Can anyone tell me how to test the vacuum control unit that sits on top the IP and controls vacuum to the tranny modulator on my 81 SD.I have a mighty vac........ thanks

William Rogers.........

Remove the black line to the tranny and setup the MityVac there. Take a reading at idle, a short WOT burst, and with the arm 10mm from the stop. It should be 15-17", 0-2", 5-6.5"hg respectively. Another test I like to do is remove the line off of the valve and see if it holds vacuum to 15"hg, most of them which aren't that great in the above range also leak like this....

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Jeff M.
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