TH400 stuck in first!?!?
Thread Starter
Racer
Joined: Sep 2002
Posts: 389
Likes: 0
From: san diego ca
TH400 stuck in first!?!?
My '73 auto with a TH400 seems to be stuck in first!!!
I just recovered from 3 months downtime replacing radiator+hardware+misc. and took it for a drive tonite.
Now my tranny seems to be "stuck" in first - in double quotes because reverse, neutral work fine. But any forward motion seems to be stuck in first gear.
My tranny fluid was a bit low, because I spilled some during the radiator removal/replacement. So I topped it off but it didn't seem to help.
I took it for many test drives, manually shifting, revving high, etc. trying to "un-stick" it, but no luck.
Any guesses/suggestions? Can't really be related to 3 mos. downtime, can it?
I just recovered from 3 months downtime replacing radiator+hardware+misc. and took it for a drive tonite.
Now my tranny seems to be "stuck" in first - in double quotes because reverse, neutral work fine. But any forward motion seems to be stuck in first gear.
My tranny fluid was a bit low, because I spilled some during the radiator removal/replacement. So I topped it off but it didn't seem to help.
I took it for many test drives, manually shifting, revving high, etc. trying to "un-stick" it, but no luck.
Any guesses/suggestions? Can't really be related to 3 mos. downtime, can it?
Race Director
Joined: Mar 2006
Posts: 14,112
Likes: 28
From: Florida
If it's not the modulator valve then it's tome for a rebuild. Seals inside are shot.
When you have exhausted all other possibilities, you may try 2-4 oz. brake fluid. Sometimes this can swell the seals enough to make it work for a while.
When you have exhausted all other possibilities, you may try 2-4 oz. brake fluid. Sometimes this can swell the seals enough to make it work for a while.
Tech Contributor
Joined: Aug 1999
Posts: 14,379
Likes: 6,390
From: At my Bar drinking and wrenching in Lafayette Colorado
Pull your governor out and check the governor wieights, the valve in the governor, and verify that the governor gear has not "apple-cored." If the governor has any problem, the tranny will think that the car is either not moving or miving very slow, and it will not allow the TH400 to shift out of 1st.
A bad modulator will produce high shift points, but the tranny will shift at very high rpm.
A bad modulator will produce high shift points, but the tranny will shift at very high rpm.
Le Mans Master
Joined: Apr 2006
Posts: 5,403
Likes: 95
Sounds like the rubber hose has come off down on the modulator.
without vacuum to it your car will not shift out of low gear. I had
mine come off a couple times on a turbo 400 pickup. Pickups set high off the ground just reached up underneath stuck it
back on had three gears again.
without vacuum to it your car will not shift out of low gear. I had
mine come off a couple times on a turbo 400 pickup. Pickups set high off the ground just reached up underneath stuck it
back on had three gears again.
Last edited by Little Mouse; Jul 21, 2006 at 04:03 PM.
Thread Starter
Racer
Joined: Sep 2002
Posts: 389
Likes: 0
From: san diego ca
Originally Posted by Me2
Check your vacuum connection to the vacuum modulator.
It sounds like the common "first thing" to check, and simple enough, but I"m clueless.
I'll start doing some research...
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Le Mans Master
Joined: Apr 2006
Posts: 5,403
Likes: 95
the valve is round and on the right side of your trans. it will have a very short hose atached to a metal vacuum tube that runs from it
up to a vacuum source on your intake manifold check the hose at
round mod. valve side to see if it has come off or if it has become rotted and split at the end. if there is nothing wrong at the mod. valve end, check
the small length of rubber hose up on the intake manifold end.
up to a vacuum source on your intake manifold check the hose at
round mod. valve side to see if it has come off or if it has become rotted and split at the end. if there is nothing wrong at the mod. valve end, check
the small length of rubber hose up on the intake manifold end.
Thread Starter
Racer
Joined: Sep 2002
Posts: 389
Likes: 0
From: san diego ca
Originally Posted by Little Mouse
the valve is round and on the right side of your trans. it will have a very short hose atached to a metal vacuum tube that runs from it
up to a vacuum source on your intake manifold check the hose at
round mod. valve side to see if it has come off or if it has become rotted and split at the end. if there is nothing wrong at the mod. valve end, check
the small length of rubber hose up on the intake manifold end.
up to a vacuum source on your intake manifold check the hose at
round mod. valve side to see if it has come off or if it has become rotted and split at the end. if there is nothing wrong at the mod. valve end, check
the small length of rubber hose up on the intake manifold end.
The good news: yep, this is my problem - I have about 5" of hose on the tranny side; how it got cut/shortened/snapped isn't obvious. So this will be a cheap fix.
The bad news: since the hose is broken, not just loose/removed I won't be able to fix it in time for tonite's date-nite.
I hate to be so clueless, but can I get more details on where the other end attaches to the intake manifold?
Thread Starter
Racer
Joined: Sep 2002
Posts: 389
Likes: 0
From: san diego ca
aha, thanks Little Mouse.
I finally found a decent page in the assy. manual, removed the air cleaner, and then re-read your post again. I was confused on how much of the hose was supposed to be rubber, and how much of it was a fixed metal tube. I think my 4-5" piece of rubber hose on the tranny end just came off, and needs to be reconnected. I'll try it tomorrow and report back (just in case anybody else is like me, and searches the old posts for good data).
I finally found a decent page in the assy. manual, removed the air cleaner, and then re-read your post again. I was confused on how much of the hose was supposed to be rubber, and how much of it was a fixed metal tube. I think my 4-5" piece of rubber hose on the tranny end just came off, and needs to be reconnected. I'll try it tomorrow and report back (just in case anybody else is like me, and searches the old posts for good data).
