----- Original Message -----
From: <lstein6@gmail.com>
To: <triumphs@autox.team.net>
Sent: Monday, September 04, 2006 11:18 PM
Subject: [TR] tr7 power brake booster vacuum leak
> when i step on the brake pedal approaching say a red light, after initial
> pressure, the pedal kind of "breaks through", you hear sqwoosh, like the
> vacuum boost is pushed out somewhere, the pedal suddenly goes another inch
> toward the floor and then all is well. i replaced the master cylinder
> recently with another used one, because the top plastic reservoir was
> broken. is it possible the rubber seal at the front of the master
> cylinder is where it is leaking? hard to tell when you are driving, but
> the sound is pronounced. can you buy to replace just that rubber seal?
> thanks, larry
Larry-
It is unlikely that the vacuum leak is from the base of the master
cylinder. The vacuum booster is a sealed unit and the master cylinder
opening should not be an "open" area. The most likely culprits are the
vacuum check valve and the booster diaphragm.
To check the valve: Locate by looking at the booster and finding the
hose that connects the booster to the intake manifold. The check valve is
the elbow into the booster. Remove the valve and try to blow through the
manifold side of the check valve. It should be completely blocked. If there
is flow, it should be replaced. If you have a Mity-Vac tool, try to pull
vacuum through the booster side of the check valve- it should be blocked, if
not replace the valve. Also check for vacuum leaks at the check valve seal
as well as the supply line from the intake manifold. Run engine and shut it
off, wait 5 minutes and apply the brakes. You should have power assist for
at least one pedal stroke. If there is no power assist, the check valve has
leaked down and needs to be replaced.
To test the booster: Start engine and let idle to supply normal vacuum
to booster. Close windows with hood up, slowly apply pedal and listen for an
engine stumble or rough running condition. If the hissing noise increases at
the pedal pushrod, the booster has an internal vacuum leak. It is normal for
air rushing noise when pedal is first depressed.
Another test for the booster is to turn engine off. Repeatedly pump the
pedal to remove all residual vacuum from the booster. Hold the brake
pedal down firmly and start the engine. The pedal should move down slightly
then stop. Only a small amount of pedal effort should be needed to hold the
pedal down.
Good luck-
Tim Hutchisen
71 TR6 w/booster
70 GT6+ w/o booster
=== This list supported in part by The Vintage Triumph Register
=== http://www.vtr.org
|