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Old 10-21-2012, 10:35 AM
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plugged vacuum modulator T-400

Im curious as to why the th400 I bought has a plug in the vacuum modulator hole. Also a metal plate bolted over the location. Is this something a shop does to protect for storage or is this a bypass mod? I was on my way to buy a modulator but im also struggling with different options.. I need whatever is best for helping a buick 3.8l v6 operate this trans..
appreciate any thoughts and time, Mike.
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Old 10-21-2012, 11:53 AM
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Usually done on a trans with a manual valve body installed. Thats a lot of trans for a 3.8.
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Old 10-21-2012, 01:27 PM
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manual valve body? what does that mean? I just got back from the parts house with a modulator from a 1968 sports van but im still not sure its the one i need. Ive read that they made different modulators for v6 engines with th400 trans. Should i try to install this or is the trans designed for a different part?
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Old 10-21-2012, 01:29 PM
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Originally Posted by BOBCRMAN@aol.com View Post

Thats a lot of trans for a 3.8.
Yes but better than no trans for a 3.8
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Old 10-21-2012, 01:31 PM
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Originally Posted by 0trbo4myCHEVUICK View Post
Yes but better than no trans for a 3.8
i hope anyways
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Old 10-21-2012, 04:48 PM
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Well i installed the modulator. Hooked up to a vacuum line on the carb that was getting vacuum at idle. No change. adjusted screw both ways and test drove for an hour. No shift. Started to notice a slight clatter in drive and reverse. Guess I bought me a polished turd.

Last edited by 0trbo4myCHEVUICK; 10-21-2012 at 04:54 PM.
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Old 10-21-2012, 06:23 PM
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Was there a valve in the hole under the modulator?

Does this trans shift from 1-2 when the shifter is moved from 1-2? Same with 2-3? Does it stay in the gear that is indicated on the shifter?
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Old 10-21-2012, 07:16 PM
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Quote:
Originally Posted by BOBCRMAN@aol.com View Post
Was there a valve in the hole under the modulator?

Does this trans shift from 1-2 when the shifter is moved from 1-2? Same with 2-3? Does it stay in the gear that is indicated on the shifter?

I do not know if there was a valve in the hole under the modulator but I will take it off and look as soon as I get home from work.

No, the 400 does not shift at all when the stick is moved to 1 or 2. I put it in drive, it engages, and I take off fine. Problem is, I take off all the way to 4k and no shift.
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Old 10-21-2012, 09:44 PM
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pulled the modulator and after a quart of cinnamon swirl fluid i can see some sort of valve in there.

Pulled the governer plate off and I can see plastic gears with other internals but is there some sort of rod or something that slides into this finger sized cylindrical slot?
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Old 10-21-2012, 09:50 PM
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Old 10-22-2012, 03:04 PM
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Well i just installed a governor in the dang thing and it still doesent shift
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Old 10-22-2012, 08:05 PM
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Trans acts the same with a gov and mod installed as it did with neither one installed. guess its time to first gear it up to the shop
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Old 10-24-2012, 01:34 AM
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If i throw the shifter all the way down, it slips. If i put it in drive i take off but it wont shift on its own, i have to move one down on the shifter and i can get it to like 35mph. lame lemon
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Old 10-24-2012, 12:23 PM
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If I remember correctly.....there is suppose to be a small pin about an inch long in the modulator hole. Without it, it won't shift. I remember changing out a leaking modulator once and it didn't shift anymore after that. Turns out the pin came out with the old modulator and I didn't notice it. Replaced the pin and it shifted normally.
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Old 10-24-2012, 01:20 PM
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Quote:
Originally Posted by txturbo View Post
If I remember correctly.....there is suppose to be a small pin about an inch long in the modulator hole. Without it, it won't shift. I remember changing out a leaking modulator once and it didn't shift anymore after that. Turns out the pin came out with the old modulator and I didn't notice it. Replaced the pin and it shifted normally.
im gonna look into that right now.
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