Help from the rear end experts

[grewag]

I had used Auburn posi unit put in my 69 firebird and it is making a clunking sound when I take off in 1 st and reverse. I don't notice any noise when I'm driving it down the road. It is only when I am barely moving with and with tention on the wheels. It will even do it with the clutch in. For example I notice when I and pulling strait forward or in reverse in and out of garage. The posi unit came out of a 1970 olds. A new install kit was used and the mechanic used synthetic oil with the limited slip additive. Any advice what it could be?

Thanks

[b1lk1]

Use conventional gear oil. Auburn does not recommend using synthetic fluids and I have hear od other people having issues with synthetics in these diffs. I have an Auburn in my 2002 Mustang and it is quiet as a mouse with conventional (plus the LSD additive of course).