Has anyone experienced a faulty brake booster? What are the symtoms?

My mini currently seems to be running a bit lean (plugs are white) although I have the mixture set quite rich. So I think there may be an air leak somewhere and the only thing that hasn't been checked is the booster. The booster is working but the brakes are not as good as they should be but I have no fluid leaks. Also if i clamp closed the booster hose to the inlet manifold the car will stall.

Does this sound like a leaking or faulty brake booster?

Thanks any help would be appreciated.

G'Day Mini68,
If you stop the engine and disconnect the hose from the inlet to the booster, you should still have a vacuum in the booster, you should be able to hear a rush of air when you break the seal. The end of the vacuum pipe that plugs into the booster should have a plastic (one way) valve to stop air getting back into the booster chamber. Manifold sucks the air out of the chamber, valve blocks air going back in. Check hose for cracks, replace (with correct hose) if in doubt, and use hose clamps. Check also the big rubber seal on the booster body that the valve plugs into and replace if perished.
Dino

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Over 1,000,000Km, but now my retirement restoration project

with the engine off put your foot on the brake pedal, crank over and start the engine, if the pedal doesn't go down it's faulty.

Thanks Dino. I haven't noticed any air escaping when the valve is removed from the booster but will check again tonight.

When idling, put your foot on the brake pedal. If revs increase, there is a faulty valve on the brake booster or a leak in the hose from manifold. Took me months to work out what was going on, replaced the valve (and the rubber grommet around it) and all was fine.

Yeah I have done this and it does drop as it should. Maybe its not holding the vacuuum so not operating all the time. Not sure ??

Is it normal that the engine stalls when I clamp off the booster hose while the engine is running? I'm guessing that its getting air through the booster and when I cut this air off it stalls cause the mixture is then way to rich.

While idling if I push hard on the brake and hold the revs drop and it stalls or nearly stalls. Will check out the valve and seal though as the plastic valve looks a bit dodgey.

If your engine stalls due to not getting enough air because you blocked the vacumn hose then there is something wrong with the brake booster I would say. A properly working brake booster shouldn't be the source of vacumn leaks (this might be the reason why your brakes aren't as good as they should be) the booster might be providing some assistance but not enough.

Just out of interest what happens if you block off the vent on the brake booster? This might tell you if the vacumn leak is coming through the booster.

I am guessing...

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Roads need more corners
A Deluxe(CG13DE), 2 Clubbies(998 and 1275) and 2 Morris 1100Ss

Just out of interest what happens if you block off the vent on the brake booster? This might tell you if the vacumn leak is coming through the booster.

Will try tonight and see what happens. Thanks.

How did you check for manifld or vacuum leaks? Run the car at idle and slowly pour water over the manifold gasket face and every other vacuum hose & connection. If the motor changes speed then you have found a leak.

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Chris

Everything I like is either
illegal, immoral or fattening.

The bit about the engine nearly stalling when you brake hard is interesting a while back I was trying to work out how brake boosters work I found an article on www.howstuffworks.com anyway it goes like this from memory;
the vacumn from the manifold creates a vacumn on both sides of the diaphram (diaphram is neutral providing effort niether way) whilst the pedal is up (there is a valve that is open between the two) as you brake this valve closes and there is a valve that lets air into the back of the booster which opens this new air (under pressure compared to th front chamber) pushes the diapham forward helping the braking effort. As the pedal is let off the valve between the two sides allows the pressure to equalize and the valve to the outside is closed. The inlet manifold vacumn is then used to restore the initial level of vacumn.

Ok so if the engine is getting extra air through the booster when the valve between the two sides of the diapham is open then when the pedal is pushed the valve is closed and the engine is starved of air but it does sort of help with the braking effort. Maybe this is it but then I don't know. So that would mean that the valve which is supposed to open when you put you foot down to let air into the back of the booster is staying open causing the leak but the leak stops when you brake.

Ok enough of my thinking out loud I have to do real work for a bit now

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Roads need more corners
A Deluxe(CG13DE), 2 Clubbies(998 and 1275) and 2 Morris 1100Ss

Ok thanks for the replies. I checked it out again last nigt and found that I am getting constant suction through the booster filter. So I am getting a constant air leak through the booster which is screwing with my carbie mixture and brakes. I also found that the Haynes manual has a fairly simple discription of how a booster works and the BMC/Leyland manual has a pretty complex description.

So I guess I will be removing the booster for the time being which will at least free up some much needed engine bay space.

G'Day Mini68,
<<snip>>"Haynes manual has a fairly simple discription of how a booster works and the BMC/Leyland manual has a pretty complex description."
Weellll, the old BMC manual has a much simpler description for doing work on your motor....
1) Remove Engine.

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Over 1,000,000Km, but now my retirement restoration project