Slipping trans ?

[padgett]

Had occasion to drive one with rather high milage (closer to 200k than 100k) and the transmission seemed to be slipping as if it had a high stall converter. On mine if I put it in gear on the flat, idle is good for 3-5 mph. This one needed to rev to about 1500 rom before it would move at all. Did not think this was a failure mode, anyone know what would cause (besides low trans fluid) ?

[reattadudes]

sounds like it is in need of a fluid change. this symptom is typical of a plugged filter. requires a lot of pressure to get going.

Mike

[sahein]

My first guess would be the fluid level or pickup o-ring.

Second guess would be a failed sprag in the torque converter.

[Guest trofeo73]

Maybee a possible modulator vacum leam or malfunction??? I had that similar problems when my modulator was at fault. I would rather deal with a smoking engine than a slipping trans... I can reasonably fix just about anything on the engine, but when it comes to major tranny malfunctions; off to the shop!!!

[VicW]

There is a web site that focuses on the 4t40. I'll have to search again to find it. A point of enlightenment is that the 4T40 is different in that it has a Throttle Valve and the Vacuum Modulator. The Throttle valve adjustment controls shift points and the Vacuum Modulator controls the shift speed or whether hard or soft.

I found vacuum leaks all over when I first bought this 1990. Replacing the vacuum lines helped. I also replaced the modulator with a newer adjustable one. The older non adjustable modulator passed the vacuum tests but the movement seemed to be less responsive at similar vacuum levels. Besides it was a buck at the yard.

I still had shift issues. Shift points to high. Stall speed was high. for example if stopped at a light on a hill I'd have to revit up as if it was a manual, no idle creep.

I then adjusted the throttle valve to each extreme to see how it responded. I eventually found an adjustment that gave a good shift point and stall speed. I now avoid the urge to push the accelerator to the floor when the engine is not running. You know the old carburated habit of pump the pedal a couple of times before you start. This will cause the throttle valve to reposition. The book procedure for the throttle valve adjustment is just that. With the engine off, extend the cable and move the accelerator until it clicks. For mine that procedure doesn't give me shift points and stall speeds that are functional.

I haven't messed with adjusting the Vacuum modulator the tranny shifts quickly now so until some more time is available I wont experiment.

I still need to replace the filter and fluid as a part of maintenance. I don't know when it was last done and that could be a part of it.