TH400 problem in 72 vette
TH400 problem in 72 vette Car had been sitting for seven years until last month. Only prior TH400 issue was it leaks and won't down shift into 2nd if you floor it. Otherwise, the TH400 has been perfect. It's never been rebuilt. I've had the car for 25 years.
Car is a small block vette with aftermarket sway bars, cam and headers and other wise stock.
About ten days ago, my 72 vette didn't want to upshift to 3rd when out on the highway. I pulled off stopped restarted the car and everything was ok for the rest of the trip to work. Car did the samething on the way home.
Car was up jack stands for a week to do some brake work. Replaced a leaking caliper, master cylinder, brake booters and several brake lines.
Drove the car day before yesterday and it did the won't go into 3rd briefly when shifted to 3rd and was ok. Total drive ~8 miles.
Drove the car yesterday to a friends house, started out ok, when wouldn't go into 3rd, pulled in his driveway and neither reverse or 1st would work. Played with the shifter and finally 1st engaged. Tried to limp the car home. Wouldn't go into 3rd. Pulled over 1st wouldn't engage etc neither would reverse. Shifted thru the gears etc finally 1st engaged. Manual shift to 2nd engine windmilled like it was in neutral. Car only seemed to want to pull at low rpm tranny felt like it was slipping at times.
Stupid question, is the valve body vacuum operated? Are there any electrical connections to a TH400?
The TH400 had always been trouble free, so I know next to nothing about it.
Thanks
Car is a small block vette with aftermarket sway bars, cam and headers and other wise stock.
About ten days ago, my 72 vette didn't want to upshift to 3rd when out on the highway. I pulled off stopped restarted the car and everything was ok for the rest of the trip to work. Car did the samething on the way home.
Car was up jack stands for a week to do some brake work. Replaced a leaking caliper, master cylinder, brake booters and several brake lines.
Drove the car day before yesterday and it did the won't go into 3rd briefly when shifted to 3rd and was ok. Total drive ~8 miles.
Drove the car yesterday to a friends house, started out ok, when wouldn't go into 3rd, pulled in his driveway and neither reverse or 1st would work. Played with the shifter and finally 1st engaged. Tried to limp the car home. Wouldn't go into 3rd. Pulled over 1st wouldn't engage etc neither would reverse. Shifted thru the gears etc finally 1st engaged. Manual shift to 2nd engine windmilled like it was in neutral. Car only seemed to want to pull at low rpm tranny felt like it was slipping at times.
Stupid question, is the valve body vacuum operated? Are there any electrical connections to a TH400?
The TH400 had always been trouble free, so I know next to nothing about it.
Thanks
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From: Az
The vacuum Modulator on the side is controlled by manifold vacuum. You will get upshift problems if this is not connected properly. I would verify the fluid level first, slipping in first and reverse is either fluid, pump or a converter problem.
Also with a trans that old and setting for 7 years the seals etc can harden , Its likely you need a rebuild
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Performa beat me to it. Also, check the mod for atf in the line as the diaphram could be seeping. As for the no downshift, check the orange wire on the driver side for power when someone depresses the throttle peddle to the floor with the key on-engine off. You may not be energizing the solenoid. Check under the dash for the correct adjustment for the kickdown. If that is ok, then check for power to the switch. You probably need the internal seals, (rebuild) as most trannies can't sit for more than 3 years without heat cycles and fluid to keep the seals soft. Good Luck.
Y'all are right. It's fried.
When we loaded it on to my friends roll back you could smell the tranny just driving on the roll back. It's fried. Took it to a local shop with a good rep for a complete rebuild. The good news is a TH400 isn't all that expensive to rebuild.
Am going with Transgo shift kit and a custom elite Yank 3200 as an upgrade.
Thanks guys
When we loaded it on to my friends roll back you could smell the tranny just driving on the roll back. It's fried. Took it to a local shop with a good rep for a complete rebuild. The good news is a TH400 isn't all that expensive to rebuild.
Am going with Transgo shift kit and a custom elite Yank 3200 as an upgrade.
Thanks guys
Last edited by 99 Black Bird T/A; Jan 13, 2009 at 02:23 PM.
