C4 Transmission issue

[Bill Harris]

It's a little hard to correlate how changing the gear ratios would affect the 2-3 shift action, but perhaps it has to do with the torque and rotational speeds of the drums involved. A 2-3 flare is actually the transmission state going 2-1-3, with the brief first gear state causing the engine RPM flare. 2-3 shift is two actions on the direct drum. In 2nd gear, the drum is held stationary by the band, and to shift to 3rd the band has to release and the direct clutch has to apply which causes that drum to go from stopped to engine RPM in a very short period of time. If the band is released before the clutch is applied, that is actually first gear and the drum starts to rotate in the reverse direction (!!) before the clutch application catches it and gets it rotating in the forward direction. Maybe the higher first gear is applying more torque and a higher reverse RPM to the drum before the direct clutch can catch it. The lower gear ratio would also increase the load on the direct clutch, making it harder to stop the drum ... thus the increased flair. Like SS3011 says, if the direct clutch is slipping, or doesn't have enough capacity to stop that drum which now has more inertia, that would show up as a flair. If that is the case, it's going to burn it up eventually. You may have to play with different band servos to clear it up completely. Maybe call Joel's on Joy and see if they can recommend a servo to go with that 2.92 ratio. That is a LOT steeper ratio than the OEM which is around 2.46 (if I remember right).

[fordteacherguy]

A possible cause of weird flares is end play out of specs affecting sealing ring performance especially considering hard parts replaced that might change stacked clearances. End play spec is .004-.044 but I prefer under .020 or less for race trans and near the low end if it is rollerized. There is not much going on inside one of these...Excessive direct clutch clearance or band adjustment way off will affect the 2-3, but not 1-2.

Those are the most common problems I see if the VB was the same and worked fine before. Probably something simple....I share with my students my 4 rules of auto trans.

always check the pump
always check end play
always check clutch clearances
always air check before VB goes on.
If it passes these 4 checks the worst you usually have is a VB problem which you can fix in the car..all the rest, its coming back out!