Bill,
It is truly, truly vital, that you find out where the problem is before you
plow ahead and start fixing things that ain't broke. I think your brakes
are suffering because of poor engine performance and not the other way
around. I think you have a blown head gasket because this is a better way
to describe the loss of compression on more than one cylinder. The booster
unit only takes vacuum from one cylinder, the one immediately in front of the
driver, commonly known, I think as number eight. If you lack compression
on 4 & 6, I think you said, then I find it hard to blame the brakes.
Before you go the trouble and expense of changing the booster and all the
attendant issues you will have will bleeding the brakes, etc, etc, you need to
find out what the engines problems really are. There is an easy way to check to see if it is the booster. Remove the
air hoses that go to it and use one of the hoses to simply run back to where the
other one came from, thus simply cutting the brakes booster out of the loop. I
have removed my booster unit several times. It is quite a booger of a
task. A special wrench, one of the ones with a flexible metallic
shaft, will prove to be invaluable as some of the nuts are hard to reach.
There are also two different sizes of nut. Over the years at least some
brake fluid will had found it way back there and you may find that the pins
holding the nuts are corroded to a greater or lesser extent. The manual is
extremely useful under these circumstances.
Hugh
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