Author Topic: Th400 issues  (Read 895 times)

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Offline Mitch5690

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Th400 issues
« on: June 15, 2019, 03:18:23 PM »
Hello! Having some issues with a TH400. Firstly I believe the vacuum modulator is bad. Shifts too late, shifts hard.

However what would be wrong to allow me to start the car in any gear?

The other day it stopped engaging reverse. You can feel the transmission when it is shifted from say Park, to neutral or drive but nothing for reverse.

Probably should have fixed the issue before driving it 30 miles but hey... was excited to buy it lol.

Offline 78w72

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Re: Th400 issues
« Reply #1 on: June 15, 2019, 05:00:13 PM »
if the vac mod is bad, replace it, they are cheap. shifting hard could be from a "shift kit" a previous owner installed.  shifting late at mid-full throttle is related to the governor in the trans.

starting in any gear is from a seperate mechanical linkage for the ignition lockout connected to the steering column. check if its still there, they get removed for headers & engine installs.

no reverse could be from an internal problem where its losing reverse.  or it could be low on fluid, or a linkage adjustment.  check the fluid first on a level surface with the trans fully warmed up from a drive if possible, check in park engine running. add the correct fluid if needed.

 
« Last Edit: June 15, 2019, 05:03:58 PM by 78w72 »
78 w72 ws6 4 speed
81 turbo pace car
lots of other past t/a's

Offline Aus78Formula

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Re: Th400 issues
« Reply #2 on: June 16, 2019, 02:56:25 AM »
Good reply. There's electrical kits available to add to your shifter so that you can only start in safe gears and regain your back-up lights.

Offline Mitch5690

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Re: Th400 issues
« Reply #3 on: June 16, 2019, 02:49:06 PM »
Guess Iíll start with replacing the vac mod. And the filter.

I need to crawl under the car anyway as the previous owner said the engine was nine matching yet it matches. Maybe Iíll get lucky and it will have a matching trans too.

Thanks for the replies.

Offline 78w72

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Re: Th400 issues
« Reply #4 on: June 26, 2019, 10:46:51 AM »
i would change the modulator & check/fill the fluid first.  the filter is probably ok for now & most th400's use a metal screen filter that doesnt usually need changed unless you have major wear & debris are clogging the filter.

also check all vac lines for leaks or disconnect as a vac leak will lower the vac signal going to the modulator.

did you verify the engine matches by confirming the vin number on the block?
78 w72 ws6 4 speed
81 turbo pace car
lots of other past t/a's