Vacuum line one-way valve

[Clem Clement]

I'm learning that the 40 and newer had a one-way valve in the vacuum line to protect their windshield wipers from a back fire. Do I need one in my '39 peeekup? I know that the vacuum line enters the manifold toward the rear of the engine and that later on it enters under the cab mounting. ( I do have a filter to keep Chebby's from being sucked up my exhaust pipe...)

[Kube]

Originally Posted by Clem Clement

I'm learning that the 40 and newer had a one-way valve in the vacuum line to protect their windshield wipers from a back fire. Do I need one in my '39 peeekup? I know that the vacuum line enters the manifold toward the rear of the engine and that later on it enters under the cab mounting. ( I do have a filter to keep Chebby's from being sucked up my exhaust pipe...)

Actually it's '42 - '48. Was it really necessary? Probably not. If your car back fires, you have another, more serious issue than worrying about the wiper motor.

[Bruce Lancaster]

That funny mushroom on the hookup isn't a one way valve...it is a silencer supposed to quiet that strange hiss as wipers are turned on and off. The round part is supposed to be filled with felt, but the felt is generally long gone.
Onliest time I ever had engine do anything funny to the wipers was a sudden engine shutdown I had when I was about 18...car just stopped running, and, oddly, wipers came on for about 1/2 stroke as the engine stopped and I coasted to the shoulder. I poked around ignition and carb for a while but remained utterly baffled...
I trudged into the nearby metropolitan center of Snead, Alabama and fortunately encountered and old and very experienced mechanic. "Wipers came on? Timing gear."
Towed it in and tore it down in complete confidence without further analysis, and he was right...stole a gear set from an N tractor, done, and wipers were unharmed. Back on the road to Pennsylvania and college...

[trike84]

What would cause the wiper to operate,

[Bruce Lancaster]

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Well...I never fully doped that out...but crank was spinning at 70 miles per hour driven by the car after the instant of failure, valves stayed right were they were. Violence entered the manifold...maybe I just don't want to know. Poor wiper motor probably caught stray combustion pressure through its "park" hose and got blasted from park to full lock the other way. And survived!
Whatever happened would have been fully stopped or at least reduced by the shut-off valve in an earlier Ford with no park return built in.