TH400 problems

[1979C20]

Ive got an 89 V2500 burb with a 350, TH400, NP241 combo. Its cable speedo, vacuum modulated, non torque converter lock up, electric kick down. I had to pull some idiot out of a big hole out offroading last night, and on the way home my transmission wasnt shifting right. It hard shifts between 1 and 2, and takes forever. It hard shifts from 2 to 3, then if I let off the throttle in 3, itll try to downshift and acts like its stuck between 2nd  and 3rd, or stuck in 2nd. I checked fluid, its good. I checked the vacuum line at the modulator and its good, but I didnt check for vacuum. Then I found the wire for the kickdown pinched between my trans breather hose and the bellhousing. I moved the wire and it started driving normal again, but after about 5, mins of driving, it was messing up again. I unplugged the kickdown wire and no change. Any ideas? The guy I got the truck from said the trans was doing the same thing to him, then the reverse went out and he had it rebuilt. That was a little over a year ago.

[Powerdriver1958]

Twice with 400s I have transmission governor trouble . Either wouldn't shift or wouldn't when it was suppose to . along the right side of the transmisson  just above the back end of the tranny pan there is a 4 bolt cover .

sorry about the poor pic




The governor just slides in and out . not a big deal . I would try this before running to a tranny shop .
here is a pic of a 350 governor  . Only other one for a 400 is in use and looks wise they are close .

[1979C20]

What should I look for on it, problem wise?

[1979C20]

Just an update, I checked all my vacuum lines and have vacuum to the modulator. I have not checked the diaphragm on the modulator as I dont have any vacuum hose laying around. I have also discovered that it only starts "slipping" 3rd after the truck is at running temp. So that leads me to believe the direct drive clutches for 3rd and reverse is going out. My buddy who I got the truck from found the invoice from when he had it rebuilt, and its for part and labor and still valid, so im going to have him take it back to the trans shop for the warranty work. Ill let you know what they say is wrong with it.

[1979C20]

Got a quick update, I was doing some troubleshooting since I havent had time to take it to the trans shop yet. It will stay in 3rd gear if im going over 55mph. But if im going under 55 and I let off the gas, it "downshifts" and doesnt have direct drive anymore. I can shift it into 2nd then back to 3rd and itll stay until I let off the gas again. That and my reverse still works fine. So, would you guys recommend trying some external parts first, or just take it to the trans shop?

[1979C20]

Another update. Pulled the governor out, the weights are moving freely and the springs are intact. Pulled the vac modulator and it holds vacuum, and the rod behind it moves freely. Must be internal?

[81_Chevy]

im in the same boat as your are now! for me i think its my clutches that are worn down, and i had my trans rebuilt in sep of 2011

[1979C20]

I think I might have figured it.out, but I need to test the theory. I think my detent solenoid is stuck, cause the transmission to force downshift all the time. I dont have a tach, so im not sure when it shifts. But I got on the free way again, slowed down enough to make it down shift, then floored it and it shifted back to 3rd and stayed. I unplugged my kickdown switch from the trans the day I had problems and its been unhooked since, so I assumed it wasnt the problem. But, what if its stuck?

[Powerdriver1958]

I have never been able to see what was wrong with the governors I just swapped them and cured my troubles . Your vision may be better than mine tho ...

[1979C20]

So, I took it to the trans shop today. The invoice says

-rebuilt th400
-hard parts(center support, direct drum, rear planet)
-R.R GM04:rebuilt torque converter
-labor to R&I transmission
-trans fluid

The guy said he will take a look at it, but if the problem is something that he didnt replace originally it will cost me extra to fix it. So I told him to diagnose it and let me know and if anything ill fix it myself.

[1979C20]

So after 3 days, the trans shop hadnt even touched it so I took my truck back. He did say he would give me the kickdown solenoid for free and im going to ask him to give me a filter kit and fluid. Also, my vacuum brake booster eent out today. Any way these two problems could be connected? Like, brake booster has had a small vacuum leak for a while and is causing the trans not to shift?

[1979C20]

I FIXED IT!!!!! I dropped the pan this afternoon and found the filter had fallen off the fill tube. So I replaced the kickdown solenoid since I was in there and replace the filter. Put the pan back on and filled it and it finally shifted normally again.

[bd]

It's GREAT that you got it fixed!!  But, why did the filter fall off?

[1979C20]

Well, as I said, I was offroading before the problem started. We were on a really bumpy, rocky path. It was so rough I had to creep over each rock and still shook the crap out of the whole truck. All of the sudden drops off the rocks jolted the trans filter loose and it fell off the fill tube. Im actually surprised it didnt happen sooner, because I run my truck pretty hard and washboard roads.