Resleeving a motorcycle master cylinder

Hello,
I have a 1984 BMW R65. The master cylinder is leaking, for the second time since I've owned it. The little steel piston with rubber seals costs over 100USD. I'm loathe to by a second one so soon. I did polish the barrel before replacing this part. The barrel is just cast aluminum and prone, I think, to typical corrosion that limits the life of the sharp lip on the seals.

I've inquired about reboring and have been told that it's as much or more than the new piston/seals (just the rubber seals themselves are not available). It HAS to be a precision bore which must be done professionally. And then a larger ID piston/seal must be used to match the bore.

This is the part,


I wonder if it's possible for me to order an appropriately sized stainless steel precision sleeve, 11mm ID,

...and redrill the cylinders bore to snug fit the OD of the sleeve on my own drill press. This bore is not critical. Insert sleeve with thin film of appropriate brake fluid/glycol resistant adhesive. Now I have a precision 11mm bore in my part. 11mm pistons/seals are readily available for less than 20 dollars. This would seem to be an excellent, and far more reliable, fix.

Any sound objections to this idea?

Thank you all very much.

The concept is fine,I have done this with clutch slave cylinders, but I don't think your drill press is the proper tool to do it.

I guess that would work but I wouldn't attempt it on a drill press. Are you sure you want to start modifying a critical component? I mean, $100 two times in 35 years seems ok to me.

Lots of options and quite a few companies will do this for you if you don’t have the equipment.

Karps Brake Service-sleeving

https://www.practicalmachinist.com/vb/search.php?searchid=19412752

Brass is typically used for this. Green locktite to secure it. Ream or bore the cylinder
so there is clearance for the locktite., You will need to drill and de-burr all the small
ports inside.

Thank you, thank you, thank you Jim R. Just needed one nod of encouragement. This didn't sound like it was beyond me. And I think a suitably set up drill press ought to do just fine. I have the green Loctite. Hope you won't mind a few followup questions as I go. Basic phosphor bronze bushing stock?
Any other tips or links on how this is accomplished? Are these bores a few thousandths over? Or is it not critical with rubber master cylinder seal lips? Does the ID need to be polished mirror smooth?

No a drill press is not the piece of equipment capable of doing this.

If you don't have a lathe and tooling such as micrometers bore gauges etc it will be cheaper to send it out rather than ruining your core part.

Street said:

No a drill press is not the piece of equipment capable of doing this.

If you don't have a lathe and tooling such as micrometers bore gauges etc it will be cheaper to send it out rather than ruining your core part.

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Street is correct, send it to a specialist. The Co. moton guru suggested is good. I have seen it done with brass but stainless steel is more common. If you do it yourself the 2 little holes you see at the bottom of the reservoir going into the bore are critical, get them right. The first time I heard of it was when I had the Iron 4 piston calipers on my '68 Corvette done in the late 70's. Hemmings always has ads For companies that do it. I have the knowledge and the equipment to do it properly, for what it costs I send it out.

I did a 1975 R75/6 this way. There was a poster here (Joe Rogers) who did these. He suggested
brass. The '75 BMWs use an under-tank master cyl which were made of the worst grade of
cast iron imaginable. I had replaced the rubber cups a few times, each time honing it out with
a ball hone. The bores were inch sized. But they always tore the cups up after a year and I got
tired of rebuilding them.

The brass was thin-walled tubing from Small Parts corp. and while I did fixture the m/c up in the
lathe, no way I could have bored it with a boring bar, as the aspect ratio was pretty deep. I seem
to recall I was able to drill it most of the way, and then reamed up to size. I cut a few shallow
grooves on the OD of the brass tubing to give the locktite something to bit on. Again the tough
part was carefully drilling up the various comp. ports, and deburring them so the burrs would not
tear up the rubber cups.

I think that fix was probably done about 15 years ago, and I've not had to replace the components
since then, and no leakage by.

Because you could call Bobs BMW and purchase a brand new set of master cylinder
and piston/cups you could go out on a limb and try this, even if turns out a disaster you
can recover by buying what you need.

1) you need to find the correct size tubing. If you cannot get the ID at the correct final size, no way will
you be able to size it without a lathe. Real tough. You also need to use the exact same size bore
because if you change that, the brake action will be considerably modified. Probably bad.

2) best if you can find a tubing with an OD that permits reaming to size, and you need to get that reamer.
Because the older cast iron m/c was inch sized, it was an easy fix for me. You might not be that lucky.

I did this because all the NOS master cylinders would be the same crappy castings. It's a known bug for the
under-tank masters. If I could have bought new, good condition replacements, I probably would have done that.
Having a new enough bike that brand new parts are available is actually a nice experience. I recommend new
whenever brake parts are involved.

Good luck whichever way you go.

wsemajb said:

And I think a suitably set up drill press ought to do just fine.

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No, it won't. Why did you even ask if you were going to ignore the advice of the experts here, experts who have done this?

Make no mistake, I read through the responses and NO ONE is encouraging you to do such a high-precision, safety critical job on the wrong machine tool (a drill press).

And when I say safety critical, if it was just you, fine. Go ahead, fabricate a new one with PVC pipe and Elmer's glue using your drill press. Win a Darwin Award. But someone blithely ignoring warnings and doing something dangerous and outside their experience has a way of affecting others.

If you ask a question, it helps if you listen to the answer, and not just to hear the answer you want to hear.

"NO ONE is encouraging you to do such a high-precision, safety critical job on the wrong machine tool (a drill press)."

Well the bike has *two* brakes, eh?

Would help if the real problem with the drill press were detailed - the part needs to be fixtured up quite solidly so
a) the spindle axis is exactly on line with the part being bored, and b) solid so there's no chatter, and c) the speed
needs to be pretty slow if a reamer is in use. Most drill press spindles are not really rigid enough to do a good job.

In my case it was basically just drilling and reaming, but great pains were taken to get the bore of the part in line with the
spindle axis. Which was tough because the assembly could only be clamped off axis which meant a four jaw
chuck, with a pin in the bore to indicate to. Some tweaking to get it right on. I think the reamer was run with the spindle
in back gears, pretty slow, lots of sulfurized cutting oil even though it was cast iron and all.

If he tries it and it winds up bugger-all, it'll be pretty obvious as there will be brake fluid all over. It's a toss up in terms of
cost if a re-sleeve will be cheaper than buying new I suspect. Bob's microfich will cover this part and they'll have
the price right there.

Grrr. Looks like even this part is NLA from Bobs, "hand unit right," or associated parts:

http://store.bobsbmw.com/microfiche...1897&Diagram=3991&Spline=32_0743#availability

It's either 13 or 16 mm bore, so your best bet may indeed be sending out for re-sleeving.

1984 is NOT that old a bike.

Ive done hundreds of resleeves for various brake repair businesses......brass originally,or maybe bronze,....but for some reason the Transport dept here banned all else but hard drawn stainless.......I dont know why......The thinwall stainless is very expensive ,and is only supplied in lengths.........however some of the brake places doing resleeveing are terrible,and leaks between the liner and cylinder are common...........yes,green loctite is used generally.......EDIT....resleeves are often problematic because the transfer and compensating ports(holes) in the new liner are drilled way oversize,and then the rubbers extrude into the sharp edged holes and get cut or abraded........its very difficult to drill the correct sized (tiny) holes in hard stainless,so they go oversize.......I give 90% of master cylinder sleeves a fail for this reason.

john.k said:

Ive done hundreds of resleeves for various brake repair businesses......brass originally,or maybe bronze,....but for some reason the Transport dept here banned all else but hard drawn stainless.......I dont know why......The thinwall stainless is very expensive ,and is only supplied in lengths.........however some of the brake places doing resleeveing are terrible,and leaks between the liner and cylinder are common...........yes,green loctite is used generally.......EDIT....resleeves are often problematic because the transfer and compensating ports(holes) in the new liner are drilled way oversize,and then the rubbers extrude into the sharp edged holes and get cut or abraded........its very difficult to drill the correct sized (tiny) holes in hard stainless,so they go oversize.......I give 90% of master cylinder sleeves a fail for this reason.

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I have not seen leaks but I have seen problems with the holes as I mentioned in my post and pointed out again by john k. jim rosen going on and on about this mythical drill press with back gears and a rigid spindle, maybe he is really talking about a Bridgeport. jim rosen I know you ride, I am amazed by your "bikes have 2 brakes" comment. anyone with any real amount of experience riding knows probably 80-90% of braking is done by the front wheel, the rear mostly being mostly useless.

" maybe he is really talking about a Bridgeport"

Was not clear but "in a four jaw chuck" implied, done in a lathe.
No a drill press will not work.

Bikes do have two independent brake circuits. The guy rides. He understands
the irony of my statement.

Never use the front brakes. You'll flip right over the handlebars..... eh?

moonlight machine said:

anyone with any real amount of experience riding knows probably 80-90% of braking is done by the front wheel, the rear mostly being mostly useless.

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Unless you're running a straight-laced spool 21"er on the front, with an Avon Speedmaster .... or an XR at San Jose

White Post restorations has been the go to for brake cylinder resleeving for decades. don't know if they are still tops, or if all the million dollar ground up concours grade jobs have gotten in the way?

jim rozen said:

" maybe he is really talking about a Bridgeport"

Was not clear but "in a four jaw chuck" implied, done in a lathe.
No a drill press will not work.

Bikes do have two independent brake circuits. The guy rides. He understands
the irony of my statement.

Never use the front brakes. You'll flip right over the handlebars..... eh?

Click to expand...

Never use the front brake and DIE.

When sleeving something like a break component and using green locktite to secure and seal the fit, is it a slip fit or a light interference (pressed) fit? If it is a slip fit what should the clearance be?

moonlight machine said:

Never use the front brake and DIE.

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Hey - you're going to die, I'm going to die. We're all going to. Motorcycles involved, or not....

Using locktite to put in a sleeve like that means you need to have some clearance for the
adhesive. I seem to recall I used around one to two thou on the diameter, this was for
a appx. 5/8 diameter bore.

Again for the OP, your best bet is probably sending this out for repair.