THM 400 transmission not shifting

1971gto

THM 400 transmission not shifting

Unread post by 1971gto » Tue Aug 24, 2010 9:15 am

why is my GM THM 400 is not shifting first gear ontime? it will shift after the enging starts to rev-up. all other gears seam to be working fine.

MeccBoy

Re: THM 400 trasmission

Unread post by MeccBoy » Fri Aug 27, 2010 12:11 am

Could be a vacuum problem to the modulator.
Check that its vacuum hose is good.
Also may need an adjustment.
There is a phillips screw insde the vacuum port on the modulator.

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