Stuart,
Assuming you have cleaned and lubricated the gears, the problem is either
electrical (most likely) or mechanical (wiper arms dragging or gear shafts
not turning smoothly).
Most of the wiper motors that come to me for service that exhibit the
symptoms you describe usually have a winding that is burned up on the
armature. It is a basic 3 pole motor with each pole having two windings. The
large winding on each pole is made up of about 300 turns of very fine wire.
That is the bulk of the winding. However, over each of the three poles is a
shunt winding. This is about 20 turns of a very fine resistance wire. The
purpose of the shunt winding is to increase the current flow, thus giving a
greater amount of torque to the motor. Most often it is the shunt winding
that has burned - usually due to lack of lubrication causing increased
current flow beyond what the armature is able to handle. If you look
closely, you are likely to find threads of this very fine wire coming off
the armature. This is a sure sign you need to have the armature rewound.
If the armature looks OK, it could still be bad, but usually the problem is
then elsewhere. Since you say that during a part of the arc the torque seems
OK, then I would strongly suspect a binding in the gearbox. Be sure there is
a thrust washer under the gears. This is a very thin washer which often gets
lost when some DPO tries to fix the wiper. There is usually very little wear
on the gears, but again be sure the gear shafts are scrupulously clean and
well lubricated. High temp grease is not the best as it is too stiff to
allow for free operation. Use a light to medium white lithium grease. Then
be sure all the gears spin freely through their entire rotation.
I repair wiper motors horns and fuel pumps for other club members and would
be happy to look at yours, if you like. My fee is very nominal. I don't do
it to make money, but to keep these cars on the road. Just be advised that I
cannot rewind armatures, so if that is the problem, I cannot help. I have a
batch of them myself that also need to be rewound, but have yet to find
someone that can rewind them for a reasonable amount. $65 seems to be the
going rate.
Let me know if I can help further.
Regards,
Lew Palmer
-----Original Message-----
From: owner-mg-t@autox.team.net [mailto:owner-mg-t@autox.team.net]On
Behalf Of Stuart Keen
Sent: Tuesday, May 30, 2000 6:09 PM
To: MG
Subject: TD Wiper
On a recent jaunt with my TD (2,891 miles!), I was forced to use my
wipers for the first time in actual stormy conditions. Usually with
Rain-X on the windscreen, wipers are not necessary, but because of mud
being flung up by passing trucks, wipers had to be used.
After about two cycles, they quit. Nice being able to rotate the wipers
by hand (try that in a modern car), but I'd like to get the wipers back
to a fully operating condition.
I find they will cycle, but have very little torque and if manually
stopped, will not restart. I have lubricated, repacked the gears with
high temp grease, cleaned the armature, checked the brushes, etc., all
to no avail. I even straightened out the connecting rod between the two
wipers (it was bent), but this did not help.
When the wipers are cycling, if I manually stop them mid way, they just
sit there (and would eventually burn up the armature or blow a fuse).
When the wipers are away from the bottom of the arc, there seems to be
more torque, at least if I manually stop the wiper there, they will
start up again immediately. But not so when at the bottom of the arc.
Since I have no experience with TD wipers, I do not know what is
"normal" torque. I am even thinking that the new wiper arms from Moss
may be exerting too strong of a force on the windscreen and thus
excessive dragging. Has anyone any experience with wipers and solutions?
Stu Keen
1951 MGTD MkII
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