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Discussion Starter · #1 ·
I put a TH400 in my car and now I can't hold the car in first gear above 4600 rpm. It will shift into 2nd gear by itself. How do I stop this from happening? :confused:
 

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I don't want to sound like a smart ass, but is the Th-400 in first (low) or drive?
 

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I like to party!!
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Discussion Starter · #3 ·
Shifter is adjusted to reflect all gears correctly. That is with the shifter in 1st gear(low). when I let out of it, after it slows enough it will shift itself back down into 1st gear again if I don't move the shifter.
 

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Stock 400 transmissions will shift out of manual 1st to 2nd at 5000 rpm. You have to remove the valve body and modify the 1-2 shift valve and plug the vent hole in the valve body.
Do a search as this has been discussed numerous times on this site. If I find it I will repost it......
 

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Does anyone have a link on what/how you modify the 1-2 shift valve? I'm helping a buddie with his. It shifts @ 4000 into 2nd on its own under WOT.
 

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Does anyone have a link on what/how you modify the 1-2 shift valve? I'm helping a buddie with his. It shifts @ 4000 into 2nd on its own under WOT.
It's simple: Grind two flats about 3/8-1/2 inch wide on the land with the arrow above. Just enough to bypass oil and with the hole plugged in the valve body, it will not shift out of first at any speed.

Also, it will go into first at any speed, so be careful.

Jim
 
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