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 is required to run a modulator on a Turbo 400 transmission?
Can you use a vacuum modulator on a GM TH400?
This unit is designed for use with select applications, including GM TH400 and TH350 transmissions. Please note: If you have a big camshaft and your engine does not make adequate vacuum, you will not be able to make the stock or B&M modulator work properly, usually resulting in late, hard shifts.
What kind of vacuum modulator does hot rod lifestyle use?
Hot Rod Lifestyle The B&M Adjustable Vacuum Modulator (Part# 20234) comes pre-adjusted for ‘normal’ shift points, but it is fully adjustable (see below), allowing you to customize the shift points (within a range of 2-4 mph). This unit is designed for use with select applications, including GM TH400 and TH350 transmissions.
What is a vacuum modulator?
Vacuum Modulator is an engine load sensing device that converts engine vacuum into a transmission valve body input. Can you run a TH400 without vacuum? TH350 / TH400 Cable Operated Modulator, no vacuum needed. This works well for superchargers and on diesel motors without a vacuum regulator. This modulator uses a 700R4 throttle valve cable.
How do I know if my modulator valve is bad?
When you have a bad modulator valve, some or all of the following symptoms will begin to manifest themselves: White smoke coming out of the exhaust (from a leaking diaphragm) Early or late shifting. A rough idle. How much vacuum does a modulator valve need? You should have at least 15in of vacuum to make it shift correctly.
What does a bad vacuum modulator do?
A modulator valve is in charge of transmission shifts. When it's not working properly, your transmission's shifting suffers. Worse, if you leave the worn out valve in place, your engine can actually start burning transmission fluid. This is because the modulator valve is operated by a engine vacuum.
How do you adjust a th400 vacuum modulator?
1:099:27Turbo 400 Transmission Vacuum Modulator Adjustment Explained ...YouTubeStart of suggested clipEnd of suggested clipSo you take a small tip screwdriver it'll fit in here and there's a little slotted valve to makeMoreSo you take a small tip screwdriver it'll fit in here and there's a little slotted valve to make your shift. Points firmer harder shifts you're going to want to turn this clockwise.
How do I make my th400 shift harder?
1:295:22Th400 Shift Modifications! Street Testing! - YouTubeYouTubeStart of suggested clipEnd of suggested clipAnd you can actually drill these out I had this transmission built it has a 32 or 36 element spragMoreAnd you can actually drill these out I had this transmission built it has a 32 or 36 element sprag clutch whatever it is and like new clutches and steels.
How does a transmission 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.
Can a vacuum line cause transmission problems?
The transmission is electronically operated and controlled. A vacuum leak will cause the engine performance to suffer, causing possible load and throttle position issues, which could indirectly affect transmission shifting.
How do you test a vacuum modulator?
5:488:36How to test Toyota EGR System(VSV, Vacuum Modulator, EGR valve)YouTubeStart of suggested clipEnd of suggested clipAnd to test that what you need to do is tap in with the T fitting. And a vacuum line to the outputMoreAnd to test that what you need to do is tap in with the T fitting. And a vacuum line to the output of the vacuum modulator or port Q.
How many times does a TH400 shift?
I tested it at least 6-8 times and this is what I found. The trans. will shift from 1st-2nd under WOT between 4200 rpm and 4500 rpm's. It seems to favor the lower end some. The 2nd-3rd shift under WOT happens between 4100 to 4300 rpm's.
Whats a shift kit do?
A shift kit is a set of components for automobiles designed to improve how well the car shifts between gears. Kits are made for both automatic and manual transmissions.
How does a TH400 transmission work?
The TH400 transmission takes advantage of an electrical slide switch controlled by the throttle linkage. On the other hand, the TH350 uses a mechanical cable kick-down that is connected to the throttle linkage. Despite the difference, the TH400 is considered the heavy-duty version of the Turbo-Hydramatic 350.
Can a vacuum leak cause a transmission not to shift properly?
A vacuum leak will cause the engine performance to suffer, causing load and throttle position issues which could affect transmission shifting.
What can cause a transmission to shift hard?
Reasons for hard gear shifts with an automatic transmissionCold weather. ... Not enough transmission fluid. ... Worn out transmission fluid or oil. ... Wrong transmission fluid. ... Damaged transmission components. ... Damaged sensors or TCU (Transmission Control Unit) ... Transmission vacuum problems. ... Worn-out automatic transmission.More items...•
How much vacuum does an automatic transmission need?
Automatic transmissions typically need a minimum of 12 in. Hg. at idle. Throttle position increases should produce a quick decrease in the vacuum reading at the modulator.
How do you adjust the modulator valve on a Turbo 350?
8:1611:28Turbo 400 350 Vacuum Modulator Valve And Modulator Installation ...YouTubeStart of suggested clipEnd of suggested clipTake your little screwdriver. And you turn it to the right half a turn one turn half a turn twoMoreTake your little screwdriver. And you turn it to the right half a turn one turn half a turn two turns okay all right and what you're doing there is when these things are made when you're brand.
How do you change a transmission modulator valve?
0:432:55Install: B&M Vacuum Modulator for GM TH350 & TH400 ... - YouTubeYouTubeStart of suggested clipEnd of suggested clipOkay I want to go ahead and put the new modulator on the went ahead just put a little bit ofMoreOkay I want to go ahead and put the new modulator on the went ahead just put a little bit of transmission fluid around the o-ring to help it slide in. And you can hear it snap in place.
How do you change the shift point on a th350?
0:344:11How To Set Shift Points on a TH350/TH400 with an Adjustable ...YouTubeStart of suggested clipEnd of suggested clipIf you take a small screwdriver like this and turn it clockwise to tighten it counterclockwise toMoreIf you take a small screwdriver like this and turn it clockwise to tighten it counterclockwise to loosen.
How does a c4 transmission shift?
1:144:10Manual Shifting in C4 Ford Transmission - YouTubeYouTubeStart of suggested clipEnd of suggested clipInto we're going to rim up the engine get it get the rpms moving to like 3500 we're going to jump itMoreInto we're going to rim up the engine get it get the rpms moving to like 3500 we're going to jump it into drive which is the green dot. That's drive in this c4 transmission the early c4 transmission.
How to force fluid to the other side?
Jack the car up on the passenger side only to force the fluid to the other side. Remove the vacuum hose, bracket, and pull the modulator straight out. Have the other one handy to go right in to limit the amount of fluid loss. Reinstall bracket, vacuum hose, clean up mess and lower the car.
How to adjust kickdown switch?
You may be able to get your kickdown switch to come into adjustment by pulling up and bending the throttle lever arm under the dash a bit and then play with the adjustment.
Does a modulator make a difference in shift points?
Just a note, the modulator is not going to make a big difference in shift points, The governor controls that. Hard shifting can be caused if the vacuum line is hooked to ported vacuum.
What is the B&M 20234?
The B&M Adjustable Vacuum Modulator (Part# 20234) comes pre-adjusted for ‘normal’ shift points, but it is fully adjustable (see below), allowing you to customize the shift points (within a range of 2-4 mph). This unit is designed for use with select applications, including GM TH400 and TH350 transmissions.
How much vacuum is needed for a B&M modulator?
A minimum of 12″ Hg engine vacuum is required for proper operation.
What is the phone number for B&M?
Need a product recommendation for your vehicle or application? Give B&M a call at (866) 464-6553
