Does it just spin one tire, or does it make grinding sounds when turning? Mine has been grinding lately. I think it's almost time to retire the damn truck.

Could it be the full-synthetic oil the guy who put my new gear in used? Yes we did use the friction additive.

I bought some regular oil and more additive for it, but haven't had time to change it yet.

 

pretty sure you are suppose to use synthetic with the stock rear.

my diff just blew to pieces when it went bad. took out everything. i would expect a grinding noise to be something other than the g80. bearing or brakes.

 

It's an aftermarket Eaton 8.5" with the clutch packs. The sound only happens when turning and is coming from the back, so I assume it is the differential.

What do you think? Do the aftermarket clutch pack differentials wear out differently than the G80?

BTW I still have your ASM headers on my truck from WAY back in the Whipple days

 

If you're referring to the aftermarket (not a gov-lock) version of the differential unit you can't run synthetic in there. You have to run non synthetic with the additive or you can get groaning with possibly clutch slippage.

 

service it and add the friction modifier and it will be fine.

 

I run straight 80/90 non-synthetic and always have with my Eaton posi. They are definately not compatible with synthetic. Mine doesn't require friction modifiers but the instructions for the 10.5 may be different from the 8.5/8.6.

 

I broke some teeth off the spider gears in my Eaton Posi but it would catch and pop at anything other than absolute straight rather than making a grinding sound. Rebuilt it with new spider gears and all is well thus far.

 

It was the oil. I changed it today to regular oil and it instantly stopped. I told the guy when he fixed it that I didn't think synthetic was a good idea, but he said it would be ok. Guess I proved him wrong lol.

The synthetic is just too slippery for the clutches.

 

glad to hear its fixed, i hate little hang ups like that but i guess that is how we learn right?

 

almost was an expensive way to learn..