I've noticed a grinding noise/vibration coming from the rear of my Formula. It only happens during tight right turns and only when power is applied in the turn. I just recently changed the fluid in the rear to synthetic with posi additive though it wasn't the GM fluid. Anyone have any thoughts?

 

Are you sure it's a posi?

Pull the cover and check for excessive metal shavings, and pull the axle shafts out and check the bearings. Also check the tightness of the pinion gear, but I would think either something in the carrier or the bearings on one side are at fault. You may want to put it on jackstands and see if you hear the noise before you tear it apart though.

 

Well it has started doing it when I turn either right or left. I did the fluid change about a week ago and everything was fine. I used Mobil 1 75/90W gear oil with TransX posi additive. I've always used the GM additive prior to this. And yes it definitely is a posi. I had an Auburn put in when I had the 3.73 gears put in.

 

I had an Eaton posi in my truck and I tried every additive known to man to make it quiet. The only thing that worked was the additive from GM. This was eight years ago so there might now be something out that works just as well.

 

Auburn is very specific about using a non synthetic, and GM additive...
I just bought a HP Auburn Posi last week, and it's on the first page in bold

I don't know if that will help, but that’s straight from Auburn...


Ron

 

My Auburn is 11 years old so I'm not so sure that the non synthetic rule applies. I have always used the GM additive though. I just changed the fluid again and used the GM additive and almost immediately the noise stopped.

 

Well, I'm going to go out in get that GM stuff, cause I have a tube of something I bought at Checker Auto.

Hey, did you have to get the GM stuff at the dealer? Does anybody else sale it?

Ron

 

Yep,it's a GM only product. You'll have to go to your local dealer.

 

The GM additive is worth its weight in gold. I had the same problem the GM stuff fixed immediatly. The other additive out there only seem to do a half *** job of fixing the chatter. It cost about $8 a bottle through GM. I was researching this before and I think I read on the Auburn web site that this chatter does not damage the posi at all. I found it hard to believe because the noise/vibration it makes is terrible.