ArcticWhite

I'm going in to do a rear end seal fix. I've got a stock set up rear end, but am pushing 590rwhp through it. Would 75W140 be better than stock weight? I know RPM recommends 75W140, but their rear ends aren't set up like stock.

Car is only street driven, but sometimes gets a workout.

Z0HPLZ

anyone have any good input on this question?

neutron82

RPM built my c6z diff, it's a c6z case with wavetrac diff, dss shafts, and stock c6z pinion/ring gear... car makes about 850 and they said the 75/90 was fine... I've been using that since I did the swap and haven't had any issues... fwiw I put a little over 700 through the stock c5z trans/diff for a couple years with amsoil atf in the trans and 75/90 in the diff and it never gave me any problems either

ArtClassShank

I used 75W/90 with no issues. Stock trans/rear.

leadfoot4

Anthony F

It's designed and built to use 75w-90, i wouldn't attempt 140.

NSFW

How much of it for the trans, and how much for the diff?

TastyBacon

I accidentally bought a bottle of each last time I changed the fluid, and I didn't notice until I had already pumped the quart of 75W-140 into the diff. Purists may gasp that I would treat my precious vette this way, but I just pumped the 75W-90 in after it and have been running half-and-half for the last couple years. Been through a track day and lots of street miles since then, no problems. As others have noted, I don't think there's a good reason to run 75W-140, but it doesn't really seem to matter much.

'Shifter

75w140 will actually increase diff temp if the tolerances are cut for 75w90. Change it more frequently if you feel the need, but you're better of buying a cooler assy for it...(expensive as all get out though)