R100RS rear master cylinder

[SteveD]

I have a spare that I want to pull apart and see if I can clean it up.
I have it dismantled as far as I can go, but the master cylinder bits are still in the bore. Do I just put something like a drill bit thru the hole at one end and tap the bits out via the other end?

[ME 109]

Do I just put something like a drill bit thru the hole at one end and tap the bits out via the other end?

I'm starting to have an effect on people.....

I've never pulled my rear mc apart, but surely there must be a circlip or sumpin'?

[SteveD]

Can't see one. At one end is a hole at the bottom of the threaded bit that the steel line attaches to. The other end is the plunger end, and all I can see down there is what looks like a seal.

[Deleted User 62]

Did you try compressed air?

[SteveD]

Did you try compressed air?

Good idea. I gave that a shot...it worked. It did enough to move the assembly to a point where I was happy to then push it out. I used a piece of stiff wire, like an old coat hanger. It's just held in via a push fit, two scraper seals along the shaft of the device. No circlip.

rearbrakemc.jpg (156.81 KiB) Viewed 1132 times

mcassembly.jpg (109.94 KiB) Viewed 1132 times

[SteveD]

Mine is missing the top hat spacer from the first picture. Were they discontinued at some stage I wonder? According to the maxfiche, nope. It seems the top hat spacer is included in both the 15mm and the 14mm master cylinder. Mine has a different shape to the shaft too.

[Jean]

Just (past winter) rebuilt the rear MC on my '78 R100s. All the parts shown in the first pic were needed, "top hat" bumper also.
It was hard to get the insides out of the body tho, I had to give it a good hard knock with a length of rod to break it loose as the steel ring was rusty around the edges and was stuck tight. Lots of cleaning-up to do during the rebuild job, but the insides were not scored!!
Bleeding the system was the biggest pain.

[SteveD]

The bleed of the rear setup is often complained about, as is the usefulness of the brake.
Many talk about removing the caliper and moving it around so that the nipple is uppermost.

However, there is no need to remove it to get the nipple uppermost. All that's needed is to undo two fasteners.
1. The nut/bolt at the torque arm
2. The axle tightening nut/bolt at the left end of the swingarm, caliper side.

Once the torque arm is disconnected and the other one is loose and the hydraulic line is released from the plastic retaining clip (if it's still there), the caliper can be swung with the nipples at 11-12 o'clock and the job done a little easier.

I've always used the syringe/tube retrograde fill method to replace the brake fluid. I find it easy and it also flushes junk into the reservoir for easy removal. BUT, last week I got lazy and installed some spring loaded bleed nipples, or speedbleeders. Too bloody easy by far. https://www.speedbleeder.com

[SteveD]

Do I just put something like a drill bit thru the hole at one end and tap the bits out via the other end?

I'm starting to have an effect on people.....

I've never pulled my rear mc apart, but surely there must be a circlip or sumpin'?

I think it's safe to do it that way as any tool shoved in there is within the spring, preventing scoring of the bore.

[SteveD]

Notice the difference in the design of the shaft. The second one is the replacement from MaxBMW. Can anyone see why it would be redesigned?