TH400 downshift problems - Pontiac GTO Forum
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post #1 of 6 (permalink) Old 07-11-2019, 08:01 AM Thread Starter
 
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TH400 downshift problems

Hey everyone it's been a while since I've posted meaning I've actually been out driving my car and not wrestling with it but one issue is finally getting to me. My th400 refuses to down shift when coming to a stop until I sit there for a full 3 seconds. And if I manually shift it down to first when I come to a stop it slams and lurches me forward an inch. It's rebuilt, has a 2200 stall converter and new vacuum solenoid and fill vacuum from the manifold. The only thing I didn't get hooked up was the electric throttle downshift that you put on the carb to the trans. I thought that only had to deal with full throttle down shifts so I didn't think it mattered but maybe it's part of it? Any help is appreciated!

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post #2 of 6 (permalink) Old 07-11-2019, 10:45 PM
 
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More info needed. Most important is what year?
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post #3 of 6 (permalink) Old 07-12-2019, 03:06 PM Thread Starter
 
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It's a 69 LeMans with a 73 455.i believe the th400 is from 73/74 but I'm really unsure. I don't know what info you need sorry. It shifts fine once taking off from a dead stop. The rebuild was done with new clutch packs and different springs for firmer shifts. My vacuum line tees off my intake manifold with the brake booster. Umm anything else?

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post #4 of 6 (permalink) Old 07-12-2019, 06:49 PM
 
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what carb are you running
if a q jet what is its part number 7043273 ?? or ?

how about a couple pics with the air cleaner off...
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post #5 of 6 (permalink) Old 07-12-2019, 07:46 PM Thread Starter
 
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So it's a quadrajet 7057256 at the back there you can see my tee fitting with one going to the brake booster and one to the hard trans line off to the left. I never installed a kickdown switch.
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post #6 of 6 (permalink) Old Today, 08:52 PM
 
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The ‘69 used an electric switch mounted on the accelerator pedal bracket for downshifting when equipped with a two speed or TH400 transmission. The TH350 uses a cable mounted on the carburetor linkage. Not sure if that would be part of your problems though.
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  Pontiac GTO Forum > The 1964-1974 Pontiac Tempest, Lemans & GTO > 1964-1974 Tempest, Lemans & GTO Undercarriage, Frame, Transmission and Differential Discussions.

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