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Discussion Starter · #1 ·
I'm building a th400 and I know how to make it full manual shift, but the only way I know how is with disregarding the modulator valve and front band. I want to keep the band for engine braking and keep modulated oil pressure instead of constant full line pressure. Can anyone tell me how to do the full manual conversion and keep these two features? The instructions on the crankshaft coalition does not cover keeping the modulator and the band.
Thanks in advance.

Nitro
 

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1979 Chevrolet Malibu 496-TH400-9" (cruiser). 1992 Chevrolet S10 355-700r4-7.625" (daily driver).
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I'm just a hobbyist here and not really a transmission guy. I can try to explain what I think I know. That TH400 tech post is great! Hopefully one of the authors (Crosley) or any other expert can chime in if I don't have any of this correct.

Do as you would do on the full manual conversion:
-remove governor tubes, plug the holes, drill the bypass hole in the valve body to loop the governor fluid
-the 1-2 shift valve modification (grind the land, plug the exhaust hole)

Do the usual (or your preferred) feed hole sizes, dual feeding the direct, block/restrict 2-3 accumulator, etc. (Not exclusive to just full manual) I was always told to do everything exactly the way that tech post describes the modifications.

Do not modify the boost valve and I don't believe you have to disable the reverse boost circuit.

You end up installing the modulator connected to a vacuum source instead of the aluminum plug to trap the modulator valve.

As far as the engine braking band goes, I assume this was previously omitted when you went to a case saver? I used a Jake's Performance case saver. If you specify your desire to keep the engine braking band they can modify the aluminum case saver to allow for the band. I was told most of the pros can supply the same modified part if you check around.
 

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Discussion Starter · #3 ·
I built this trans to be auto/manual, but I've changed my mind, and it's still on the stand so now's the time to do it. I want to add the case saver and keep the engine braking band.
 

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I built this trans to be auto/manual, but I've changed my mind, and it's still on the stand so now's the time to do it. I want to add the case saver and keep the engine braking band.

Then leave the braking band in . You will need to have the vehicle near stopped to down shift to 1st gear. The brake band is ''slightly'' slow to release as you downshift back to 1st gear from 2nd. The rear low band applies quickly, the brake band releases slower and there is a tie up , a binding feel as the trans shifts gears.

Leave the vacuum modulator in.. Do not modify the PR valve or block the indicated hole when the PR valve is modified. This mod is for full line pressure control in all gear ranges.
 

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Discussion Starter · #5 ·
Thanks, what has me concerned with leaving the band out is going from 3rd to 2nd gear. I've read your not supposed to downshift from 3rd to 2nd, but if you're under full throttle would it be ok?

I may remove the band after all. I didn't know that it binded up like that. Plus I do like the idea of the full size case saver.
 

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1979 Chevrolet Malibu 496-TH400-9" (cruiser). 1992 Chevrolet S10 355-700r4-7.625" (daily driver).
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Thanks, what has me concerned with leaving the band out is going from 3rd to 2nd gear. I've read your not supposed to downshift from 3rd to 2nd, but if you're under full throttle would it be ok?
For the sake of curiosity, what is the application/power level for this build? I feel like knowing that may shed light what may or may not be appropriate advice to give.

The broad strokes answer is, yes, you can 3-2 downshift. I think the best way to make sense of what is OK to do from a 3-2 downshift (in the absence of the front braking band) is to consider how the transmission would handle downshifts if you had the factory original set up and had the shifter in DRIVE. Think of what circumstances would make the 3-2 kickdown happen and let that be your guide. The transmission would be doing those things without engaging that forward braking band. If you don't have your foot in the throttle, the transmission wouldn't downshift on it's own. That tells you what you shouldn't be doing.
 
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