Bad kick down on NEW th400

I have a new th400 with about 1500mi on it. The problem is the kick down is not set right or something. it does fine till I get to about 40mph at that point if accelerate AT ALL it will shift back to 2nd for about 1sec then back to 3rd for about 1 sec, and keep doing this till I step on it, or get over 60mph. It does not do this if I lay in to it. But under slow or normal acceleration the kick down goes CRAZY. How can I fix this? Thanks for your help!

Garth

 

Not knowing what modulator you have, I would suspect either a vauum leak at the modulator, or you need to put a restrictor in the vacuum line going to the modulator.

If you don't have a restrictor, what sometimes happens is an upshift drops the engine vacuum enough to cause a downshift; then the downshift raises the vacuum enough to cause an upshift; this continues to cause shifting back and forth.

If you have the newer adjustable modulator it should have a restrictor that is visible inside the end of the hose nipple. The big black factory type modulators often relied on an in-line restrictor that often gets eliminated due to plugging, rust, or line replacement.

 

Hey Adam, I have the adjustable (gold) modulator, that I tried to adjust, but saw no change. I don't really know what the heck I'm doing though. uzzled:

Thanks for the input, Garth

 

At part throttle, I still think it is something to do with your modulator line-pressure.

Along Larry's line of thinking, you could just unplug the kick-down switch at the gas pedal and totally eliminate that as an option.

After that, maybe make sure your kick-down soleniod is not leaking or else you have a valve-body problem.

I'm not a trans expert, just following the path of likelihood. Have you checked a service manual diagnosis chart?

 

I pulled the kick down switch like you said adam, and had no change. So like you said at part throttle, the switch really shoudn't be coming in to play. The soleniod is good as well. So it must be the modulator line-pressure. which means I have no idea what I'm doing, seeing how last time I adjusted it (or thought I was) I saw no change what so ever. So could someone walk me through the adjustment?

 

also the kick down is not kicking in at higher speeds (70 mph). Any help would be great!

Thanks, Garth

 

OK, you need to first verify that your modulator is in fact good. pull it out, compress the piston, and hold your finger over the vacuum port. Does the piston come out, or will it hold as long as your finger is over the port? Use a vacuum pump and gauge to test it if you have one.

Screwing the little screw inside the vacuum port in should raise your part-throttle shift points while backing it out should lower them. It's as simple as that!