Kansas City Tdi
& CoolAirVw Repair
01M Failure
Analysis1
Ross brought me this 01m with a complaint
of “no reverse without giving it some gas warm”. Here are the steps I took to diagnose it and
the internal failure that made his problem.
Note:
order of analysis changed for dramatic effect. 2nd Note: Sometimes, I use some “general” terms that
are used in transmission industry, not necessarily VW terms.
First I road tested the car. The trans worked
exceptionally, I graphed TCC and it was very good. It had none of the slipping I’ve documented
in other places. I saved a graph, but it’s
on another computer. I’ll add it later.
01m’s tend to be slow going into gear normally, this is not what Ross had. His car would go into reverse normally cold
but once it warmed up, after placed in reverse it would just sit there like in
neutral, till you raised the rpm just a bit.
Then it would “thunk” into gear and back up as
it should. Important piece of info here
is that it would NOT do this scenario in forward. This means it’s probably not due to low fluid,
but of course you should check this anyway just to be sure.
I put a pressure gauge on to see what it
showed. No action shots, but in reverse warm, with problem
happening, pressure was 15 psi lower than when cold,
without problem happening. Goosing the
gas just a bit, would bring pressure up to normal and above, making reverse “clunk”
in. In forward there was no significant
difference in pressure hot to cold.
This behavior is plain and simply a
pressure loss to reverse. It not a
problem cold, because the fluid is thicker cold and the thicker fluid would
have a harder time, “leaking” off. So the question is, as always, is it fixable
or does the trans need to come out.
In reverse the B1 brake and B2 clutch are
on. Reverse pressure passes from the
valve body, into the B1 piston housing through the case through the “reverse
feed tube” in the following picture. Its
location is shown in the 2nd picture.
Notice that the “reverse feed tube” has 2
o-rings on it. It has one on the bottom
to seal against the B1 piston housing, and one to seal against the case. If either of these is cut or “flat” it could
leak the B1 brake pressure. These O-rings are the only hope of repair in
this situation, so it’s worth pulling the valve body to check them. Everything else that could leak pressure in
reverse is inside, requiring complete trans removal and disassembly to
access. This usually means most shops
would recommend rebuild or replacement. Unfortunately for Ross, his o-rings were
fine.
The next step was to pinpoint if the leak
was in the B1 brake or the K2 clutch. You
can do this with an aircheck of the B1 brake. I’m
showing this step with trans on the bench but just as
possible with the trans in the car.
When air checking a clutch you should pull
the trigger on the blow gun, then immediately let off the trigger. On a good air check you would hear a “thunk” of the clutches applying then immediately yank the
blow nozzle out and you should get a burst of air back out of the hole,
indicating good sealing and the piston return springs pushing the piston back,
making the air rush back at you. Some
leaking of air is normal on some circuits with sealing rings, but this circuit
doesn’t have any. Actually on this
circuit you can see the clutches apply, there to the right of the blow nozzle
under the detent spring.
Ross’s B1 brake I could pull the trigger
on the blow nozzle up to about 60%, and just let it blow and it would never
apply the clutch. If I took the trigger
to above 60% it then the clutch would apply.
This is a significant leak!
Obviously Ross had a B1 brake leak, causing his “no reverse without giving
it some gas” complaint.
Air check of the B1 showed the problem and
it’s a bit harder to air check the K2 so I didn’t air check the K2.
What I left out, and why the pictures are
on the bench instead on in the car, is because when I pulled the pan to pull
the valve body to check the B1 feed tube o-rings, I found this.
You can see the large chunk. Notice
how it looks striped? I’ve found this
same chunk before in other 01ms. Plus
the magnet has more than normal sludge on it, and the bottom of the pan looks like
“panning” for silver.
Always remember when pulling your pan, to
break open your filter, because the pump makes suction through the filter and
it can suck up these pieces and you could pull the pan and think your pan is
clean yet chunks are trapped in the filter.
Here’s what inside the filter looked like.
So when I discovered this Ross had a important choice to make.
He chose to replace it with a good remanufactured trans
with a 5 year, 75,000 mile warranty.
Here’s
what I found on the inside. These are
the needle bearing from the thrust bearing that goes between the planet and the
sun gear. Oddly enough none of these needles made it
into the pan.
Pictured is inside the case with most
parts removed. The clutch in the pic is the B1 brake.
The hole in the case is where the B1 feed tube passes through the case
to seal against the B1 piston housing.
Here’s a good thrust bearing out of
another trans.
Bearing rides on the sun
gear shell and damaged it pretty good, though it can’t be seen in the picture. Excess clearance due to failed bearing
allowed sun gear shell to move and contact the B1 piston housing.
And here’s where the “striped
chunk” came from.
And I have to say all of
this is just a interesting side note. All the metal and broken stuff failing was
not related to the b1 pressure leak. Here is its cause.
On the B1 brake piston, the
rubber lip seal that is Molded onto the piston had come
apart separating from the piston. If it
weren’t for the broken up bearing and damaged planet this piston by itself
could have fixed this 01m.
Of course “while your in there”…….