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.

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.

Likewise, what are the symptoms of a bad vacuum modulator? When you have a bad modulator valve, some or all of the following symptoms will begin to manifest themselves:

  • A whistling sound (from a leaking diaphragm)
  • White smoke coming out of the exhaust (from a leaking diaphragm)
  • Early or late shifting.
  • Hard shifts (usually causing the car to jerk)
  • A rough idle.

Thereof, what does a vacuum modulator do?

Vacuum Modulator is an engine load sensing device that converts engine vacuum into a transmission valve body input.

Does a th350 need a kickdown cable?

See all 8 photos Other than the convenience of automatic downshifts into passing gear at highway speeds, there’s no real need for a simple kickdown cable on those transmissions like this TH350 that have a vacuum modulator. “Kickdown” and “TV” cables aren’t really the same thing.

Will a th350 shift without vacuum?

Unless it has a manual valve body it won’t shift without vacuum until very high RPM’s. Besides the fact that when you disconect the vacumn line the line pressure goes to full which can wreak havock inside the transmission, I don’t think that it will shift into high gear.

How can you tell th350 from th400?

TH350 has a Mechanical (cable) Detent Cable. TH400 has an Electrical Detent Switch. Easiest way is the shape of the drainpan.

How do you adjust a modulator valve?

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.

How do I adjust the cable on my th350?

How to Adjust the Kickdown Cable on a Turbo 350 Park the vehicle in an area away from traffic, turn off the engine and allow it to cool. Remove the engine air cleaner from the carburetor. Locate the throttle lever on the carburetor. Loosen the lock-nut on the kickdown cable with an adjustable wrench.

How do you test a vacuum modulator on a transmission?

Testing the Modulator Block the rear wheels. Locate the vacuum modulator on the passenger side rear of the transmission. Pull the vacuum hose off the modulator and install the vacuum pump. Look for any transmission fluid running out of the vacuum port on the modulator, indicating a broken diaphragm.

Is a th400 a good transmission?

The TH400 is an automatic shift, three-speed, longitudinally positioned transmission. It is widely regarded to be a supremely durable and legendary transmission. The TH400 is conservatively rated at 450 ft.

What did a Turbo 350 come in?

The Turbo 350 automatic found its way into Chevrolet Camaros, Pontiac Firebirds and Chewy and GMC trucks. Although the transmission most notably matched GM vehicles with small-block V-8s, it also matched the block-block 396 V-8s, V-6s and the small Iron Duke in-line four-cylinder models.

How does a th400 shift?

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.

How does a vacuum modulator work?

The transmission vacuum modulator effectively works by consistently computing the load in your car’s engine with the diaphragm. As soon as a gear change is executed in line with the load demand, the diaphragm pushes the valve to prompt the spring to move in the reverse direction of the diaphragm.

What does the governor do on a th350?

The transmission governor is connected to an automatic transmission’s output shaft and regulates hydraulic pressure based on vehicle speed, contributing to when the transmission shifts. The governor cover conceals the hole where the governor is located and holds it in place on the transmission.

Where does the transmission modulator hose 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.