Brake Master Cylinder Repair help

[hmsports]

I'm rebuilding my brake master cylinder - Tokiko off a '71. I have all the fittings removed as well as the set screws. My manual doesn't say how to get the pistons out. There's no place to get a grip on it. The only exposed end is a concave cup. Anyone have any suggestions? Should I try to use air like you do for caliper pistons?

Thanks,

Rick

[2ManyZs]

Never did it before, but by the diagram in the old service manual the only thing that could be stopping it from coming out is the stopper bolt on the bottom behind the rear reservoir. If this is out I guess the only way to get the piston out to a point you can get a hold of it would be to use a little air pressure in one of the front ports. Good luck.

Quite a bit cheaper to re-build the early master than buying one isn't it? I saw the price of a new one and just about :tapemouth

[hmsports]

I think I could probably upgrade to a newer master, but figured... "hey, how hard can it be to bebuild one". The end had some corrosion/rust which I was able to scrape off. All the stop bolts have been removed. I'll shine a light into the hole the see if I can get a bit of hard rod (I have some dental tools) and pry it a tiny bit. I'm not sure if its rusted in or not - don't know how much air pressure it will take - or if it will work. Who needs brakes anyway...

Thanks for responding, 2Many.

Rick

[hmsports]

Ok, so I went out and tried to pry it - no good. At this point... out comes the BFH. I figured that the pedal presses on the concave end - so I took a 12" long 3/8" rod and whacked it a few times into the piston. That loosened it from the rusted up groadie end. A few squirts of miracle oil and then I just pressed down using the rod and then quickly removed the rod. After several times, the piston jumped out the end - well, at least the first half. The second part is still way in there. I'm letting it soak overnight and will try some other means of gentle persuasion tomorrow.

[hmsports]

I finally got things figured out. I'm buying a replacement for a 1972 (at $36.00) installing it and reversing the two lines so the larger resevoir will coorespond to the front brakes as it should.

[EScanlon]

Hey Rick:

This may be totally a moot point, but check the microfiche if you have it, if not check for when the change was in the brake system.

I seem to recall a conversation regarding the change from one year to the next where the brake master cylinder went from servicing the front half of the brake system with the REAR half of the cylinder to servicing it from the FRONT half. This may be the situation you are looking at.

I'll have to do some research, but I'm pretty sure that it was right in the 71-73 era.

2¢

[hmsports]

This is exactly what the problem is. The 72 and later has the front/rear resevoirs reversed from the 70-71. The 70-71 replacement master cylinder is $150 - if you can find it. I purchased the rebuild kit but the rear (front) piston assembly won't come out of the bore. And I think the bore is a bit pitted so the core probably isn't usable anyway. A 72 and later master cylinder is only $36 from the local auto parts store. All I need to do is run the original lines in my 71 to the correct ports on the new master. Since I'm not concerned with originality of the car, this won't be a problem.

I appreciate your 2 cents tough... that's what makes this a great club!

[hmsports]

It took about 30 minutes, but I got the new 72 master installed. All I did was swap the two lines that go from the master to the splitter. The only modification I had to do was bend the front line a bit to meet the new master. Now I only have to rebuild the calipers and replace the driver's side wheel cylinder and the brake system is ready to go.

[DeMoore]

Reviving and old thread here...

I'm rebuilding the BMC on my 78 and I'm having the same problem as Rick, the second piston doesn't want to come out. I removed the bleeder screw, so there shouldn't be anything stopping the piston from coming out. Also, the big screw caps on the bottom don't want to come off either. How much torque can I apply trying to get them off before the cylinder breaks?

[Bonzi Lon]

The big screw caps ARE torqued on there. I finally got them off by carefully chucking the MC in a large vice and used a crescent wrench (all I had that large) and a 3 foot cheater pipe, slowly pulling until they broke loose, they are on there.

I appologize for the hijack to ask...Should the copper washer (under the cap) be replaced or annealed before reassembly? What is the torque on these caps?

Bonzi Lon

[sblake01]

According to the FSM, the torque is 2.9-3.6 ft-lb. It say to replace the washers if they are damaged, worn, weak, or expanded.

[Bonzi Lon]

They were on there a whole lot tighter than that. Do you agree with that, DeMoore?

Thats why I asked about the copper washer thinking it had its "soft" squished out of it and needed to be replaced or annealed to put the "soft" back in for a good seal. Put it back together but not 'nearly' as tight as it was, but tight. After sitting over 6 months there appears to be some weepage. The whole brake and clutch systems will be gone through and flushed within a week. Interior, exhaust, minor electrical, engine broke in and a few other things before Branson.

Bonzi Lon