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May 2, 2020


Windshield Wiper Motor

GT6 cars came with screen wipers powered by an electric motor.  The Lucas motor was pretty ubiquitous at the time, being used in a range of British and other European cars.  Lucas actually provided several variants of the motor over the years.  Mine was a 14W, a two-speed model with automatic arm parking.

I guess can't blame the 51 year old motor for looking dirty and tired.  Tested from a 12 volt power supply, it didn't run.




I cleaned the grime from the outside, and opened up the gearbox.  Speed reduction is by means of a worm gear with a ratio of 46:1 if I counted the teeth correctly..  It was cleaner inside, but the grease was pretty stiff.




Pulling the motor body off revealed that it was a permanent magnet motor.  The Bakelite brush board was fitted with three brushes.  The extra brush is how the second speed was accomplished.  One of the brushes seemed a little short.




The brushes were hardwired to the park switch, which was mounted to the back of the gearbox.  The innards of the park switch were mostly missing.




As for the armature itself, it looked pretty bad.  Several of the coils looked burnt.




So, summing up the situation, I had an inoperative wiper motor with worn brushes, a trashed park switch, and a knackered armature.  A perfect candidate for resurrection!  I was encouraged by the fact that a British company was offering new armatures for a pretty reasonable price, so I ordered one.  I also ordered a new brush plate and a park switch from a US supplier.  I was ready to order new bronze bushes, but honestly, the originals were still tight enough that I didn't bother.

While waiting for the parts, I cleaned up the motor housing.  I wanted to powder coat it, so I pulled out the magnets so they wouldn't be subjected to the oven heat.  I removed the paint, then the rust, and shot it with powder.




The park switch was the first part to come in.  It worried me a little that it looked quite a bit different from my original.  The original was attached with two screws, while the new one just had a little metal clip for fastening.  Before calling the vendor, I did some research and found that what I had was an "old style" wiper motor, as evidenced by the "A" suffix to the part number stamped on the cover.  I also found that park switch for the old style motors are apparently no longer available.

It looked like the mounting was the only difference in the switches, so I looked at modifying the pot metal gearbox housing to accept the newer switch.  The first pic is the early housing from the GT6, the other is the later housing from my TR6.  I had to make the GT6 part look like the TR6 one.




I cut a slot in the housing, and made a little steel bridge for the switch's clip to grab.  The last pic also shows my really rough hammertone powdercoat.  I'm not sure what happened there.  The bad areas are mostly out of sight, but if it bothers me enough, I'll strip it and re-coat.




This shows the switch mounted.




About this time, the brush plate came in.  I guess I shouldn't have been surprised, but it was also different from my old one. 




I had to reshape the Bakelite plate to clear some features of the housing, and, since the brushes were mounted differently, I had to space the plate up about an eighth of an inch so it would be centered on the commutator..




Well, at this point, I had a fair amount of work in this wiper motor, which made it even more irritating when I got a message from the British armature supplier saying that they didn't really have the armatures after all.

There were a couple of options: forfeit all the work to date and take my chances buying a used or a reproduction assembly, or try to rebuild the armature.

I had no intention of even considering rewinding the armature at the beginning of this project, and even though I had zero experience with the process, I knew it was possible, and the challenge sort of appealed to me.

With nothing to lose, I started by unwinding the armature, carefully recording how everything was wound and connected.




Then did some research on armature winding, and while the actual winding didn't appear too hard, there ware quite a few different coil arrangements to choose from.  Based on my unwinding records, I chose a technique called "chorded split loop winding".  It is not the simplest way to do it, but it has the advantage of being symmetrical so it produces an armature with better mechanical balance than simpler methods.  Also, it was the way it was originally wound.

So, I got some 22 gauge lacquered wire and some "fish paper" used to insulate the coils.




Ten coils of 35 turns each, and I had a new looking armature.




Popped the motor back together and tried it out.  After a little fiddling, it seemed to run fine.




Hooked up the park switch and installed the worm gear.




And buttoned her up for storage.  I'll put off packing the gearbox with grease until installation time.

 


New rubber for mounting.




This project was maybe more trouble than it was worth.  On the up side though, the cost was only around $50, and I acquired a new skill.

Comments to Ed at elhollin1@yahoo.com

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