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I have had a hard second gear shift on my TH400 since I got the car 5 years ago. I just decided to address it. I checked fluid level, vacuum at modulator is 15 and engine is tuned but problem exists. I bought a B &M adjustable modulator. After install no difference. I adjusted it out two turns and it was a little better. I was going to back it out some more but am afraid of damaging the tranny. I'm below novice level on transmissions. This was my last attempt before buying another transmission.

Thanks
 

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The adjustment range on those modulators is not all that much in terms of the actual change in performance.

But I don't think you'll damage anything by backing the screw out farther.
 

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Can you post pics of this modulator screw, please? My corvette has a TH400 thats shifts hard into second, and then goes straight to third gear. It's done it ever since I've owned it. Aamco told me the whole transmission would have to come apart to correct this. Sorry, didnt mean to hack a thread. But I appreciate any advice. Jason
 

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I have had a hard second gear shift on my TH400 since I got the car 5 years ago. I just decided to address it. I checked fluid level, vacuum at modulator is 15 and engine is tuned but problem exists. I bought a B &M adjustable modulator. After install no difference. I adjusted it out two turns and it was a little better. I was going to back it out some more but am afraid of damaging the tranny. I'm below novice level on transmissions. This was my last attempt before buying another transmission.

Thanks[/QUOTE

Sounds like changes have been made to the valve body. If so you will not change much by adjusting the modulator.

This explains tricks that some do to changes TH 400 shifts.
This make it shift hard.
Scrol down to find
http://www.hotrodders.com/forum/t-400-build-tips-photos-145318.html
Making your own valve body kit.

The TH400 doesn't require anything super fancy to get a firm shifting unit.

You need to drill the feed holes shown in this picture. I recommend drilling them both to .125". The 3rd feed hole can go bigger, but I would recommend .140" as the high end.

You also block the 2-3 accumulator feed hole in the valve body. This requires a 5/16" set screw and proper tap. You will remove the 2-3 accumulator piston, discard the spring.

Tap the hole that feed the backside, or spring side, of the accumulator piston. Install the set screw. Re-install the accumulator piston.

What this does is eliminates accumulator function on the 2-3 shift. This results in a very positive 2-3 shift. You could leave 2-3 accumulator function in place and go slightly bigger on the feed hole.



You have to change the Valve Body and plate to remove these changes.
:anim_25:
 

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Can you post pics of this modulator screw, please? My corvette has a TH400 thats shifts hard into second, and then goes straight to third gear. It's done it ever since I've owned it. Aamco told me the whole transmission would have to come apart to correct this. Sorry, didnt mean to hack a thread. But I appreciate any advice. Jason
Jason, Not all modulators are adjustable. If you want to try this buy and install an adjustable modulator and start from there.
 

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Jason, Not all modulators are adjustable. If you want to try this buy and install an adjustable modulator and start from there.
Thanks bruce, ill try to pick one up. J
 

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Can you post pics of this modulator screw, please? My corvette has a TH400 thats shifts hard into second, and then goes straight to third gear. It's done it ever since I've owned it. Aamco told me the whole transmission would have to come apart to correct this. Sorry, didnt mean to hack a thread. But I appreciate any advice. Jason
Multiple problems are usually hard to get right the first time.. Stack shifts can usually be adjusted out by the governor springs, but if you only have a quick shift into 3rd and 1-2 are fine, then it could be something else either inside the valve body or inside the unit.

You can try another Valve body and plate, and then start over from there. If the VB and plate make 2nd shift easy but it still stacks 3rd, then you probably got a trans that has a shift kit already installed but has an internal problem making 3rd come in so quick.

Any adjustments made to correct a problem in one gear will effect all gears, like if you put weaker springs in the governor to prolong the 2-3 shift then the 1-2 shift will also be later. :anim_25:
 
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