The vacuum modulator is a vital component of automatic transmissions. It tells the transmission what kind of load is being put on it, allowing the transmission to react with the proper line pressures and shift points. Simply adjust the screw inside the vacuum nipple for more or less diaphragm pre-load.
How does the kickdown switch work on a TH400?
Instead of a linkage or cable, the TH400 uses an electrical switch that is most often mounted on the carburetor. This electrical input powers up a solenoid in the transmission that accomplishes the same results, with higher line pressure and a signal to downshift the transmission.
Does a TH400 need vacuum?
It must hold the vacuum for a few minutes without dramatic loss of vacuum or the diaphragm is bad. Shut off the engine and allow it to cool for 20 minutes. Remove the bolt in the modulator hold-down clamp using a wrench. Remove the clamp and with a slight twist, pull the modulator out of the transmission.
Will a Turbo 400 shift without vacuum?
Under wide open throttle there is no vacuum and the governor will then take over the shifting duties. Depending on what rpm you want the trans to shift at, you can buy governors that will shift the trans in Automatic at lets say 6,500rpm (W.O.T.) without moving the shifter.
How do you adjust a transmission modulator on a vacuum?
Remove the vacuum line from the end of the vacuum modulator. Use a small slotted screwdriver to turn the adjuster that is located inside of the vacuum fitting. Turn the adjuster clockwise for earlier shifts and counterclockwise for later shifts. Make small adjustments of 1/8 to 1/4 turn at a time.
Does a Turbo 400 need a kickdown cable?
Any hobbyist who transplants a Turbo 400 into an older Pontiac originally equipped with another transmission must also install some type of kickdown switch, or proper downshifts cannot occur.
Where is the vacuum modulator on a TH400?
Locate the vacuum modulator on the passenger side rear of the transmission. Look at the hose leading to it from the engine and examine it for cracks that could cause a leak. Shut off the engine and replace the hose if any problems are found.
What does the governor do in a TH400 transmission?
The TH400 governor’s function is to maintain the speed that your transmission delivers, keeping your vehicle moving at the desired speed selection of the driver, no matter what kind of load you may add on.
How do you adjust a c4 vacuum modulator?
Turn the modulator adjustment screw in a clockwise direction with the screwdriver to firm up and delay the up-shift of the transmission. Do not adjust the screw more than four turns in either direction.
Where does the transmission vacuum line go?
If the truck has a vacuum hose to the transmission (to the vacuum modulator), the line will be a metal tube attached to the large tube that the transmission dipstick is in. It will come up and connect to a hose that will run to the base of the carburetor.
What does the vacuum modulator do on a Turbo 400?
What does the vacuum modulator do on a Turbo 400? It is equipped with a vacuum modulator that senses change in the engine’s vacuum due to throttle position and load changes. As these changes occur, the modulator adjusts the shift timing of the transmission according to the demand of the engine.
What kind of kickdown switch does a GM TH400 have?
But, GM’s TH400 uses a combination of vacuum line at low speeds and an electric switch at speeds above 30 mph. We are going to try to take some of the mystery and scariness out of fixing the kickdown switch on our 1970 Caprice with it’s 454 and TH400.
Can a TH350 kickdown cable be replaced with a TH400?
B&M designed this kit for car owners who are replacing a TH350 with a TH400. The instructions say you should reuse the TH350 kickdown cable bracket. If you don’t have one’ you can get a universal kick down cable bracket from Holley, TransDapt, Spectre, and many others; or make your own.
What does a transmission modulator do on a Turbo 350?
As these changes occur, the modulator adjusts the shift timing of the transmission according to the demand of the engine. Click to see full answer. Hereof, what does the vacuum modulator on a Turbo 350 do?
