Brake master leak. Need advice.

Hey guys,

On my 74 Mazda REPU I replaced the Master cylinder with a rebuilt one (only thing available for the truck) last Spring. Fast forward to a week or so ago, when I was in the garage replacing the now faile clutch master,and slave I notice the brake master is wet around the rear barb of the reservoir. I unscrewed the cap,and sure enough the rear portion of the master cylinder is almost completely empty. I investigated further, and it appears the fluid is seeping out around the underside of the rubber grommet that the reservoir barb is pushed into. For the record the new rebuilt MC didn't come with a new reservoir, so I had to re-use what is probably the factory unit. I then pumped out as much fluid as I could, and removed the reservoir to investigate the rubber grommet and the reservoir barb. I didn't find anything obviously bad with anything, but after putting it all back together the rear is still leaking.

I checked with Rock auto and they don't list a new MC anymore (the one I bought was at AutoZone), but they do list a rebuild service through Cardone. My local NAPA can't get a new or rebuilt one either. Seems getting this part will either prove difficult at best, and impossible at worst. Not what I need for this fun little truck.

I am the type that usually doesn't throw away parts like this so I probably have the factory MC still in the garage somewhere. Should I try using the rubber grommet from that unit in the new MC? Any other suggestions?

Any help would be much appreciated.

Chris

Is the MC itself OK and just the connection between the reservoir and the MC leaking? Or is the reservoir leaking? Either way, it wouldn't hurt to try your old ones. If you're careful, you might not even need to bleed the system.

I bought a brake MC for the Rolla at O'Reilley's. The box had greasy fingerprints on it. I inspected it carefully, looking for signs of it having been installed already, like fluid in the reservoir, etc. Couldn't find anything, so I put it on. It was as bad as the one I replaced. I brought it back and got another one that is working. I think they just sent out the RMA'ed piece of E36 M3 that was laying around the warehouse.

Make your own. Totally affiliated, completely mine:

http://grassrootsmotorsports.com/forum/200x-classifieds/lockheed-master-cylinders-25/44725/page1/

Assuming it's the reservoir that's the problem, if you can't find a replacement that fits you might be able to rig something with a remote reservoir so you don't have to worry about spacing. The BMW 2002 unit should be readily available. It would be a bit more involved, but would allow you to keep the truck on the road.

Dr. Hess wrote: Is the MC itself OK and just the connection between the reservoir and the MC leaking? Or is the reservoir leaking?

Just the connection between the MC and reservior. The reservior looks to be fine,and so does the MC, but they are play nice with each other. I have been told that the reservoir for a 79-80 RX-7 will fit the MC with a lil grunt. I contacted Cardone to see if they had replacement grommets but they don't sell them. I think I may try to find a rebuild kit for this and maybe rebuild my old one. I want to keep this truck on the road.

What about adapting a different vehicle's master cylinder in that matches the same specs as the orginal? Find one with the same cylinder diameter and with front discs and rear drums (if that's the REPU setup). Maybe even call up Wilwood and ask what they have that could fit.

Dr. Hess wrote: If you're careful, you might not even need to bleed the system.

even if you do have to bleed it, 99% of the time when you replace an MC you can just fill it, bench bleed it if you want to and have rubber hoses to fit in the threads, install it, pump the brakes, use brake pedal depressor or friend to hold the pedal down, and crack the lines one by one for a second or two each. repeat and all that stuff.
We have a master cylinder recall at work for imprezas and outbacks, and I've done a couple dozen MC replacements, and this is what I do every time. it takes like 10 minutes and you don't have to get under the car or anything.

Would it be possible to source just a replacement grommet from an industrial supply house?

Good question pigeon. I wouldn't know who would have this, but it may be an option.

Gromet?

I cant find it anywhere but maybe if you go to a mazda dealership who has a parts guy that has been there for a looooong time they will know if you can find one or not lol. I've found caliper kits and wheel cylinder kits, so it's possible.