Military-Vehicles: [MV] M38 vacuum system

[MV] M38 vacuum system

SBJohnston@aol.com
Sun, 6 Jul 1997 00:52:08 -0400 (EDT)

As I inspect the engine of my newly acquired 1951 M38... more and more
questions come up. I'm so new to this sort of vehicle...please bear with my
curiousity.

There have clearly been some mods done to the vacuum system of my jeep's
engine. The vacuum portion of the relatively new-looking fuel/vacuum pump is
completely disconnected. No vacuum lines run to/from the pump at all. The
tech manual shows the vacuum line coming from the manifold down to the vacuum
pump, getting boosted there I guess, then going on to a tee connector and
splitting to the the distributor and windshield wipers.

Instead, on my engine the vacuum tee is mounted right on the the manifold
directly -- and lines from the tee go to the wipers and distributor.

I've been troubleshooting an overall lack of power, and along the way
suspected a vacuum system leak, but my vacuum gauge shows a very steady 20
inches of vacuum at idle speed, kicking down and back upon acceleration as
expected. I did find a couple very loose vacuum line connections and
tightened them up, but even so, all seemed OK, except that the vacuum pump is
not present in the system at all.

I guess the vacuum pump only serves the distributor and wipers. The wipers
move fine without the pump (trivial perhaps, but a clue), but I don't know
what the distributor is doing with the vacuum. Does it use the changing
vacuum to advance/retard the spark timing?

Any opinions? Could lack of "pumped vacuum" to the distributor explain the
lack of power? Is it acceptable to run for now without the vacuum pump?
(considering only performance, not the issue of proper restoration, of
course) Thanks for any thoughts...

Steve Johnston

sbjohnston@aol.com

----------------------------------------------------
"Jeepobsession" -- a new fragrance by Cavin Willys.
Smells like 90-weight gear oil leaking onto a garage floor.
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