# TH400 downshift problems



## KowalskiCW (Jul 11, 2016)

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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## dd68gto (Nov 14, 2012)

More info needed. Most important is what year?


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## KowalskiCW (Jul 11, 2016)

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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## BLK69JUDGE (Jun 10, 2010)

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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## KowalskiCW (Jul 11, 2016)

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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## TK69tempest (Feb 28, 2011)

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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## KowalskiCW (Jul 11, 2016)

So no one else has any thoughts on the trans not wanting to down shift or slamming into gear? I'm really at a loss. If anyone else thinks it might be the electric down shift switch let me know and I'll go spend the money and install one. Thanks!


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## BLK69JUDGE (Jun 10, 2010)

have you been here ??

https://www.google.com/search?ei=8r...hUKEwjSuvSYyN_jAhUV7J4KHTrnDs4Q4dUDCAo&uact=5


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## KowalskiCW (Jul 11, 2016)

Yeah I guess when the transmission was refreshed I'm not sure the governor was replaced or even checked. Maybe I'll have my transmission guy look into that. Anything else to check guys?


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## Nicholas (Jan 16, 2017)

I've been watching this thread and I don't think you have a real unique issue. I know, it's easy for me to say, right??? I agree that a real good experienced automatic transmission mechanic, can figure this out and correct it. That's what I would do. Have him look at it. I have a similar problem, not identical, to yours with my '71 GTO TH400. Mine likes to upshift quite quickly from 1st to 2nd. It won't downshift again to 1st without being almost completely stopped. If driving in the 1st gear range, with it in 2nd gear, I have to really mash the pedal to get it to kick down to 1st gear. I have the factory electrical kickdown switch on the gas pedal. I tried making some adjustments with springs and other things, not successful, so I gave up on it. I might take my own advice and seek out a transmission mechanic. The car as a whole operates just fine. But, this transmission issue is irritating, Nicholas.


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## KowalskiCW (Jul 11, 2016)

Thanks Nicholas and yes it's very irritating. I just want to not burn out my 2nd gear always starting from a dead take off in it! And I don't want to break my first gear down shifting at a dang stop. Guess I'll take to someone else local about it.


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## cobraace2 (Aug 28, 2019)

I rarely do this but its near impossible to solve a problem like this without seat of the pants info . #1 how does it work when cold ?


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## cobraace2 (Aug 28, 2019)

By the way i am a transmission rebuilder retired now # 2? once it shifts to 1st after the 3 seconds and you start to drive under light throttle at what mph does it shift to second .


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## KowalskiCW (Jul 11, 2016)

So I took it out for a spin and it's now smelling like I'm burning clutches. That smell is pretty distinct. Anyways it acts harsher when cold. The warmer it gets the less harsh the shift. When I start in 1st and light throttle it shifts at 18-1900. I've got a 2k stall in it. I don't know but I think I see another rebuild in the near future. Wish I could just swap it to manual.


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## KowalskiCW (Jul 11, 2016)

Well anyone have any other things I can check? I'm about to give up and put it in storage for the winter and try again in spring.
Again it's a mild 455 with a rebuilt th400 with a 2k stall in it. During mild acceleration it shifts around 1900rpm. My issue is I don't have a kick down hooked up so I manually downshift a lot. 3 to 2 is fine but when I go 2 to 1 any speed or even when stopped it slams into 1st. If I stop and wait 2-3 seconds it auto shifts to 1st with no issues. Warm or cold it does this, less after fully warming but still does it hard enough it worries me. Now the last 2,3 runs I've started to smell the burning clutch smell when hammering on it. It seems to keep revving but not going any faster above 4500rpms. Any thoughts help!


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## 1968gto421 (Mar 28, 2014)

KowalskiCW said:


> Well anyone have any other things I can check? I'm about to give up and put it in storage for the winter and try again in spring.
> Again it's a mild 455 with a rebuilt th400 with a 2k stall in it. During mild acceleration it shifts around 1900rpm. My issue is I don't have a kick down hooked up so I manually downshift a lot. 3 to 2 is fine but when I go 2 to 1 any speed or even when stopped it slams into 1st. If I stop and wait 2-3 seconds it auto shifts to 1st with no issues. Warm or cold it does this, less after fully warming but still does it hard enough it worries me. Now the last 2,3 runs I've started to smell the burning clutch smell when hammering on it. It seems to keep revving but not going any faster above 4500rpms. Any thoughts help!


I suspect the previous rebuilder did something incorrectly, possibly valve body or accumulator. I fear another rebuild by someone else who is competent and experienced with these trans is in your future (as well as mine which has problems inherited from the previous owner. Chit:frown3: )

(Good to see you on the forum again but not with problems like this.)


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