Better Beaters - Building Cars and Daily Drivers

Rebuilding the windshield wiper motor on my '46 Plymouth. Part One.

That was either a very old felt sound deadening pad
or a thick layer of dust. I'm still not sure which.

Even though my Plymouth doesn't have a heater or defroster, a working wiper would be of some benefit.

The last time I took my Plymouth to a Cars and Coffee was in November. I had taken it out of the garage the night before, and parked it in the driveway,as these events start quite early, at 0730 hrs. I had covered up the car so in the morning, I took the cover off, wiped the front windshield and drove off.

I had never driven it in cold weather so I was surprised to see that the windshield was fogging up a bit, but on the outside. I figured that this would dissipate as I drove the car. Instead it got worse and when I turned into the early morning sun I was blinded by the glare. I had to immediately pull over, park, and wipe off the outside of the windshield. 

This was good enough to clear the screen but it did cloud over a bit during the rest of the fifteen minute drive. 

Since I had been a long time motorcycle rider I was familiar with RainX and FogX, these were products applied to the outside and inside of motorcycle helmet face shields. I'm going to buy these products and keep them in the glove box to use when necessary. 

However, a working windshield wiper would be handy. The wiper on the Plymouth was inoperative, the seller has advised me of that before purchase. I had owned a car with a vacuum wipers motor, a '57 Cadillac. Even on this expensive car the performance of the wiper motor was not very impressive.

The nature of vacuum wipers is that they work best when vacuum is high: at idle, and at steady engine speed. Accelerate and the wiper would slow and eventually come to a complete stop. As you can imagine, this was not too reassuring during a downpour! This required some adaptation on the part of the driver. I had to back off the throttle momentarily to allow the wipers to clean the windshield, then continue accelerating. 

I had to fix the wipers on the Cadillac so I was not unfamiliar about how the wiper motor operated and what it looked like inside and what was required.

I found a very detailed video on YouTube that describes how to dismantle and rebuild a Trico Vacuum motor. The motor in the video was missing it's output shaft and the guy had to machine a replacement. All I have to do is rebuild what I've got.

You can watch the video now and gain an understanding of how the motor works and what's involved in the rebuild.

The motor and linkage are accessible from under the dashboard.

You can see that cable makes a huge loop then crosses itself.

The wiper motor sits under the middle of the dashboard. The knob that activates the motor is located on top of the dash. This knob appears to be a replacement choke cable assembly; it was extremely long and wound in a big loop before being attached to the motor control lever.

The knob could not be pulled out to move the control lever, I will shorten this cable after I rebuild the motor, which is a familiar Trico model. These vacuum wipers had been used from the late 20's in many cars, even Model A Fords. I found a very good video online that showed how to rebuild this unit.

Inside the motor there is a "paddle" which is pulled in one direction when vacuum is applied. When it reaches the end of it's travel, a switch applies vacuum to the opposite side of the paddle pulling it back. The switch causes it to move in the opposite direction. This is how the wiper moves back and forth, like a metronome, swish-click, swish-click. The linkage for the wiper arms is equally simple, it moves one direction and then comes back the same way.

The output shaft is attached to the paddle.

I have to remove the output shaft and attach it to the supplied paddle.
The tear shaped rubber is part of the "park" mechanism.

These channels cast in the top direct vacuum
to both sides of the chamber. The round structure is part of the "park" system

.

This is the switch chamber. The three holes in the top piece are uncovered
by a sliding valve which reverses the direction of the paddle/arm.

This plate slides back and forth to activate the motor.

You can disassemble the entire unit. It is held together
with these unusual oval head screws. 

Those ports are uncovered by the sliding plate. There is only one position available.

The rebuild kit consists of a new top gasket, a gasket for the on/off switch, a new paddle, and a small spring for the switch.

First thing after I diassembled the motor was to thoroughly clean everything. 

I found a very good video on the internet entitled "Trico vacuum motor resurrection." This video shows the rebuild of a vacuum motor that was used on a Model A Ford! The motor is essentially the same as used on my car. This technology had been around for a very long time by the time my Plymouth had been built.

The video was invaluable in showing how the switching mechanism goes back together. The rebuild kit that I ordered did not include the phenolic plastic, shield shaped, part that trips the switch. I will take some photos and trace the  outline of the piece before I reassemble it. I think that my Wife might be able to scan the drawing and reproduce the part using her GlowForge.

On the next installment I'll finish the rebuild and show how I can shorten the cable and hopefully, make it work properly.

Then I'll have to source a right side wiper arm and a pair of new wiper blades.