Just got my 400 trans in and it has the vacuum modulator on it. It has a full manual reverse valve body in it so the modulator doesnt even need to be on there anymore. Is it ok to just leave the modulator on there without being hooked up, up do i need to plug the vacuum port or remove the entire modulator istelf and use something to plug it?
buick46270 (wished I knew your name), it has been my experience that if you leave the original modulator valve (in the case) and use a vacuum modulator to "plug the hole" you may experience a dramatic pressure drop when shifting to high(3rd) gear as pressure against the mod valve will actually overcome the spring tension of the vacuum modulator causing slippage/overheating of the direct clutch pack. We generally use the aluminum plug furnished with some shift kits, drill & tap it for 1/4-20 set screw, install the plug and preload the mod valve with the set screw to prevent valve movement. Of course this will not apply to transbrake optioned transmissions. This may all be for naught as I don't know your trans builder's preferences or techniques. Jay
Kyle Bryant Im running a supercharger and under boost, i dont know if that air being forced into the modulator will do any harm to the trans, thats basically what im trying to figure out.
Hello Kyle, yes there is the possibility of a problem. If the vacuum modulator remains attached to the induction system and the line doesn't blow off, there is the possibility of rupturing the diaphram and actually applying manifold pressure (boost) to the trans case. This in turn would pressurize the case blowing ATF out of the trans vent tube & if bad enough, pushing the pan gasket out blowing even more ATF out onto the exhaust system creating a HUGE FIRE RISK TO THE ENTIRE VEHICLE & YOURSELF! It would probably be best, at the minimum, to leave the modulator disconnected from the induction system. Good luck! Jay
