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January 5, 2015

Windshield Wiper Motor & Wheel Boxes

[Click the pics for a larger view]

The TR6 uses a 12 volt DC motor to operate the windshield wipers.  The motor drives an integral crank gear that moves an arm in reciprocal motion.  The arm connects to a "flexible rack" drive cable that communicates the reciprocal motion to two wheel boxes where the wiper arms attach.

This motor and gear assembly is used on a variety of British cars.  Mine was in working order, but old and dirty.  It seemed like a good idea to freshen up at least the internal lubrication and whatever else might need attention.

Taking off the top cover reveals the internal mechanics of the rotary to reciprocal conversion.  A worm shaft from the motor drives a worm wheel, which in turn drives a crank arm.  The crank arm slides a block back and forth in a nylon lined channel.

Removing the through bolts releases the motor from the gearbox casting.  This shows the brush board.  The small brush at an angle to the others is for the slow speed.

I cleaned up the main die casting and gave the exterior a light bead blast.

Before I took the motor apart, I had ordered a new brush set.  However, the original was in such good shape, I didn't use it.  My thinking was that putting new brushes in would increase commutator wear during the seating period of the new brushes.  The original brushes were already seated on the commutator.

So here are most of the parts for the wiper motor.  The commutator was lightly cleaned, the motor case and the gear case exterior were repainted, and the gear cover was replated.  All of the internal bearing bushes were still tight and smooth, so they were just cleaned and re-lubed.

This is the wiper park switch.  It is a switch operated by a cam on the worm gear.  When the wiper switch on the dashboard is turned off, the park switch keeps the motor energized until the wipers are in their "parked" position.

The plastic track that the reciprocating block rides in was still in good condition.

I mounted the motor and the rest of the mechanics...

...and buttoned her up.

Then there were the wheel boxes.  I had a hell of a time removing them from the car, mainly because the chromed  nuts holding them in the cowl were seized.  I ended up cutting the nuts off, but not before I'd done a good job twisting the guide tubes for the drive cable.

The wheel boxes themselves consist of a special wheel that mates to the drive cable like a pinion to a rack.  The wheelbox housing carries the shaft to the wiper arm connection, and a plate to clamp the guide tubes in alignment with the wheel.

The wheel boxes were rusty in places, and I wanted to remove the shafts from the wheel boxes so I could replate the boxes and properly lubricate the shafts.  When something isn't designed to be disassembled, it doesn't mean you can't take it apart.  On the other hand, just because you can take something apart, it doesn't mean you should.  

I assumed that I could remove the wheels from the shafts, and the shafts would slide out.  This turned out not to be true.  I got the wheels off, bit the splines on the shafts were bigger than the shafts.  These must have bee assembled by putting the wheels on the shafts, then sliding the shafts in place, and staking the wiper arm mounts to the shafts.

Removing the wheels did make it easier to clean out the old dried up grease behind them, and to flush out the shaft bore with solvent, so maybe it was worth it.

Since I washed all of the lube from the bores, I used this vacuum pump contraption to suck grease back into the bores with the shafts in place.

Then made some new guide tubes by putting double flare ends on 5/16" brake line.   I initially forgot the little short tube at the far end of the cable.  I had to make that later.  The tube with the connector nut has to be bent, but I'll do that when I install the wiper system.

I painted the wheel boxes, plated the covers, relubed the shafts, pushed the wheels back on, and did a trial assembly and test.  Everything seemed to work quietly and smoothly..

Total cost for this project was pretty small.  I did buy the brush set, but didn't use it.  The brake line for the guide tubes was about $6.  I still have to buy the chrome nuts I destroyed, and the plastic housings for the washer nozzles appear to be toast, but those will come later.

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