what weight gear oil 8.75?

[moparnut]

I do have to add that my 2002 f250 diesel 4x4 has a posi in the rear.The dealer calls for 75/140 gear oil and the only gear oil in that weight is SYN, its only made in Syn. So if the syn damages a posi, the manufacturer wouldnt recommend it.

[bb71challenger]

well i already have the syn,
I believe you dont need additive unless you have a clutch type suregrip, mine are cone

The one that got trashed was a cone type.

[moparnut]

could very well be just a coincidence, things do break some times

[bb71challenger]

I do have to add that my 2002 f250 diesel 4x4 has a posi in the rear.The dealer calls for 75/140 gear oil and the only gear oil in that weight is SYN, its only made in Syn. So if the syn damages a posi, the manufacturer wouldnt recommend it.

I dont think synthetic oil damages anything, it just does not have the hypoid gear additive that our sure grips require.

[moparnut]

any syn that i have looked at has gl5 for hypoids(posi's)
API Category GL-5 designates the type of service characteristic of gears, particularly hypoids in automotive axles under high-speed and/or low-speed, high-torque conditions. Lubricants qualified under U.S. Military specification MIL-L-2105D (formerly MIL-L-2015C), MIL-PRF-2105E and SAE J2360 satisfy the requirements of the API GL-5 service designation.

[Tonefiend]

I do have to add that my 2002 f250 diesel 4x4 has a posi in the rear.The dealer calls for 75/140 gear oil and the only gear oil in that weight is SYN, its only made in Syn. So if the syn damages a posi, the manufacturer wouldnt recommend it.

I got some Valvoline dyno oil in that weight at Autozone.  My diff mechanic recommended I use a 140 weight in there.