Check the non-return valve in the vacuum line to the brake booster.
Sounds like it;s not completely closing and allowing a vacuum leak, hence
the rise in RPM.
Rick Morrison
72 MGBGT
74 Midget
On Tue, 3 Feb 1998 09:09:36 -0500 "John A. Wise" <wise@db.erau.edu>
writes:
>Re: '77 MGB, 190K miles
>
>As I ease off the brake pedal AFTER a stop, I hear what appears to be
>a
>slight hiss. The sound only appears when the brake pedal is at
>partial
>pressure - e.g., sitting a traffic light.When it is fully applied or
>fully
>of - there is no detectable sound. It also only apears after the car
>has
>been driven. When I try to replicate the sound in the garage - so my
>son
>or I can try to localize it - it does not occur.
>
>I have also noticed a slight increase in RPM when I hear the hissing.
>
>The brakes seem to be working fine.
>
>I have replaced the vacumme line. Will I need to rebuild the booster
>unit.
>If so is that a job a moderately skilled person can handle. I noted
>in the
>VB catelog that they feel rebuilding a loockheed unit is best left to
>a
>professional. How does one tell if you have a Bendix or Lockheed
>servo??
>
>Any suggesttions????
>
>John
>
>
>John A. Wise, Ph.D., CHFP Tel: (+1) (904)
>226-6384
>Department of Human Factors & Systems Fax: (+1) (904)
>226-7050
>Embry-Riddle Aeronautical University E-mail:
>wise@db.erau.edu
>600 South Clyde Morris Blvd.
>Daytona Beach, FL 32114-3900 USA
>
>
>
>
>
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