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Old October 10th 04, 05:52 AM
KWS
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Default Power Window Fix

Today's task was to fix the power window in the '90B that failed yesterday.
It went about half way down and that was all she wrote.

As the affectionatos know: there is a differential cable system that pulls
the window up or down. You get to either crank it manually or, as in my
case, a motor does the cranking for you. The cables terminate on a "drum"
such that as one is extended, one is retracted. Simple arrangement and it
served me well for about 168K miles.

What happened is that the cable termination at the window lift mechanism
came free. My attempts to put the window back up caused the now loose cable
to wrap around the drum and jam the mechanism. The motor, sensing this
resistance, went into the same mode it goes into when you reach either the
"up" or "down" limit: it shuts down.

Once I got everything apart, I seemed to have about three choices:

1. Buy a new lift mechanism from the good folks at Trussville for about
eighty something dollars
2. Find someone to fix the end
3. Fix it myself

A local motorcycle shop gave me the name of a company here in the SF Bay
area that makes custom cables. That means it doesn't get done today and,
possibly, I may have been better off just buying the new part. Of course,
today is Saturday, which means local sources of help might not be available.

I have no idea what "brazing" is, but it sounded like a possibility. I
bought some brazing rods and turned the propane torch on it to see what it
would do. Interestingly enough, it got hot and melted. That's a good start!
I took the end of the disconnected cable that I pulled out of it's sheath
and cut off the end that used to be anchored in the termination. I had to do
this to get it through the sheath once again. That was easy and I figured
that normal stretching and tolerances in the system should allow me to cut
off a few millimeters with no serious problems.

Once I threaded the required plastic pieces back on the cable, I heated up
the brazing rod till it was near that point of being liquid and also turned
the torch on the end of the cable that needed a termination. I kept the heat
going as I formed a big blob of whatever the brazing rod material is on the
end of the cable. Not too big, as it needs to fit into the plastic piece
that connects the "up" and "down" cable ends together. This was successful.
Sort of round end vs. the OEM cylindrical end; we shall see if it is a
problem or not.

Put it all back together and ran the window up and down a bunch of times.
Looks like a winner, folks!

A couple of hints for those who might try this at home:

1. If you take the motor apart, be prepared to have to deal with getting
the brushes back together again. It's like humpty dumpty. I've done motors
for years and knew it was coming. My solution was to put the brushes and
springs back in, one at a time, and hold them in place with a piece of metal
tape over the top of the assembly. Once the armature is re-assembled (it's a
DC motor with magnets...oooh boy...fun, fun, fun) you remove the tape and
ensure the brushes are making contact. Brush wear, by the way, seemed
modest. I suspect the motors will go another couple of hundred thousand
miles at this rate.

2. To wind the cable on the plastic drum, it is a good idea to take up the
cable slack. I made a simple wood strip with key slots that went over the
cables to compress the tension springs at the motor body and held this in
place with a woodworking clamp. I had to redo this a few times to really
take up the slack and slightly reposition the lift mechanism to get the
square hole in the drum to align with the square drive axle.

3. The owner's manual didn't cover any of this stuff. It did, however,
suggest removal of the rubberized weather strip that is on the exterior side
of the glass. It seemed like a fool's errand, so I left it in place and
carefully worked around it when putting the glass back in. Seems ok for now;
no real damage that I can see.

Pretty much all of this didn't go as smoothly as I would lead you to
believe. Meditation exercises or outright swearing will be required.
Whatever works for you.

Ken






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