The Magnette Wiper Motor Park Switch
I serviced the wiper motor on my MGA
but since it is the same as the Magnette, I thought I'd share the little
article...
I had to strip everything off the heater shelf on my MGA since the master
cylinder had been leaking for a couple of years. As far as I can tell the PO
just kept adding fluid to it. The shelf was very much rusted all the way to
under the heater box. When I pulled the wiper motor out, apart from it being
very grungy, I noticed electrical tape around the wiper park switch wire. Very
suspicious. The earth lead was disconnected. Also suspicious. When I removed the
tape I found that the wire’s insulation had perished and was pretty much gone.
So, I decided to repair it. I took these pics while I was doing it. If I’d known
I would do a tutorial on it I would have taken more pics but I’m finished now so
that’s done. This wiper motor looks identical to the one used on the MG Magnette
ZA/ZB so I’m sure the same principles apply to it.
The interesting part will be to get the wiper motor out from under the driver’s
side wing. I already had the MC out so it was merely difficult. How you would
get it out without removing the MC is up to you. You need to get the wiper motor
loose so you can ease it around into position to remove the 4 hex head screws.
.
This shows the wiper motor after I’d repaired it so it’s nice and clean. To get the drive mechanism loose from the cable that drives the wiper boxes you need to remove the 4 hex head screws that hold the cover plate and the park switch (the dome looking thing with the wire) off. You can lift the plate and switch off to reveal the drive guts. Remove the leads that come from the wiper switch on the dash from the motor first. The two screws on the motor housing hold the motor coil to the housing. Leave them in place for now.
You can see the arm that slides back and forth; it has a fat pin at the end
and the cable hooks into it. At the gear end of the arm there is a circlip that
holds the arm, with a spacer, to the pivot shaft on the gear. Ease the circlip
off and the arm will come up off the gear shaft. With the arm off the shaft you
can unhook the arm’s pin from the cable. I put the arm, washer, and circlip back
on the shaft for safe keeping.
You can now remove the wiper motor on its bracket to a work bench.
At this point it is advantageous to know how the whole thing goes together. The
motor’s end cap is held on by the two long screws on either side. The end cap
also holds the motor’s housing to the drive mechanism so when you take the end
cap off the housing is free, too. So, take the two long screws out and ease the
end cap off.
You will see where the park switch wire is soldered to the leftmost terminal (
marked #1 on the end cap) on coil. Either unsolder it or cut it. Note how the
wire runs up along side the coil. You can now pull the wire back out and free
the cover plate from the end of the housing and the park switch from the drive
mechanism. Set those guys aside.
If your only desire
is to replace the wire you can leave the motor sitting on the drive mechanism
although the housing is not attached and can come loose if you’re not careful.
If that is what you want to do then skip the next part about pulling the motor.
I wanted to clean and paint mine so a full strip down was done.
You can now pull the motor housing away from the drive mechanism. But, be
careful, the armature will want to stay engaged with the drive mechanism. I
found it easier to pull the housing and the armature at the same time so as to
not damage the brush holders. The pinion gear on the armature just spun the
drive gear quite easily and the whole thing just came right out. Once the
motor/housing is out, you can withdraw the armature from the housing by gently
spreading the brush holders. The coil and the brush assembly are held in by the
two screws that go through the housing. Remove these carefully, they are weird.
I broke one off putting them back but was able to get the stump out and put new
ones in. They are a sheetmetal type of screw, not a machine screw, and will bind
in a skinny second when you try to put them back in.
Here is the whole
shebang. Note the bare wire that comes through the drive mechanism case. That
was the park switch lead. The armature is just sitting on the coil assembly.
Again, take care when handling the armature. The brush assembly can be dislodged
or broken if handled roughly. If the brushes fall out, no big deal. On the right
side of the pic, by the end cap, you can see the long screws that go through the
end cap and housing to the drive mechanism.
Look carefully at the brushes; you can see that there is a wear curve on the
face of the brush where it contacts the armature. The brush has to go back in
with this wear curve correctly on the face of the armature. When you are ready
to put everything back together lean the brush holder out and put the brush in
it. When you get the brush back in the holder look closely at how the brush sits
against the armature. You can see that the brush is not supposed to be centered
on the armature but sits up a bit on the armature radius. If the brush is in
upside down its face will not rest fully against the armature and there will be
a sizeable gap between most of the brush face and the armature.. Flip it over
and you will see that the face now sits nicely against the armature.
Take a look at the switch itself:
The switch is very simple. Remember the place that you
removed the circlip from? That is the mechanical contact that pushes on the
switch to ground or unground the wire. To replace the wire heat the terminal and
pull the old wire out. This switch shows my new blue, 18ga wire already in
place. You may want to test it with a meter to make sure it grounds and
ungrounds the wire to the switch housing when pressed. I used the old wire as a
length gauge to cut the new wire.
Clean and paint the motor housing as desired.
Once you have the switch wire repaired you can put the motor back together.
Slide the coil back into the housing. Put the screws back that hold the coil to
the housing. Take your time and make sure they are not cross threaded, they will
break if they get started wrong and you start torqueing down on them.
Ease the armature back in making sure you spread the brush holders to let the
commutator pass between them. Lift the housing and armature back up, as one, and
slide in it back onto the drive mechanism. Seat it firmly; the four little tab
castings on the housing will hold it steady. One thing that helps to know if the
armature in going in correctly is to watch it and make sure it doesn’t get out
of position with the brush holders while you ease the housing back down onto the
drive mechanism.
Now you can feed the wire from the switch through the hole in the drive
mechanism and into the motor housing. Make double sure that you have put the
switch into the cover plate first; the wire has to sit over the top of the cover
plate. Look again at the first pic.
Once you have the wire up at the terminal end of the motor, solder it to the
leftmost terminal (marked #1 on the end cap). Take the end cap and ease it onto
the armature by fitting the end of the armature into the end cap. Press it down
and it should go right together. Put the two long screws in and snug them up.
Put the cover plate and switch back in place. You can now test for proper
operation. You can use a battery charger or a 12vdc power supply. The motor, not
hooked to anything, draws about 3 amps.
Hook the positive lead to the #2 terminal and the negative lead to the #1
terminal and also to the “E” earth terminal. With the power on, the motor should
run smoothly. Remove the negative lead from the #1 terminal (but not the “E”
terminal) and the motor should stop after running for a split second more, as it
would when parking the wipers. The actual place where the wipers park is set by
loosening the cover plate and rotating the park switch.
There you have it. Removing the wiper motor and replacing it on the heater box
shelf is much more of a job than actually fixing it.
Wray Lemke
Mt. Pleasant, SC
Groons72@hotmail.com
