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Old 03-28-2007, 08:17 PM
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TH400 upshift problems

I have a TH400 behind a mild 350 sbc with a 4.11 rear. When I ran a 0 to 60 recently the tranny would not shift from 1st to 2nd without letting up on the throttle. As soon I put the hammer down again it then downshifts from 2nd to 1st. At this point the engine is screaming past 6000 rpm (I progressively adjusted the tach shift light until I stopped at 6000 rpm). I have the tranny out of the car now and the governor seems to be O.K. I do have a Lokar downshift kit on it and I am wondering if this is causing the problem. It seems to be adjusted according to the instructions. The only other issue may be the vacuum line to the modulator. It Y's off to a vacuum gauge at one point. I was wondering if that may be slightly reducing the vacuum to the modulator. Thanks in advance.

Kevin

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Old 03-31-2007, 12:49 AM
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sounds to me like you have too high line pressure causing the governer to down shift
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Old 03-31-2007, 01:00 AM
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Are you sure the modulator valve is indeed OK? They can cause some wacky shifting conditions. Check the end of the vacuum line (that went to it) and see if it looks moist up in there.

Also, before you pulled the trans, did you disconnect the lokar downshift "kit" to make sure it was not the problem?

We had issues with a C5 (ford) trans and simply unhooked the kickdown for our testing. Yep...that was it (in that particular case).
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Old 03-31-2007, 06:50 AM
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Th-400

I would agree with the vacuum to the vacuum modulator. That's what they do.
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Old 03-31-2007, 07:42 AM
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every body has addressed the manifold vacuum feed directly to the modulator so I will not.

What is the history of this trans? Recent build? Old timer?

Did the trans operated fine then start this problem?

It sounds like the kick down switch could be activated , leaking , broken .

Next place I would look is the shifter linkage for proper adjustment

Governor has no problems as you mention? Plastic gear is tight , springs and weights are OK?

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Old 03-31-2007, 03:34 PM
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Th400 upshift problems

Regarding the history of the trans I purchased the rod a few years back. In the paperwork supplied with the car it said TH400 trans rebuilt heavy duty. Don't have clue what that entailed. It has a stamped tag on the side which says 086 in the middle and below it says 86-FMA and 58459. I think the rod was built about 1990. I have no contact with the original owner/builder.
I never really did any 0 to 60s until last fall.
I added the Lokar downshift kit during the summer. The downshift kit is just a plunger connected to a cable which in turn connects to the throttle on the carburetor. When you push the throttle to the floor the plunger activates a switch which then energizes the solenoid on the side of the trans. I spoke with one of the local rodders and he seems to think its being caused by the downshift kit. He ended up taking off his kit. I checked the archives here and at one point someone suggested that the engaging the downshift solenoid somehow raises the shift point. I just can't understand how this would have worked in its original car/setup.
As far as the shift linkage goes there may the possibility it could be moving the linkage with the power on and power off. The engine mounts are new but poorly designed with lots of free play. I will look at that possibility when I put everything back together.
The governor appears to be in excellent condition. No wear on the gear and the plunger down the center and the weights seem to operate smoothly. Last fall before I pulled the engine & tranny apart I bought a B&M governor counterweight shift kit. I presumed before hand that someone already modified the weights to get the high shift point. Much to my dismay the governor appears to be stock. The real problem with this rod is that it is very difficult to do any mods to the trans (do to the enclosed cross member) once its in the car. So I hope to get it right before it goes together.
Anyway thanks for everyones advice. I think I will implement the changes one by one until I get to the bottom of the problem.

Kevin
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Old 04-01-2007, 05:32 AM
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From the "Ron Sessions" manual...
No 1-2 shift, Governor malfunktion.
-Check free movment
-Check for jammed weights
-Check for worn or loose nylon governor gear
-Check for loose or worn stop pin

-Could also be valve body, loose feed pipes, loose bolts, clogged pipes, stuck valvetrain.

-Or, faulty detent solenoid operation

/Pete
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