View single post by Jim Ketcham
 Posted: 09-16-2014 02:25 pm
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Jim Ketcham


Joined: 03-13-2005
Location: Salt Point, New York USA
Posts: 198
I do not see how the booster can be partially faulty. If it holds vacuum it should be fine. If it is faulty pedal effort is very noticeable.
Low vacuum to the booster means either an external leak or an internal one. External is easy to check. Internal, unfortunately, means worn engine. If engine is running fine that is improbable.
It does not take much difference in master cylinder piston size to make a big difference in pedal effort. If my math is correct, the difference in area between a 3/4" and 7/8" diameter piston is >35%. That would significantly affect pedal effort.
Having tried a pre-89 SWB LR master I noticed increased pedal effort. I was able to correct it somewhat with high performance pads. I eventually pulled the LR master and measured the piston. It was slightly less than 7/8" in diameter. The original JH master measured a hair over 3/4". I switched to a TR6 master and pedal effort was marked improved to the point that I no longer have any concerns about braking.
My bet is if there is no vac leak it's the master cylinder.
Good luck,