Taylor
1/2 ton status
Had my first drive with the new TH400 in today. Its shifting around 2500 RPM, is that to high? I'm pulling the vacume source off the manifold not the carb. Is high shifting an indication of too much or too little vacume?
CK5
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Th400 Shift points
- Thread starter Taylor
- Start date
If you pull the vaccum line off the tranny's vaccum modulator, you can adjust the vaccum with a small skrewdriver thru the vaccum hole. Might be hard to get a skrewdriver in there with the exhaust right in the way, but i know this is how you adjust it. Its on the pass side of trans.
K5dreamer
1/2 ton status
i dont have a tach on my diesel, but my TH400 shifts into 2nd at 25mph, and into 3rd at 45mph, with 33in tires and 3.08 gears. using an online rpm calculator puts those shifts at right around 2000 rpm.
im no tranny guy so i really cant say whether your 2500rpm shifts are good, bad, or ugly.
im no tranny guy so i really cant say whether your 2500rpm shifts are good, bad, or ugly.
Did your th400 come stock behind a diesel?
mrdrinksalil
1/2 ton status
Not tryin to hijack but If you do have a TH400 that originaly came behind a diesel what do you have to change besides the torque converter?
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since diesels make no vaccum, id assume the valve body? idunno
Taylor
1/2 ton status
No its from a gasser. I'll try adjusting the modulator, how does it work clockwise to raise and counter to lower shift points? So like what rpm range should I be shifting in?
mrdrinksalil
1/2 ton status
the diesel th400 still has a vaccum modulator
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K5dreamer
1/2 ton status
ill assume the diesel TH400 question is aimed at me, and the answer is yes. to my knowledge, all military blazers and trucks came with the 6.2/TH400 combo.
i do know there is a vacuum pump on the back of the 6.2, right about where the distributor would be on a sbc, perhaps that supplies the vacuum for the tranny that you guys are talking about?
i do know there is a vacuum pump on the back of the 6.2, right about where the distributor would be on a sbc, perhaps that supplies the vacuum for the tranny that you guys are talking about?
rwright07
1/2 ton status
no, diesel th400's have a cable actuated vacuum modulator, mine utilizes a 700r4 tv cable that is of course controlled by the throttle
TH400's control shift PRESSURE via the modulator. Shift "RPM" (really output shaft speed) is controlled by the governor.
You can get some difference in shift RPM from the modulator, IME it was at most 5MPH difference.
You can get some difference in shift RPM from the modulator, IME it was at most 5MPH difference.
mrdrinksalil
1/2 ton status
This is new to me. Got a pick of this cable? I have a diesel th400 thats still has a vaccum modulator
Automatic shift points are controlled by a combination of modulator pressure and governor pressure. As output speeds go up gov. press. increases. As throttle pressure or load increase vacuum decreases and mod. pressure decreases. Removing the vacuum line from the modulator will allow shifts to be controlled by gov. press. only, which means a higher shift point. The rpm range for gov. press. can be raised by decreasing the weight of the flyweights or increasing the spring tension in the gov.
Gus
Gus
