rear diff oil burnt! Help!

:screwy: 1996 silverado, 160K miles, Z71, manual trans. Hauling 5K lb boat 2 hours, smalled burnt oil. rear diff oil was changed 25K mile ago. Whining from rear end. Changed oil in rear end. Unloaded boat/trailer (with surge brakes). Drove 2 hours home. Whining noise, not as bad, coming from rear end. What did I smoke? Don't know what rear end I have. Should I upgrade to a better towing rear end. Any help would be appreciated. Thx.

:screwy: 1996 silverado, 160K miles, Z71, manual trans. Hauling 5K lb boat 2 hours, smalled burnt oil. rear diff oil was changed 25K mile ago. Whining from rear end. Changed oil in rear end. Unloaded boat/trailer (with surge brakes). Drove 2 hours home. Whining noise, not as bad, coming from rear end. What did I smoke? Don't know what rear end I have. Should I upgrade to a better towing rear end. Any help would be appreciated. Thx.


when replacing the rear diff gear oil the cover must come off ...you then cleanout all the metal debris...use a magnet/clean rag and if necessary mineral spirts paint thinner...



use of the proper lubricant is important so you must use your vin# to find out what rear diff you have...


If the diff oil is replaced without cleaning the metal debris out why bother ?

No metal debris in rear diff. Used correct oil.

No metal debris in rear diff. Used correct oil.

If you removed the diff cover and found no debris I can't say what you burned...

gear oil when heated will smell very bad, did it....?

what diff do you have? locking , limited, or standard..?


what oil did you use when you replaced last time?

If you removed the diff cover and found no debris I can't say what you burned...

gear oil when heated will smell very bad, did it....?

what diff do you have? locking , limited, or standard..?


what oil did you use when you replaced last time?


the other possibility is the rear wheel bearing seals leak and got on to the brakes...

There is a chance the ring and pinion have been "cooked" too and needs to be replaced.I have seen this happen in a Dodge Durango due to an oil change place not checking the fluid level in the rear end.Synthetic gear lube will do this too and I know of 3 rear ends burned up due to synthetic gear lube.My father's friend Rich has replaced two ring and pinion sets due synthetic gear lube.Problem with synthetic gear lube it is too hard on ring and pinions.

General Motors differentials come with synthetic gear oil from the factory. There are thousands upon thousands of trucks running around with synthetic gear oil with out any problems. I myself have used synthetic gear oil in my differentials for 20 years with out a single problem.

Have a good one,

Don

General Motors differentials come with synthetic gear oil from the factory. There are thousands upon thousands of trucks running around with synthetic gear oil with out any problems. I myself have used synthetic gear oil in my differentials for 20 years with out a single problem.

Have a good one,

Don

I also agree ....fact is this person does not say what diff he has and exactly what oil he uses....It would be very interesting what occured but I guess we will never find out.....

This is true and I know my father's friend Rich also.One was just fine before switching to synthetic gear lube without noises.Right after the switch,very noisy and loud.After it was torn down.The gear teeth were down to a size of a pencil tip.Synthetic gear lube is not recomended for Detroit lockers either,will screw them up and my father's friend Rich was this told by the place where he got his 9 inch Ford for his 1983 Chevy Monte Carlo

This is true and I know my father's friend Rich also.One was just fine before switching to synthetic gear lube without noises.Right after the switch,very noisy and loud.After it was torn down.The gear teeth were down to a size of a pencil tip.Synthetic gear lube is not recomended for Detroit lockers either,will screw them up and my father's friend Rich was this told by the place where he got his 9 inch Ford for his 1983 Chevy Monte Carlo


my experience with this is , use the lubricant recommended by the manufacturer....switching to synthetic on a vehicle that calls for another lubricant is destructive...on the older vehicles, this is not good to use, synthetic with these older diff's..will as you say screw them up...

If your axle is has posi-traction (usually RPO code G80) there is an additive that must be added to the gear oil to prevent slippage...K & W is one such brand. Amsoil is another. Otherwise, noise, whining, slippage, and damage could result. Sounds like you've already cooked the posi-trac. Either have a technician check it for heat damage or just replace it. Hope this helps!

I was under the impression that the G80 is mechanical locker (built by Eaton) ...all gears, no clutches. The clutches are what needs the anti-slip additive. You can just use regular differential oil on the GM 10 bolt with G80 locker. So technically it isnt even a limited slip, as it doesn't transfer power to the other wheel, both wheels spin at the same speed regardless of traction from one side to another.

Whoops, I stand corrected. G80 is the locking diff, G86 is the limited slip diff. It's been a while since I've owned a truck, so I referred to my Haynes manual for back-up. Here's what is stated:

"Front axles use SAE 80W-90, GL-5 Gear Lubricant. Rear axles use SAE 80W-90 gear oil. Posi-traction axles must use special lubricant available from dealers and most auto parts stores. If the special fluid is not used, noise, uneven operation, and damage will result. There is also a Posi-traction additive used to cure noise and slippage. Posi-traction axles have an identifying tag, as well as a warning sticker near the jack or on the rear wheel well."

It specifically states that posi-traction requires the special additive. And frankly, I have forgotten to use the additive before in my Jimmy. Did it grenade the diff? No. But thinking back, I do recall a noticeable whine as time went on, without doing any towing. So, I'd use it in both G80 and G86 cases, especially when you're going to be towing with your truck. Why chance it?

Amsoil, Red Line, Royal Purple, and Lucas make diff lube that includes this "friction modifier". I'm sure there are others, but these are the popular ones.

[quote=jdmccright]Whoops, I stand corrected. G80 is the locking diff, G86 is the limited slip diff. It's been a while since I've owned a truck, so I referred to my Haynes manual for back-up. Here's what is stated:

So, I'd use it in both G80 and G86 cases, especially when you're going to be towing with your truck. Why chance it?

It is not recommended to use any additive in the locking diff..these 99-on up diff's on trucks use 75-90 wt synthetic..........no additives.......when in doubt as to what diff you have call the dealer with your vin#.....



Only the limited slip uses the additive..some have found 2 of the 5oz bottles is better...than just the spec calling for one...I have had no problems with the limited slip on the 96 impala but I do find this oil needs frequent changing as this vehicle is used in mostly city type driving..this does cause the clutches to work more...


the locking diff on the 2000 silverado is synthetic 75-90 wt and the diff is far superior to the limited diff ...stronger and only engages when one wheel rotates more than the other, then quickly disengages....can go longer on fluid change less wear, and most importantly the wheels lock solid,, unlike the very limited limited slip diff'...

The G-80 is the Eaton locker. When one wheel spins 100 or so RPM faster than the other both wheels lock. They unlock over 25 MPH. GM says no additive is needed in the G-80. The G-80 does come from the factory with synthetic gear oil.

The G-86 is a true limited slip and needs the additive, but was only offered in trucks with quadisteer.


Have a good one,

Don

The G-80 is the Eaton locker. When one wheel spins 100 or so RPM faster than the other both wheels lock. They unlock over 25 MPH.

Have a good one,

Don

I have found when doing my defective park brakes that 2/3 rotations of the rear wheel with the other wheel on the ground will engage the lock....


so whenever I do the park brakes I must lift both wheels off the ground to properly adjust the shoes.......

speed is not a factor ...just simple rotation will get it to lock/unlock....

Thanks for the clarification though I'm concerned that the repair manual says it is required.

Perhaps then the opposite is true in rognmel's case...an additive was used when it shouldn't have? Think I'll stand on the sideline from now on on this topic. Thanks again for the great input.

Here's a thread I found that has a good explanation from Eaton on the proper lube to use and break-in procedure for new trucks:

http://www.gm-trucks.com/forums/lofiversion/index.php?t5652.html

Basically, pre-1998 axles should use mineral-based oil, not synthetic. And neither call for a friction modifier. Finally, they recommend a GL5-compliant, 70W-140 weight for heavy trailer towing.

Talk about a crash course in rear diffs....

How G-80 works

http://www.youtube.com/watch?v=KbMZ9vcYVSg&feature=related

You can click on other G-80 videos to the right of this one.

Thanks for the clarification though I'm concerned that the repair manual says it is required.

Perhaps then the opposite is true in rognmel's case...an additive was used when it shouldn't have? Think I'll stand on the sideline from now on on this topic. Thanks again for the great input.


I was checking your 100rpm statement....It appears that if the vehicle speed is under 20mph and there is a difference of 100rpm the rear wheels will FULLY lock....

with my problem encountered when working on the park brakes this is what is called the PARTIAL locking .. obviously the partial locking I encounted was sufficient to prevent my park brake adjustments as I could not rotate the wheel...off the ground..


above 20mph the locking is cut out ....I never knew that ....

Ahhhh....The G80 a time bomb just waiting to go off. I have seen quite a few of them grenade, most with people running over size tires. BUT have seen it on stock tires as well.