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To reduce traffic I am going to try to answer several questions in one letter.
Slipping AT:
Your problem has nothing to do with the torque convertor. You mentioned
that it slipped only while trying to shift from second to third. Since the
torque passing through the convertor is passed fine both before and after
the shift it is clear that the torque is no problem for the convertor.
The problem arises as the transmission is trying to shift from 2nd to 3rd.
The situation is different in the shift from 1st to 2nd. In the latter case
the drive transfers from a one way clutch drive (1st) to the higher 2nd.
The 1-2 transfer is always smooth because 2nd gear picks up whenever its
clutch, called a band, tightens up enough to take the drive away from the
1st gear one way clutch. At this point the one way clutch is just merrily
overrunning--no problem.
The 2-3 shift is COMPLETELY different. In this case the second gear drive
must disengage and the third must engage. If any significant time passes
while this is happening then the engine will race briefly because the car is
actually in neutral! The trick is to get this moment to pass so quickly
that you (and the engine) never notice it.
The usual symptom of this is that casual driving has terrible 2-3 shifts,
but if you really put your foot into it, then the 2-3 shift will happen at
much higher speed and will go smoothly.
There are a couple of things you can do to improve this. First buy the
Bentley manual and read the automatic transmission chapter over and over
again until you actually understand it. You will need to eat, sleep, and
breathe ATF for a couple of weeks before you will succeed at this. Then
adjust the third gear band. Follow the instructions. Second, adjust the
vacuum modulator. You need a 50 psi pressure gauge with 1/8 NPT male
threads and a 3 or 4 mm allen wrench. Once again follow the manual.
Note: '69-'71s take the early "A" vacuum modulator; it has a diaphram body
about 1/2" thick. '72-'73s take the late "C" modulator; its body is about
1" thick. The "B" modulator was used on dual carb engines, and I've never
seen one. Make sure your car has the right one before you waste your time
trying to adjust the wrong one. Likewise don't accept any replacement that
does not have the correct VW number stamped right into it!
If this doesn't help, then the problem is most likely to be a clogged filter
or a worn ATF pump (lack of pressure/flow.)
This can be a tough problem to fix. My wife's car is still not up to my
standads. I find that the '72-3 cars are worse here.
Another "final" note: The Type III Automatic transmission is lubricated
separately from the final drive. While it is easy to check and top up the
Dexron ATF (from the engine compartment) the final drive GL-5 fluid must be
checked from below. The check and fill plug is above and forward of the
right side output drive shaft. It should be full up to the bottom of the
fill hole. If you can't find the level with a finger, I recommend you drain
it all and fill with fresh GL-5.
Leaking fresh air box:
This is one of the most common Type III problems. All the answers so far
have been correct, but I would add one more: dirt/leaves in the hoses or
box(es).
So.... Check the following.
1) There are two hoses present and in good condition.
2) The hoses are properly connected at both ends.
3) The hoses are unobstructed.
4) The drains into the hoses are clear.
I find that the best way to clear them out is to remove the hoses and blow
them out with my mouth. Go ahead, see how far you can toss that wad of
leaves. It's a good idea to take a bucket in the car with you when you pull
off the hoses just to catch the water that comes out when you pull the hoses
off.
Once the hoses are clear, poke a wire up the nipple where you pulled the
hose off and make sure that passage is clear. On early (-69) cars you can
poke a wire down from above--through the grate in front of the windshield
and through the large hole in the plastic, and clear from above. It is
sometimes useful to do this while running water down the drain to help flush
out stuff that you are loosening up. Once again, it's best to do this into
the bucket!
M-numbers:
M numbers are modification numbers. They were used to desiginate standard
variations that were made to be sold for particular uses or in particluar
markets. Just a kind of shorthand that the factory could use. They are all
listed on the microfilm. I have never seen any indication printed on the
car, except for the engine, of what M's the car was originally supplied with.
M220 is limited slip differential
M236 is fuel injection
M249 is automatic transmission.
M265 is welded-in side window panels, center and back.
Jim
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Melissa Kepner Jim Adney
jadney@vwtype3.org jadney@vwtype3.org
Laura Kepner-Adney
Madison, Wisconsin
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