Author Topic: Th400 shifting issue  (Read 287 times)

Offline Joe.cummings

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Th400 shifting issue
« on: December 11, 2018, 09:07:04 AM »
Issue: th400 not shifting correctly. Feels like when the truck shifts into 2nd that first gear does not disengage.

Additional information: I never used this transmission before so I do not know the history of the trans. Also, I did do a complete rebuild including installing a 4l80 direct drum and 32 element sprag. It does need to be said that this is my first trans rebuild and I easily could have messed something up.

I did replace the vacuum modulator and ensured the vacuum line is coming from manifold vacuum. Any help is greatly appreciated.

Online Rapid Roy

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Re: Th400 shifting issue
« Reply #1 on: December 11, 2018, 09:08:14 AM »
Welcome
1974 Cheyenne 10 LWB 350/TH350/AC/4 BBL Quadrajet

Offline Ozark

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Re: Th400 shifting issue
« Reply #2 on: December 11, 2018, 10:29:33 AM »
Maybe worth replacing the check valve at the brake booster?

Offline Joe.cummings

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Re: Th400 shifting issue
« Reply #3 on: December 11, 2018, 02:52:51 PM »
Why would this cause an issue?

Online VileZambonie

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Re: Th400 shifting issue
« Reply #4 on: December 12, 2018, 04:26:05 AM »
Disconnect the detent solenoid to see if any change.

Recheck the manual valve before you pull it apart.
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