blk97z28

iTrader: (3)

97 camaro z28. I've owned since 2005 with 68,200 now it has 75,800. At 70,000 miles I did rear end fluid change with vavoline 75W-90 full synthetic SYN power with 2oz of a 4oz bottle of GM limited slip. The read end was replaced at 20,000 in the history log but I couldn't obtain further details as to why.

Flash forward to now:

Rebuilding with Richmond mega install kit, all new bearings and seals + motive high performance orange box 373 gears (started with 273's). So for the shop I provided everything including Royal Purple 75W-90 3 quarts (going with the TA cover and stud kit), and the one bottle GM additive. The car is all done and ready to go today, when he took apart the rear he said it was in brand new condition he took it all apart cleaned and inspected everything. All the while I was using the synthetic gear oil which was recommended to me on this site back in 2010.

Now I was searching on it because I have the yellow springs in the posi so that means Auburn rear end? And threads on here say do not use synthetic oil, I have to do a 500 mile breakin period for the gears and then the same shop is going to take the cover oil, check gear path and order from TA a magnetic drain plug as one was not provided. In 500 miles with the synthetic oil kill the gears or the posi unit? I mean it was 100% in perfect shape, should I just have them redrain the oil and put in 80W-90 plus additive or will I be alright?

Thanks in advance

BALLSS

I think in the short term (500 mi) you would be OK

Auburn and Eaton both spec using a mineral based oil aka Dino oil. It is the clutch material that is used in the LS differential that does not like synthetics.

Any G5 rated 70-90 wt gear oil and a 4 oz bottle of the GM or Ford friction modifier. My Eaton came with a bottle of the Ford stuff

blk97z28

iTrader: (3)

So you recommend 70-90 gear oil or do they make Dino oil in 75-90? I've seen a lot use like 80w-90? I'll have everything ready to go then after the initial breakin

BALLSS

80-90 or 75-90 is fine. Just non-synthetic. Any store or major brand as long as it is GL5 rated

using mineral based oil is because of the clutch material in Auburn & Eaton LS diffs. The metal gears themselves don't care so for those running a locker type diff synthetics are fine

blk97z28

iTrader: (3)

Called them up had the oil switched and the bottle of LS from gm dealer added it. Originally the synthetic oil had the additive so they didn't add the additive in. I drove about 20 miles so far (did 5 miles then another 10 miles). Varied speed via stop and go between across town up to 55 mph. I downloaded the app speedometer after my speedo and shift point calibration and it is dead on money on the first try.

They used 80W-90 Conventional oil in the rear end before I picked it up today. I listened very closely for any howling on acceleration or deccel; so far no issues at all. I can already tell a difference in the gears; pulls hard and I've been babying the throttle.