Th400 transmission shifting late/hard..?

[bmorrow]

Recently my transmission will not shift out of 2nd until about 40 mph. It will shift out if 1st around 15-20 mph. If I'm running about 35 and it's not shifting I can manually put it into 2nd and back into drive and then it will shift into 3rd and 35 mph but other than that it requires being around 40mph for it do to it change gears by itself. What do you guys think would cause this and how should I fix it?

 

[NovacaineFix]

It may be the vacuum pump, that thing that in the place where a distributor should go on the back of the engine.


There is a vacuum port on the injector pump , should be 2 ports with a vacuum line for each, check to see if you have vacuum on the hose that is coming from the pump, the other goes to the modulator that is on the tranny right next to where the dipstick plugs in.

If you have vacuum, then it could be the modulator itself, these are cheap, usually less than $20. Only 1 bolt holding it in, but it will leak ATF when you pop the modulator out so be careful.
If the pump is bad, you can always just install an adjustable modulator and adjust it with an allen wrench to achieve the desired shift point. The pump if bad, will probably set you back between $60-$120, depending on where you get it

 

[Gripy]

check the vacuum lines. You should be getting around 20-25 psi vacuum at the pump. And 8psi (per TM's) after the regulator (i have mine set to 10 or 12 for smoother shifting.) Vacuum regulator is on the pass. side of the IP.

Common problem is the rubber tube that connects the hard line to the transmission.

 

[MarcusOReallyus]

check the vacuum lines.

This. First place to go. They are probably in bad shape. For well under twenty bucks you can replace them all. That will cure most transmission problems on these old beasties. If that doesn't cure the problem,well, it needed to be done anyway, and THEN you move on to the vacuum pump and regulator.

 

[Warthog]

As stated above check the vacuum lines first. If that doesn't fix it the TM 9-2320-289-20 tech manual has a step-by-step procedure to test the system.

Also check out this thread from the CUCV Helpful Threads sticky

http://www.steelsoldiers.com/showthread.php?50568-CUCV-Throttle-Vacuum-Valve-Adjustment

 

[rsh4364]

To help troubleshoot vacuum issues I keep a cheap vac/boost gauge in my tool box,Sunpro cp8203 at Summit 8$,after replacing rubber hoses it helped narrow things down.On my first 1009 it needed a new pump,regulator and modulator.On my second 1009 the gauge helped me narrow things down to just the modulator.