Posted: Sat Nov 03, 2018 7:29 pm Post subject: vacuum gage hook up
When using the vacuum gage on a M38.Should the suction(vacuum) line from the vacuum pump be disconnected ? If so would this be at the brass tee on the intake manifold nearest the firewall? How much difference--if any would there be if it was not disconnected?THANKS IN ADVANCE
as long as the input side of the vacuum section of the pump is not open to air it will be fine to leave it in place. _________________ 1952 Dodge M37, 1942 MB script, 1948 FrankenJeep CJ2A/M38, 1951 M38, !942 WC-57 Command Car Undergoing factory original restoration, 1944 WC-51 Weapons , (2) M1941 Sperry 60" Anti-Aircraft Searchlight, John Deere M-gators
Joined: Jan 27, 2014 Posts: 99 Location: West Palm Beach FL area
Posted: Tue Nov 06, 2018 11:10 am Post subject:
I have pondered this same question. Does the air/fuel mixture change when you turn on the vacuum wipers?
Just thinking out loud... isn't the "input side" always open.... even if the wiper suction needle valve is closed?
Consider the path from the wiper T to the distributor and the dizzy to the air cleaner.
That said, wouldn't you want to measure vacuum with the engine in the state in which it is "normally" operating?
This should smoke out some of our vacuum diagnostic experts on the forum into this thread. _________________ 1951 M38 restoration project - Flightline Jeep MC 23923 DoD 6-51
1947 Willys CJ2A - Harvest Green
1954 Ford F-100 Parts chaser - blueprinted Y-Block
Yes the fuel air ratio changes, but insignificantly. The displacement of the wiper motors is about 2 cubic inches each per stoke and slow. But the engine is using thousands of cubic inches or air per minute, so the difference is so far down in the noise that it matters not.
The "input" side of the vacuum pump is closed effectively when the wipers are off.
Wiper Tee to the distributor? the Tee on the air cleaner supplies clean air to the distributor which is drawn through into the cross over pipe. the other side of that tee goes to the wipers so that when they are operating they are getting clean dry air to replace the air that is being vacuumed out the other side to the vacuum pump during operation. _________________ 1952 Dodge M37, 1942 MB script, 1948 FrankenJeep CJ2A/M38, 1951 M38, !942 WC-57 Command Car Undergoing factory original restoration, 1944 WC-51 Weapons , (2) M1941 Sperry 60" Anti-Aircraft Searchlight, John Deere M-gators
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