Re: Vac Leak on the brakes

[jlandry@domain.elided (John A. Landry)]

As the little green aliens inserted a searing hot probe into the sternum of
Tom Mandera <tsm1@domain.elided>, a blood curdling scream was heard...

>It appears to simply be a smooth bore hole, below the m/c, between the 
>m/c and booster, and slightly in front of the booster.  Like I said, the 
>hole is horizontal.. parallel to the ground and parallel to the front bumper.
>
>Any idea why this is there?  Suggestions on plugging it?

Tom,

I think I've seen this hole before on a MC.  I think it's actually a
passageway cut to the rear of the MC.  I always assumed it was to drain
leaking brake fluid away from the booster in the event the rear MC seal
ruptured.  So if it sucking vacuum, this would make sense that the hole leads
back to the booster at the rear of the MC.

As far as the vacuum leak itself goes, I took a look at the booster diagrams
in the IH shop manual, and I'm 99% sure the front booster seal is *supposed*
to completely prevent vacuum from passing the pushrod.  For one thing, the
booster is designed to hold vacuum in the event the engine dies.  If the front
seal is leaking, that sort of defeats the whole purpose.

If you were to seal the rear of the MC against the booster (by blocking the
weep hole you discovered), I would think a strong vacuum against the rear of
the MC can't be great for the rear MC seal.

Your front booster seal is probably worn or torn.  You're only real choice at
this point is to by a rebuilt brake booster and swap it out before Darrel
Kline comes after you with his brake safety SWAT team.

Take care,

John L.
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