TH400 issue
Thread Starter
Racer
Joined: Jan 2007
Posts: 314
Likes: 0
From: Pittsfield, Ohio
TH400 issue
(1976 L-82 350 w/ TH400)
Heres what happened- I installed a B&M shift improver kit following the "street/strip" instructions with no noticed problems, changed the ATF filter and install new fluid. Took it for about a 5 mile drive afterwards and it worked as it always did but with a nice snappy shift.
As I turn around to head back home I got on it a little just have it act like it was low on fluid (slipping). I pulled over checked it in park and it was about 1/2 quart or so low. I had fluid with me so I added 1/2 qt. I let it idle a little and shifted it throught the different shift points. All seemed to be normal again.
Once I started down the road the tranny wouldn't shift to second. If I made it go to 5300 rpms or so it shifted good. I figure the governors working fine then- Must be the modulator right? Well its new and was put on 200 miles ago. I pulled it off and all seems ok with it and the vaccum line. I drove it a few short trips for a total of 10 miles with no sign of improvement over the last couple of days.
Could it be the servo? I pulled it out and tested it with 12volts and it clicked as it should. Maybe it's still bad? The ATF pan and servo is currently off the transmission. Any advice for trouble shooting is greatly appreciated. THANKS ~Shannon
Heres what happened- I installed a B&M shift improver kit following the "street/strip" instructions with no noticed problems, changed the ATF filter and install new fluid. Took it for about a 5 mile drive afterwards and it worked as it always did but with a nice snappy shift.
As I turn around to head back home I got on it a little just have it act like it was low on fluid (slipping). I pulled over checked it in park and it was about 1/2 quart or so low. I had fluid with me so I added 1/2 qt. I let it idle a little and shifted it throught the different shift points. All seemed to be normal again.
Once I started down the road the tranny wouldn't shift to second. If I made it go to 5300 rpms or so it shifted good. I figure the governors working fine then- Must be the modulator right? Well its new and was put on 200 miles ago. I pulled it off and all seems ok with it and the vaccum line. I drove it a few short trips for a total of 10 miles with no sign of improvement over the last couple of days.
Could it be the servo? I pulled it out and tested it with 12volts and it clicked as it should. Maybe it's still bad? The ATF pan and servo is currently off the transmission. Any advice for trouble shooting is greatly appreciated. THANKS ~Shannon
Burning Brakes
Joined: Feb 2006
Posts: 1,024
Likes: 1
From: AL
i'm no expert, only rebuilt one TH400 - but one thing i learned is that the shift and other valves have to slide in their bores perfectly. any slight hangups might (dunno?) cause intermittent problems. (don't recall how much dissassembly the B&M shift kit requires).
seems like you should be able to use a volt meter to test the voltage at the solenoid (assume you meant solenoid instead of servo) - will need a helper to mash the gas pedal. if always engaged, it might not shift into second until high rpm.
seems like you should be able to use a volt meter to test the voltage at the solenoid (assume you meant solenoid instead of servo) - will need a helper to mash the gas pedal. if always engaged, it might not shift into second until high rpm.
Thread Starter
Racer
Joined: Jan 2007
Posts: 314
Likes: 0
From: Pittsfield, Ohio
i'm no expert, only rebuilt one TH400 - but one thing i learned is that the shift and other valves have to slide in their bores perfectly. any slight hangups might (dunno?) cause intermittent problems. (don't recall how much dissassembly the B&M shift kit requires).
seems like you should be able to use a volt meter to test the voltage at the solenoid (assume you meant solenoid instead of servo) - will need a helper to mash the gas pedal. if always engaged, it might not shift into second until high rpm.
seems like you should be able to use a volt meter to test the voltage at the solenoid (assume you meant solenoid instead of servo) - will need a helper to mash the gas pedal. if always engaged, it might not shift into second until high rpm.
I just would hate to install a new solenoid, the pan, and ATF just to have the same problem still. Know what I mean vern?
Thread Starter
Racer
Joined: Jan 2007
Posts: 314
Likes: 0
From: Pittsfield, Ohio
i'm no expert, only rebuilt one TH400 - but one thing i learned is that the shift and other valves have to slide in their bores perfectly. any slight hangups might (dunno?) cause intermittent problems. (don't recall how much dissassembly the B&M shift kit requires).
seems like you should be able to use a volt meter to test the voltage at the solenoid (assume you meant solenoid instead of servo) - will need a helper to mash the gas pedal. if always engaged, it might not shift into second until high rpm.
seems like you should be able to use a volt meter to test the voltage at the solenoid (assume you meant solenoid instead of servo) - will need a helper to mash the gas pedal. if always engaged, it might not shift into second until high rpm.
Thread Starter
Racer
Joined: Jan 2007
Posts: 314
Likes: 0
From: Pittsfield, Ohio
Well I just hooked the solenoid back up, turn on the ignition and tied a string to the activation switch under the dash (by the gas pedal). The switch seams to work fine when activated at WOT. The solenoid clicks and the little pluger part moves.
Guess I'm barking up the wrong tree??
Going back out to play with it I suppose. I'll check back later..
Guess I'm barking up the wrong tree??
Going back out to play with it I suppose. I'll check back later..
Instructor
Joined: Dec 2005
Posts: 241
Likes: 0
From: Aubrey TX
I'm not an expert at this but here is an experience that I had.
My TH-400 all of a sudden would not want to upshift into second. I checked the modulator and it was fine so next I disconnected the kick down solenoid and took it for a spin. It works fine now so I am assuming that I have a bad or sticky switch. I have not had time to check it out.
Try disconnecting the kickdown switch and taking it for a ride. My thoughts are that if you went for a cruse after you installed the kit and everything was fine you did the job correctly. You may have a sticky switch or solenoid which is not allowing you're tranny to upshift.
My TH-400 all of a sudden would not want to upshift into second. I checked the modulator and it was fine so next I disconnected the kick down solenoid and took it for a spin. It works fine now so I am assuming that I have a bad or sticky switch. I have not had time to check it out.
Try disconnecting the kickdown switch and taking it for a ride. My thoughts are that if you went for a cruse after you installed the kit and everything was fine you did the job correctly. You may have a sticky switch or solenoid which is not allowing you're tranny to upshift.
Thread Starter
Racer
Joined: Jan 2007
Posts: 314
Likes: 0
From: Pittsfield, Ohio
I'm not an expert at this but here is an experience that I had.
My TH-400 all of a sudden would not want to upshift into second. I checked the modulator and it was fine so next I disconnected the kick down solenoid and took it for a spin. It works fine now so I am assuming that I have a bad or sticky switch. I have not had time to check it out.
Try disconnecting the kickdown switch and taking it for a ride. My thoughts are that if you went for a cruse after you installed the kit and everything was fine you did the job correctly. You may have a sticky switch or solenoid which is not allowing you're tranny to upshift.
My TH-400 all of a sudden would not want to upshift into second. I checked the modulator and it was fine so next I disconnected the kick down solenoid and took it for a spin. It works fine now so I am assuming that I have a bad or sticky switch. I have not had time to check it out.
Try disconnecting the kickdown switch and taking it for a ride. My thoughts are that if you went for a cruse after you installed the kit and everything was fine you did the job correctly. You may have a sticky switch or solenoid which is not allowing you're tranny to upshift.
Thats what I was thinking too. I'll go to napa tomorrow to price one out since it looks rough anyways. I just read in the B&M instructions that if the square can style detent solenoid seal is damaged, loose, or damaged unit in general it will stay in passing gear all the time. I guess that means
1st gear??
I'd try what you said but I dont want to install the pan and fluid again until after I install a new detent solenoid. It can't be that expensive..
could it..:o
Last edited by 2armor; Sep 7, 2007 at 04:25 PM.
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Thread Starter
Racer
Joined: Jan 2007
Posts: 314
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From: Pittsfield, Ohio
NCM Grand Opening Veteran
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From: South of giving a damn
St. Jude Donor '11, '17
The solenoid is only for WOT kickdown, it has nothing to do with normal driving. Vacuum & line pressure controls normal function. I drove from Little Rock to San Antonio with no connection to the solenoid and never knew it because I never stomped the gas pedal. The tranny shifted normally. More likely a piece of dirt in a check valve. What did you use to hold the check ***** in place during assembly? Sounds like line pressure is not building enough to kick the tranny into 2nd.
Thread Starter
Racer
Joined: Jan 2007
Posts: 314
Likes: 0
From: Pittsfield, Ohio
The solenoid is only for WOT kickdown, it has nothing to do with normal driving. Vacuum & line pressure controls normal function. I drove from Little Rock to San Antonio with no connection to the solenoid and never knew it because I never stomped the gas pedal. The tranny shifted normally. More likely a piece of dirt in a check valve. What did you use to hold the check ***** in place during assembly? Sounds like line pressure is not building enough to kick the tranny into 2nd.
What could cause an issue with that after driving for several miles? I though something just crapped out on me.
Thread Starter
Racer
Joined: Jan 2007
Posts: 314
Likes: 0
From: Pittsfield, Ohio
Now that you mentioned line pressure, I recall a cone shape filter falling out of one of the 2 governor tubes. I wonder if I put it in the wrong way OR in the wrong tube. Would that cause a delayed problem if I installed it incorrectly?
NCM Grand Opening Veteran
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From: South of giving a damn
St. Jude Donor '11, '17
I'm away from home & don't have my books & diagrams, so I can't answer the specific question. A piece of junk floating around wouldn't cause trouble until it got sucked up and stuck somewhere. I'd vote for debris. It worked for a while so you did the upgrade correctly, then something has happened that prevents the tranny from shifting.
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What filter is in it? Back when I ran autos and rebuilt them a lot...I found that the cheap filters would often *suck up* when used with a shift kit that increased line pressure. They often acted just as you describe...everything fine until you got on it hard once or twice. I pulled trans back out a couple of times and found nothing wrong until I replaced the *new* filter with a better one. On T-400s the better ones were ones you couldn't see the filter media through the intake hole. It was open and you saw metal. The cheaper ones had the material visible right there.
The little screens are governor screens and keep trash from getting to it.
Have you checked the governor piston for movement? They are pretty picky!
JIM
The little screens are governor screens and keep trash from getting to it.
Have you checked the governor piston for movement? They are pretty picky!
JIM
Thread Starter
Racer
Joined: Jan 2007
Posts: 314
Likes: 0
From: Pittsfield, Ohio
I'm away from home & don't have my books & diagrams, so I can't answer the specific question. A piece of junk floating around wouldn't cause trouble until it got sucked up and stuck somewhere. I'd vote for debris. It worked for a while so you did the upgrade correctly, then something has happened that prevents the tranny from shifting.
Thread Starter
Racer
Joined: Jan 2007
Posts: 314
Likes: 0
From: Pittsfield, Ohio
What filter is in it? Back when I ran autos and rebuilt them a lot...I found that the cheap filters would often *suck up* when used with a shift kit that increased line pressure. They often acted just as you describe...everything fine until you got on it hard once or twice. I pulled trans back out a couple of times and found nothing wrong until I replaced the *new* filter with a better one. On T-400s the better ones were ones you couldn't see the filter media through the intake hole. It was open and you saw metal. The cheaper ones had the material visible right there.
The little screens are governor screens and keep trash from getting to it.
Have you checked the governor piston for movement? They are pretty picky!
JIM
The little screens are governor screens and keep trash from getting to it.
Have you checked the governor piston for movement? They are pretty picky!
JIM
Thanks jim, I did put a good brass screen TCI filter at the oem location. It also has a Perma-cool remote filter under the hood with SS braided lines and all AN fittings. When I finished installing the shift kit with new fluid, I also installed a Fram PH8 filter to replace the original Perma-cool filter. This would be the first time its ever had a fram oil filter on the Tranny cooling line. You think this could cause a restriction issue? Perm-cool lists it as an acceptable replacement though..
Governor piston -no. What should I look for? I have heard about the little plastic gear failing but figured since it shifted at 5000rpm the governor was working. I dont know- Not much experience with automatics.. Wish I had a 4 spd in it!
Last edited by 2armor; Sep 7, 2007 at 08:10 PM.
Thread Starter
Racer
Joined: Jan 2007
Posts: 314
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From: Pittsfield, Ohio
I just used grease cause I was already in the garage where the grease is, not the bed room
Should I tear it all out and clean real good then reassemble?