The vacuum modulator is located on the passenger side of the transmission, just above the tranny oil pan. It has a vacuum line going to it. It actuates a valve in the tranny for upshifts.
No because this will not be the proper signal from manifold vacuum that tells the transmission what kind of throttle position and load the engine is under.
Check the vacuum source to the vacuum modulator. If it's good, try a new modulator.
There is no adjustments to a 350 Turbo Transmission (GM). The only external thing that would cause shift problems is the vacuum modulator on the side. This is replaceable easily. Check for proper vacuum signal to the modulator. Make sure there are no holes and or kinks in the vacuum line from the engine to the modulator. If none is found, replace the modulator for shift complaints. If it is slipping, the tranmission will require removal and overhaul. This transmission uses wet clutch plates and automatically compensates for wear in the plates to a certain point.
The TH 400 has the vacuum modulator attached to the passenger side of transmission.The TH 350 has the vacuum modulator attached to the rear of transmission.The transmission oil pan on the TH 400 is anything but square.
If your speaking of the vacuum modulator for the transmission, they no longer use them on the transmissions with overdrive and electronics. The powerglide, turbo 350 and turbo 400 used to use them.
The vacuum modulator is on the passenger side under the cooler lines on a turbo 400. It's held in with one bolt that goes through a clamp that holds the modulator in. To change it put a drain pan under the modulator, pull the vacuum line off it, remove the bolt and clamp, pull the modulator out. Make sure the o-ring seal comes out with it, be sure there's a new o-ring on the new modulator and put it in, replace the clamp and bolt that holds it in and hook up the vacuum line (if it's an adjustable replacement modulator you might need to use a little bit longer rubber line if it has a steel line running down with a short rubber line at the end since some of the old turbo 400's originally had a big canister modulator and the new one will probably be smaller). Then start the engine, check for leaks and refill the transmission as needed. Same procedure on a turbo 350 but the modulator is in the rear on the passenger side pointing towards the back of the car/truck on a turbo 350.
the modulator valve does not have a screw, however, the modulator located outside the modulator valve may or may not have one.
The TH 400 has the vacuum modulator attached to the passenger side of transmission.The TH 350 has the vacuum modulator attached to the rear of transmission.The transmission oil pan on the TH 400 is anything but square.
It must be connected to a full-time vacuum source such as the intake manifold.
The engine itself creates Vacuum once it is running.
Check to verify that the vacuum line is properly connected to the modulator, and there are no broken springs in the governor assembly.
A 350 has a vacuum modulator back at the tailshaft on the passenger side. Also the pan's shape is different.