A Chink in the Armour

My dedicated 928 track car, know as the Coke car, has been decently reliable for its several owners.  However at the last SEMPCA HPDE day at Waterford on June 25, something happened on my third session.  Since June 25th also happened to be my wife’s birthday, some would argue that I defied the laws of the universe and despite her permission, attended the track day in lieu of focusing my attention on her.  I know karma can bite you sometimes, but I’d like to think this was due to age and stress and not some voodoo doll squirrelled away in my wife’s dresser.

The Coke car is on the lift for a transmission-ectomy!

When I came back in from my third session, our beloved Jeff Amos and Marc Molzon came over to ask what the noise was.  Noise?  What noise?  I couldn’t hear anything because of my helmet.  A quick spin around the paddock reveled that is was something in the transmission drive line.  There was a whirring sound that occurred when the car was in gear and under load.  With the clutch disengaged (pedal in) the sound went away.  Coasting in neutral also caused the sound to go away.  Because the 928 uses a transaxle (transmission at the rear axle) this led me to believe the culprit was probably in the transmission and not in the engine, clutch or drive shaft.
 
The strange thing was that aside from the noise, there was no other evidence that the transmission was suffering.  It shifted fine and seemed generally healthy.  The 928 manual transmissions do have a known issue where the reverse lockout spring will fatigue, break off and fall down.  Similarly the neutral centering spring has been known to break off as well.  I was hoping it was the reverse lock out spring that had broken off and was lying against a gearset causing the noise.  Usually in this case, it will simply fall to the bottom of the tgearbox and just sit there without harm.  But the noise was not going away and I didn’t want to damage the transmission if I could avoid it.  So I thought it would be a good thing to drain and inspect.
 
It took me two weeks to finally get the time to put it up on the lift and inspect the transmission.  Externally there were no signs of damage or other issues.  If you want to change your manual transmission fluid (or final drive on an automatic), always be sure to remove the fill plug first.  This is because these plugs can be difficult to remove sometimes, and you want to be sure you can re-fill it before draining the fluid out.  The 928 requires a 17mm allen head socket.  Luckily mine came out without any issue.
 
There are two drain plugs on the 928, one on the rear just below the fill plug and one at the front.  Both drain plugs are fitted with magnets that are designed to grab and secure any small metal filings that may be produced.  The rear magnet on the Coke car had some things stuck to the magnet, but when I rubbed them between my fingers, it felt smooth indicating these were very fine pieces – nothing to worry about.
 

However when I went to the front drain plug, sadly I was greeted with a different story.  There were some small and not-so-small chunks of metal.  They looked like they had a brass coating, which is typical of a synchro ring, but these piece were mostly straight and synchros are generally all curved.  So I had a mystery.
 
While the transmission was drained, I used a mechanics magnet to fish around for other pieces (like a reverse lockout spring), but none were found.  I used my endoscope to look inside the transmission, but it is so tight inside, I really couldn’t find anything revealing.  As a last ditch effort, I decided to refill the gearbox with some fresh fluid and see if the noise had somehow magically cured itself, but sadly, it did not.  The noise it still there. 
 
At this point, I now need to remove the transmission and inspect it more thoroughly.  On a 944 it only takes and hour or so to remove the transmission, but on a 928, it takes a full day.  I will need to remove the entire rear suspension, and rear cross member, then lower the transmission and slide it off the driveshaft. 
 
I have ordered a replacement transmission so I can hopefully just swap it in and minimize the down time.  But the plan is to open this sick gearbox, diagnose, and hopefully repair it.  Out of curiosity, I priced a new 1-2 gearset, and it was over $3,000!  Yikes.  A synchro, on the other hand, is a much more reasonable $150.  Let’s hope its just that reverse lockout spring or a synchro.  Should I buy a lottery ticket?
 
The 928 crew has a monthly beer night on the second Wednesday of each month from 7 PM to 10 PM at Sneakers Pub located at 22628 Woodward Ave., Ferndale, MI 48220.  Everyone is welcome to join.  If you would like to get on the 928 mailing list, drop me a line at andrewmolson@yahoo.com or call/text me at 734-837-7908.