View Full Version : Master Brake Cylinder Question

09-27-2007, 09:35 PM
So, my brakes broke (ha! I'm hilarious). Anyway... We have determined that it's the master cylinder and we're trying to rebuild it. One problem, we can't get the second plunger out. Haynes manual says tap gently to get it out, but even hard whacks haven't done it. We've tried a magnetic tool and that hasn't worked either. It seems to be stuck. Any suggestions?


09-28-2007, 12:20 AM
Take it to a shop where they can use air pressure to blow through the port behind the valve, with the master cylinder large orifice down against a rag on the bench.

09-28-2007, 07:56 AM

09-28-2007, 05:49 PM
That didn't work...

09-28-2007, 06:10 PM
Melissa, if you can get a grease fitting to screw into the brake line port, use a regular grease gun to pump grease in there. It'll free up 99% of stuck pistons. The 1% it won't aren't worth fixing anyway. /bcforum/images/%%GRAEMLIN_URL%%/grin.gif

09-28-2007, 07:33 PM
Okay, what Jeff says would be next. There is another try with the pneumatic.

Does the piston move at all in the cylinder? i.e. can you push it down in the cylinder at all, or shake it at all?

I'm curious if there is some kind of retaining wire clip in the cylinder preventing it from moving out.

If it is entirely frozen, then next step would be to get a bucket of carb cleaner(dip style) usually about 30 for a two gallon size(out here in Hawaii). Soak the mcyl in the carb solvent overnight. Occasionally removing it and tapping on the piston.

If that doesn't do it, then the piston is chemically bonded to the cylinder bore and it's time to send it off to a rebuilder.

09-30-2007, 11:22 PM
Thanks, both of you! We'll try that. We went t the junk yard today to see if we could find one that we could modify to work and we found one off a vw bug that we could play with (a new one is just out of the question price wise) So, worse comes to worst, we'll be modifying that.


10-01-2007, 09:47 PM
Melissa, I can't remember what year your car is. Can you repeat that info and if possible post a picture of the master cylinder?

Before you cross-pollinate your LBC with German parts... keep trying to remove the stuck piston. To adapt the German bits you get into questions of piston diameter and different fitting sizes. It will be easier and safer to stick with Mini parts.

If you're going to consider used, there is an eBay seller from French Canada who can certainly get you a good used Mini part (JC... something). I've bought a few things from him. In the northeast there's also Mad House Minis. They will certainly be able to find a good used part for you.

WOW... talk about timing. Cosimo from Mad House Minis appears to have just joined our forum on 9/28 (see thread about Rover vs. Austin). Cosimo posted this link for their company:

10-02-2007, 08:54 AM
My mini is a 1980. It's a dual line one, but I can't seem to find a picture of it on any of the parts places and my boyfriend has it right now, so I can't take a picture. Could the automatic ones have had a different master cylinder?

Thanks for the link!

10-02-2007, 11:43 AM
Is this it?
Part #GMC227
I'll bet Cosimo can help you out with a good used one.

Is your car an automatic? I don't think the autos use different brake parts.

EDIT: For some reason, the picture link isn't working. When it comes up with file not found... delete off the "https://" bit at the front and hit enter to reload the page. It eventually worked for me after doing that. Otherwise, go to the MiniSpares web site and key in the part number for a complete listing/description.

10-02-2007, 03:58 PM
That looks like the right one. Yeah, I'll ask him.. thanks for the advice!

10-04-2007, 03:57 PM
That mc looks just like the one for the dual-line Midget (1969 & up) but just with a funny resorvior on it. If that is so then there is a snap ring about 3inches deep in there (under the white plastic ring which is also a real pain to remove).
If this is the case I have always just drilled a 1/16" hole in the Delrin (plastic) ring, screwed a small woodscrew into it,pulled it and then used a snap-ring pliers to finish the job.
It is easy after that.
See this site:
https://www.britishcarforum.com/bcforum/u...true#Post246944 (https://www.britishcarforum.com/bcforum/ubbthreads.php?ubb=showflat&Board=18&Number=246944&Searchpage=1&Main=26554&Words=delrin&topic=0&Search=true#Post246944)

10-08-2007, 01:27 PM
While that really seems like the likely answer and was sooo excited when I read your post... it doesn't look like we have those rings in there. :-(

Thanks, though!