Up to 800km on the k75 resurrection.

Brake master cylinder starting to leak, a few drops on the fairing .
My question:
Do these leak from the same spot, a known trouble spot?
Who  has kits for these?
Anyone had good luck just cleaning parts and resembling?

Thoughts welcome

Ps looked at old posts

I had a leak on my 4v K100RS for a couple years.  Finally had to bend over and get a new master cylinder from EuroMotoElectrics.  $400!

I just did a search and it looks like Motobins has what you need for $242CAD. 

https://www.motobins.co.uk/

Don't waste your time and money on a rebuild kit.  Those POS Magura master cylinder castings corrode and can't be reliably serviced.  Like I said, bend over and get a new unit.  It will be cheaper in the long run.

4V master cylinders and 2V master cylinders are not the same.
I agree with the fragility of the 20mm Magura MCs and that it's worth buying a new one before they're unvailable: I've changed one -again- on my K1 sidecar two days ago.
But K75 MCs are different, much cheaper and can easily be rebuilt. Check the piston hole and, if OK, buy a service kit with new piston and seals.

Have you established it's the piston/seal and not the banjo bolt/outlet fitting - or even the o-ringed seal between the reservoir and the master cylinder body?

So you're gonna blow $100+ on a rebuild kit?  To quote Harry Callahan, "so, do you feel lucky?".

My experience with the 4(2 rear and 2 front, 2v and 4v) total garbage master cylinders that BMW puts on their machines is that foolishly trying to rebuild them only wastes valuable time and makes the finished job over a hundred dollars more expensive than if you just went and replaced the sh!t master cylinder in the first place.  I swear the crap alloy they use to make them is eaten for breakfast by DOT 4.

I recall that the last one I got was hard anodized in the bore to prevent the corrosion that destroys the casting and causes the leaks so it appears that after 40 years the rocket surgeons at Magura finally  figured out they had a problem.   So, at least, there is the hope that future owners won't have to replace that master cylinder.

My experience is not so catastrophic.
I've owned many K, since 1991. Maybe 20... and serviced 10 times more.
I still use daily a '86 K75, a '84 K100, a '89 K100LT, they all have their genuine master cylinder.  I never had to worry about master cylinders on the K75 and K100 2V. Yet I have some rebuild kits on a shelf, bought a NOS to a former BMW dealer 10 years ago...and never used them but once on a customer bike.
On the other hand, I had to rebuild then to change the 20mm master cylinder on one of my '92 K1 (never had to on the other one) and I boughy a new MC for my sidecar K100 to cope with the extra caliper.
But, the MC of my '93 K1100LT is fine, so are the MC on my '94 R1100GS and my 99 R1100RT.

So what? Is rebuilding or changing a 25 years old master cylinder a solid proof it is a crap? I don't think so. Most of vehicles won't last so long, neither will their MC.
But, on such old reliables bikes, who cares about replacing every year the brake fluid as recommended?
I think that this explains a lot of MC leaks...

I've had some luck just taking MCs apart and cleaning them. The only cost is time and effort if it doesn't work. If the bore of the master cylinder is pitted or damaged then you need a new or good used one.

Rear master example:
http://www.kbikeparts.com/classickbikes.com/ckb.tech/0.ckb.tech.files/master.leak/master.leak.htm

Regularly changing the fluid will reduce the chance of problems. I put a kit through my front cylinder 20 + years ago and I change my fluid on a regular basis. I changed my rear to a Chinese one March 2017. There was nothing wrong with my rear one but I put a kit in it as a spare, and it is now fitted to Bruces K75. I'd rather change the fluid every 12-18 months than have problems.
Regards Martin.

The various pos did not change the fluid. Was hard to get the lid off ms. I changed the fluid dot4 just after I got it. The leak started a week ago.
I soldier on.

Folllow Duck's post. When you get to end of disassembly, hold the casting up to the light and have a good look down the bore. As he says, you'll spot any corrosion or pitting straight away. The bore should be black anodised; if you can see any silver shiny bits in there then it's almost certainly worn-out toast.

Dai wrote:Folllow Duck's post. When you get to end of disassembly, hold the casting up to the light and have a good look down the bore. As he says, you'll spot any corrosion or pitting straight away. The bore should be black anodised; if you can see any silver shiny bits in there then it's almost certainly worn-out toast.

I've done a several rears and two front 4Vs. All were silver in the bore. Haven't done a 2V front in ages so can't remember.

K1100 front master:

Hmm. Then from what was said above, it's highly possible I was looking at a later one. I'd scrub the post, but it would just confuse the quote.

Although we don't use salt on our roads in QLD I've found it beneficial to pack the entry to the front cylinder with heavy silicone grease. I also pack grease under the rear cylinder boot and redo occasionally. I've never suffered from corrosion around the entry, the grease keeps out the moisture and road crap.
Regards Martin.

Took the bike for a run of 60K this morning. Mc leaked a bit on way out, stopped cleaned area up with rag drove home. No leak!
When home pumped the daylights out of it, no sign of leak at end of cylinder.
When I changed the fluid a while ago the bellows in mc had disintegrated and was bits of the thing floating around in the reservoir, sucked and fished all I could out and bled lines.
I wonder if these rubber bits are what is causing the leak in the seals.
If it starts again will pull it apart.

Just got in from doing another brake bleed. Took out more bellows bits from the reservoir and found some in the clean cup used to catch fluid from the bleed screw on the caliper. Lever very firm ,no visible leaks. Time will tell.

Rain today so opened up master cylinder to have a look see.
Seals looked okay, no cuts but likely worn. Bore is the issue, several long scores. Back on bike will wrap a rag around it to catch the leaking fluid. Will order a new ms from motobin when I get a list off other stuff.
Without this website life in Beemer land would be a torment!

lucki wrote:wrap a rag around it to catch the leaking fluid.

When mine was leaking I folded up some paper towel to fill up the square plastic "cup" that goes underneath it. That caught the leak until I was able to deal with it.

lucki wrote: Will order a new ms from motobin when I get a list off other stuff.
Without this website life in Beemer land would be a torment!

Well, most of the parts are still available from BMW dealers, and usually cheaper than at independant specialists.
Here we don't deal anymore with Motobins since the Brexit because of huge costs of transport and importation.

jbt wrote:Well, most of the parts are still available from BMW dealers, and usually cheaper than at independant specialists.

It appears that BMW N.A. has somewhat different pricing strategies from the European distributors.  

There are very few, if any, parts that can be had from a BMW dealer for less than from independents.  The only one I can think of is the submersible fuel line that goes in the tank.  The last time I checked, the BMW price was approximately the same as on the open market, and in some cases a few cents per foot lower.

I imagine there are many owners like me who only go to the dealer for parts as a last resort.  This is especially true considering the aggressive price increases that have been implemented in the past 10 years on K bike parts.

Point-Seven-five wrote:I imagine there are many owners like me who only go to the dealer for parts as a last resort. 

It's possible that the NA market is different.
In Europe, independant dealers are usually more expensive than BMW dealers.
And , thanks to a long time real life contact, as I have excellent relationship with the spare parts employee at the local BMW shop, I have the biggest discount on parts he can do. 20 to 35%. Plus free urgent order, parts available in 24 hours.
He hates his boss more than he loves me... and he love me a lot!

there is a lot of K parts turning up at british bike jumbles now ? its cheap so may start buying some , the only problem i have ever had with the front master is the po had rounded off the top 3 long screws , easy fix , maybe the seals do not fair as well in hotter countries but in the UK all good so far . great bike , the harley and honda have not moved for weeks 

Please explain "British Bike Jumbles".
Thanks in advance

Organised yard sale. Frequently a very large organised yard sale

In the US Jumble is a newspaper word game:
https://fun.chicagotribune.com/game/tca-jumble-daily

duck wrote:In the US Jumble is a newspaper word game:
https://fun.chicagotribune.com/game/tca-jumble-daily

A "British Bike" Jumble is when you solve it while riding a 1952 Ariel.

or 1950 (the one i have)

Update:
Got new front master cylinder from motobin. From Spalding England to Ontario Canada in 6 days! Amazing, freight was not bad had to pay vat tax at origin and hst this end. Still way cheaper thanmotoradcanada
Fiddled and farted with old one, pointless.
!

When I have purchased from motobins in the past I have not had to pay the VAT or any HST (which is pst and gst in BC). Only paid for the shipping as per the Queen's King's Mail rate and it usually arrived in less than two weeks.

I wanted mail but that option was not given at the checkout stage. I will check the site and ask that question.