Rear differential flush and fill.
Thread Starter
Race Director
Joined: Apr 2003
Posts: 19,352
Likes: 654
From: Tampa, Florida
Rear differential flush and fill.
My car is finally on the road so I'm able to properly drain and refill both the rear differential and 4sp. tranny.
I've read different theories about flushing rear differentials and was curious as to what you guys thought.
I'm going to assume the fuid in my differential has been there since 1970. My plan:
1. Drive it around the block a few times to warm it up.
2. Drain and refill
2. Drive it around again and drain and refill
My questions are:
1. After I drain it the first time would filling it with ATF to flush it out hurt anything or should I fill it with regular diff fluid?
2. Should I put friction modifier in it for the previous step?
3. For the final fill should I stay with regular fluid or go with synthetic?
4. How much friction modifier for the final fill?
Engine is relatively stock.
Thanks,
Jim
I've read different theories about flushing rear differentials and was curious as to what you guys thought.
I'm going to assume the fuid in my differential has been there since 1970. My plan:
1. Drive it around the block a few times to warm it up.
2. Drain and refill
2. Drive it around again and drain and refill
My questions are:
1. After I drain it the first time would filling it with ATF to flush it out hurt anything or should I fill it with regular diff fluid?
2. Should I put friction modifier in it for the previous step?
3. For the final fill should I stay with regular fluid or go with synthetic?
4. How much friction modifier for the final fill?
Engine is relatively stock.
Thanks,
Jim
Tech Contributor
Joined: Aug 1999
Posts: 15,177
Likes: 3,994
From: Connecticut, USA
Use 90Wt gear oil in the tranny
Use GM posi additive & 85-140 Lucas non synthetic gear oil in the diff.
If the diff hammers you may need 2 bottles of additive.
You don't need to use ATF in it. If it's old and baked that's not going to clean it and if you haven't installed a drain plug you won't get all the muck out anyway.
Use GM posi additive & 85-140 Lucas non synthetic gear oil in the diff.
If the diff hammers you may need 2 bottles of additive.
You don't need to use ATF in it. If it's old and baked that's not going to clean it and if you haven't installed a drain plug you won't get all the muck out anyway.
