Hard Shift On 904

The only thing I've seen cause a hard 1-2 shift is when the accumulator spring breaks or someone removes the spring under the accumulator and installs a blocker rod. This is an old school back yard type shift improver that mainly affects the 1-2 shift. I do this on cars with high stall converters in high HP apps because the converter softens the shift quite a bit but I never recommend doing it with a stock converter, or even one lower than 2200-2300 stall. Even then I warn the customer it may shift rough going into 2nd.

You have to pull the front pump to change the bushing, but that's not all that contributes to converter drain back. Worn reaction shaft sealing rings also lend to drain back. They can also be changed with the pump out. If you tighten the front band down good and snug it'll hold the clutch packs in place so you can pull the pump out to do the work on it. Just remember to re-adjust the front band after your done. A worn manual valve in the valve body would also cause drain back. Trans-go, as well as other mfg.'s has a manual valve kit that gives you a modified manual valve so it fills in park (although slowly). I use them in all the trans I do not just to make it fill in park but to replace the almost always worn out manual valve.