The Kempner Power Wagon Museum

Frequently Asked Question


QUESTION:  How can I convert vacuum to electric wipers?

The vacuum wipers slow down or quit whenever I accelerate.

First of all, there are no parts in the vacuum wiper motor installation that can be used in an electric motor installation.  Even the wiper arms and blades are different.  In addition, the right and left vacuum motors are not interchangeable.  Early / late part numbers are 787 915 / 1261 431 for the left and 787 914 / 1261 430 for the right.  Early was up to SN 83908274 (Detroit) and 88759606 (L.A.)  Also the wiper arms were part number 837 974 for early right and left, and 1261 432 late right and 1261 433 late left.

Here's the exploded parts view from an original Power Wagon Parts List.

Wiper.jpg (62664 bytes)

Several years ago I bought a 1947 WDX that had no rust-through, very little surface rust, and was 99% complete based on a pre-purchase inventory using the MOPAR Power Wagon Parts List.  Only the wipers were not there.  One unserviceable vacuum wiper motor was lying in the original, fiberboard glove box. 

The WDX had been converted to 12v.  I decided to leave it 12v and install electric wipers. I ordered the 12v replacement electric wiper motors from Vintage Power Wagons.  They were standard American Bosch, 12v, single-speed motors and Vintage sent a hand full of brass shims to align the electric motor in the hole where the wiper motors went through the cab skin. 

I was not smart enough to make these shims work. The real "show stopper" is an angled bracket integral to the original electric motors on 2WD civilian cabs 1939 - 1947 and "flat fender" Power Wagons.  It is shown on the front of the electric motor.  The motors from VPW were correct substitutes for the original motors, but did not have the angled bracket that is critical to the installation. Not only does this bracket hold the motor in proper alignment with the cab skin, it also handles the higher torque of the electric motors.  NOTE: Electric wiper motors work on either side.  Watch routing the electric cable. 

The second part essential for installing an electric motor is the outer spacer, part number  23-67-100.   A screw goes through the outer spacer, through the cab skin, and into a threaded hole in the angled bracket to handle the higher torque of the electric motors. 

On a vacuum motor, the inner and outer spacer ( part number 23-67-100 on the vacuum wiper parts view ) handles the lower torque by a lug cast on the inner spacer that aligns the motor to the cab top. The hole for the wiper motor shaft has a notch to engage the lug.  The motor is aligned when the inner and outer spacers are clamped by the nut 23-67-189.

I had a WD-15 ('41 - '47 3/4 ton 2WD pickup) with 6v electric wipers.  All the parts shown above were there.  The angled brackets are steel but they were attached to the soft metal of the electric motors - possibly riveted or perhaps attached while the soft metal fronts were cast.  I was able to remove the angled brackets from the 6v motors and use them to install the 12v motors.  I took the '47 WDX to Fairfield and tried the electric wipers for the first time driving 24 miles in the rain back to Fairfield from the group supper in Mount Pleasant.  The electric wipers are one speed, but that is adequate on the nearly vertical windshield.  The only complaint is that the individual wiper switches are on either side and I had trouble reaching the right switch - just the same as with vacuum wipers.  If I ever decide that is a problem, I can run both wipers from the switch on the left and leave the right switch there for original appearance.

Can you mount electric wipers without having an original angle bracket and outer spacer?

Yes, but it will take more than using shims with a clamp nut on the motor shaft. The torque of the wiper back and forth will loosen the nut.  Tightening it will eventually strip the threads requiring the motor to be replaced.  It could be very dangerous for the mounting to fail during a heavy rain.  A better option would be to reproduce the angled bracket or even carve an adapter that had the same angle for aligning the motor with the cab skin.  This adapter would need a close fitting lip that went back under the wiper motor at least 1/8th inch to stop the motor from twisting - torque, remember.  The outer spacer would have to match the mounting angle and have a provision for the torque control screw to go through and into the adapter on the inside.  The original outer spacers were stamped stainless steel.  The replacements could be carved from solid stock.  When I say, "carved", I include whittling them from wood, or solid nylon, as well as sawing, filing, and machining them from brass, steel, or the metal of your choice. 

I feel the electric's are very desirable and, while they are not a top priority, they will be part of the restoration of my W300M. I have a pair of outside spacers, so I'll be on the lookout for the inside angled brackets, original or made as described above.


WOW!  Thursday, February 11, 2010 Ron in San Mateo, posted a picture of his solution for the inside angled bracket on the Dodge Power Wagon Forum.

 This is great.  However, there is still a requirement for the outside spacer, part 23-67-100 in the electric wiper parts picture above.


What can I do to have decent performance with vacuum wipers?

First, check to see all available vacuum is getting to the motors.  Vacuum gauge readings should be the same at the intake manifold and at the motors.  Replace pinched, clogged, or leaking vacuum hoses.

Next, check to see if the motors are clean and lubricated. Outside air at atmospheric pressure enters the valving system through an air inlet that usually has a felt filter.  The filter may be dirty or missing. Not all wipers have a filter. The air inlet may be under the valving system cover.  If you can get to it without taking anything apart, be sure it is clean.  Put a few drops of sewing machine (light weight) oil in the air inlet with a vacuum source and the wiper motor turned on. You can help the motor but do not apply any amount of force.  Many times the fiber part that actuates the flipper valve to reverse the motor is broken and you are applying force against the motor's normal direction.  It would be a good idea to have a "catch" jar in the vacuum line so any "crud" (technical term) can be observed and prevented from going to the truck motor.  This may clean and lubricate the motor and restore it to normal operation.  I have heard of mechanics doing this by holding the vacuum motor in a tub of kerosene and just letting the kerosene be sucked into the engine.  Keep in mind, I'm older than any Power Wagon and have seen and heard many things.

So this doesn't work and you are going to take it apart.  WATCH OUT!   Vacuum motor design is older than all known space programs - even Buck Rogers - but a vacuum motor has several small parts that will launch themselves into a Moon orbit if they can escape.  There's a chance that a prior owner already participated in a parts launch.  This is why it is worthwhile to send the motors to a professional.  If you lose a part, you will need a replacement - and the auto parts counter at Sears can't help.  Disassembly of the motor takes you to the valving system first. There are tiny springs that fly or stretch, and resin impregnated fiber parts that are brittle and break easily.  How do I know this?   Guess!  A wiper repair web site that has been mentioned several times on the Power Wagon Page Forum is at   I have had no dealings there but those who have used it seemed satisfied.   

Hopefully you are lucky and you have a wiper motor that goes both ways. (This is not a moral issue.)  You have lubed it and it moves freely with slight resistance.  It works well in the test mode - engine at fast idle and maximum vacuum reading, and the wiper blades raised so there's no drag.   Spray some water on the windshield and see if the blades move well.  It is hard to find the correct blades.  Be sure yours are not too long.  Barely touching the windshield frame could be just enough to keep the valving system from working correctly. 

If the blades sweep perfectly, you can be pretty sure the problem is related to the load on the engine.  If you have converted your differentials for speed runs at Bonneville Salt Flats, the engine is always going to be working hard and have low vacuum.  If your Bonneville modifications include a multi-carburetor intake manifold or a turbo or supercharger, you will need an auxiliary vacuum pump.  These engines are very forgiving about not having good tune-ups.   I've had them start more than once when I had the carburetor off and was checking fuel flow.  Gas from the fuel line squirted into the manifold and it ran - not well and not smoothly - but it ran.  Without the carb butterfly, there was no vacuum.   Be sure your carburetor is in good condition.  A butterfly that does not close properly can be compensated for with idle jets and other adjustments that let the truck be driven without developing full vacuum.  I doubt that many of you tune the trucks with the engine under load on a dynamometer.

Okay, the motor is tuned and running sweetly.   There's still the issues of valves and rings that affect available vacuum.   What more can I say?

The last thing is the simple fact that there is just enough vacuum for running the wipers on a level road at a steady speed.  You are fine until you accelerate.  My 1950 Plymouth had a double action fuel pump.   Both sides of the diaphragm were sealed - one side moved fuel and the other created vacuum.  The wipers had full vacuum at all engine loads.  My Power Wagon Parts List does not show a double action fuel pump.  So cars had them and trucks did not.   Roberts Motor Parts and others that supply parts for old MOPAR cars have double action fuel pumps - but you have to PAY for them.  From the late '50's, cars have had vacuum reservoirs to sustain the average vacuum in a system.   Mostly this was a requirement for vacuum boosted power brakes.  The reservoirs often looked like a Number 10 can from a food market with a single tube inlet/outlet.   It was "tee'd" into the vacuum line.  This might help during short periods of increased engine load.

What's the bottom line?

How often do you drive in the rain?  Is your trip so urgent that you not wait until a really heavy rain subsides?  Do you have windshield defrosters to keep the inside as clear as the wipers do the outside?  We are used to modern vehicles. We have to leave that behind when we climb into one of these great trucks.  Power Wagons were "low tech" vehicles where the various inconveniences of "the good old days" were accepted.  We can only bring them so far.  A good set of vacuum wipers with a well tuned and maintained motor will give pretty good service.  Some of us old folks had that as our only option for many years. 

Electric wipers are better.  Converting to electric should cost no more than replacing a vacuum system - maybe less. If you can do a good installation that won't fail at the wrong time, you will be ahead over the many years you will probably continue to drive your Power Wagon. Your choice...

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