Front Brake Soft/Useless

[Robster]

Ok, so another issue that's just reared its head - my front brake has become soft and spongy to the point where it's near useless.

First pull of the lever and it'll come right back to the bars with no resistance at all and no braking – give it another couple of quick pulls and you can start to feel a little pressure and the brake will start to bite, but not very well by any means. However, leave it a few minutes and it's back to square one with the lever coming back to the bars again.


I've bled the system several times now both upwards and downwards, and flushed new fluid right the way through, but the problem persists. The first time I noticed the issue, there was some slight weeping from the cap on the Master Cylinder, so I popped the lid off, repositioned and retightened. Made little to no difference.

I spoke to the guys in my local bike shop, and they suggested potentially a caliper rebuild kit was in order next by way of elimination.

Any ideas where to lay my hands on such a kit – nobody seems to sell them! I can't believe one doesn't exist. I've just read an article on ADV Rider suggesting replacing the lever might also help, as the socket can wear over time... guess that's worth a go again by way of elimination.

Failing that, any other ideas to remedy the issue?

 

[Smug]

Have you tried pumping up the lever and then clamping the lever to the bar and leave overnight?

 

[JohnnyBoxer]

KTM parts may be similar (BREMBO) - the rear is the same as the 640 Adventure

 

[GFJ]

I have found my front one on occasions difficult to bleed - something I put down to the fact that the brake line goes higher than the master cylinder before it heads down to the caliper, so I did wonder at one point whether air was collecting there instead of bleeding out.

Try removing the lever and master cylinder from the handlebars and raise it overnight to see if the air will come up and expel through the reservoir. Sounds a bit bizarre and possibly boll*x, but something I did sorted it and I'm not sure really what it was!

 

[Myke Rocks]

Sponginess may be due to things other than air in the brake fluid.

Since it came on you without your having "serviced" the bike, I would suggest you look elsewhere. For example, a piston sticking in a caliper can cause the problem.
So can a brake pad detaching some of it's friction materiel.
So can a warped brake disk, or even (0nce) a detached brake disk ( Renault Clio, 2 days after MOT. brake disk separated from it's hub. Corrosion)
No, I am not saying it is this, just pointing out that it may not be a hydraulic problem.
Myke

 

[rossi]

Ok, so another issue that's just reared its head - my front brake has become soft and spongy to the point where it's near useless.

I've bled the system several times now both upwards and downwards but the problem persists.

Any ideas where to lay my hands on such a kit – nobody seems to sell them! I can't believe one doesn't exist. I've just read an article on ADV Rider suggesting replacing the lever might also help, as the socket can wear over time... guess that's worth a go again by way of elimination.

Failing that, any other ideas to remedy the issue?

Replace the lever. I probably replaced mine 3 or 4 times in the 46k miles I had the bike. A pattern lever for a CB500 twin fits perfectly and can be had for a fiver. My money is on the lever and it is much easier than trying to rebuild a calliper. If I'm wrong you'll have a spare lever in case you ever drop the bike and snap one. Not much to lose.

And yes, over on ADV I am the jester.

 

[Robster]

Nice one Rossi – good tip on the CB500 Lever! However, I've already replaced the lever, and it's made little or no difference.

Not using the bike much at the moment as I've got a time shortage and my hands full with a new baby, but I have assembled what I think should be a full rebuild kit for the front caliper and the master cylinder.

I'm loathe to post up here part numbers, links etc as the parts are as yet unfitted and untested (see lack of time comment above!), but once the job's done, hopefully over the next couple of weeks, and I'm happy with the results I'll share!

 

[Losttheplot]

I have found my front one on occasions difficult to bleed - something I put down to the fact that the brake line goes higher than the master cylinder before it heads down to the caliper, so I did wonder at one point whether air was collecting there instead of bleeding out.

Try removing the lever and master cylinder from the handlebars and raise it overnight to see if the air will come up and expel through the reservoir. Sounds a bit bizarre and possibly boll*x, but something I did sorted it and I'm not sure really what it was!

^ what he said

 

[Robster]

Hurrah...I have a front brake again, and it's sharp as a needle

Due to my lack of available spannering time (and, admittedly a lack of knowledge/confidence in tackling this job) I had to put it in to my local workshop[ to be sorted. I did try some or maybe all of the suggestions above and they worked with greater or lesser degrees of success... but only for about 5 minutes!

As I mentioned before though, I was able with a little internet sleuth work to source a caliper rebuild kit, a piston kit and a master cylinder rebuild kit – none of which Herr BMW is keen to sell you for the XChallenge. Now that those parts are fitted, working and tested I feel happy to share the knowledge with you!

So...

Brembo Front Caliper Rebuild Kit (actually specified for a KTM 950 Adventure): http://www.trevorpopemotorcycles.co.uk/index.php?main_page=product_info&products_id=6812


Brembo Front Caliper Piston Kit (actually specified for a KTM 950 Adventure): http://www.trevorpopemotorcycles.co.uk/index.php?main_page=product_info&products_id=14598


Brembo Front Master Cylinder Rebuild Kit 13mm (actually specified for the BMW F650 GS/CS & G650 GS): https://www.motobins.co.uk/displayfinal.php?q=ZZ32648&topsearch=1&go=GO


Hopefully that'll help some of you out - something to add to the Knowledge Bank maybe?