1987 2.9L with overdrive auto tranny. I parked vehichle everything fine, few hours later start driving and now have this problem. The tranny will not down shift unless the rpm's are way low. I noticed that at 55 mph I now run about 400 rpm's less than I did before. When in overdrive it will not go out of overdrive. Took vehichle to tranny shop and they test drove it. They said that the torque was not locking up, same thing I thought. Now my question. What will make this condition? Being an electronic tranny (I think), what sensor will cause this or is it an internal problem? On upshifts everything is fine, no slips or nothing, just will not downshift like it should. I posted in the tranny forum but not much luck their. Thanks.

 

Is the problem only downshifting from OD or all gears?

I don't see a connection between the TC not locking and no downshift.

Are you getting any codes?

 

Upshifts ok. Seems to do it on all downshifts. Lets take overdrive, cruising along at 55 mph and I decide to pass somebody. Not in big hurry so I start to push gas pedal down slow, it will no do any downshift until a just about have it to floor. While speeding up if I hit the brake pedal to tell it to get out of overdrive it does nothing. Now lets say I am on a country road with the gear shifter in the D position. As I start up some steep hills it will not downshift until the rpm's are way low and when it does shift it is a hard shift, stay in that lower gear for a few seconds (just enough to gain some speed) and then it goes back into the higher gear. Even on flat ground at stop sogn it will bog the bronco down to 300 rpm or so before it shifts into 1st gear so I can take off.
The people working on it said it showed a bad speed sensor, they repalce it test dove and it made no difference. They are tracing some wiring and going to check another sensor or two but are not really sure what is wrong. Thanks.

 

Is the kickdown connected/adjusted?

 

I am going to assume that it is adjusted correctly. I can manuelly upshift thru all gears, but it will not downshift like it should. I don't think the linkage would have anything to do with the tranny going from overdrive to drive. That just has to do with the torque lockin or unlocking, doesn't it? Is this an electronic controlled overdrive? Is the computer responsible for the shifting? Could it be the TPS? What about vacuum modulator, if it has one.
For highway cruising I like it the way it is now but I'm afraid its going to cause more damage. Thanks

 

Check / adjust your kickdown linkage (this is connected to the throttle body and is actuated by the throttle linkages/cables, etc.), check / replace the vacuum modulator (check for vacuum leaks, too). I don't recall if there are any electrical / electronic servos on the '87 A4LD auto tranny. You may also have a torque converter issue... like the pump... you might also want to check / replace your transmission fluid / filter. These are the only 'common' things I can think of for any automatic transmission. Hope this helps.

 

The torque converter lockup has nothing to do with shifting.

The ECU does not control the shifts, even the 3-4 is vacuum controled.

The modulator could cause problems but I would expect upshifting issues, I still suspect the kickdown linkage.

 

Ken00, you said lockup has nothing to do with shifting. That is why I think the linkage is okay. On level ground in overdrive at 55 MPH should it go down to drive if I touch the brake while maintaining a constant pressure on the gas pedal, because mine will not. Well as far as I can tell everything external looks okay. Now pulling tranny to replace the torque. Don't know what else to do. What rpms should I be turning at 55 MPH in overdrive? Everything stock. I think I was running high to begin with but want to know what others think. This could have been a slow degrade in performance but never paid much attention until this obvious failure. Thanks.

 

Since your tranny is not control by the ECU the brakes probably won't kick it out of OD.

Can anyone comment on the rpms at 55 when in OD??

 

I'd have to agree. The modulator, clutchplates, etc., and valve body in the transmission would generally cause upshifting issues and not downshifting issues. I'd suspect that the kickdown linkage/cable is worn or out of adjustment. I would check everything possible just to elimiate each possibility.

RPMs in OD @ 55mph should be around 2000-2100... at most 2200... unless the transmission ratio is different from 5th/OD in a manual and my axle ratio(s) are different. *shrug*

 

I was running 2500 to 2600 rpms at 55 MPH. Then the shift problem started and it actually dropped to 2000 to 2100 rpms. As far as I can tell everything external checks out. Have the tranny out to replace the torque.

 

Replaced torque, did not fix it. Now have no clue what to do next.

 

If everything else has been done (fluid/filter, kickdown linkage, modulator, converter) you might also want to check to make sure there is no other blockages in the transmission fluid flow ... cooler/lines, etc. If everything checks out, then it might be internal...

Have you tried just flooring the accelerator quickly to see if it will kickdown faster? If you 'punch it' and it doesn't kickdown right away at cruising speed, then you may want to seriously look at the fluid/filter and modulator and kickdown adjustments. If you accelerate to 55 mph and then stomp on it and it doesn't kick down at least one or two gears, something is DEFINITELY wrong.

 

Found a computer cheap, going to switch it out. Going to wide open throttle bypasses alot of sensors so I don't think that is a good idea to find a problem. Like I said in previous post tranny shop said nothing wrong with the tranny itself. The torque just will not lockup.

 

It was the computer.