changing brake booster

[craigb]

Just looking for advice from anyone who has changed a booster. Grabbed a booster off a wreck to replace my stuffed one yesterday. Easier than I thought to unbolt but harder to actually pull it out (false sense of security that I was there!) Being a wreck, I totally removed the master and dragged the hydraulic lines right out of the way and even then it was a struggle. Any suggestions how to make it easier? Is taking the rubber boot on the pedal side off any assistance do you think? Ideally I would like to leave the master and lines all in place and slip the old out and new in, so if anyone has achieved this feat I am very interested. If the master has to come off and rebleed then so be it.

Also the booster off the wreck has some fluid in it I can see from the hole where the master goes. I assume this is brake fluid from a leaky master. I was going to syringe it out but does anyone see any problems here? I also wondered about testing it by say connecting the vac line to it, start the car and push on the arm to the pedal and listen for hissing like is coming from my stuffed one. I am assuming that I would have to bolt an old master up to it? Does it suck on that side of the diaphragm?

Any help appreciated.

[koan]

I've had my booster out a couple of times, it's out at the moment. I disconnect the vacuum and hydraulic lines (and pedal of course) and lift it out as one bit.

It's a bit of an awkward job, not enough room for it to slide out and lift. A lot easier with a helper as my wife did last time - shock, horror.

Don't think removing the pedal rod boot would help.

The end of the rod coming out the booster has a small dome shaped end piece and a washer. In trying to get the booster in between the firewall and the master cylinder you could dislodge these parts.

The fluid in the chamber shouldn't have done any damage, clean it up as best you can, don't think squirting solvents in to flush it out would be a good idea though.

There always be an initial hiss when the pedal is pushed but it shouldn't be continuous, if it is it suggest the valve on the pedal push rod is stuffed. Take a bit of care installing the booster, I've read that too much off axis force on the push rod can damage the valve.

There's vacuum on both sides of the diaphragm, pushing the pedal opens the valve lets air into the pedal side and the diaphragm moves until the valve closes again.

The big hole where the master cylinder mounts would need to be blocked off for vacuum tests.

Seem to remember there's a lump of foam to quieten the hissing noises.

koan

[craigb]

Thanks Koan, really useful info. Apart from my pedal going hard very quickly, there is a constant loud hiss once you are on the pedal that also makes the engine run rough at idle, so I was guessing there was a big rip in the diaphragm, but from what you are saying, if that was the case it might hiss all the time and more likely to be associated with the valve. Regardless it needs to come out and at $350 for a rebuild or $28 for a 3 month guaranteed item from the wrecker, I will give it a go.

[Papalangi]

Don't forget the O-ring between the master cylinder and booster.  Mine had wandered off somewhere resulting in a rather large vacuum leak.

Michael