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Posted by Ed Tavernier on Tuesday, April 21, 2009 at 20:32:53 :
In Reply to: electric wipers verse vacuum posted by Steve Simon on Tuesday, April 21, 2009 at 19:04:29 :
Steve,
The vacuum wiper system runs off of the vacuum of the engine. When the engine idles the intake butterfly is closed, and vacuum is maximum. When the throttle is wide open, so is the butterfly and vacuum is greatly decreased. The vacuum wipers respond to the changes in amount of vacuum by varying the speed. Unfortunately when you are travelling at highest speeds the vacuum is low and the wipers go S L O W L Y and sometimes even STOP. Conversley when the engine is not under load the wipers will cycle very quickly. Vacuum can be helped by placing a vacuum canister to store extra vaccum...basically an empty cannister that stores extra vacuum "pressure"...really a lack there of...that is used up when the engine is under load.
So the vacuum wipers are intermittant, but it is in response to the vacuum generated by the engine and the loads the engine incurs while driving. Slow going up hill; fast coasting down hill.
Eddie
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