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MG MGA - Overhauling the wiper motor

I’m working on a square-bodied, single speed wiper motor from an MGA. What I read on this site and its archives tells me that the motor should run with ground on terminal 1 and 12V on terminal 2. It doesn’t run when I do this, and I’ve checked to be sure that my power source is putting out 12V. I’ve lubricated the rotating lower bearing for the motor shaft, and I’ve also backed off the small screw that pushes on the upper end of the shaft, so the armature doesn’t seem to be binding in either place.
I have 3 questions.
First, I’ve removed the top plate and parking drum from the wheel box. There is continuity between the E terminal and the copper contact inside the drum. Archives warn me that the motor won’t run won’t run if it is in the parked position, so my question is how to determine if it is in park.
Second, with the wheel box cover off and the parking drum removed, should not the motor run if I ground Terminal 1 and put 12V on terminal 2? It doesn’t.
Third, I’ve checked the field coil wiring as described in the MGB Electrical Systems book, which says on p. 158 that there should be a resistance of 7-10 ohms. My meter shows 10 ohms, so the coil seems good. The same book also says that there should be a resistance of 1.5-2 ohms between opposite segments of the commutator. I get about 1.6 ohms between every opposing pair. Is there anything else that I should be checking?
I hate to give up on the motor, so I hope that some of you will have ideas on where to go next. Thanks in advance for your help! This site is a life-saver!

Mike
M.E. Whalen

Mike
The workshop manual wiring diagrams suggest that the connections and wiring for the wiper motor are different for the 1500 and 1600. I can't find a mention of this in Clausager.
The 1500 motor has three terminals ... 12v (green wire), chassis (black wire) and switch (black with green)
The 1600 has three terminals, but only two are used ... 12v (terminal 2, green) and switch (terminal 1, black with green), the body of the motor being used as the connection to the chassis. This may not be significant if the unused terminal is connected to the motor body. It could be a simple cost saving with no change in function, or it could mean Lucas changed the motor internal wiring.

Have you checked for resistance between terminal 2 and motor body? Lack of continuity would suggest no connection between the brushes and commutator. Also is there good contiuity between terminal 2 and terminal 3 (motor ground)?

David
D Brown

All MGA wiper motors have the same wiring. The odd looking connection in the 1600 type diagram is just a convention of the way the diagram is drawn. The earth wire really is connected to the screw terminal, and the "E" terminal is common with the motor case. See here: http://mgaguru.com/mgtech/electric/circ_f1.htm
Barney Gaylord

I would remove the WWM from the car and unsolder the wire that emerges from the housing where it is clipped to the circular park switch assembly. You would then remove any complication from the switch part. If the resistance from wire to case is a few ohms try putting 12v across. When the motor is running it will consume 3 amps or so.

I had a problem within my park switch area where there was a faulty high resistance contact from where the above wire is soldered to just inside but it was easy to diagnose with a meter.........................Mike
m.j. moore

Mike,
You need to ground the case (marked "E") near the screw hole, and apply 12V to "2". Then applying gnd to "1" should make the motor run.
Peter.
P. Tilbury

Thanks to everybody for their most helpful comments!

After a complete re-lubrication and tinkering with the brushes, I now have the motor running. However, it seems a bit sluggish.

It takes 4-5 seconds to complete one in-out-in cycle of the drive cable. I have lubricated the drive cable track.

I have read the MGA wiper motor isn't very strong, but is what I'm seeing normal?

Mike
M.E. Whalen

It should do a complete 360 degree cycle in about one second. Maybe a little slower with rubber blades dragging on dry glass, or a little faster if the arms are not attached.
Barney Gaylord

Mike,
I have been working on a wiper motor in an early car. The problem we had was that the motor would not stop running. We had to bend the "park" contact as it was not touching the "park" cam on the arm.
Your slow running now seems to suggest an abnormally high resistance somewhere in the circuit. Have you removed the motor cover, i.e. the two long screws, and looked at the brushes. Maybe they are worn? Or the Comutator could be dirty and needs a wipe with some fine emery paper, perhaps.
Be very carful when removing the motor cover as it holds the screw plate in the cover slot, and the brushes are just clipped to this plate with a spring across them. (Sorry no photos).
Peter.
P. Tilbury

This thread was discussed between 07/12/2013 and 14/12/2013

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