Look at the check valve that is in line from the manifold (or were the system
gets vacuum). It could be letting the air flow back.
Just a thought.
Mike R
Florrie & Allen Bachelder wrote:
> Hi List -
>
> ' Sorry this is rather long, but I need some advice. Back in May I started
> having problems with a soft low brake pedal on my '76 B. It's never been
> firm like my non-servo Bs but it got quite a bit worse. A Roanoke Brit Car
> Resto guy noted the engine idle was affected by the brake pedal and
> suggested it was probably a vacuum leak in the servo. So I sent a servo
> from my '76 parts car off to Apple Hydraulics and got it rebuilt.
>
> While at it, I put in brand new master cylinders (clutch and brake) from
> Moss and on advice of the same guy in Roanoke, flushed out the whole system
> and converted to DOT 5. I did bench-bleed the MC first. Still got a soft
> pedal and within three days my left front caliper was leaking (I've never
> had a caliper leak in all my 15 years experience with MGBs).
>
> ' Was about to rebuild calipers (as I've done on other Bs) and discovered
> Advance Auto has rebuilt calipers with OE pistons for $35.99 - with
> lifetime warranty. So I flushed out the system - thoroughly - converting
> back to Castrol GT/LMA DOT4 before installing rebuilt calipers. Again, I
> bled the whole system thoroughly - starting with left rear, then right
> rear, right front and finally left front. There's no DOT 5 left in the
> system.
>
> Still soft pedal. Pads are good. The brake hoses were replaced about two
> years ago, as was the left rear wheel cylinder which I discovered leaking
> at that time. Shoes looked good then. Car has gone about 15,000 miles
> since.
>
> The right rear wheel cylinder is the only item in the system that I haven't
> replaced. It is working and although I haven't had the drum off, there is
> no outside sign of leaking. I am aware that lots of DIYers put rear brake
> shoes on wrong and mine are right - like in the Bentley illustrations. The
> rears are set as high as I can get 'em without overheating the hubs - in
> fact I had to back my left rear off a bit. Even when it was set too high,
> soft pedal.
>
> If I pump the brakes once, on the second application, they feel good. I
> know this is a classic symptom of rears in need of setting up, but that's
> not the problem. At its worst, the pedal may feel awful but the brakes do
> work well - although the right rear tends to lock up first on hard stops.
>
> I even turned the brake light switch in about 1/2-turn - which minimizes
> the 1/8th-inch pedal freeplay and, not surprisingly, makes no difference.
> The pedal does not "leak down" nor am I losing any brake fluid. In fact, I
> swear the level in the reservoir went UP slightly after a 40-mile test
> drive. Could there still be an air bubble in the system...? I suppose
> although it seems unlikely. What could I be overlooking? Should I replace
> rear brake shoes?
>
> Many thanks!
>
> Allen
>
> ******************************************
> Allen H. Bachelder =iii=<
> Sinking Creek Home for Wayward MGs
> New Castle, VA 24127
> USA
> 540/544-7333
> ******************************************
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