So, after finally getting chance to take a look at my leaky front master cylinder, I discovered a couple of things.

1. It's a bit leakier than I thought 
2. Some of the small phillips head screws are actually made of soft cheese.

I'm pretty sure I need to order of one these...

Master Cylinder Repair Kit BMW K1100 R1100 RT GS R BMW No:32722332037 | eBay

Here's how it's looking so far...







My Clymer manual (page 638) tells me to 'Loosen and remove the brake lever mounting pin'.


How (what tool) do I remove this pin?...

Interesting. That should be a slot head, not (what appears to be) a torx head. Give it a good scrub and take another look with a torch. As for the screws: to really screw (!! ) things up, there are three X-shaped heads - crosshead, Phillips and JIS (Japanese Industrial Standard). I haven't had a standard m/c on either of my bikes for a while now, but I'm guessing you may have been trying to use a Phillips screwdriver in a crosshead screw (or the other way round) so the screwdriver kept camming out (spelling is correct! ).

Hi Dai,

Yes, I was trying a phillips head driver (actually a rather wonderful King Dick 1 for 6) and thought I had a real good connection with the screw, alas it was seemingly welded in and so the head is now history 

And the mounting pin looks right against the Clymer book...



..but I haven't got anything that will marry up with that either  

All in all, pretty poor day regarding getting the brake sorted 

That diagram still looks like a Torx head, but I would go with an allen bolt theory - at least, until your torch proves me wrong tomorrow!

According to Anton Largiader, we're looking at a 5mm hexhead socket screw. He explains the removal procedure at this link in Step 6. He's working on an R1100 but the pivot pin part number is the same on both the K1100 and the R1100. Don't neglect using penetrant and heat.

Laitch wrote:According to Anton Largiader, we're looking at a 5mm hexhead socket screw. He explains the removal procedure at this link in Step 6. He's working on an R1100 but the pivot pin part number is the same on both the K1100 and the R1100. Don't neglect using penetrant and heat.

Ooh, great link Laitch, cheers 

5mm Allen. Even when it gets to the end of the threads it is still difficult to remove which Anton alludes to in his write-up.

I wouldn't be in the least surprised if BMW put that damn red Loctite on that screw.  I know I had a heck of a time getting mine out.

Point-Seven-five wrote:I wouldn't be in the least surprised if BMW put that damn red Loctite on that screw.  I know I had a heck of a time getting mine out.

Blue

A mechanic's trick for unscrewing a stripped Allen head is to pound a Torx bit into it.

Thanks Laitch & Duck. 5mm it indeed was, and it came out without issue -for once 





More to come.

Yep, we're in a better place today - many thanks to the link to Anton's instructions.

With a little compressed air, the piston popped out...




..and a clean up got ride of the dried up debri ready for the new boot...





Anton mentions that the rebuild kit: 32 72 2 332 037 doesn't come with the boot, but looking at the Motorworks eBay link in my first post suggests it does 

Judging from the way the exterior of the master cylinder looks, I would guess that a rebuild kit is going to be a waste of money, and will only make the final cost for making the front brakes work that much higher. 

No need to ask me how I know this,  I was down this road before...

...Twice.  

K75 rear master cylinder and a K100 front master cylinder.  They are made out of the shittiest pot metal I have ever seen.  The new front master cylinder I installed appears to have an anodized bore that might help prevent corrosion.

Point-Seven-five wrote:They are made out of the shittiest pot metal I have ever seen. 

You should have see the pot metal of the S&W Model 3 topbreak cap gun I had in fourth grade. I didn't realize it then but the quality was a ripoff.   It fell out of its holster on a wild downhill bicycle run while I was chasing bandits and broke up on the pavement. A melee ensued, followed by lemonade.

Point-Seven-five wrote:Judging from the way the exterior of the master cylinder looks, I would guess that a rebuild kit is going to be a waste of money, and will only make the final cost for making the front brakes work that much higher. 

No need to ask me how I know this,  I was down this road before...

...Twice.  

K75 rear master cylinder and a K100 front master cylinder.  They are made out of the shittiest pot metal I have ever seen.  The new front master cylinder I installed appears to have an anodized bore that might help prevent corrosion.

The bore has actually cleaned up ok, but I appreciate the benefit of your experience.

Which new front master cylinder did you replace it with?

I think the original master cylinders were made from recycled 1950's vintage Made in Japan cap pistols alloyed with old beer cans.  Laitch's old S&W may now be stopping someone's brick.  

I got my replacement Master cylinder from EuroMotoElctrics in Denver.  I'm sure that the big aftermarket guys in the U.K. will have what you need.

Point-Seven-five wrote:I got my replacement Master cylinder from EuroMotoElctrics in Denver.  I'm sure that the big aftermarket guys in the U.K. will have what you need.

I wasn't sure if you meant you opted for a completely different aftermarket m/c or one of the 'originals' like this ...

Master cylinder front: Brake master cylinder (james-sherlock.co.uk)

For the front I wanted something that was compatible with the throttle and the combination switch so I opted for the OEM replacement.

There's no aftermarket m/c unless you're willing to throw away all of the OEM stuff, fit something Japanese that's suitable and redo part of the wiring loom. You also need to change the indicator relay and make a couple of new cables (throttle, clutch and fast idle). Okay, three cables.

Yes, I've done it . See here: https://www.k100-forum.com/t10150-wiring-in-non-bmw-handlebar-switches. In addition to what I have written there, there is no reason why you can't use (say) left and right switches from pretty much any Japanese bike or any of the new Brit bikes. If you peruse ebay carefully you'll find many of the l/h switches have a built-in fast-idle lever. Currently Low Flying Brick has a Suzuki SV650 l/h switch with a Bandit 600 clutch lever and a Triump Sprint r/h switch with a m/c that came from a Guzzi California 1100. The majority of the world's motorcycles are fitted with switches made by Domino in Italy; the casings and the switch shapes might be slightly different fron m/fer to m/fer, but once you take the buggers apart they are the same on the inside.

[Edit] I'll give you another reason why you may not want to do this. Most Domino switches (and Chinese knock-offs thereof) are held in place with a peg that locates into a hole in the handlebars, so you'd need to decide the switch block angle and then drill the bars to suit. You could just remove the peg, but then you'd need to put a single turn of insulating tape around the bars to take up the difference between the 22mm BMW bars and the 7/8" that everyone else uses.

If you want to change the handlebars for non-BMW, it can be done with a bit of cheating. Buy a pair of handlebar risers and file/sand 0.22mm off the lower side of the riser until it fits the existing OEM risers. Now fit the handlebars of your choice.

Cheers for that Dai.

I'll give the rebuild kit a go at £45, if thats a no go I'll be tempted to call it a day.