TH400 Trouble

[Zack172]

My turbo 400 doesn't work. I was wondering why. I checked the fluid, it was good, replaced it anyways. The problem is that it slips a lot in drive. It barely moves (like 2 mph) if at all, but it sort of works in reverse. Once it catches in reverse it doesn't slip at all. So can anyone tell me what the deal is? And how much it would cost to replace? Thanks

[Zack172]

tongue.gif I didn't mean replace, I meant repair.

[River Beast]

Time for a rebuild is what it sounds like...the master rebuild kits are around $50 at NAPA.

You need 3 special tools on the TH400 that only come in a tranny builders tool kit for around $500 or better.

I hate to say it... but you may in the neighborhood of around $400-$800 for a rebuild.

But hang on....

Couple of questions first...this is a longshot, but trying to help you out. ;)

Has is slowly gotten worse...or just all of sudden... what did you do (any work or maintenance) that may have caused this...this could be the key to your solution.

What year? with a TH400 you could have a Dana 20 or a Quadratrac.

Now if you have the QT unit... do you have the front shaft installed? The QT is a full time case that NEEDS the front shaft installed to operate correctly UNLESS you have it locked in E-Drive (switch in the glove box)

If you have the Dana 20... time for a rebuild.

[Stolen76]

Buy the Haynes manual for GM transmission repair. It's all pictures ! Get the Napa kit for 50 and you are up to $70. If you have the ability to get it out yourself and are very anal about following directions, it's really not too difficult to replace your clutches, steel, bands and seals. I did mine without the special tools, you just have to be patient with c-clamps as a substitue in a couple of the steps.

I'm not a big fan of Haynes manuals, but this one kicks butt.

[Joe J-Truck]

I just had a th400 rebuilt for my big chevy (Bu-ack powered) work truck. I asked around and bugged everybody for a deal until I found a guy in town who did it for $350 including the parts.
He was a mechanic at a shop who did the work as a "side job" so I had to wait a few more days and I don't get a warranty. That's alright, because I got it done for 1/2 price a tranny shop would have charged me.
When you do get your trans working, make sure you are keeping it cool enough. That's how I killed mine, by overheating the fluid, and it toasted the clutches.
Another idea is buy one cheap from someone on this club parting a rig out, that's how I got my th400 for my jeep truck!

[Zack172]

Thanks for the help. I have a QT bolted up to mine. I just bought it a little while ago so I don't know if it just went out or if it was slow to die. Everyone has told me its the bands and clutches, so it looks like I'm gonna do that. Thanks again.

[AzFrank aka Desertson]

Check vacuum modulator on the passenger side of tranny, pull the manifold vacuum line off the mod and see if any t-fluid is present.If there is, the mod is shot, causing the rod that "shifts" tranny under certain loads, (rpms etc)not to work.
You can buy a modulator that does not require that 45deg elbow, and it will still be out of harms reach of the frt drive shaft, Go to a good tranny shop to get one, dont rely on your friendly local pimple faced parts kid at Autozone to hand ya' the right one.
I've got a '79 AMC issued service manual that has the MOST extencive teardown and rebuild chapter on the 400.Over 80+ pages of info.
Can photcopy and send ya.
Also the one thing I was told by the guys at Trail Transsmison,(awsome tranny shop)is the acumulator piston are nylon and after awhile they crack,loosing fluid pressure in the control valve. its a given for the 400's :(

[ May 19, 2002: Message edited by: AzFrank aka Desertson ]</p>

[blackjeep2002]

I agre with all. First check the QT, if it is ok then it is time for the rebuild. I recently had trouble with mine and after payin 400 bucks to have it done (incorrectly :mad: ), I did it myself following the Haynes manual. It is a good book. Just plan a weekend to do it and you should be rolling again by Monday tongue.gif .
Keith :cool:

[River Beast]

Don't take this the wrong way.. but ensure that you are FULLY engaged in the QT... if you have a lo range lever on the driver side hump under your seat... mash that puppy to the floor for high range.... pull it up for lo range... there is a small area for neutral in there... you could be stuck in the middle.

If no lo range is installed...sounds like you have some investigating to do....sorry

[gsmikie]

sounds like the front clutch pack seals/clutches are gone reverse will work fine but no foward 1/2/3/ just when you engage the foward gears you feel a lunge then nonthing ..............front clutch pack ........pick up the rebuild kit