I posted it in the g80 sticky but no replies. Does anyone know why it would be stuck engaged? i'm gonna open up the rear diff this weekend. it really is a pain in the ass.
Broken springs. Stab the gas in reverse a couple times if you haven't, sometimes they wear a little and don't disengage without a couple reverse rotations. If it doesn't let go from that, then prepare to at least replace a few pieces if you can get them separate.
That's because most people grenade them shortly after rather than getting the chance to fix it. It all depends on which part fails, there's only one or two that won't wipe out part of the carrier if they break free into the gears.
I had mine stuck locked after I changed the fluid to Mobil-1 75w90 with LS (limited slip) additive in it. We aren't LS, we are full lock, and it messed with it. I changed it out to Amsoil Severe Gear 75w90 and it hasn't had an issue since.
Mine locked after a session in heavy sand; reversed it a couple of times, drove around the block and got released. It has locked/unlocked several times after that one with no problems so far.
The G80 is a mechanical locker, which relies on the speed of the axle and the differentiation of left/right axle speeds to lock/unlock. It's a centrifugal type locking mechanism. The additive causes the workings and mechanism to stay "locked" longer than normal. That's why those who have the additive are experiencing issues with the G80 staying locked.
The G80 is NOT limited slip. It's a bona-fide locking axle that's controlled automatically.
How does limited slip additive make it stay "locked" longer?......the additive only makes things slicker. I just don't see how the additive could possibly have a negative effect on any type of locking diff.
Surface tension. Ever watch those skeeters zipping across the water? They don't get wet due to the water's surface tension. LS adds to the oil's surface tension, making it harder for bits & pieces to unlock, where in an limited-slip differential, the little clutch discs need that tension to work properly.
My experience doesn't jive with that. Literally 2 days after I went from AC Delco to Mobil 1 LS it started having issues unlocking and after a few weeks I pulled it and went to Amsoil Severe Gear.
Hasn't had the issue since. Maybe the Mobil 1 I got was not to spec?
Just found this after calling my buddy (Stealership Service Manager)
Per GM tech 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.
When oils lose friction modifiers, the shear of the entire fluid is affected -- not just across the the engagement surface; there is no 'differential shear', the entire shear rate changes. I don't know enough about the G80 to add more to this conversation, but there are some flaws in the above argument concerning viscous coupling & shear rates concerning friction modifiers (part of my job is to model drilling fluids in the oil & gas industry).
The inside wheel clutches in a turn need to slip smoothly or else there will be chatter or jerky differentiation in a turn. The addative allows the inboard clutches to slip smoothly. Addative is pnot needed unless limited slip chatter can felt/heard.
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.
So here I am in this what seems to be a big debackle over axle lube. Yesterday I decided to drain and fill my axles and after draining and filling the front I noticed that the Mobile 1 75w90 LS fluid I bought has the friction modifier included. I'm now wondering is it ok for the front axle and maybe not so much for the rear g80? I think I'm going to hold off on draining the rear til I get to the bottom of this. If it's ok for the front it will save me the hassle of draining and filling again plus the $24 in fluid I would waste. I'm sure I will get both answers here but thought I'd ask. Thx
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