tommyt79

My brakes has progressively gotten worse and now they just go to the floor. I blead them to see if I could "just get the air out" but when getting in there I noticed that the Mater Cylinder and the Booster leak/runs out when pedal pressure is applied. The leak is located where the master is mated to the booster. Nowhere else. SO....

Question: do I just replace the master cylinder and reblead the lines? and is there anything that's gonna need to be reset or measured when installing the new master? I know on this one car, (68' 911) I had to "gap" the distance between the upper pedal hammer and the master cyl. piston.
AND do I NEED to bench bleed this before I install?
Thanks eveyone
Is there a sticky for this job?

7t9l82

yes bench bleed. your adjustment will probably be fine. you will need to bleed the entire system. easy half hour job,except bleeding

dgood

Tommy,
there is a sticky up at the top of the page, last of the stickies. very good one also. Bench bleed and then bleed the each line and you are good to go. check your rubber brake lines while you are each brake. they are cheap and this is good time to replace if necessary.

tommyt79

I didn't get any rubber seals or o-ring with this rebuilt master Part store guy said I should use my old one? Or buy a rebuild kit and use that one? is that The way to go? Cause if the seals leaking then what the point of using the old one cause thats probably my source of the leak, right?

LB66383

If you bought a rebuilt master cylinder, complete, then that should be all you need. The seals are internal to the master cylinder. There may be a gasket between the master cylinder and the brake booster, not sure about that. If there is, it needs to be replaced because it's been soaked in brake fluid.

I would recommend replacing the booster while you're at it. I had the same problem as you did on a Camaro, so I replaced the master cylinder. A short time later the booster went bad. I believe it was because of the brake fluid that leaked into it.

tommyt79

Thanks for the info. I'm gonna try and get a booster/master cyl. seal. and see if it works. The booster is stock and I've heard that fluid gets in there and makes it goes bad. Don't know till this weekend when I get home and get it off. oh Joy!

tommyt79

anyone know where to get just the booster/master seal? or how to make one?

noonie

Rebuilt mc don't have a good reputation.
Brand new premium Napa mc is only around 50 bucks.

The rod/master/booster seals don't often fail, nor do the diaphragms.
It may be worth trying it first.
Some booster remanufacturers will sell a seal separately.

Tooonz

I know this is an old post, but I'm at this same junction, How did it work out, did you have to replace the seal? My new master cylinder didn't come with a seal either. And it's only leaking at the back of the master cylinder

Sayfoo

I don't think there is a "seal" between the booster and the mc. Both are sealed internally and just bolt together. You can make a gasket if you'd like. If your mc is leaking out the back, it is bad.
Yes, bench bleed. I had a new mc leak out the back while bench bleeding. Had to return it.
Master cylinders have been a real problem lately. I got fed up with rebuilt units that were bad right out of the box or failed after a few years. I bought a new AC Delco (made in China) a few years ago and it started to bleed down after about a year and 1500 miles. Seems to be a total crap shoot if you get a good one or not.
Make sure that your new mc has the same "dimple" in the rear end. Some are deeper and need a adapter plug or a longer rod in the booster.
I wouldn't change the booster if it is still working. Total pain in the *** to change.

Tooonz

I changed mine out tonight, had a slow leak at the back, found the booster seal in tact with minimal fluid against it, cleaned it up well, repainted the booster, put the new one on, and I bought a new MC not a rebuilt bleed em tomorrow night and now should be good. The old MC initially didn't leak but after replacing all the calipers and bleeding the system real good, the old MC started to let go. Thanks.