Spongy front brake

[spm0912]

So the front brakes on my 2013 GSA had started to get a bit spongey. Bikes done 60k miles, ridden all year. Also a couple of the pistons were sticking as well. I bit the bullet and bought a calliper re build kit and duly serviced the callipers. I bled until there were no air bubbles in the tube but brake is still spongey. I noticed that when pulling on the lever it creates a series of bubbles in the Master Cylinder. Has my master Cylinder gone kaput?? With the linked brakes could I have air in the ABS side of the system?. I've tied the brake lever to the bars in the vain hope it'll get rid of any trapped air in the system. I don't want to invest in a new master cylinder if it could be something else at fault.

Any advice from the collective here would be much appreciated

 

[Bendy toy]

It's likely you need new seals in the master cylinder but I suspect BMW don't sell any.

I had similar issues with the clutch. Move the lever very slowly and watch the bubbles escape. Also leave the bike overnight with the brake lever tied back

 

[Mistacat]

Probably need to do the bleed test with a GS911.
Have had later ABS systems firm up the lever after running the pump whilst operating the lever using the GS911.

 

[NZRalphy]

Yup new master cylinder parts. BMW may not sell parts but someone will have them.

 

[spm0912]

Thanks, will strip the master cylinder first and go from there

 

[Blackal]

Thanks, will strip the master cylinder first and go from there

Get parts to replace any damaged - before stripping anything.

 

[ShakeyGS]

Try this first.

Tie the brake lever back to the grip and leave it compressed for a few hours (overnight is good).
Hold the lever back whilst you release whatever you tied it back with and then quickly release the lever.

Hopefully, any tiny air bubbles (difficult to remove by conventional bleeding) will have become larger air bubbles and will find their way into the reservoir.

 

[spm0912]

Try this first.

Tie the brake lever back to the grip and leave it compressed for a few hours (overnight is good).
Hold the lever back whilst you release whatever you tied it back with and then quickly release the lever.

Hopefully, any tiny air bubbles (difficult to remove by conventional bleeding) will have become larger air bubbles and will find their way into the reservoir.

Already done that but thanks. Pretty sure that it's the mc now. I've ordered a 2nd hand one off eBay and will endeavour to get the original rebuilt. Seems I also need a gs911 to purge the fluid from the abs unit and as you be been looking for an excus to get one for ages......

 

[Pukmeister]

Buy a mityvac and suck bubble-free fluid through from m/cyl to caliper.

Also witness pads when operating m/cyl to ensure they have equal travel onto disk face, uneven pad travel can give long brake lever travel and poor brake feel as the disk gets bent sideways instead of clamped between the pads.

 

[Blackal]

Buy a mityvac and suck bubble-free fluid through from m/cyl to caliper.

Also witness pads when operating m/cyl to ensure they have equal travel onto disk face, uneven pad travel can give long brake lever travel and poor brake feel as the disk gets bent sideways instead of clamped between the pads.

Not sure about longer brake lever travel - that doesn't make sense to me?

There is a finite travel (and hence volume of fluid) to clamp the disc.

Al

 

[Pukmeister]

Had it years ago on an YZF600R where the lever almost came back to the bars. The disk was being pushed sideways by uneven pad travel. Re-centreing the pads on the disk by using a screwdriver to hold off the closer pad temporarily meant that both pads then clamped the disk evenly immediately and I got full pressure for little lever travel. I hope that makes sense.

 

[Bendy toy]

My bike is an 08. The brakes at both ends bleed normally with no need for GS911 to do any clever stuff. Ive had back front callipers rebuilt and removed the frame back end which required the rear brake circuit to be disconnected.

 

[spm0912]

2nd hand MC fitted today from eBay, £45. Bled front and back brakes and I now have the ability to stop in a timely fashion which is always helpful.

I still want to rebuild the original, I know BMW don't do a kit but does anyone know what seals will fit please.

Thanks

 

[Bendy toy]

2nd hand MC fitted today from eBay, £45. Bled front and back brakes and I now have the ability to stop in a timely fashion which is always helpful.

I still want to rebuild the original, I know BMW don't do a kit but does anyone know what seals will fit please.

Thanks

Do have a pal at the Brembo parts centre who can help find the correct seals?