Wednesday, August 7, 2013

Why is your car moving forward or rolling when applying the transbrake in your powerglide?

A common problem for powerglide racing transmissions equipped with transbrake valve bodies is any kind of movement when the transbrake is activated and the car is staged.  This happening during a race can often result in an instant red light and loss.

Normal transbrake operation:

  1. You activate the transbrake solenoid in low gear when staging.  The solenoid pushes the brake valve to a position in the valve body that redirects fluid.
  2. Fluid rushes within the transmission to apply the reverse clutch piston and reverse clutches.  This locks the transmission in a 1:1 fight between low gear and reverse.
  3. You increase engine RPM to prepare the car for launch.  The transbrake remains locked and keeps the car in place.
  4. You release the transbrake solenoid switch which removes fluid pressure from the reverse piston and clutches.  The car now has forward movement in low gear and accelerates down the track.
If the car is moving forward any during the transbrake setting and staging process, it is likely due to one of the following problems:

  • Staging at an RPM that does not supply sufficient fluid volume -  OEM or weak pumps need additional RPMs to move fluid quickly and adequately to apply the reverse clutches.  Increasing your RPM before setting the transbrake is the first solution to try.
  • Reverse is not being engaged with enough pressure or not at all
    • From the solenoid to the reverse clutches, something is not applying the full force of the reverse circuit to give the transmission a firm transbrake hold.  
    • Examine your transbrake solenoid operation and engagement.  Is it getting enough power?  Is it too old and need replacing?  Is it engaging all of the way?
    • The reverse piston may have have a damaged seal, be worn, or just stuck all together.
    • Make sure the valve body and governor support are properly secured.  A leak internally can affect the reverse fluid circuit.
A new powerglide pump like our high volume powerglide pump is a great replacement for the OEM unit.

With a fully operational reverse circuit, your powerglide transmission should be holding steady and not rocking when it is time to race.

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