Anyone know why there is a replaceable spring in a vacuum advance? Unfortunately the repo is not serviced. I'm curious if it has enough tension? Just curious I can't find any information.
That spring controls the rate (not the amount) of vacuum advance. A stronger spring delays the point at which the ported vacuum overcomes the spring tension and allows full advance during light throttle cruise conditions. As soon as you step into the throttle a tiny bit, all that advance goes away until you return to light throttle cruise. If you have a chassis dyno and a few thousand dollars' worth of other test equipment, it would be possible to wring out the last few fractions of gas mileage and performance by tinkering with the spring tension. In practical terms, buy a handful of slightly different springs, and spend several months keeping very meticulous records on fuel consumption, uphill performance on the exact same road for dozens or runs, etc. Be sure to compensate for variations in temperature, atmospheric pressure, relative humidity, and about half a dozen other variables. That's how the researchers who designed the thing in the first place did it. Have fun, and be sure to publish your findings here so we can argue about them! Jerry
"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt! There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway Love your enemies and drive 'em nuts!
Jerry I assumed there was great thought put into the reason it's there. Just didn't understand why it was a serviceable part in the old days. Thought maybe automatic was different from manual transmission maybe. Thanks for the info. Like I said just curious wasn't in my shop manual . .
Vacuum advance is mostly there to give a gas mileage boost at very light throttle. An engine that's doing any pulling at all doesn't need it. Lots of industrial and/or truck engines had no vacuum advance at all. Such things as having a standard or automatic transmission, or even a different rear end ratio might require a different calibration of the advance springs- - - -both centrifugal (engine speed) and vacuum (throttle position/manifold vacuum). It's about equal parts of educated guesswork and voodoo in the automotive engineering world, plus a considerable amount of SWAG ("Scientific Wild-Donkey Guess")! Jerry
"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt! There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway Love your enemies and drive 'em nuts!
One I have has a bunch of shims wired to the advance spring. It might be from my old 50 Stude or it might be from some I6 Chev. I have boxes of stuff like that for my wife to paw through after I die.
My friend Rick left his wife 2 class-8 truck tractors and the shop to work on them when he died. When he was too sick to go out to the shop I took my camera and photographed an endless number of parts that he identified. That was a great help for her.
1951 3800 1-ton "Earning its keep from the get-go" In the DITY Gallery 1962 261 (w/cam, Fenton headers, 2 carbs, MSD ign.), SM420 & Brown-Lipe 6231A 3spd aux. trans, stock axles & brakes. Owned since 1971.
