Thread: Brake booster problem

All good info. No complaint from me.

ok Ive done some more work to try to fix the problem - not solved yet.

On the booster where the vac hose connects is a filter/one way valve. It was restricted so cleaned that up with turps and is a lot better now.

Ive also applied vacuum to booster and it seems to suck ok but will not allow air in. Im assuming there must be a one way valve in there too somewhere. The vacuum flow is not as good as the outside one way valve but seems ok. Also, air going out of the booster but not in suggests to me the diaphragm is probably ok.

I havent removed the booster to check/clean the inside filter/valve as it seems ok. Also, I looks like a painful job to get it off. Does removing the booster involve removing the pedal box, and then removing the pedal?
Alternatively, if I unbolt the booster will it come away from the pedal box enough to check the inside breather?

Assuming the inside breather is not the problem, any further suggestions about where the problem could be?

thanks

Easy job to get the booster off mate. Unbolt the MC and carefully move it forward off the booster (with all brake lines attached). Take the two plastic grommets on each sides of the pedal box off and you will see a pin joining the booster fork to the pedal shaft. There is a split pin on one side of this pin, usually the inside, take it out (long nosed pliers) then you can remove the connecting pin. Hey presto, booster is disconnected. Undo the 3 bolts connecting it to the pedal box and it will come out. One hint, when you sort out the problem and put it back in smear the area where the MC fits into it with never seize also the end of the MC. Every one I have changed has been rusty in both areas.

Originally Posted by rar110

ok Ive done some more work to try to fix the problem - not solved yet.

On the booster where the vac hose connects is a filter/one way valve. It was restricted so cleaned that up with turps and is a lot better now.

Ive also applied vacuum to booster and it seems to suck ok but will not allow air in. Im assuming there must be a one way valve in there too somewhere. The vacuum flow is not as good as the outside one way valve but seems ok. Also, air going out of the booster but not in suggests to me the diaphragm is probably ok.

I havent removed the booster to check/clean the inside filter/valve as it seems ok. Also, I looks like a painful job to get it off. Does removing the booster involve removing the pedal box, and then removing the pedal?
Alternatively, if I unbolt the booster will it come away from the pedal box enough to check the inside breather?

Assuming the inside breather is not the problem, any further suggestions about where the problem could be?

thanks

the parts most likely in question from wrinklearthurs post are

the poppet (and retainter) the valve plunger and the reaction disc

the silencers can also be collapsed.

The poppet valve is really 2 valves in one...

in the closed position it opens the section closest to the driver to the low pressure area closest to the master cylinder while closing off the access to the inlet in the center.

then when you put the brakes on it closes off the port between the two chambers and opens up the center air inlet to the chamber closest to the driver this is what provides the assist, the air pushing on the plate in the middle

when its in balance all the ports are closed, when you release the pedal it returns to the closed position and the big spring pushes everything back.

thanks Brian & Dave,

I'll have a go at this tomorrow. I was kind of hoping I didnt have to get in behind the grommets. Only 4 mths ago I installed a ARB compressor to the driver side of the pedal box. So there is not much room to get into that space. I took the MC off today, just as you described, to clean the valve attached to the outside of the booster. I noticed the MC is leaking behind where it bolts to the booster, despite a rebuild only 4 or 5 months ago.

I cant think of anything else it could be other than the valves behind the booster.

regards

pete

if brake fluid has gotten onto the reaction disc it can stick and prevent the poppet valve from functioning correctly.

just occasionally they fail in the apply position so the brakes come on as soon as the engine starts.

I've finally got back to this job. I've ended up taking out the pedal box which made accessing to the split pin much easier. I've taken off the booster, and removed the foam breather filters. I then reconnected the vacuum hose. I can get vacuum assist with one application of pressure, then need to wait for vacuum to build again. Does this mean the vacuum pump needs replacing? Also when I removed the booster brake fluid pored out of the hole where the vacuum connects. I rinsed the booster out with water and detergent. Then dried the inside by rinsing with metho. Is brake fluid in the booster likely to affect the booster?

I've reassembled the booster and connected the vacuum again. It doesn't feel like I'm getting any vacuum assist as pedal resistance (mc not connected) is the same whether or not vacuum hose is connected.

I assume that means a problem with the booster or vacuum pump.