[alfa] Diagnosing a bad brake booster

["Jay Mackro" <jmackro@xxxxxxxxxxxx>]

Kevin Trent <trentkc@domain.elided> described the symptoms
of his Spider's brakes (hard pedal, etc).  Yea, the symptoms you
describe definitely sound like a bad booster.  There is a valve at 
the back of the intake manifold, but that's just a simple one-way 
valve to maximize the vacuum (e.g., minimize the pressure) in the 
booster.  I guess you could unscrew it from the manifold, and use 
the simple "blow in it from both directions, and confirm that air 
will only flow one way".  I would bet that the valve will check out 
OK.  While you are putting off the inevitable, you could also
check the flex hose between that valve and the booster - make
sure it isn't cracked/leaking.
 
Boosters tend to die as a result of the seal at the back of the brake 
master cylinder wearing, and allowing brake fluid to get into the
booster.  The brake fluid eventually causes the diaphragm in the
booster to leak (whether it dissolves it, corrodes it, causes it to
stiffen & crack, or ??? I don't know - but you'd think that a brake
booster diaphragm would be made of a material that resists brake
fluid!).  

The good news is that brake boosters CAN be rebuilt, and it isn't
that expensive.  Unless you live out in the boonies, check your
Yellow Pages, and make some calls.  Or, buy a new one from one
of the Digest sponsors.  Yea, you could also swap in your used
one, but as you point out, there is some labor involved in the swap,
and when you are dealing with braking systems, there is something
comforting about new or recently rebuilt components.  Actually,
R&R'ing a booster isn't that hard - at least you can do it standing
up!  The trick is threading the pedals back through the hole in
the firewall when you are putting it back together.  You will
definitely need to remove the rubber pads on the pedals.
 
Good luck

Jay Mackro, San Juan Capistrano, Ca.
--
to be removed from alfa, see /bin/digest-subs.cgi
or email "unsubscribe alfa" to majordomo@domain.elided