO will thin the gear oil out way too much in my opinion...

 

I have used it several times to remedy differential noise. In all cases I have had it cured it, clutch or gear noise. It may thin the mix that is true.

 

Jbo

[KMGZ400]

it is normal for it to lock up.. happens a lot if you like to play around with your truck. the first time it happend i shit my self i had no idea what is was.. thought my rear end was done..

[Stex]

Good thread, thanks for the info Don.