I am looking for a high quality vacuum modulator for a TH400. The one in the transmission now is from NAPA and seems to be having some issues, seems to be leaking internally. It is adjustable and it would be nice to have that again. Any suggestions for a supplier that specializes in automatic transmissions would be fine but a real TH400 expert would be best. Thanks
I got one via a local transmission shop. It will be installed as soon as I can get the schedules to sink up.
Most of the adjustable vacuum modulators are made by Rostra Precision Controls in the U.S.A. http://www.rostratransmission.com/vacuum-modulators-by-rostra-transmission.php http://www.rostratransmission.com/pdf/rostra-modulator-application-guide.pdf The dual red stripe modulators give a little more adjustment range. http://www.ebay.com/itm/TH350-TH400...m51a354560c:m:mcQPCfhLE6ks3zy3xxspvPg&vxp=mtr
It's inside the vacuum nipple. You pull off the hose and turn the screw. The big black can modulators have the adjustment screw on the other end. With the stock type modulator, you must seal the threads anytime you make an adjustment. Not so with the small brass ones.
Interesting. Do you recommend or have one of the smaller brass ones? I would like to try to change the routine 1-2 shift point on my TH400. It upshifts to second almost immediately at part throttle it is really no fun.
The brass ones are very common. I have had them on my transmissions for some time. You can adjust the minimum and part throttle shift points a range of 2-5 MPH.
Cool I might pick one up. I assume it fits the my BA TH400 tranny because the add clearly omits Buick (surprise). "GMC CHEVY PONTIAC OLDSMOBILE CADILLAC"
I see the vac modulator as more for adjusting harshness of shifts, and the governor calibration (springs and weights) as for setting mph shift points. Bruce Roe
It will depend on the cam and torque converter. A stock engine will have higher vacuum and the stock converter will drag that vacuum down more, affecting the shift points (minimum and part throttle) more. You will get the maximum adjustment range (2-5 MPH) with a stock configuration. With a moderate cam, vacuum is lower, and a higher stall converter will have less effect on engine vacuum at lower throttle openings, so the modulator adjustment will have less or no effect on minimum or part throttle shift points, but some effect on harshness. The governor calibration will therefore be the best way to adjust shift points. I recently found this out when I went from the switch pitch to a fixed pitch 10" converter.
I've installed the new modulator and also changed the vacuum hoses on both the engine side and the modulator. Now the car shifts better that it ever has. Mission accomplished.
