What controls the auto transmission shift points?

[243]

Does the 12V have a vacuum pump feeding a vacuum modulator on the transmission or a mechanical linkage?

 

[formula]

The 1-2-3 shifts are hydraulically controlled by the transmission via the kickdown cable on the throttle linkage. The 3-4 shift is electronically controled by the Throttle Position Sensor and the computer.



SP

 

[Joe G.]

If your transmission works like the 47RH in my '95 and I think it does, then the governor pressure is controlled by a flyball type of gadget on the tailshaft. You should see 1 PSI per MPH at the governor test port; eg. 10 PSI at 10 MPH. The valve body reaction to the governor pressure is modified by the kick down lever. The transmission in my '82 Imperial works the same way.

 

[243]

This subject is really for the Cummins Conversion board but I thought that First Gen's might give me a clue even though they have a different make automatic.



I want to run a 4BT in my Cherokee which has a TH400 which they also use in panel vans. My concern, and the reason I am procrastinating is I don't know how to control shift points without a vacuum source tied to rpm.



Any thoughts?

 

[fox]

You can buy a cable kit that replaces the vacuum modulator on the t-400. This will make it non-vacuum and it will be throttle sensitive.

I am not sure how they were set up in the bread trucks, but the cummins can be set up with a vacuum pump.

Try talking to the speed shops if there are any in your area or call a good trans shop.

 

[243]

Cable operated?



I will continue to research this, thanks!