Missed shifts- what causes them

[SADARE@xxxxxxx]

David Holeman asked:

>I have picked up a few threads about the miss shift that the 95 M3 is
prone to.  Mine has about 50k miles on it.  I picked up that with that
kind of mileage there is enough normal wear and tear that a miss shift
is far more likely in a high rev situation.  Both my wife and I
autocross the car at the same events and drive the car hard.  Next
season we will start in on some driver's schools and I would like to
better understand this problem and what steps I can take to minimize the
risk.  I saw some disjointed info about cams, valves, and springs.  Can
someone confirm the miss shift risk and advise an upgrade path that
makes sense.<

Dave: There are a lot of opinions about what causes missed shifts, and their
potential to result in an overrev. I've got to say that a well maintained car
certainly makes shifting easier, but worn parts don't cause missed shifts,
driver error does.

I know I'm going to get some "holier than thou" responses to that statement,
but it's true. If you don't put the car in the wrong gear, then it can't get
in the wrong gear. Now, look at your shifter. There are springs in the neutral
gate that align the lever with 3rd &4th gear. To get first, pull the lever
left, and push forward. Second, pull left, pull back. Third, push forward,
allowing the springs in the neutral gate to line the lever up with third gear
on the way through. Etc, etc.

What often happens in autocross, driver school, or other harried or
thoughtless moments is that people try to rush the shifts and manhandle the
lever into the next gear. When you take a fist full of shift lever and try to
force it from second to third gear, and don't let the neutral springs help
you, you push the lever into first, let out the clutch, and POW. 

If you push the lever from second to third with the palm of your hand only,
fingers pointing upward, the lever will jump to the right as it passes through
neutral and be right in front of third gear. People have blamed engine torque
for moving the position of the gate in relation to your body. I don't think
most drivers can tell if the gate is moved over a half inch, especially those
who can't feel the springs working on the lever as they pass through neutral.

If you treat the shift lever as an egg, and caress it from gear to gear, you
should have no trouble. Manhandle it, and who knows what will happen. Look at
the section of Bob Bondurant's book that deals with driving position if you
want a better description.

Scott Adare
Spokane, Wa
'95 M3

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