windshield wipers

Deadguy · Post by **Deadguy** » Tue Dec 18, 2012 3:04 pm

I installed the correct, 7/32 vacuum hoses Wes recommended, and I have rebuilt wipers from John at Midwest Military. He accidentally sent me the ones for a M38, but told me how to adjust them. The metal collars the windshield screws pass through were slightly to long, and I had to grind them down a little so the wiper arms don't rub against the frame of the windshield. They work fine at idle now, but dramatically slow down whenever I hit the gas. Is this normal?

RICKG · Post by **RICKG** » Tue Dec 18, 2012 3:07 pm

Post by **wesk** » Tue Dec 18, 2012 8:55 pm

dramatically slow down whenever I hit the gas. Is this normal?

The natural order of things is what you are observing. I will assume you were not a licensed driver before 1960

Wipers require vacuum or suction to function. The specific amount is about 12" of mercury at 1500 RPM and up. Under acceleration the manifold (intake) suction drops drastically. Thus the vacuum available to the wipers is reduced and they slow down. The vacuum side of the dual action fuel/vacuum pumps helps a bit but once you crack that throttle wide open the vacuum will drop to almost zero.

In the 50's the luxury cars that still used vacuum wipers used the dual action fuel/vacuum pump and also incorporated large vacuum storage cylinders to help the wipers thru the acceleration cycle.

When I was driving my first 7 or 8 cars which all came with vacuum wipers I simply did what all folks did back then. We tried not to overdrive our wipers which means the same as trying not to overdrive your head lights at night.

madmike · Post by **madmike** » Wed Dec 19, 2012 11:07 am

Speaking of the wipers, I was just installing my units and the vacuum switch last night and was testing the action when I noticed that I could draw air though one side of the switch after turning the lever but the other side did not seem to draw in either position. There was a slight leakage or draw but the switch is not readily serviceable to see if there is blockage. Running a probe inside did not indicate evidence of crud.

Is the switch designed to be closed on both sides and open and both sides when turned? I hope I have described what I am asking well enough to get the answer.

Mike