Transmission 3-2 Downshift is hard

[Icepick]

I have a '87 Cutlass Calais with a V6- 3.0 and a 125-C Trans. It started downshifting hard just a few days after I did a trans fluid flush and filter change.

When the transmission downshifts from 3rd to 2nd, it bangs into gear hard. It does it at exactly 15mph.
Also, it seems to do it only when it has warmed up and driven about 10 minutes. It doesn't bang when it's cold in the morning.

It "upshifts" perfectly fine without any problems.

I tried changing the governor and speed sensor, but it did nothing. My next try will be to drop the pan again and inspect the servo and accumulator check valve.

Does anyone have any ideas of what it could be?? Could there be a problem in the Valve Body??

[GTP Dad]

Could be a problem with the valve body but the transmission flush may have damaged the clutches to the point where they are not seating properly and you may end up changing the transmission. You may want to try some sea foam or lucas oil transmission treatment, as this may help the problem.

[Icepick]

I would agree with your "damaged clutch" theory if the transmission was upshifting badly, or slipping, but the rest of the transmission's functionality is perfect. Upshifts smoothly 1-2, 2-3, and 3-lockup. No slipping. Kickdown works great, and except for the 3-2 downshift, the lockup-3, and 2-1 downshift works normal.
I know that the accumulator controls the force in the 1-2 shift, but what controls the 3-2 downshift and the force in which it is applied?!?
What does the Accumulator "Check Valve" next to the Servo have to do with the shifting?!?

[Chris Stewart]

Is the torque converter clutch releasing? You might try disconnecting the signal wire to it then check the downshift. Wobbly motor mount might let the motor move too much while decelerating also.

[Icepick]

<<Is the torque converter clutch releasing?>>

I assume you are talking about the "lock-up converter and solenoid?? If so....Yes, the Lock-up Converter is releasing normally. Only the 3-2 downshift is harsh. While braking, decelerating, or coasting to a stop, the 3-2 downshift is hard. And it happens at 15 mph every time!!

<<Wobbly motor mount might let the motor move too much while decelerating also.>>

I actually had to change two mounts because they got worn out prematurely by the hard downshifting. The rear motor mount brocket also cracked from the banging downshift.

FOOTNOTE/UPDATE: If I "manualy shift to 2nd while driving faster than 20 mph, it will downshift 3-2 perfectly without a bang. I tried to do this manual downshift at different speeds from 20mph up to 40mph. Everytime, it downshifted 3-2 correctly and without a bang. If I tried to manualy downshift to 2nd while traveling at less than 20mph, then the banging started again. Another note worth mentioning is that if I applied the brake (with my left foot) and kept the RPM above 1,100rpms(with my right foot), then the downshift occured normally at 15mph without being harsh and without a bang.

This is getting wild!

[Icepick]

******UPDATE*********
I dropped the pan over the weekend and found the problem. The "Servo" spring was broken in two pieces. After replacing the spring and reassembling, the road test proved that the harsh 3-2 downshift was the fault of the broken Intermediate Band Servo Spring. FIXED!!

[Chris Stewart]

Thanks for the update...have you considered trans work for a living?