Spongy Front Brakes

[scooterme]

So I need to access the R12R brain trust. I am struggling with a front brake problem on my '08 R. The front brake does not have initial 'bite' when I pull the lever, so I am forced to release the lever and pull it in again. The second pull is much as it should be, plenty of strong stopping power.
My first guess was air in the line somewhere, so I had the shop bleed the brakes. They could not find any air in the lines, or indeed suggest any other explanations or solutions. Any ideas?

[ammolab]

Bad master cylinder or piston seal in a caliper.

[David R]

The shop agrees the brakes are spongy and sent you out the door?

Blows my mind.

Could be a lot of things.

What about sitting still. If you grab the brake once how is it. Now "pump" it once and see how it is again. Wait a half minute and squeeze it again. Still good or not? Do the same while riding the bike. Is it different when the bike is rolling? If it is, it could be wheel bearings or warped rotor pushing the pads back too far.

You can put very light pressure on the handle, and keep it there. see if the handle "sinks" slowly with light pressure. This would be a bad master cylinder.

I would also check for any binding of calipers. Make sure they slide back and forth. If you have floating rotors, make sure they are not stuck.

Air would make the second pull still spongy.
A stuck caliper or bad rotor would cause the pads to go back too far and need two pulls on the lever.

A leaking caliper seal would be visible.

David

[mogu83]

Before you make yourself crazy.

Check another R1200R. The front brake lever has a rather peculiar feel to it. If you search this list you'll find some references to the way the brake feels on the initial pull. I think the consensus was to just live with it,that's what I've done and the brakes have performed magnificently when I've grabbed them in a crisis situation.

Naturally I'm not there to feel your lever, maybe you do have a problem, but this has come up before.

[Dr. Strangelove]

aren't these brakes linked, front and rear?
could there be air in the rear circuit? That would be hard to tell with the foot pedal, or harder to tell than the hand lever.

That sounds a lot like air. A dog with three legs is still a dog.

[omg1010]

Sounds like improper bleeding to me. Bleeding the hexheads is quite a task which can drive you mad. I always suggest using either the stahlbus valves or as a replacement you could also use bicycle valves (simply insert same in the bleeding tube). Proceed in the correct order. Finally consider putting the bike on the side-stand (so that the brake reservoir becomes the topmost element of your brake-circuit). Pull the lever and fix same with a strap or zip-tie and leave overnight. Any bubbles will move up the circuit. Consider some mild bangs with a plastic hammer on the brake calipers ... Next morning bleed again starting on the lever and thereafter the rest. Thats how I got it working on my R1200S.

Brgds
Oliver

[deilenberger]

Having done all the suggested bleeding - many times (I change/flush my fluid once a year anyway), and having gotten a master cylinder replacement under warranty.. I have to agree with what the service manager at the dealership said when replacing the master cylinder (he rides an R12R..): "It will come back shortly.." and it did. You can lessen the first pull soft-feeling by doing all the bleeding/flushing/whatever, but it does come back.

What's happening is piston retraction. Brake caliper pistons are sealed in the bore with a seal that rolls slightly when extended (twisting in the process) and then provides a small pull-back force when brake pressure is relieved. The piston slowly moves forward as the pads wear when it moves enough that this seal slides. The first time you use the brake the piston is retracted a tiny bit from the pad (intentional to prevent the pads heating by contact with the rotor) - and your use pushes it forward toward the disk. It takes a bit of time for it to retract again so the lever feels harder on the next use.

My gauge for how much is too much is a finger between the lever and my grip (with "grip-puppies" on the grip, which increases the diameter.) If a finger is pinched hard, that's too much and I'll play with it a bit. If not - as Harry said - the brakes will still stop you, you will be able to apply enough force to kick in the ABS, so nothing is gained by trying to "cure" it.

FWIW - this effect seems less with new pads in the front. I suspect pushing the pistons back in resets the seals, and then it basically slides on the bore until the pads are tight on the disk. I've accomplished the same thing by pushing the pistons back in (with worn pads) and then pumping them out. That also seems to reset it.

If you do go to push the pistons back - make sure you have room in the reservoir for the fluid. You should not "top off" fluid between pad changes. The fluid should only be topped off with the pistons fully retracted. There is enough fluid in the reservoir that you aren't going to suck air even when the pads are fully worn.

[scooterme]

Many thanks for all your responses, perhaps I do need to live with it. It's just that they do feel 'worse' than when I got the bike... which it sounds like could be quite normal... I will compare to another R when I get the chance.

What about sitting still. If you grab the brake once how is it. Now "pump" it once and see how it is again. Wait a half minute and squeeze it again. Still good or not? Do the same while riding the bike. Is it different when the bike is rolling? If it is, it could be wheel bearings or warped rotor pushing the pads back too far.

So, due to the wonderful weather in Maine, snow on top of more snow, with yet more on the horizon, I have not been able to get out and ride to test this all but sitting still in the garage, it seems to me that when I do give it the two pumps, then wait 30 seconds I have returned to needing to pump it up again. From memory, this is exactly the same when riding.

You can put very light pressure on the handle, and keep it there. see if the handle "sinks" slowly with light pressure. This would be a bad master cylinder.

There is no sign of the handle sinking, it stays at the same distance pulled in.

I would also check for any binding of calipers. Make sure they slide back and forth. If you have floating rotors, make sure they are not stuck.

Air would make the second pull still spongy.
A stuck caliper or bad rotor would cause the pads to go back too far and need two pulls on the lever.

How do I check for the movement of the caliper?

A leaking caliper seal would be visible.

David

There is no sign of leaks at the calipers.

[deilenberger]

Just a FWIW..

The front calipers are not floating, and if you grab one and try to wiggle it - there should be no movement between it and the fork tube. The front floating disks may contribute a bit to the push-back problem, but if you lift the front of the bike, and can spin the wheel without it binding at any one particular point, that's unlikely as a cause. And they would only contribute to it if the wheel IS turning.

The rear caliper does float (actually it's a single-piston pin-mounted caliper) - and some movement in it when grabbed and wiggled is normal. These are more often at fault for not releasing fully on the rotor causing short pad life and a hot rotor. I haven't heard of any knock-back problems on the rear, and it's unclear to me that this would change the feel of the front lever. There is no rotor knock-back due to either front or rear rotors if the wheels are not turning, and in my experience, as yours - it does this when stationary on the centerstand, which to me means it pretty much leaves the seal pull-back to blame.