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TH 400 issue

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Old Aug 30, 2022 | 07:49 PM
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Default UPDATED: TH 400 issue

Hello All,

My 75 ran and shifted great until it developed a fuel leak at the carburetor.

After having the carburetor rebuilt, now my transmission doesn't want to shift out of 1st. Fluid level is fine and the only change was the carb being rebuilt.

Any ideas where to start looking? All help appreciated.

Last edited by Steve Stroman; Sep 12, 2022 at 08:35 PM. Reason: Update
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Old Aug 30, 2022 | 08:02 PM
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Did the vacuum modulator hose get knocked off?
Check up top and down below. Common issue.
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Old Aug 30, 2022 | 08:06 PM
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What Greg said. Sounds like the vacuum hose for the modulator is either off or cracked
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Old Sep 7, 2022 | 09:11 PM
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OK, I checked both ends and they seem fine, but I replaced the hoses anyway.

Shifts great until it warms up (car never gets above 195*) and then it won't shift again. Should I consider a new vacuum modulator?
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Old Sep 7, 2022 | 10:00 PM
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Originally Posted by Steve Stroman
OK, I checked both ends and they seem fine, but I replaced the hoses anyway.

Shifts great until it warms up (car never gets above 195*) and then it won't shift again. Should I consider a new vacuum modulator?
Mine never completely stopped shifting but there were times after it was warmed up that it only really just eased from 2nd to 3rd. I replaced my modulator and the problem went away. '72 TH400....
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Old Sep 12, 2022 | 12:13 AM
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Default UPDATED TH 400 issue

I put in a new modulator and thought it was all good. Drove for about 45 minutes with no problem, shifting OK.

Later I went for a drive and got on it some, now no more shifting again.

Any other ideas?
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Old Sep 12, 2022 | 12:47 AM
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Change the transmission filter and post pics of the residue in the bottom of the pan before you clean the pan.
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Old Sep 12, 2022 | 04:59 PM
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Well, I haven't done anything at all, but it is shifting again.

Has anyone had this experience? Very frustrating ...
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