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Discussion Starter · #1 ·
Sorry about this subject here, I know there is a transmission forum. I posted it there, and didn't get a response...maybe it was just too dumb of a question. It was:

>>The transmissions in my F-250 and Infiniti are shifted by the EFI computers, which manipulate solenoids according to operational parameters like RPM, MAP and other stuff. Perfectly calculated, no-brainer shifts under any condition or demand.

What shifts a TH400? It has a vacuum line going to it, and the kick down solenoid, but how does it work in general? If it is watching vacuum to know when to shift? If so, what happens with a wild cammed engine which idles at 6", drops to 1" on acceleration, and cruises at only 17"?<<

The TH400 transmission is the next car component I want to dip into, it is the same shape/configuration as when I bought the car. It is "kitted" (whatever that really means) and has a pretty high stall. The two pin electical connector kick down solenoid does not work, it doesn't even click or make a sound when 12V are placed directly on it. It shifts very firm under power. It barks the tires when shifting into reverse from park idling at 1200 rpm. When driving it will seek its way to high gear, and will not downshift by itself until the car is nearly stopped. If needed, I just downshift manually. But those downshifts are so firm that I have to be on the gas first, of the backlash clunk sounds like someone hitting the driveline with a sledge hammer. For fast acceleration shifting at 6000 RPM, I have to shift it manually or otherwise it would shift itself at about 4000 RPM.

Sound like a weird set up?

chevelles.com/showroom/gibbons68.jpg
 

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The barking into reverse sounds odd, the shift kit is probably what is making it shift hard as a rock. Or maybe your idle at 1200... kinda high. I hate shift kits personally. Just drive it like you stole it until the tranny goes out so then you have an excuse to fix the problem.
 

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Part throttle shifts are controlled by the vac modulator and the governor. Full throttle shifts are controlled solely by the governor. You can but a tuning kit for it. Its nothing but a bunch of weights and springs. B&M sell one and summit carries it even though its not listed in all of there catalogs. The governor is assesible through a small cover on the side of the trans, no need to drop the pan. Do this to change the full throttle shift points. 1200rpm at idle is high. I would do something about that.

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Undee's70SS
 

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Discussion Starter · #4 ·
I would love to do something about the 1200 rpm idle, but it's the cam's fault. I like the cam otherwise.

So, these springs and weights in the governor...is it as easy as asking for a 6000 RPM set, or do I need part numbers? Is there some kind of bench test for the vacuum modulator? Are there kits which disable the modulator in favor or more performance?
 

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gibbons, for your 1,200 rpm idle have you tried running more initial ignition advance (and then adjusting the weights and springs to properly limit total advance). Usually a big cam will smooth out and idle lower if you run more initial advance.

Thomas
 

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<BLOCKQUOTE>quote:</font><HR>Originally posted by gibbons:


So, these springs and weights in the governor...B]<HR></BLOCKQUOTE>Yes
<BLOCKQUOTE>quote:</font><HR>Originally posted by gibbons:
is it as easy as asking for a 6000 RPM set, or do I need part numbers? B]<HR></BLOCKQUOTE> No, the kit comes with a bunch of springs and weights. Combine different weights and springs to achieve the desired shift points. It has to be done on a trial and error basis. <BLOCKQUOTE>quote:</font><HR>Originally posted by gibbons:
Is there some kind of bench test for the vacuum modulator? B]<HR></BLOCKQUOTE>
You could use a hand pump to check for a vacuum leak. If yours is an aftermarket or newer model there is a small screw to adjust it. Take off the vacuum line and it is in the small tube on the vacuum modulator. Remember the vacuum modulator only effects part throttle shift points. At WOT there is no vacuum to operate it. Work on the governor first to get your desired WOT shift points, then the vacuum modulator to adjust part throttle shift points. <BLOCKQUOTE>quote:</font><HR>Originally posted by gibbons:
Are there kits which disable the modulator in favor or more performance? B]<HR></BLOCKQUOTE> Yes but they are more for a blownengine. I have never used one on a N/A engine but I don't see why one wouldn't work. I believe B&M sells these too.

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