Brakes Problem

[dum]

Yesterday while driving my early 250 I suddenly had to push much harder the breaks in order to stop the car.
I know that our cars have a two circuit system, so I guess that this implies that one went off.
Can you briefly advise on what could have gone wrong so suddenly and how I can correct it?

[dum]

Or is it a problem with vacuum?

I noticed that when I pushed the break pedal, the engine revs increased (a lot).

[Naj ✝︎]

I suspect the diaphragm in the vacuum servo has ruptured...

Also worth checking the one way valve in the vacuum line from the inlet manifold.

naj

[glenn]

Dum, If the revs went up 300/400 or more, sounds like it was running pretty rich???

[dum]

Yes it is running rich....

So would engine adjustment help?

Many thanks,

Dum

[abe280SL]

Also replace the old vacumm line not just  the one way valve. Make sure the clamps are tight and no leaks. Since this is an easy job..its worth trying first.
If that fails...then the brake booster may be the issue.  I don't think your engine running rich contributed the problem.
abe

[waqas]

I suspect the diaphragm in the vacuum servo has ruptured...

Also worth checking the one way valve in the vacuum line from the inlet manifold.

Naj is spot-on. My booster diaphragm also ruptured suddenly.

This problem and the rich running issue have no relationship, although the brake fault has automatically run half the Blacklick air/fuel ratio test (e.g. see http://www.sl113.org/forums/index.php?topic=11162.msg74726#msg74726)

[glenn]

Yes, they are separate problems.   But, when the booster leaks air into the intake manifold, two things can happen--- Engine slows(too much air now) or engine speeds up(too much fuel before).   A booster leak is the same as adjusting the idle air screw to more open???