Transmission help Needed, th400 not shifting.

I recently replace my tranny with a used one that was sitting for about 20yrs. It won't upshift at all at any speed all I have is first gear, I pulled the governor and that looks fine but I replaced it with the one from my other tranny just in case and still to change, I replaced the vacuum modulator and still no difference, I unplugged the detent solenoid but there was still no difference so now I belive it is an internal problem. The guy I bought the tranny from said that it functioned just fine when he pulled it out of the car but now here it is 20yrs. later and it won't upshift, I replaced the filter before I install the tranny and I didn't find anything unusual in the pan. The car drives fine in first and does not seem sluggish and will still burn the tires, I am just wondering what internal parts I should look at because if I tear into it then I am only doing it once.

 

Are you positive that the trans isn't stuck in Low1....1st gear

 

How would I know? and how would I fix it, I don't believe it is because when I put it in drive it won't upshift and when I put it into manual 2nd there is no change but if I put it in manual 1st then it goes right into low gear.

 

are you putting it in drive, and waiting to see if it will shift on it's own ?
will it shift past 1st if you manually shift it ?
moisture could have gotten in and could have cause some critical passages in the valve body to get gummed up.
is the passing gear cable free ?
there's alot of things that can cause this, but it's more than likely an internal problem. if you can shift from park to reverse (and if it actually goes into them) the cable / linkage is probably fine.
what kind of shifter are you using by the way ?

 

I would try flushing it out 2 or 3 times with clean fluid. fill it, run it until it is warm, shift through all gears. Drain and refill. Then do it again.
If you can use a toulene based or similar additive, put that in as well.

when it sits that long, the fluid gets all gummy in the passageways, and the little check balls might all be stuck, so fluid is not going to flow through the valve body like its supposed to.

I'd give that a try before actually pulling the valve body and cleaning it.

 

I have already flushed it once and I have driven it about 8-10 times already and driving around the city I have put probably 10-15 miles on it so it seems like things should loosen up.

 

Its not just going to loosen up. each time you flush it, it removes a little bit of the gunk at a time. You don't want to leave that shit in there, hence the multiple flushes.
Go buy something like Trans-X and put that in, it will speed up the process.

I would not reccommend that process if it didn't work. I've done it time and time again with mostly positive results. But sometimes they are just too far gone.

 

I'm having problems with my TH400 as well. I recently finished my 30' sedan just enough to take it for a spin around the block. The motor (Cad 472) runs like a top, the TH400 is another story. It was sitting for a number of years before I installed it. The fluid needs to be pretty full for the tranny to respond. I can put it in gear, but it feels as if I'm stuck in a high gear. I really need to rev to get it to move. After about 2 to 3 minutes, tranny fluid comes back out of the filler tube. I chaned the filter before firing it up the first time. Do you all think I should try multiple flushes, or is that a waste of $$? I was considering just upgrading the complete valve body, but I don't want to throw money the wrong way. Any imput here is appreciated.

 

Pull the valve body off and see if any of the valves are stuck. (Carefully take a small screwdriver and try and move all of the valves in the valve body against each valve's spring.) I bet you have one that is rusted in place. If the valve body is ok, just yank that thing out and go through it, paying close attention to the the intermediate clutch and the intermediate sprag. That's a real simple trans and you should be able to handle it just fine. Follow your repair manual if you are scared...

 

I'm going to attempt this while the tranny is installed. I know to install the check balls on the separator plate, when reassembling. Anything else to consider??

 

My reply was directed at the original poster's complaint. I'm thinking you have a different problem. You can try to inspect the valve body, but I'm thinking that your trans will have to come out and be torn apart...

 

You did remember to refill the torque converter, right?

 

99.9999% sure. I'll make sure when I pull it though.

 

tear it down buy a kit for 45 plus 25 for a th 400 builders guide

 

I had a simular problem with my 400, it would not upshift till very high RPM, turned out being the kick down solenoid, it leaked. The trans thought it was in passing gear all the time.

 

Maybe you have a check ball rusted in one of the valleys not letting fluid by. Have to drop the valve body and tear it apart. Might as well install a shift kit while your at it.

 

The converter had less than a quart (like 1/2) when I pulled it. There's still some fluid inside, so it wasn't dry. I'm going to pull the tranny and go through it / upgrade valve body, shift kit etc..

 

govener gear

 

Ok guys, I'm digging up an older thread, so I need some help. I'm having trouble with my TH400, roughly the same issues described by Scallop. I have Park, Reverse, and First. Transmissions are all black magic to me, auto and manual. All I have done so far is pull the governor out, and it looks great (not that I know what I'm looking for). I'm thinking I'll check the vacuum modulator next, but I have no idea how to check it. Can someone point me in the right direction? I have also read some about the kickdown not working properly, but mine is not even hooked up right not, is it still a possible problem?

Here's my governor:




And here's a video of the last test drive. You can hear the tranny refusing to go into 2nd:

<iframe src="http://www.youtube.com/embed/cwmpAtv4bVk" allowfullscreen="" frameborder="0" height="315" width="560"></iframe>

 

Before you pull that tranny, I would check 2 things. First, make sure your governor valve is free. Here's how to check it: hold it by the plastic gear, and snap the weights in and out while watching the inner valve. It should be sliding up and down. If it's stuck, drive the 1/8" roll pin out, pull the plastic gear out, and then pull the valve out. Clean it out, lube it with WD40 and make sure it's free when you put it back together. Also check your modulator valve, it's in the case, behind the vacuum modulator. While it is possible for one of the shift valves in the valve body to stick, it's not likely.

 

I agree with Potshot. Also the kickdown solenoid could cause it not to shift. It doesn't have to be plugged in to cause a problem. Take the one off your other trans.

 

Ok, the valve on the governor seems to be in good working order. Too bad though, I was hoping for an easy fix. Dumb question, how do you remove the kickdown solenoid? Does the pan have to be dropped? I don't know if it matters or not, but I can hear the solenoid engage if I hit 12+ to it. I plan to check the modulator valve next. Do I just remove the vacuum modulator and see what's going on behind it?

Thanks for the help guys. I hate transmissions.

 

Sunday bump

 

Find a bottle of automatic transmission conditioner.

I have seen that shit solve a lot of problems.

I have no idea whats in it, but it will not hurt the tranny if it's screwed.

Give it a try.

 

All good advice, to the OP are you sure you are hooked up to manifold vacuum for the modulator? If the governor is working a stock Th400 will upshift from 1st at full throttle no matter what forward gear the shifter is in, but it will be high RPM. These old transmissions are easy to work on so dive in, you will be glad you did it yourself. Just leave the RTV sealer on the shelf.

 

Alright, I'm back with yet another problem! I replaced the vacuum modulator and all of the lines to the intake manifold and then went for a drive... I'm pretty sure that it shifted at least once, but I was more concerned that the truck can't seem to get into first without stalling out. It took me about 10 minutes to get the truck up the driveway I finally decided to back it up instead of driving it up.

So quick recap of my new problem, I can't put the tranny in first without the truck stalling out. I can gun it and go (but apparently not up hill) and reverse seems to be fine.. I'm thinking my torque converter is locked up. Any other ideas? If you think I'm right, any quick solutions?

Just so you don't have to search back through this thread, I have a TH400 on a 350 TBI.

Thanks again guys!

 

After reading through all of the previous posts it sound like youve exhausted all of the external issues. Sounds like it might be tear down time. Dont be intimidated these are very simple and brutually strong transmissions. The fact that it sat for 20 years isnt very good on paper valve body gaskets and piston seals. Overhaul kits arent that much and there is plenty of help and advise here on the hamb.

 

This tranny only sat for a year in an 86 Chevy, and I was told it was a good running transmission (we all know how that story goes). I'm wondering if I messed something up when I mounted it to the engine. I still think the internals might be good since it seems to be shifting now. This is the first time I have ever swapped a transmission; what all could I have done wrong?

 

I dont think you did anything wrong bolting it up to engine. I dont think you have a convertor problem being that you can back up. if the convertor was locked up itwould stall immediately no matter what gear you choose. How is reverse to drive if your just idling?Does it stall or does it stay running ok? Vacuum leak after changing out the vacuum lines?

 

The truck will stall in reverse too, but not as easily as it does in first. From a stand still, if I put it in any gear, first or reverse, the truck will stall out after a couple of seconds. If I let off the break just long enough in reverse, the engine will usually come back to life. Any chance it's a case of too much tranny fluid? I'm not sure what that would do. I'm pretty confident about my new vacuum lines. Sorry to keep looking for easy ways out, I would just hate to spend time and money on something that didn't need to be done.

Thanks again for any and all help.