How-To:  Evaluating a Used Transmission
Bill Trench

Here are a few things you can check to determine if a used tranny might be a good candidate for your car.  Of course, none of these indicators on its own indicate a bad tranny.  We're also assuming here that certain parts haven't been switched during its life.

• Examine the throw-out (or release) bearing fork.  Check to see how worn the top hole for the bearing is.  A new one is round.  The more elongated it is, the more use that the tranny has seen.
  
• Look at the connection between the slave cylinder rod and the throw-out bearing fork.  The hole in the shaft was once round, with a little play.  If it's really sloppy, there are lots of miles on it.
  
• Check out the inner drivers.  Feel the faces of the flats inside.  If there's a pronounced groove or dent in the face, where it "pushes" the half-shaft bearings, this indicates either a lot of miles or severe lack of lubrication.  By the way, these drivers can may be swapped side-to-side to present a smooth driving face to the bearings, reducing some "judder" on acceleration.
  
• Put the tranny in fourth gear and turn the input shaft back and forth.  If the freewheel is good, you should be able to drive the gears turning it clockwise, but not anti-clockwise.
  
• Lock out the freewheel and grab both drivers.  Turning them back and forth, there should not be a lot of play in the differential or ring and pinion gears.  There should also not be clunking or rattling from inside the case.  The speedometer drive should also turn smoothly without play between directions.
  
• Take off the top cover.  Look for wear on the shifter rod arm in the cover, as well as the faces in the grooves of the gear selector forks in the case.
  
• Examine the bronze synchros.  Check to see how much wear is on the teeth.  If the teeth are worn down to sharp little points, it's a good sign of a lot of miles.
  
• Examine the faces of the shifter forks where they contact the synchro slider rings.  Shiny, worn grooves indicate many miles as well.
  
• Look at the teeth on the gear sets for wear pitting or rust and watch for play as you turn the drivers.
  
• Unscrew the drain plug and look for metal filings on the magnet. There always seems to be a small amount of very fine stuff, but large pieces would be bad. 
  
• Separate the two halves of the case and look at the teeth on the ring and pinion gears.  If there are no deep grooves worn in them and not a lot of play, this is good.  If the pinion shaft bounces around, that's bad.  
  
• Look at the teeth on both the lockout slider and the freewheel hub.  You will be able to tell if these have a lot of wear.  If they are very small and worn or even broken off, that shows high mileage or abuse.  If the freewheel works, it doesn't really matter, as long as the broken teeth aren't floating around somewhere.  If you want to drive with the freewheel locked out and they're not too bad, you can elongate the hole in the nylon slide on top of the tranny to allow the slider to engage further into the freewheel hub.
  
• Check the number of teeth on the ring and pinion gears to see if you might have a Sonett tranny.  8/32 is the standard trans.  I think the Sonett is 9/43 (?).  This is also etched into the edge of the ring gear.
  
• If you want to be really adventurous, pull off the rear cover.  Check your shop manual for how to deal with the poppet balls on the gear selector shafts.
  
• Once off, look for play in the rear bearings.  The nuts on the shafts have a bad habit of backing off.  Sometimes they can be removed and the locking tabs straightened out and re-tourqued, but if they're really sloppy then the bearings and the gear teeth are probably too worn.
  

If you have more than one tranny you can compare these wear points to tell if one is better than the other.  And some components can be swapped without tearing the tranny down too far.  Of course, all of this may not seem too bad, and you might still have a nice whine while driving. (Not that I am advocating drinking and driving. That's up to you.) Sometimes you can still find a really low mileage tranny that was taken out of car that rusted out prematurely or was wrecked.  Other than rustout, this was truly the weak link in the car, and a lot of owners never figured out the proper way to use the freewheel.

Bill Trench, 11/00

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