Windshield Wiper Operation Question

[w30bob]

Hi Guys,

I'll 'fess right up here.....I bought my M in March of 2012, and drove it around the yard a time or two before I parked it to restore. So I didn't try out all the features, including the windshield wipers. Now that I've looked at them and understand how they operate I'm wondering is the wiping speed proportional to engine RPM? I realize they get vacuum from the fuel pump and not the engine, but the vacuum the fuel pump provides is determined by the engine speed....ie, how many times the fuel pump plunger is depressed per minute. So do the wipers wipe slower when the engine is at idle and then speed up as you increase engine speed?

thanks,
bob

[Cal_Gary]

Pretty sure it's the other way around-every vacuum wiper vehicle I ever drove slowed the wipers when applying more gas-just my 2 cents since I run electric wipers but the other forum folks may weigh in.
Gary

[w30bob]

Hi Gary,

That would be the case if the vacuum signal was coming from the engine....but I thought on the M37 the second diaphragm in the fuel pump was where the vacuum came from. If that's the case the pump should make more vacuum the faster it pumps. There should also be a pop-off valve in the system somewhere to bleed off the built up vacuum if the wipers weren't being used. I haven't found too much info on how the vacuum operated wipers actually work....so if I'm getting this all wrong y'all feel free to correct me.

thanks,
bob

[k8icu]

Bob,

They are suppose to run at a constant speed no matter what the motor was doing. Idle, racing etc. it didn't matter. That was the theory anyway. Most of the time the passinger side one goes like a bat out of hell and the drivers side one stops in mid swipe and doesn't continue until you let off the gas. Of course at the time you're driving up hill at night in what looks like the storm of the century....

[jim lee]

I saw that on mine except it was the passenger one that stopped. They ran exactly like they were running on manifold vacuum. Ok at idle horrible going uphill. Showed the kiddies -
"See how these old vacuum wipers work? Bla bla bla." I pull the motor and find they were plumed to the bottom of the fuel pump.

"What the heck? How can this be?" My "theory" on why they worked like they were hooked to manifold vacuum is that the pump diaphragm tore and its vented to the crank case with its vacuum PVC system. Only a theory but its the best I got. Not pulled it all apart to even see if its possible yet.

-jim lee

[w30bob]

Thanks guys.

Sounds like I'm in for some real fun when I get my M on the road.

regards,
bob

[k8icu]

Thanks guys.

Sounds like I'm in for some real fun when I get my M on the road.

regards,
bob

Oh you are...you are!

I have a few rules of MV Operations. Kind of my version of Mr. Murphys Laws.

When driving in any type of rain the water will get through the window seal and will find the drivers right foot and soak it.
Owning an MV means one will spend more time under it than driving it.
MVs will always act up mechanically when you have a mile long line of traffic behind you on a two lane non-passing road.
MVs with NDT will walk the road always no matter the condition of tires etc.
Vacume wipers will work fine in good weather and not in bad weather.

I have a few more, but you get the picture. These are only my thoughts and based on my 30 years of playing with these things. I know there are a few on here that will disagree with me, but that's fine. They are meant somewhat serious and somewhat tongue and cheek.

I hope you get to enjoy your truck soon Bob.

Joe

[PoW]

OK, you guys...follow the plumbing of the wiper system.

The Vacuum initially comes from the intake manifold, and is then 'boosted' by the second section of the fuel pump.

It will vary by engine load, and somewhat be compensated by the mechanical pump.

All in all, you know how it performs. Not too well, in fact.

Electric replacements are the easy way out, but adding a compressed air system to the truck (very handy, BTW) will allow you to run the air motors from the 2.5/5 tons. Those are so powerful they can bend blades on ice.....

Dennis

[MSG Rusty]

the worst thing is that the pivot bolt on the drivers side whindshield hing can leak and that will mess up the vacume even more. To slow down the pasenger side wiper you need to put a restrictor in the air line. the pasenger side wiper is at the begining of the vacume opening so it tends to work better. I have been thinking about adding some tubeing and making the drivers side wiper motor the end of the vacume line.

[pwrwagonfire]

Bob,

They are suppose to run at a constant speed no matter what the motor was doing. Idle, racing etc. it didn't matter. That was the theory anyway. Most of the time the passinger side one goes like a bat out of hell and the drivers side one stops in mid swipe and doesn't continue until you let off the gas. Of course at the time you're driving up hill at night in what looks like the storm of the century....

This sounds bout right