Friday, August 16, 2013

Why is your car moving backward when applying the transbrake in your powerglide?

As a follow up to our previous blog posting, the other common problem with transbrake operation in powerglide transmissions is the transmission moving in reverse when the transbrake is activated.  Again, this can cause the car to roll out of the staging lights causing an instant loss.

Once again, we will review the 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 backward 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.
  • Low gear band not holding. 
    • The low gear band can be completely worn down which would prevent it from holding low gear
    • The band needs to be re-adjusted
    • The servo piston has failed, is leaking, or has broken a sealing ring
    • The band adjustment screw has broken or is bent
Check these areas if you are having transbrake trouble in your powerglide transmission.  These are simple fixes!  If you have any questions, contact our technical department @ 1-662-851-3213.

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