TH400 transmission problems

[rustystud]

My transmission developed a problem last week. I was driving up a hill when I lost second gear. I had to drive the truck home in first gear. So this weekend I cleaned up my work bench and removed the transmission. I ruined eight U-joint strap bolts. I had previously Loctited them in and the heads stripped off trying to take them out. Fun !
After getting the transmission out I put it on my transmission holder and started to tear it down. When I got to the second clutch and band I expected to see some damage, but everything was in great shape ! I air tested the clutch and it works fine ! Now I am at a total loss as to what has happened to my transmission. So as I was sitting here reading the latest posts on Steel Soldiers a thought came to me to check the throttle kickdown switch in the cab of the truck. So I went outside with my trusty flashlight and looked under the dash and low and behold the switch was stuck in the downshift position ! So now I must wait until the gasket kit arrives and put everything back together and install it. I am so pissed off right now I cannot express how angry I am at myself since I didn't take the time to properly troubleshoot the problem ! Of course we where suppose to leave on the 20th for our vacation to Yellowstone Park. All the reservations have been made and cannot be changed as they are now all booked up ! My body hurts so much right now for working so hard to remove this stupid transmission I don't think I could make the trip now anyway !
So this is a lesson to everyone out there, take it easy when trying to diagnosis a mechanical problem. Don't ASSume anything like I did ! Since I have rebuilt transmissions for so many years I automatically ASSumed I knew what the problem was. This is like the classic problem of the engine that stopped running. After checking everything someone looked and saw there was no gas in the tank !
Basically I just did the same thing ! !!!!!

 

[infidel got me]

Don't feel bad Rustystud, we have all done this in the past. Over looking the simple stuff still gets me now and then!

 

[royalflush55]

Rustystud you should of known there wasn't anything wrong with that tranny because you had remand it yourself! You know your work is good!!

 

[Tinstar]

Everyone HAS or WILL do this.
Human nature.

Your's just happened to be a really big pain in the a**!

You could have kept quiet and no one else the wiser.
Takes guts to admit a mistake like that.

Your info will help someone stop and think.

Thank you for posting.

 

[Tow4]

Same thing happened to me in 1978. My brother bought a 1967 Firebird in Lakeland, Fl. It had a 400 CI engine and a TH400. While messing around with the carburetor getting it started, the plastic rod on the down shift switch got broken off. We didn't realize that in the process it got depressed and jammed on when it broke. When we hit the road the transmission would not shift out of first. We figured the transmission had a problem and decided to drive it home anyway. On the way home I discovered if you went fast enough it would shift into 2nd. I thought that was strange. Later it dawned on me the down shift switch might be the problem.

The next day we unplugged the switch and the transmission worked normally. I wish we had thought about that the day before.

We've all taken apart things that weren't broke. I hate it when that happens.

 

[Chaski]

Doh!

One time I tore the head off of a continental diesel that was in a skid steer loader I had, turned out it was knocking and smoking from a stuck injector. One full gasket set, about a day worth of labor and I was good to go again. The worst part was as soon as I tore the head off a buddy of mine came over with a beer in hand and said "sounds like a stuck injector". Sure enough one of the injectors that didn't even have 100 hours on it was stuck open, too bad I pulled the head off to figure that one out.

 

[rustystud]

Here's some pictures I took to help explain the difference between the normal TH400 transmission and the heavy duty TH400. The unpainted unit is the normal one and the green one is a heavy duty model. You can see in the first two pictures the difference in the flange thickness. This is where the aluminum support is bolted to. The second two pictures show the bolt holes drilled for the support. The last two pictures show the pump mounting. The normal transmission has 6 bolts and the heavy duty has 8 bolts. There is an extra area of material in the transmission itself you can see in the last picture. There is a rare 7 bolt pump case which has the thick flange also but not the extra pump bolt.
The heavy duty TH400 will also have the 5 disc direct and forward clutches while the normal TH400 will have 4 disc clutches in direct and forward, though sometimes forward will also have 5 discs depending on application (like a heavy Cadillac ) .

 

[dom1986ck30]

Aloha, and very well put... Which leads me to a question. I hope all is well with you. You have helped in the past, and Mahalo. You helped me with a VRV thread, or th400 not upshifting properly thread... Anyways, I put a new VRV and have done everything else you can imagine from the tranny to the VRV and the EV (Engine vacuum) or "main vacuum source" to the VRV. I have replaced hoses where needed, modulators, checked governor, etc. Even pulled the pan and checked downshift switch. Witch leads me to the question. I have just put in a new VRV and adjusted it to TM specs. Still not shifting properly. You mentioned in this thread that you checked the throttle kick down switch. Any correlation to my situation?

 

[dom1986ck30]

Mahalo by the way...

 

[dom1986ck30]

Holy Moly!!! I answered my question. After reading your article, again and again... It has come to be the exact same problem I have been dealing with. I wasn't educated on the function or location of the kick down switch under the dash. I only took out and checked internal switch under fluid tranny pan... Wow... I am lost for words. I went to go check on this switch under the dash and studied its function. I didn't even need to adjust a screw or bolt or even check vacuum... I simply added a couple of squirts of lubrication oil, repeatedly moved the switch in and out, back and forth, and took it for a spin. It now shifts at 15 m.p.h. and 30 m.p.h. A SUCCESS!!! MAHALO!!!