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TR4/4A Rebuildiing a wiper motor

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alanjohnturner

alanjohnturner

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This motor has a 130 degree gear-wheel and came from a TR3A most likely.
4/4A use 120 degree gear-wheels but evertyhing else is the same.

You can swap the gears about to make any such motor sweep any angle from 100 to 150 degrees.
Often these come up for sale minus the gear. The gears seem indestructible and so can usually be reused.


It ran OK, but took more current than they should do, indicating it was a bit stiff.
It always amazes me how well these have stood up and I've yet to see one that is beyond repair.

But there are a couple of common failures and so here I dismantle this and show how to restore and improve these.

It came looking like this:
https://www.flickr.co...04/12569961143/
https://www.flickr.co...04/12569960223/

There is a bit more corrosion underneath than usual but this is insignificant.

Four screws hold the top-plate, one missing but I've got new ones.
Slip off the Horseshoe clip and C-clip, don't loose the tiny thin shim from the crank-pin.
The bronze conatct is for the self-parker.
https://www.flickr.co...04/12569957713/

This is a carbon-brush set, in good order, note the orientation of the "grooves".
https://www.flickr.co...04/12569956373/

The 130 degree gear, arm and cone-washer
https://www.flickr.co...04/12570304214/
https://www.flickr.co...04/12570301184/

Store the armature carefully to prevent breaking any wires.
If the carbon brushes wear down the two arms will cut grooves into the copper.
I can "skim" these but this one is good. The black ring is normal.
https://www.flickr.co...04/12570297144/

This shows one of the common problems
https://www.flickr.co...04/12569945753/
The arm is bent up. Happens if you try to remove connection to the wire-rack without releasing the Horseshoe-clip.

The arm will scrape on the cover and the wire-rack won't go smoothly into its tube.
You can do without this extra friction.

It takes a few wiggles to get the big self-taps out of the pole-piece.
Go easy they could break off and this would be awkward to fix.
https://www.flickr.co...04/12569923693/

After 1 hour in Caustic-soda. Wear protection!
https://www.flickr.co...04/12593543515/
https://www.flickr.co...04/12593984004/
 
So now I fix up the self-parker cap.

You can see the two holes for the rivets and another small hole through the contact assembly for alignment purposes.
This allows water to get between the cap and disc and even leak into the self-parker.
https://www.flickr.co...04/12793622544/

I dismantle these so as to allow the plater to do a good job but it also allows me to fix this leak.
Also corroded rivets that don't make electrical contact is a common "mystery" problem.

Rivetting is tricky but especially so with these tiny 3/32 rivets and five layers to hold together.
These rivets are IRON not steel. Makes them much easier to form over.
https://www.flickr.co...04/12793325523/

Its not enough to just fix it. The rivets must not touch the cap or there will be a short-circuit. This is quite tricky because the bits move about as you hit the rivet. I like to solve two problems at once and so I seal all the parts using Polyurethane sealant. This makes the rivetting operation much easier.

You can see this here where the parts stay in place even though not yet rivetted.
https://www.flickr.co...04/12793652634/
https://www.flickr.co...04/12793224265/

A key thing when rivetting is to have exactly the right amount left to hit. A bit less than the diameter of the rivet should be sticking out.
https://www.flickr.co...04/12793324653/

Even then this can easily go wrong so it's a relief when the rivets form over and make a tight joint.
And even more when there is "through-contact" and no "short to the cap".
https://www.flickr.co...04/12793221375/
 
Great stuff Alan - thank you! I just went through this exercise about 2 months ago for my 3A motor - though I confess the self-parker cap did not get anything close to the treatment you did on yours!

One nagging rebuild issue I fought for a while was in putting the motor back together I seemed to bind the motor up on final assembly when tightening the case. Was that just me being inept or is there a trick you are aware of to keep the armature turning freely?
 
The case can go back on two ways, it always binds one of the ways. I usually mark the back with two slash marks to put it back the way it came apart.
jerry
 
Thanks for your replies.

There are two ways to put the case AND two ways to fit the pole-piece. So you have to be a bit careful.

Normally what goes wrong is that the big self-tappers that hold the pole-piece to the outer-case raise a burr and the pole-piece does not go flat.
Or some other burr or contamination gets in there.

I have not yet had one that didn't go back with a bit of jiggling about.

Here is s single-speed DR3A fitted with a resistor so as to duplicate the FAST/SLOW dual-speed operation of the TR4A motor.
https://flickr.com/gp/90670218@N04/r3EVgW

Any single-speed motor can take this. I've also done a couple of the DR2's. These are the same except for the gear-wheel arrangements.
 
After a little more study, I have concluded that the single speed wiper motor conversion needs to proceed as follows:
1. Open up end cap of motor, and pull out the body, cutting the park wire where it can be easily reattached.
2. Unsolder the field termination at terminal 1 and attach a wire to it.
3. Reassemble the motor bringing out the field wire through a gap in the terminal 1 hole. Resolder park wire.
4. Fused 12 V to terminal 2 probably supplied from ignition switch run/accessory
5. Ground motor case.
6. Slow speed is achieved by grounding the field wire
7. Fast speed is achieved by running field wire through a 10 ohm resistor to ground.
Obviously the switch in slow speed is used to bypass the 10 ohm right to ground
Tip of the hat to alanjohnturner who supplied the wiring diagram posted elsewhere on this site
 
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