Local F100 truck owner contacted me about this project truck with an AOD transmission not shifting into OD/4th gear. On the test drive I found the transmission engages harshly in Reverse and Drive, the shifts were firm and late with no up shift from 3rd to 4th. The transmission had been rebuilt 2 yrs ago by a local transmission shop. While the rebuild was done correctly, they didnt perform any hard part upgrades, most importantly the OD band and OD band servo. They used the smallest OD band apply servo and the stock 1.5" band, Not a good combination on a 3000 lb truck with a 300+ HP 351W.
Removed the transmission from the truck and found the 1.5" OD band is burned, no other damage was found. While I had the transmission apart I upgraded the OD band to a 2" band, this required changes to the sun shell and reverse drum. The upgraded Reverse drum not only incorporates the 2" band, but its also larger in diameter for greater mechanical leverage. The OD servo was upgraded from the smallest servo ("C servo) to the largest servo ("A" servo). I also upgraded the intermediate clutch from 3 friction discs to 4 frictions by using a thinner pressure plate.
The truck owner wanted firm shifts with out being harsh, since the truck is used for car shows and cruising the parking lots, I contacted Dan at Silver Fox transmission and ordered a SPT stage one constant pressure valve bodies. The Constant pressure set up only requires the TV cable for shift timing.