K11 Owners Group

[grant93]

Gidday,

I have a 1993 K1100LT, brakes are brakes and bikes are bikes, and maintenance is the key!!

Riding mine the other day in the aussie summer heat I noticed a few very small specks of liquid appear on the right storage compartment lid, I wiped them off while riding along thinking not much of it, then after a while I looked again and a couple more had appeared etc, hmmmmm.

Stopped for lunch and had a closure look and yep it smelt like brake fluid, looked around the handlebar and master cylinder but nothing to obvious, brakes were working fine and lever pressure was good so I just watched and kept an eye on the fluid specks on the return home.

I keep good maintenance on all my bikes, change and flush the brake fluids yearly and keep them running lovely, the brake level was working well and the fluid never drops in the eyeglass so I though nothing of it and also the master cylinder itself always is clean and non leaky etc.

That night I read up on pulling the master cylinder apart and more detailed info on the inner piston and rubbers etc, and the next day I dismantled it to find the condition of the inner piston not what it should be but also I have had the bike for 3 years and not had the internals apart..



Now the rubber seals looked fine to my eye but I may be corrected?? the cylinder bore was still great and very smooth with no markings or corrosion inside, nothing was blocked and no traces of broken rubber pieces anywhere. I cleaned everything very thoroughly and resembled, bled up and flushed out the front and back brakes and the level came up to pressure as it should and was before.

I probably should of brought a new inner piston for $75.00 but I thought it is worth a try to reuse as I have read where they may only need a good clean etc. and hopefully I caught the issue before it got worse and now that I have done it once it is not a big deal to pull apart and replace with new parts in the coming weeks if it does not hold..

So this is well worth a maintenance check one weekend, something that is hidden and forgotten about - Cheers
_________________
Cheers Grant

1994 K1100RS
1981 R100RS
1978 R100RS
1928 Chevrolet tourer

www.montythe1928chevrolet.blogspot.com.au

[jpberens1994K1100RS]

I flush my brake system in the spring after riding a while and in the fall late just as riding season is wrapping up. Brake fluid is cheap. Even the best brake fluid absorbs moisture and that's what is causing the condition you have.
My ride has all new stainless lines as of a few years ago which has helped but I know moisture will still find it's way in.
So flush flush flush some more. As if it's not caught fast enough replacement parts may be needed.
_________________
1993 K1100RS that I'd rather be riding FAST!
2014 Moto Guzzi Norge

[Grunter]

Going on the picture of the master cylinder it is time for a really deep clean. The evident corrosion around the mouth is normal - yes quite normal. I had the same problem twice in 18 months of ownership because I had not cleaned the cylinder properly.

If it isn't cleaned properly, bleeding a brake cylinder can be compromised with detritus left inside the cylinder. You say the cylinder was clean when you checked, but I am certain that if it had been washed out as I described, minute pieces of corrosion will remain. The 1st replacement piston and seal was ruined in the space of 4 months because the work had not been done.

You have to be quite robust cleaning the corrosion and then the inside of the cylinder must be polished. I did this with a felt mop attached to an 8mm rod and fitted to an electric drill run at a slow speed. Using a little bit of metal polish on the mop, 2-3 mins with the drill and felt mop made sure the cylinder was polished like new.

Afterwards thoroughly rinse out the cylinder with brake cleaner, don't skimp on this.

With the new piston, smear the edges of the seals with brake grease (usually silcone based) and the internals of the cylinder liberaly wet with brake fluid insert the piston and complete the assembly, then bleed as normal.
_________________
1997 K1100LT
1994 R1100RS

[grant93]

Gidday,

Ok so my new BMW front master cylinder brake piston showed up in the mail the other day, yes I took the plunge and brought a new one just to be on the safe side.

Yesterday I pulled the front brake apart again and installed the new "black" piston, the old one was brass as you can see by the previous photos but the new one is black (no photo of the new one).

piston goes in, put back together and the brakes will not bleed up, I tired for 30 minutes and nothing, so out came the new piston again and I check things all over and started again..

Piston in and nothing, it just would not bleed up, so I reserved bled it and still nothing, right now I'm starting to get pissed as the brakes ALWAYS bleed up very easily on this bike, ALWAYS...

Out comes the new black piston again and i install the old brass piston back in the master cylinder, bolt it back together and the brakes bled up instantly, now I am getting somewhere back with the old part installed.

Out comes the old brass piston and I compare them side by side on the bench and yes the new black piston is a faction smaller, and when I put it back in the cylinder barrel, it is firm but not snug.
I removed the new piston and then install the old brass piston and it fits really snug in the cylinder barrel.

I ring the Australia BMW dealer where I purchased the piston and they assure me that the black piston is the original colour and 20mm size for the K1100 and that the brass piston is the colour of an after market piston and that the cylinder barrel has been re-sleeved etc. ?? Any thoughts about the brass piston? has anyone else found these over the years.

So now I have the original brass one fitted back in the bike with a new rubber boot fitted, it is not leaking now but was leaking last month as the rubber boot was stuffed also, and that was when I spotted the dots of fluid while riding.

The newly fitted rubber boot will only hold the leaking fluid from the old piston back for so long, then leak again and I need a better fix.

I did not measure the brass piston and I should of but there was very little difference between the two but I could notice it with my eye when side by side.

Just wondering can the two rubber rings on the original brass piston be "upgraded" to new again, is this possible and I just refit it ?? and would a auto braking or clutch business stock this sort of part off the shelf?

Oh the joys of motorcycle ownership..
_________________
Cheers Grant

1994 K1100RS
1981 R100RS
1978 R100RS
1928 Chevrolet tourer

www.montythe1928chevrolet.blogspot.com.au

[Grunter]

As you will have seen, I have a good bit of experience with these parts. I suppose I have changed pistons on 8-9 BMW's of various ages and models and each one was black. I have never seen a brass coloured one.

I would go with what your dealer suggests that it is an after market bit which doesn't quite come up to specification which is why it is leaking.

I still have a spare new one in the garage and will measure it for you to make sure you have the right one.

I'll get back tomorrow.

Just a thought. How old is your bike? I had something similar happen with the brakes on my K1100 after draining the fluid. The flexible hoses to the callipers were shot (they don't last forever} and the pipes were blocked with rubber detritus where the pipes were breaking down. New pipes and the job's sorted.
_________________
1997 K1100LT
1994 R1100RS

[grant93]

Gidday

Hi Grunter and thanks for your time.

I have had the bike for 4 years, all in excellent condition and riding order, brake fluids changed yearly, ABS11 work perfect and the bike stops and pulls up lovely when needed.

I actually goggled searched images of BMW K1100 master cylinder pistons and an imagine of some brass ones showed up, so they are out there in cyber land being used.

Let me know your measurements and I will compare with mine, but I will have to remove the brass one from the MC one night this week..

Chat soon
_________________
Cheers Grant

1994 K1100RS
1981 R100RS
1978 R100RS
1928 Chevrolet tourer

www.montythe1928chevrolet.blogspot.com.au

[Jim]

Grant - a rebuild kit (which is actually for one of the R bikes) is available - same master cylinder as the K. You might want to look into getting a kit.
_________________
Jim
1997 K1100LTSE 94,000 - still has gremlins!
1995 R100RT Classic 16,650 crashed - repaired!
1992 K75RTP 46,000

"We shall not all die, but we shall all be changed."

[Grunter]

I have confirmed with a Motorad dealer here that the rebuild kit piston is always anodised black. Never brass or silvered.

The overall length of the piston is 34.4mm

The width of the piston at the inner end is 18.3mm

The width of the piston at the open end is 19.31mm

I could not measure the overall width of the seals because the lips distorted too easily.

I also checked an old piston, this was the one I had removed 3 months ago and the dimensions were exactly the same as above. I used a vernier gauge so it would be quite easy to check with your pattern brass one and the last genuine one you replaced.
_________________
1997 K1100LT
1994 R1100RS

[grant93]

Gidday

Gunter just so we are on the same page here my by is a K1100LT Built 8th Month 1993 - VIN No. WB1052602R0185103

I just measured both the old brass and new black piston as I pulled it all apart last night.

The measurements are from a digital gauge

New Black Piston
-
Length is 38.2mm
Width at the inner end is 18.06mm
Width at the open end is 19.07mm

Old Brass Piston
Length is 38.2mm
Width at the inner end is 18.7mm
Width at the open end is 20.60mm

Yes the seals are hard to measure also. The only marking on the master cylinder itself are a BMW logo in the side, a number 20, MASURA, Germany.

All seems a little strange
_________________
Cheers Grant

1994 K1100RS
1981 R100RS
1978 R100RS
1928 Chevrolet tourer

www.montythe1928chevrolet.blogspot.com.au

[grant93]

Gidday,

I showed the master cylinder to a local bike shop, the cylinder has been re sleeved so they said and a slightly bigger piston has been machined or matched to it with slightly bigger rubbers.

So now I have to go back to square one and look for a spare original master cylinder of ebay... or keep scratching my head
_________________
Cheers Grant

1994 K1100RS
1981 R100RS
1978 R100RS
1928 Chevrolet tourer

www.montythe1928chevrolet.blogspot.com.au

[grant93]

Gidday

UPDATE - Called by a specialist truck brake shop, showed the bloke the old brass cylinder, rubbers etc. He measured them, got out his old greasy book and matched up some numbers, went out the back and he had one size in stock that fitted like a bum in a bucket, the other size is now on order, here in a few day.

Easy fixer in the end
_________________
Cheers Grant

1994 K1100RS
1981 R100RS
1978 R100RS
1928 Chevrolet tourer

www.montythe1928chevrolet.blogspot.com.au