Brake Lines or Master Cylinder ?

[sgms2]

Hello,

I have a recently purchased 1986 K100RS.

Everything is fine after replacing lots of aged things and obtaining a "roadworthy certificate"  ( as it is called in Victoria, Australia ) .

I have discovered an odd problem.

On a hill, stopped at traffic lights I can feel the front brake lever give a little, like a creeping feeling. It is more noticable when the bike has been ridden for a while and is hot.

There are no signs of leaking fluid from the Master cylinder or either front caliper.

The brake lines look original so they are probably 27 years old.

I read "somewhere " old lines on these bikes get soft and feel spongy. Could this be the give I feel in the brake lever ? Maybe the line from the master cylinder to the splitter thing is getting hot from the engine and going soft. 

Or, as advised elsewhere , have one of the internal seals inside the master cylinder developed a leak ?


I've spent a little fortune so far. I might sound cheap but in the interim I would like to avoid fixing it all at once
Thanks

Stuart

Melbourne, Australia .

[robleyd]

If the lever is creeping down as you stand, it is most likely the primary seal in the master cylinder leaking back. If you can grab the lever and it keeps coming in to the handlebars, it is definitely the primary seal. Old, tired hoses will give a spongy feel to the lever as you brake as they stretch, sort of like having a little air in the system.

Munich MC seem to have a kit http://www.munichmotorcycles.com.au/product_info.php?products_id=2220 complete with piston for $110 - maybe call them to confirm it suits your brick - but you probably need to check the inside of your master cylinder for scores before installing.

If you need a new complete master cylinder, $350 will be removed from your wallet - http://www.munichmotorcycles.com.au/index.php?cPath=2681_2804_1699_2228&sort=2a&page=2

Welcome to the world of long lasting, occasionally expensive motorcycles :-)

[Scott_]

I'd suggest that no matter what you do first,(replacing the master cyl piston seal, or lines) plan on doing the other as soon as your budget allows.
Making a bike go is a good thing, but being able to stop it safely is a much better thing...... :2thumbup:

[tg4360]

Similar situation on a friend's GS recently.  We changed out the fluid and just after doing that he put pressure on the lines and one of them blew out right at the crimped ferral of one of the lines.  Turns out it had been leaking into a bulge for a while and we never knew it because that end was hidden up under the small fairing.

My bike is an '87 and just as a matter of course, I replaced every line on the bike when I first got her.

They do not last forever and changing the whole works, even with "high speed" stainless braided was not a crazy expense.

TG

[Qdude]

Making a bike go is a good thing, but being able to stop it safely is a much better thing...... :2thumbup:

+1, then + another 1, then + a few more 1's

I suspect Master Cylinder.
How does the fluid look BTW?
How is the fluid level? Does it change/drop?
You said no leakage around the master & slave cylinders, but what about elsewhere?
I find it curious that it happens more after it has been ridden a while.
Could this have anything to do with ABS?

[sgms2]

Thank you for all your comments and advice.

In light of your collective recommendations I shall purchase a new master cylinder and some new brake lines.

Sadly these things are sold by thieves here in Australia.

Luckily the couple of places I know in the UK, Motor Works and MotorBins are more affordable despite the postage and currency conversion.

To Qdude, there is no leakage anywhere. The fluid level does not change. There is no ABS. Hence my confusion about the seals leaking causing the lever creeping if there is no sign of fluid. I guess it's an internal thing in the master cylinder.

Thank you all.

Kindest regards

Stuart

Melbourne, Australia.   

[Qdude]

Sadly these things are sold by thieves here in Australia.

 :hehehe :dunno2:
Good on you for the light hearted spin on an unfortunate situation. I really hope the problem gets solved quick and that no others pop up for a good long time. Best of luck man.