Sunday, July 31, 2016

Transmission will not shift into reverse on Tremec T-56 transmission

Problem: Car suddenly and inexplicably won't shift into reverse.

The usual tricks do not work, including:
  • Shifting to first gear, then reverse
  • Shifting to fourth gear, then reverse
  • Rolling a bit forward
  • Letting car idle, stationary, with clutch out, before trying for reverse
  • Letting the clutch out a bit with the brakes on (to try and align transmission gears without moving forward)
  • Pumping clutch
  • Removing the floor mat to get an extra bit of clutch travel
  • Forcing the gear
  • Shifting into reverse with the engine is not running
If you have a reverse lockout solenoid, it may feel very much like the solenoid is preventing you from shifting.   This will seem to be "confirmed" on those few occasions when you can shift into reverse when the car is not running by overcoming the spring pressure of the solenoid/shifter mechanism, but this trick will (probably) not work consistently.

Unfortunately, this can be caused by a myriad of problems, ranging from trivial to expensive.  These include:
  • Low clutch fluid (refill clutch fluid)
  • Air in clutch lines (bleed clutch fluid)
  • Worn/low transmission fluid (change)
  • Broken reverse lockout solenoid (replace)
  • Worn master cylinder (replace)
  • Worn slave cylinder (replace)
  • Worn reverse synchro (replace)
  • Worn motor mounts (replace)
  • Worn shifter bushings (replace)
  • Worn clutch / flywheel (replace)
You will probably be convinced that you need a new reverse lockout solenoid because yours feels like it is stuck, and/or worried your clutch is about toast.

However, before you despair and resign yourself to another dealership visit for a new reverse solenoid, clutch or transmission service, check that tiny little hydraulic clutch reservoir under the hood.  In my case the reservoir was dry, meaning the clutch fluid was a touch low.  Topping up with less than 100 ml of DOT-4 brake fluid seems to have fixed the issue. 

Note that any DOT-4 will do.  If you add quite a bit, pump the clutch slowly 10-15 times after topping up.

A dry reservoir is a sign of a leak.  If you haven't had any shifting problems before, the leak may be new.  Keep an eye on it and repair as necesary.

Note: This obviously assumes you haven't done something dumb like accidentally install a CAGS eliminator on your reverse solenoid by mistake.  This can happen if you purchased the wrong CAGS for your vehicle.  This should be obvious, however, since the reverse gear will immediately stop behaving once the incorrect plug is installed, and come right back once it is removed. 

I'm not going to say which car I personally have, but the Tremec was used on several, including:

  • 1997-2007 Corvette
  • 2005-2007 Corvette Z51
  • 2001-2004 Corvette Z06
  • 1993-2002 Camaro
  • 2004-2006 Ram SRT-10
  • 1992-2007 Viper
  • 2000 Cobra R
  • 2003-2004 Cobra
  • 2004-2007 Cadillac CTS-V
 Happy reversing!

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