th400 won't 2-3 upshift at WOT

[americanmusc1e]

I recently rebuilt my th400 and then i went through it all again after the torque converter had a bad sprag and left metal in my pan.

Stock th400 rebuild with 32-element sprag and Fairbanks shift kit. Shifts normally at part throttle though it is quite a bit softer than the fairbanks equiped 46re I rebuilt for my jeep.

I finally got the kickdown wired in and about 80% of the time if I floor it on the highway it will kick down to second and hold second until greater than 6500rpm (the remaining 20% of the time it upshifts at 4000 with the kickdown on). When I let off it shifts. The 1-2 shift happens at 3600 with the kickdown.

today I pulled the governor and replaced the worn gear, made sure nothing was sticking and re-calibrated it with slightly ligher weights and springs. I took it out on the highway and for the first couple tries it shifted 1-2 at 3600 and 2-3 at 5500 with the kickdown engaged. Then after I was feeling pretty good it went back to not upshifting out of second at WOT. What should I check next?

[Bigdav160]

The kickdown solenoid on the valve body?

[YoungPup1977]

I second BigDav's post, Your detent solenoid switch is stuck open or bad...this would cause your issue you are describing as no upshifting / WOT...

Held on with two bolts thru the VB separator plate into case, replace with new gasket.

[mattfranklin]

I had a problem once with a vacuum line leaking on a TH400, but that caused high-revving shift problems at part throttle, too.

[YoungPup1977]

Originally Posted by mattfranklin

I had a problem once with a vacuum line leaking on a TH400, but that caused high-revving shift problems at part throttle, too.

Thats a great point, always look at the easier things before dropping the pan....check the vac lines for any leaks, maybe run a separate vac line first to see if its that.... GOOD LUCK !!!!

[americanmusc1e]

Hello all. Thanks for the replies.

I've done a ton of research into the hydraulic circuits and this is what i'm finding:

The 2-3 shift valve is very simple in operation. It has pressure from the modulator acting on one side and pressure from the governor acting on the other side. When the detent solenoid is activated, the modulator pressure is raised to detent pressure. So the shift should occur when the governor pressure overcomes the detent pressure of approximately 70psi.

Since it doesn't do it all the time, it seems that my problem is related to a sticking 2-3 shift valve or something sticking in the governor. Last time I drove it, it upshifted at 5500 which is what I want. I need to modify some more things in the governor for the 1-2 and part throttle shifts. When I do that, I'll pull the modulator and modulator valve and inspect. I'll also take pressure readings at full throttle. If the problem persists, I'll replace the governor. And if that doesn't fix it I'll start looking at the 2-3 and 3-2 shift valves.

[YoungPup1977]

Originally Posted by americanmusc1e

I recently rebuilt my th400 and then i went through it all again after the torque converter had a bad sprag and left metal in my pan.

Stock th400 rebuild with 32-element sprag and Fairbanks shift kit. Shifts normally at part throttle though it is quite a bit softer than the fairbanks equiped 46re I rebuilt for my jeep.

I finally got the kickdown wired in and about 80% of the time if I floor it on the highway it will kick down to second and hold second until greater than 6500rpm (the remaining 20% of the time it upshifts at 4000 with the kickdown on). When I let off it shifts. The 1-2 shift happens at 3600 with the kickdown.

today I pulled the governor and replaced the worn gear, made sure nothing was sticking and re-calibrated it with slightly ligher weights and springs. I took it out on the highway and for the first couple tries it shifted 1-2 at 3600 and 2-3 at 5500 with the kickdown engaged. Then after I was feeling pretty good it went back to not upshifting out of second at WOT. What should I check next?

You indicated you recently rebuilt this TH400 that you are having issues with....

With the sprag letting go in the converter, lots of metal in the pan....

How was the 2-3 shift valve during your rebuild ? You sand the valve for easy operation of the valve since lots of metal was in the trans before rebuild.

Did you replace the kickdown/detent switch during the rebuild ?

You indicated you replaced the gov gear after rebuild along with installing different weights, why do you think the gov is still bad ?

Did you clean out the cooler lines real well before hooking the lines to the rebuilt trans since lots of metal was ran thru this th400... How did you clean out the lines and what did you use to do this ?

[americanmusc1e]

Originally Posted by YoungPup1977

You indicated you recently rebuilt this TH400 that you are having issues with....

With the sprag letting go in the converter, lots of metal in the pan....

How was the 2-3 shift valve during your rebuild ? You sand the valve for easy operation of the valve since lots of metal was in the trans before rebuild.

Did you replace the kickdown/detent switch during the rebuild ?

You indicated you replaced the gov gear after rebuild along with installing different weights, why do you think the gov is still bad ?

Did you clean out the cooler lines real well before hooking the lines to the rebuilt trans since lots of metal was ran thru this th400... How did you clean out the lines and what did you use to do this ?

The trans was rebuilt by me twice in a period of two months. First time was the "main" rebuild. I went through everything including a very thorough disassembly and cleaning of the valve body. Once I got the transmission in, I had very sluggish performance in first gear and my 2400 stall actually stalled at 1600. I fiddled with it for a couple of weeks before I figured out that it was a bad torque converter out of the box (the stator sprag inside the torque converter had failed).

I pulled it all apart and went through the entire transmission again EXCEPT disassembling the valve body. I did make sure all valves were not stuck. I didn't find any metal except in the torque converter and the pan.

I did not replace the detent solenoid. I can verify that it is operating correctly. It kicks down when it has 12v to the solenoid. It just doesn't always shift up when the solenoid is open.

As far as the governor, I noticed the gear was pretty bad during the rebuild. I replaced the gear, but I'm reading quite a bit about governors sometimes sticking so I figured it's an easy part to replace.

I pulled the trans cooler off and ran carb cleaner through it in different orientations for about 30mins until I was confident it was clear. I also ran carb cleaner through the lines from the highest point down.