Rebuild brake cyclinder but i'm cheap.

[bjamesw]

It's in very good condition with low miles and changed the fluid every three years or so.   But it's developed "the drip".   There's always a dribble hanging off of the bottom and it gets on the paint and irritates me.

I'd like to remove the piston and plunger and oring, clean everything up spic and span,  carefully hone the barrel, and replace the plunger and oring for about 10 to 15 dollars in parts.   Possible?   Are these parts sold separately anywhere?

Anyone know of suitable off-the-shelf replacment plungers that will fit and oring, perhaps from a honda or kaw that uses the same size piston and plunger, has these parts in stock, probably fresher rubber, at quite likely 10 to 15 dollars or less?

Thanks
 Brad W

[georgesgiralt]

Hello Brad,
the repair kit is available as is the O ring between the bowl and the cylinder;
I can't tell the price, but IMHO, you should no go cheap on brakes. you may pay with your life .....
I've done the rebuild a couple of months ago and it was easy and very effective.  
Have a look at a BMW dealer or at Motobins.

[bruce_launceston]

I was unable to source universal brake parts in these small sizes.
At least with the genuine you know the parts will fit.

I have honed my cylinder twice, I used 1200 grit wet and dry paper wrapped around a timber dowell. Dont hone longitudinally, use rotational honing only and it should be okay as long as you don't have serious pitting.
Be sure to clean out the tiny fluid return hole while you have the reservoir off the cylinder.

[Bob_Roller]

If the master cylinder bore isn't pitted too badly, it can be cleaned up easily, I used a hardwood dowel, cut a notch in one end and used some scotchbrite type material to clean up the bore .

The master cylinder can be difficult to get removed from the handlebar 'perch' casting, there usually is corrosion in there .

[montmil]

Like I keep telling Crenshaw over n' over... I'm frugal, not cheap.

Us Airheads like to keep things simple.
Wooden dowel as an overhaul tool? I'm so there.

[Julio A.]

My master cylinder is really badly pitted and leaks like there no tomorrow. I tried Bruce's suggestion of using really fine grit sandpaper(I used 2000 grit) wrapped around a dowel(or a screwdriver in my case). I was sanding it wet for that extra smooth finish. It took me a around half an hour of rotating the thing inside the cylinder since I got carried away while watching a movie. When I re-installed the thing back on, it got fixed and never leaked. That was two and a half months ago. Until now, it's still not leaking. Mind you, that was a badly corroded master cylinder. It still had those pits on it but apparently, when properly bled, I think the piston never goes far enough t contact those bumps.

[tvrla]

I've heard there's a honda seal (maybe the front one?) that will work. It's been a month or two since I saw that, and would like to find it again myself. Master cylinders aren't rocket science, but on the other hand, it's gotta work or it's big trouble!

I've also had good luck cleaning the bores and leaving the pits, with no leaks and pressurizes just fine.

[bjamesw]

Sorry.   I agree that lives depend on these things, but I'm also a confident enough mechanic that I trust the limits of my skills.   Otherwise I'd defer just about everything that my life depends upon, including most drivetrain repairs (they can lock up too at highway speeds), brake repairs,  wheel removal and installation,  handlebar removal installation, steering bearing removal, installation and adjustment, etc, etc.  I feel very comfortable in my judgement as to where I can get by 'cheaply', or in the case of a 100 dollar "rebuild" for a couple of master cylinder parts which I was hoping someone had sourced more cheaply.  

This is a Magura 12 or 13 mm brake master cylinder.  Difficult to imagine that internal part is BMW proprietary sized.    If BMW does not supply the rubber replacement plunger as a separate item then I imagine another manufacturer must.  And it's likely to have been sitting on the shelf for less time.   

It's been 20 years since I rebuilt this thing, replacing at that time the entire piston/plunger/rubber itself instead of just the lipped rubber. Is that lipped rubber piston seal a removeable item?

All that can possibly leak in this system is that rubber plunger ring and the oring on the plastic cup.   With a good careful cleaning and honing this needn't be more than a 10 to 15 dollar cost in fresh parts.  

[Bob_Roller]

They are available, but in most cases, you need to order 500-1000 units and most wholesalers won't sell to private individuals, you need to be a credible business with a tax ID number .

I did some research a few years ago and that's what I came up with .

[Barry]

I agree with the basic point that bjamesw is making here. This is simple hydraulics not rocket science. Yes you have to use a proper brake seal part made of the correct rubber but if I could find a generic one that worked I'd use it. A generic part of the correct dimensions is not likely to fail in short order just because it isn't the original.  It's perhaps more common to find generic caliper piston seals which are even simpler square section seals but there are certainly generic suppliers of  master cylinder seals for most Japanese bikes so it can be done

Once upon a time you would take the old part to a local brake specialist and they would route through their stock and find something that fitted. Not so many places that will do this for you now.

[tvrla]

I remember back in the 60s going to the auto parts store and buying brake parts - they had boxes of different size seals and cups for wheel cylinders and masters. They'd look at your 3/4" cylinder and give you the parts needed. I find it completely ludicrous we have to spend $50 for a rebuild kit that has one little piston with seals and maybe an o-ring.

[georgesgiralt]

Ah !
this period is long gone. Your seller has, now, to secure the security of your ride with the parts he sold to you. so, in order to avoid the layers, he sticks to the sealed and stamped and pricey parts certified to fit.
Otherwise you can sue him and ask all his money and some of it's son and grandson's....

[fbenach]

It might be useful for the rest of the folks in the forum if you get the chance to take some photos of the process... I can´t imagine how the insides of the master cylinder look like!!

Good luck!!

[tvrla]

I agree George! It's not only the lawyers, judicial system, attorneys and laws that brought this all about, but probably the main reason is people unwilling to be responsible for their own actions. The ones who claim 'it's someone else's fault' and get rich off of that. Insurance companies aid and abet the situation.

Yeah, those days are long gone when we could buy inexpensive generic brake parts from the auto supply. Somebody got rich and it wasn't me - I'm getting poorer having to pay these high prices...

[bruce_launceston]

I recall seeing Brembo brake rubbers separately (or in kits without the piston) when I was searching on the net for ducati brake parts and thinking that they may have fitted the R65 master cylinder.
I don't appear to have bookmarked any sites so try the googlemonster!