Rear End Gear Grinding Soon after Posi Additive Added

[Terbro]

About a 18 months ago, I had my rear end totally rebuilt. New axles, GM gears and Auburn posi. About 6 months ago, it started grinding during low speed tight turns...which I recognized as a lack of posi additive. So I added a tube and it went away. Well, it started doing it again about a month ago, so I added another tube...and it went away. But it's doing it again.

What's going on here? I raced it at the track for the first time last weekend (12.38 @ 112) in 3 years. So you can see, I don't have too much power for it to handle. My trans does shift very hard, which might be putting extra stress on it...

TIA,
Terry

 

[VIN7]

Terry,

The only thing that worked in mine was two bottles of GM posi additive, any other and it clunked.

Mike

 

[Black Car]

Did you change the fluid out when you last added the posi additive?
If you "just added" the posi, then you should drain the rear end and put new 80-90 weight fluid with a bottle of posi additive to it.
I change mine every 10,000 miles.
Just my 2 cents.

Gary

 

[Terbro]

Gary -

Are you changing it because it starts to grind, or just because it's good preventative maintenence? I did change the fluid about 6 months ago and added new posi additive. I don't even think there are 10K miles since then...it shouldn't be complaining...something's amiss.

 

[PlaneMech]

Put more additive in it. Service the rear-end with 90 weight for limited slip units. And I always put at least 2 tubes of posi additive. Servicing the grease every 10 thousand seems excessive.

Thanks,

John

 

[Nick Micale]

If there is a "chatter" sound in the GM posi rear when turning it is usually the friction clutches. The posi additive will cure this since it is a friction modifier that allows more slip between the plates. However, the Auburn unit is different and may require a special lube or may have a different problem?

A "grinding" noise is more of a bad bearing or the ring/pinion gears self-destructing. Maybe you should check it out and pull the cover?

 

[Terbro]

"Special Lube"?

Well, I took a quick peak at the gears 6 months ago, when it first started doing it, and they looked beautiful. Just like healthy 12 month old gears should look.

But I'm not aware of any special limited slip 90 weight gear oil - only regular gear oil and then the separate limited slip additive.

Nick - what do you mean "special" for Auburn? I've never heard of that either.

Thanks for your feedback,
Terry

 

[GNVAIR]

The Auburn is a cone style differential. They usually take the same type of friction modifier. If there is a noice, then something is definitely wrong. Especially if the noise cropped up all of a sudden. I agree that you should pull the cover and check it out.

 

[GNsQuick]

I would say it could be another one of those Auburns going out again, just remember next time to buy a Eaton Posi unit.

 

[Terbro]

Correction! Mine is actually an Eaton...I just remembered.

 

[GNVAIR]

If it is infact an Eaton, then I would recommend pulling the cover and draining the fluid. Inspect everything. If it all looks ok, then put it back together and install regular 80/90 gear oil (not synthetic!) along with 2 bottles of the bluish/green Ford Motorsport friction modifier. The yellowish colored GM friction modifier does not seem to have the lubricity that the Ford stuff has. I have had noise problems with a lot of GM limited slip rears and the Ford friction modifier quiets it right up. Email me offline if you want me to put you in touch with a distributor for it.