master cylinder kit. is this the way to go? quality? price?

[svejkovat]

https://www.google.com/search?q=bmw%20master%20cylinder%20piston%20and%20seal&ie=utf-8&oe=utf-8&client=firefox-b-1-m#vhid=vt%3D16/prds%3DheadlineOfferDocid:-1900357051458229002,imageDocid:12709919062883220781,mno:3,productid:16546387022251322614,pvo:3,pvt:hg,query:Ym13IG1hc3RlciBjeWxpbmRlciBwaXN0b24gYW5kIHNlYWw,rds:,sori:0/vs%3DUG9wdWxhciBwcm9kdWN0cw,0,27&vssid=uvpv-713&piu=ps:16

Burns me up bit that BMW/magura didn't stainless steel sleeve this thing. This is my second seal failure.  I will rehone the barrel this time but I fear that the alum is pitted enough to just eat the seal again.  And these aren't exactly cheap.

[Burt]

For as long as I can remember BMW master cylinder parts have always been expensive.  It gives me more incentive to change the brake fluid regularly. 

[mpe]

I feel your pain. I recently replaced the leaky piston in the master cylinder. Ordered a quality replacement (Magura 13mm) from the local BMW dealer...$120 plus tax! The bike had sat for ten years prior to my purchasing, the piston was stuck in the MC, grabbed the end with visegrips and was able to pull it out. Cleaned it all, sanded the bore with 3000 grip sandpaper, didn't see any pitting and reassembled with the original piston. Fortunately the caliper was good. The brake worked fine but the outer seal on the piston was shot so it dripped externally. 
With the new piston installed the brake works great now, no more drips.

I also replaced the foam floats in the carburetor recently. $40 each but it had to be done. Cut the old floats open, they were probably the originals, strong gasoline smell, they were saturated.

[Bob_Roller]

I just went through this a few weeks ago ,
Flushed the brakes on my ‘82 LS in December last year, by May, the fluid turned dark and brake did not feel right .
Replaced the master cylinder piston all better now .
Had a leaking right carb, replaced the float and float needle problem solved .
I’ve been using Euro Moto Electric for years now .
As was mentioned the cost of $79 for the master cylinder piston ,
They have always been costly, because they can .
I got carb floats for $25 each .
I weighed the new floats before installation, 12 grams .
Never had a scale that could measure these before, so now I have a reference for determining if the floats are  saturated with fuel .

[Tony Smith]

A couple of observations about master cylinders.

BMW parts are absurdly expensive, the more so since the mid 1980s when they stopped selling the seals separately and now only sell built up pistons.

A visit to your local brake cylinder repair shop may lead to a source of individual seals, but BMW chose odd internal diameters just to make things difficult.

Sleeving a master cylinder is not the difficult process it once was. In the past you had to machine carefully to set up a good interference fit between the cylinder and sleeve so as to avoid leaks. Nowadays using modern adhesives from (for example) Loctite, no more than as easy slip fit is required as the adhesives ve will bond the parts together in a way that will never leak.

The hardest part of a resleeve is finding suitable drawn, seamless stainless steel tube. The last time I did a (I think 13mm) I had to buy a 3 metre length of tube, which was a bit excessive. Fortunately I hawked 750mm lengths to local brake and hydraulic shops and managed to defray my costs .

More recently I had a desire to get around BMW's pricing on piston kits - I was rebuilding a 12mm master cylinder.

A look at AliExpress revealed a number of 12mm OD seals in a variety of widths. But the ID was not suitable for the BMW piston.

My solution was to turn my own piston to match the seal IDs. The first piston I made from Delrin and it worked perfectly, the fly in the ointment was that I was not convinced it was rigid enough so I turned a second one from stainless steel.

My piston has now been installed for some time with no leaks and zero problems.

Measuring up the original piston so I could match lengths took a while and I stuffed up a couple of times on the lathe so it all took a bit of time.

But the seals I used cost about 20c each. Go stick your $150 piston kits BMW!

[svejkovat]

Thanks for all the input here y'all.  My real hope has been that someone might have cross referenced a Honda Kawasaki etc piston that worked for 1/3 the price.  But I suppose not.   I'll report on progress.

[svejkovat]

On another note...I just noticed that the original link I referenced in my first post indicates a 15mm plunger.  And the next two listings I discovered for an R65 BMW were also 15mm.  But everyone here is saying 13mm.   (Realizing we're talking about 12.7).

I still need to yank mine apart and measure.  But what of this?   My original cylinder is on a 1984 R65 with single front disk. 

[Bob_Roller]

There is a number cast into the underside of the master cylinder .
Confirm what size you have before ordering.

[Barry]

On another note...I just noticed that the original link I referenced in my first post indicates a 15mm plunger.  And the next two listings I discovered for an R65 BMW were also 15mm.  But everyone here is saying 13mm.   (Realizing we're talking about 12.7).

I still need to yank mine apart and measure.  But what of this?   My original cylinder is on a 1984 R65 with single front disk.

Master cylinders for a single disc were never 15mm or even 13mm after 81. Only the early model with the round master cylinder reservoir was 13mm which changed to 12mm in 81 and that was an improvement.  If you check underneath as Bob suggests and find you have anything different then it's probably off a twin disc bike.

[svejkovat]

Thank you very much all for the input here.  I had a distraction last week but I'm back to the topic at hand.

My bike is an 83/84 into service on Dec 10, 1983.   A single front disc basic R65/5.  The master cylinder is embossed underneath with MAGURA and the number 12 in very prominent digits.

So.  Very well. 

I was able to navigate my way to this exploded view. 

https://www.shopbmwmotorcycles.com/oem-parts/bmw-motorrad-piston-32722302371

With the part number 32722302371 in hand I located some vendors.

My most local dealer,. 150 miles away,  can order it for me at 109.99 USD.
I would like to support them.  However.

This is the best price online from a dealer who actually picks up their phone....
https://www.euromotoelectrics.com/product-p/bmckit371.htm
85 USD shipped for ENDURALAST brand piston only without reservoir seal


And this is from a site in Spain...
https://www.tradeinn.com/motardinn/en/magura-12-mm-bmw-2701415-front-brake-pump-repair-kit/140156888/p
57 USD shipped for MAGURA brand including reservoir seal (if the photos are to be trusted)

I was able to reliably cross reference BMW part # 32722302371 with MAGURA part # 2701415 at three separate European vendors.  So I am confident it's the same part. 


Any further advice?  Has anyone heard of or dealt with tradeinn.cim/motardin?


Saving 28 dollars to order overseas and potentially deal with return charges and non existent phone support.  You'd think that would answer my questions, but I'm a cheap bastard who never seems to learn his lesson.

Anyway...I hope this saves some footwork for anyone researching this topic in the future.

And I'll report back on anything that happens.

[ShutterPilot]

In case you missed it, here's the piston AND seal for $85 from Boxer2Valve:
https://www.boxer2valve.com/master-cylinder-repair-kit-12mm.html

[svejkovat]

Update here.

I ordered and received the Magura part from Spain.   It came a few days earlier than promised.  Genuine part and packaging.   It felt like plastic, by weight, when I first opened the package.  But removing it from the bag i discovered it's black anodized aluminum.   
 

Attached are images of the Magura part.

Also a piston I noticed that shares the dimensions, as best I could tell. It's the rear brake rebuild kit for the Polaris Sportsman ATV.  Multiple vendors online from 10USD to 20USD.  It would be very interesting to just buy one and see... if needed in the future.