TH400 won't upshift to 3rd

[GLG20]

Hey guys, new to this forum and to CJs. I've been looking for a project and have recently got a '76 CJ7 with the 304 and TH400. My problem is that it won't shift into third gear. I haven't had a 3 spd vehicle and don't really know at what speed to expect it to shift. I've done some reading and was looking for a little help.
Looks like issues could be trans fluid or filter, vacuum modulator on trans or kickdown switch are possibilities. The fluid is new and clean (not sure about filter). Could the kickdown switch be keeping the trans from shifting if it was stuck? Also, it shifts from 1st to 2nd very quickly. Don't know if that is part of any of this or normal for it to shift at ~5mph.

Any help is appreciated!!!

 

[bzahler]

Make sure you have manifold vacume to the modulator, check for power at the switch mounted above the gas pedel, check to see if the switch works, run a ground wire to the transmisionto make sure you have a good ground. try these things first and good luck!

 

[slomo]

Hey guys, new to this forum and to CJs. I've been looking for a project and have recently got a '76 CJ7 with the 304 and TH400. My problem is that it won't shift into third gear. I haven't had a 3 spd vehicle and don't really know at what speed to expect it to shift. I've done some reading and was looking for a little help.
Looks like issues could be trans fluid or filter, vacuum modulator on trans or kickdown switch are possibilities. The fluid is new and clean (not sure about filter). Could the kickdown switch be keeping the trans from shifting if it was stuck? Also, it shifts from 1st to 2nd very quickly. Don't know if that is part of any of this or normal for it to shift at ~5mph.

Any help is appreciated!!!

Sounds like the vacuum modulator needs adjustment. Or a leaking vacuum line??

slomo

 

[GLG20]

So, transmission fluid is good, filter is good, kickdown switch is working fine and when I changed the vacuum modulator, the vacuum was good and new modulator installed. Still won't shift to 3rd. I think my only other options are internal now. Might have to hand this one over to an expert. Hoping it's just the 2-3 valve and not a rebuild. Thanks for the help!

 

[mtnwhlr]

Be sure to post what they find.

 

[GLG20]

Wish I had some better technical finding for the shifting problem, but it seems I was just missing feeling the first shift. The transfer case has the low range and the 4H/4L lever was not engaging and shifting the case to HI. So, end of the day, it shifted really quickly because i was driving around in 4L.
I feel foolish =( but happy it's an easy "fix"!!!

 

[Peanut Butter]

Here is a couple of articles I wrote that may help you with you new to you Jeep.

http://www.jeep-cj.com/forums/f2/jeep-th400-technical-information-24384/

http://www.jeep-cj.com/forums/f2/quadratrac-27344/

http://www.jeep-cj.com/forums/f98/1979-jeep-cj7-27195/

First thing you should do is identify all the parts and pieces you have. What type of TH400, does you Quadratrac have a part time kit in it, what is you gear ratio in your diffs., etc. Get a full service manual. It has a lot of pictures of the parts that make up your linkage, etc. These will need to be looked at for wear. If you should ever have to have your TH400 rebuilt it is the easiest automatic transmission for the DIY individual with lots of U-Tube videos and manuals to help. Good luck.