How Much Vacuum Does A Turbo 400 Need?

What are the symptoms of a bad vacuum modulator?

Symptoms of a Bad or Failing EGR Vacuum ModulatorEngine performance issues.

One of the first problems of a potential issue with the EGR vacuum modulator is engine performance issues.

Check Engine Light comes on.

Another symptom of a potential problem with the EGR vacuum modulator is an illuminated Check Engine Light.

Failed emissions test..

What is a Turbo 400 transmission worth?

selling it as a good unit and with a “it will work” or your money back warrantee, it should be worth $150-200. There are many shops that sell a stock rebuilt TH400 for $600.

How do you test a vacuum modulator?

Testing the ModulatorBlock 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.More items…

What happens when a vacuum modulator goes bad?

The main symptom you will notice is poor engine performance. If the diaphragm of the vacuum modulator were to have a leak in it, you will have a leaky vacuum and your EGR system will shut off. If the vacuum leak is too severe, then you will notice less power in your engine as well as acceleration problems.

Which transmission is better TH350 or TH400?

Automatic transmission fans will tell you that a TH400 is a stronger transmission, but the TH350 is shorter (meaning easier to adapt in smaller-bodied cars), and it saps a lot less horsepower from the engine to make it work. … These transmissions weigh about 125 pounds.

How many gears does a 400 Turbo transmission have?

TH-400 transmissions are three-speed automatics, with a 2.48:1 first gear. Reverse gear is 2.08:1 and third gear is an even 1 to 1. Turbo 400s use three tail shaft lengths; the most preferred units for a GM swap would have the short 4-inch tail shaft.

What cars had a Turbo 400?

Generally, here’s a list of cars that used the TH400 transmission:1965-1967, 327 V8 (Rambler/AMC)1968-1971, 350 V8 (Buick)1969-1972, 225 V6 (Buick)1972-1975, 232 I6 (AMC)1975-1979, 258 I6 (AMC)1972-1979, 304 V8 (AMC)1972-1979, 360 V8 (AMC)1974-1975, 401 V8 (AMC)More items…•

Is a Turbo 400 transmission a 4 speed?

The Turbo 400 transmission was a 3 speed automatic transmission developed by General Motors. Overall the transmission remained in production an impressive 27 years before it was eventually replaced by a 4 speed electronically controlled transmission, the 4L80E, in 1991. …

How do I know if my Turbo is 350 or 400?

Measure the transmission case with a tape measure. The Turbo 350 case measures 21 3/4-inches long from the front of the bellhousing to the rear of the case. Do not include the tailshaft housing which bolts to the rear of the case. The Turbo 400 measures 24 3/8-inches long from the belllhousing to the rear of the case.

How do you adjust a TH400 vacuum modulator?

“To adjust the shift points of the transmission, disconnect the vacuum hose. With a flat blade screw driver turn the screw on the inside of the modulator end clockwise to raise the shift points and firm up the shifts. To lower the shift points turn the screw counter clockwise, this will also soften the shifts.

Where does the vacuum line go on a Turbo 400?

The vacuum line on my ’67 connects to the base of the carb, but below the throttle plates. It gets manifold vacuum that way. It is the original engine and carb, and is not modified.

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 can you tell if a modulator valve is bad?

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.More items…

Does a Turbo 400 have a kickdown cable?

Did you know that GM’s Turbo 400 three-speed automatic transmission uses an electric switch instead of a cable or mechanical linkage to downshift a gear at wide open throttle?

How much HP can a Turbo 400 handle?

About 400-450 HP/TQ is the limit on the stock TH400. With ONE almost free modification and some minor valve body calibration changes, 800 HP on an otherwise stock TH400 is not a problem if it’s assembled well (good endplay, etc), and the 34 element sprag is a wise addition above 450 HP or any drag usage.

Is a 700R4 better than a TH400?

The TH400 is much stronger, but it doesn’t have overdrive and the first gear is only 2.48:1. The 700R4 has an overdrive gear (0.7:1), and a 3.06:1 first gear, but it’s not as strong. So it depends on what your using it for and how much power you have.

What does the vacuum modulator on a Turbo 350 do?

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.

How much vacuum does a TH400 need?

Coan told me 13-14 at idle inches of vacuum is needed for a modulator to work properly.

How much does a Turbo 350 transmission cost?

If you’re looking for high-quality and affordable chevy turbo 350 transmission – you’ll find the best chevy turbo 350 transmission at great prices on Joom – from 8 to 17 USD.

What does the vacuum modulator do?

Vacuum Modulator is an engine load sensing device that converts engine vacuum into a transmission valve body input. … As the throttle blades are open the manifold or engine vacuum drops as ported vacuum (above throttle blades) increases.

Does a TH400 need 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.