reboring/resleeving brake master cylinder

Brad William /

I posted this on a machinists forum and got a bit of flame for suggesting that I might accomplish this myself with meager tooling.

I suspect we have a few more diehard diy types here so any advice would be welcomed.

The handlebar master cylinder of my '84 650 bmw is cast aluminum.

The bore is simply that. Not sleeved. It's gone through one rebuild already. Lasted a couple of years. I suspect the aluminum bore is corroded and pitted enough to make short work of a new set of seals. So I'd like to see, before I spring for 200 dollars to replace the cylinder, if I might resleeve it myself.

It's a 13mm bore presently. If I can rebore to 16mm (slightly over) I could insert and epoxy (or green Loctite)

PSM1216-12 12.05 (id) 16.04 (od) $11.09

Or similarly had dimensional linear bearing stock from online. 12mm piston/seal rebuild kits are easily and cheaply had online.

The toughest part, it would seem, is mapping and drilling the ports precisely enough.

Otherwise, I don't see the difficulty. Anyone done this? (edited)


Re: reboring/resleeving brake master cylinder

So now this is vintage motorcycle army?

Re: reboring/resleeving brake master cylinder

I tried this with some old grilling master cylinders for a formula ford and found it cheaper to buy new, just too dam much work to make it feasible.

Re: reboring/resleeving brake master cylinder

I read your entire thread on the Practical Machinist site. I think you got some real good advice there. Then your next step is to ask the same questions on a moped repair site?

Re: reboring/resleeving brake master cylinder

Brad William /

Sorry. This really should have been in off topic.

But it never fails to amuse me that even the most innocuous questions put out on the web can attract useless and unnecessary hostility. I'm not an expert machinist, so a little blowback from the pros at PM I was ready for. But even there, since you read the thread, you'll note that there was about 2 percent real nuts and bolts advice on, literally, how to do this, two percent other options, an 96 percent useless wrist slapping nonsense, social commentary, irrelevant sarcasm, and most disappointingly, forum infighting having nothing at all to do with me or my question.

You really have to wonder sometimes what percentage of all forums "netizens" are mostly in it for the trolling, plain and simple.

So I came over here in the hope that fewer pros, more diy'ers with less professional pride on the line, might be more open to how-to-get-this-done, and less needless commentary.

Oh well... at least there's consistency.

Re: reboring/resleeving brake master cylinder

Why sleeve it ? The OE was simply bored , correct?

Then why not do the same and adjust internals to match ? (edited)

Re: reboring/resleeving brake master cylinder

Brad William /

> P D Wrote:

> -------------------------------------------------------

> Why sleeve it ? The OE was simply bored , correct?


> Then why not do the same and adjust internals to match ?

That is the potential beauty of resleeving. I could never, without a precision lathe $$$$$$$, or professional shop service $$$$$$$$, achieve an accurate enough bore to run a new piston into. Resleeving does not require such accuracy. The sleeve arrives in the mail with a perfect bore id. All I need to do is drill the cylinder for a reasonably good slip fit, and epoxy the sleeve in.

I'm beginning to understand the limits of this, but it took an awful lot of oddly hurt feelings and useless temper tantrums to get there.

Primarily there's the option to get a new cylinder, reservoir, piston, for 200usd. That's a tempting breaking point to avoid the machining.

I was really hoping that someone having done this would just, simply, said this is how to do it. This is how you locate/drill the little ports, this is how you polish the ports afterward.

I'd be really surprised if it were the case that any of this is really beyond an amateur with basic shop tools and a dremel in just a few steps.

Go ahead. Someone's bound to feel hurt and need to vent something to no good purpose at all. It's like a strange background noise that can't be avoided:)) (edited)

Re: reboring/resleeving brake master cylinder

Dirty30 Dillon /

Seems like you've probably been about the website long enough to understand the climate, so the diatribe mostly falls flat.

In this case, you're buying a component for a vintage European (collectable one at that) motorcycle, and one that is pretty crucial for operating said vehicle safely. I suggest spending $200 and 0 hours of headache time, over ~$60-80 and hours of time and a potential doorstop that could very well fail under actual loaded pressure.

Re: reboring/resleeving brake master cylinder

All this based on not knowing whether or not the cylinder in question is actually bad .

So what it the new seals only last a couple of years . Pretty cheap compared to 200 bucks .

Re: reboring/resleeving brake master cylinder

Blaine- The artist formerly known as Plumber Crack "(OFMC)" /

I’d skip the sleeve for now, poke a hone in it and see just how bad the pitting is. If a little over-honing is required to remove the majority of to pitting, the cups won’t mind.

Just keep in mind where the majority of cup travel will be. I wouldn’t be concerned about pits that are deep in the bore.

I avoid even using the front brake like the plague, so it wouldn’t bother me a bit, but that’s me.

« Go to Topics — end of thread

Want to post in this forum? We'd love to have you join the discussion, but first:

Login or Create Account