Manual Trans. Oil Question.

[CAJUN C4]

Do you think it's bad to use Synthetic Gear Oil (Mobil 1 75w90) in a 4 Speed Muncie (4+3)?

 

[Ken]

I use Dexron Mercon IIIE in my Richmond six-speed.

 

[c4cruiser]

It should be OK to use in the T10 portion. You can use Mobil-1 Synthetic ATF (which is Dexron-II compatible) in the OD portion.

 

[Ken]

People who want to avoid contamination issues have used ATF in both the overdrive unit as well as the T-10 gearbox. The only issue they spoke of was the additional gear noise due to the lighter lube. There was no lubrication problem that I know of when using ATF in a manual gearbox except for the gear noise.

 

[G Winter]

I had a 1974 4 speed in a GM car about 15 yrs ago. I used 10 -40 non synthetic in it with no problems, it actually shifted better than with gear oil in it. I had it open after 50 k and no wear anywhere. In the early 80s GM use ATF in the transfer cases on 4 wheel drive pickups.