03-31-2018, 10:46 PM | #1 |
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TH400 help
I have a TH 400 that I just got in my truck and, it's not shifting right. Could it have to do with this (see pic below) is this supposed to be hooked up to a vacuum line?
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03-31-2018, 10:50 PM | #2 |
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Re: TH400 help
Yes, vacuum modulator. Hook it to vacuum & see if it shifts better.
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03-31-2018, 11:05 PM | #3 |
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Re: TH400 help
Just to clarify, it needs to be connected to manifold vacuum.
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04-01-2018, 12:03 AM | #4 |
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Re: TH400 help
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04-01-2018, 12:05 AM | #5 |
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Re: TH400 help
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04-01-2018, 10:45 PM | #6 |
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Re: TH400 help
Just some additional tidbits.......From the pic, I believe the modulator maybe adjustable as well....so you can take a small screw driver and adjust the set screw in the modulator....turn the screw clockwise will firm up the shift (later) and counter clockwise with soften the shifts (earlier) ....
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04-02-2018, 12:23 AM | #7 | |
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Re: TH400 help
Quote:
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04-05-2018, 11:39 PM | #8 |
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Re: TH400 help
Hooking up to vacuum fixed the problem. It shifts good now. I felt and looked around on the valve body, but didn't see or feel a screw to adjust how it shifts. Thanks to all for the help!
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04-06-2018, 12:37 AM | #9 |
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Re: TH400 help
The adjustment screw on a vacuum modulator is inside and accessed thru the port for the vacuum hose.
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04-06-2018, 10:22 AM | #10 |
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Re: TH400 help
This. And on a Turbo 400 the modulator is the sole control of shift points and firmness, except for the electric switch for WOT downshifts which most, but not all have.
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04-06-2018, 03:24 PM | #11 |
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Re: TH400 help
Ah, I'll check it out. It shifts fairly quick from 1st to 2nd, but from 2nd to 3rd takes a bit longer. I'll have to drive it more to see if I need to adjust it. Thanks for the info.
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04-06-2018, 03:33 PM | #12 |
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Re: TH400 help
Glad you got to the root of it. I'll bet it revved way up and then slammed the 1-2 shift. I had that vacuum hose fail once because the PO put the exhaust too close to it and burned the hose until it was extremely brittle.
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04-06-2018, 03:42 PM | #13 |
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Re: TH400 help
Be very careful and make changes 1/4 to 1/2 turn at a time. You can puncture the diaphragm in them if you crank it in too far. As me how I know...
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04-06-2018, 08:48 PM | #14 | ||
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Re: TH400 help
Also there was a steel line that ran down there from the factory. Attached at the intake behind the carb and to the modulator with a 4" piece of rubber hose. A long rubber vacuum hose going all the way down there can weaken and colapse.
Gary
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04-08-2018, 12:21 AM | #15 |
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Re: TH400 help
Thanks to everyone for the information, it is very appreciated!
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