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Discussion Starter · #1 ·
The TH400 in my 70SS shifts really hard. I mean really really hard (neck snaping). The person that owned it before me probably put a shift kit into it.

I would like to soften the shifts but don't know how to do it. Any suggestions? Can the vacuum modulator be adjusted down? Can I drop the valve body and adjust something?


Thanks,

Richard
 

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I would first check the vacume line for cracks or leaks. That would cause what you describe.

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Bob Von Kaenel
Lincoln, NE
70 SS 402ci+.030 TH400 3.73 posi Cranberry Red

We've not been called upon to hold the fort, but rather, to storm the heights!
 

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I think a lot of us are wondering where knipes got his special "neck snapping shift pre-worn transmission vacuum lines"... there might just be a market for that :)

Scott
 

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If a kit has been put in, the only way to go back to stock is to get the stock springs, separator plate and gaskets from a trans shop and swap them out. Some kits also have you modify a booster valve, so you would need that too. Maybe the accumulator springs were removed at the same time as the kit install? Unless something is broken inside, this is all I can come up with.

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Dave (NY)
70 chevelle ss396 conv
66 chevelle ss396 hdp/conv
72 chevelle
TC member #493
Never forget Earnhardt!
 

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Assuming that this thing has a really brutal shift under very light throttle, but is still in high gear by about 22-25mph, then somebody put in one of the old B&M "tear the center support out of the case" shift kits. The fluid flow restrictors in the spacer plate were probably drilled out too large, hence the short, brutal shift. Go to your nearest NAPA store, or go to http://www.natauto.com and order a 400-1 shift kit, made by TransGo. The parts list is very comprehensive, and the instructions are great. They have a new Pressure regulator spring, and spacer plate, which will fix the crazy calibration. Been using them for over 20 years, and had extremely good luck calibrating automatics for street strip. While the pan is down, pull the little cover with 6 bolts to the rear of the valve body area, and make sure that the accumulator spring is still in place. If so, follow the directions in the kit, including placement of the check balls, and you will be all set. An easy way to seat check balls, (if trans is still in car) is to put lithium grease in the check ball recess in the case, then stick the ball into the grease, before you put the spacer plate back up. Good luck.
 
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