Front brake, loss of pressure

[Frank-RR]

Hi Guys, a couple of times, when I am taking the bike out the garage, reversing down drive, there is no pressure at the lever, it's almost at the handlebar to stop, happened this morning again, however, when started up and before moving the pressure is resumed, is this normal or is the system faulty?

Cheers

 

[scooby]

think bike needs to be running for the ABS pump to be working so that might be why

 

[Frank-RR]

Sounds god to me, Scooby

 

[GixxerChuck]

Have you checked the fluid level? Shouldn't be any different with engine running on lever travel.

 

[Frank-RR]

Spoke to local dealer, he rekons it could be when I come back form a run, because I put bike away until the next sunny day(that be a long time), because the disc is hot it will push Pistons back and when it cools the piston will remain where they are causing a gap between pad and disc, so when I apply brake I need to take this gap up first,

dose use that sound correct

 

[alex]

TBH if you park it with hot brakes you're asking for warping. Always do the last mile calm to give the rotors and pads time to cool off a bit.
I'm not sure about the theory, I'd be more inclined to believe cooling=contraction via the brake fluid pulling the pistons back. But maybe.

 

[MacRR]

Yeah it could be that although I've always just slung my bikes back in the garage after a run regardless of how hard I've been using the brakes and never noticed a subsequent problem with lever pressure wheeling them back out again. Agree with Gixxer, check the fluid levels are ok, I assume the brakes are spot on when you're riding you bike?

 

[Frank-RR]

Yes I have checked fluid levels all ok, no leaking etc


Sent from my iPad using Tapatalk

 

[scooby]

TBH if you park it with hot brakes you're asking for warping. Always do the last mile calm to give the rotors and pads time to cool off a bit.
I'm not sure about the theory, I'd be more inclined to believe cooling=contraction via the brake fluid pulling the pistons back. But maybe.

parking up with hot brakes makes them warp? you do read some funny things on forums.

how does that work with track/race bikes exactly?

 

[alex]

Yeah it can. More likely with non-floating discs. Its because of the relative cooling speeds of the disc in the caliper vs out of the caliper. More likely with cars and solid discs but its still a very real thermal characteristic genius.


- Sent from Mobile

 

[fast_ryan]

Warped Discs

Excessive heat build-up can cause discs to warp especially through repeated hard braking and continuous use on trackdays. But that said I've never worried about cooling down brake discs on trackdays let alone when I used to race. You'll soon know if you have a warped brake disc as you will feel pulsing through the lever under normal braking and at higher speeds you will feel a distinct juddering sensation. You can easily check for warped discs by using a dial gauge and a vernier caliper to measure the thickness of the discs.

 

[bananaman]

Agree with Rys, never had a problem in the 3 yrs ive been racing them with standard discs. Thought it might be a problem with the z04 pads but no....

 

[alex]

Just to confirm I wasn't saying that warping was the cause. It was a side track to say that if anything was to go wrong after being left stationary I'd have expected warping not pads moving back. It wasn't meant as a discussion point, sorry about the distraction.

Causes for the issue that I can think of;
Master Brake Cylinder - mine was replaced because the lever would get longer as I used is and always had more play that other S1000 I checked. It was determined that the seals inside were starting to go.
Pad Knock Back. Going into the storage... a big bump knocks the wheel with enough force to move things (low chance).
Piston pull back - If there was significant pull back on the system to cause a vacuum when cooling the fluid I'd suspect it would be air in the system causing the issue (ABS/MBC)

 

[Frank-RR]

Hi guys, thanks for advice, Alex, i bled the front brakes, i heard a rush of air from the LHS, lever feels ok, just need to leave it a week or so, wont be hard in this weather to do that

next job, remove a clean calliper, pistons, etc

 

[Mick753]

I complained about this when I took my bike in to BMW for it's last service, occasionally if i had not used the bike for a few days I would get a lever that pulled back to the bar the very first time I used the front brake, no problems with the bike moving or with the engine running but it had me scratching my head for a while.

BMW said it was nothing to worry about and that everything was fine and that was back in April but it has now happened again twice in the last couple of weeks, both times when the bike has been standing for a week or so.

It's certainly nothing to do with the bike being parked up with hot brakes as my last ride was a 15 minute ride home in torrential rain on Supercorsa's so I literally tiptoed my way home.

But given that the braking system is supposed to be a sealed system with a small amount of air at the top of the reservoir which does counteract heat expansion I can't figure out how the lever can come all the way back to the bar as if there is no fluid in the system on the first pull and then not have any problems whatsoever for the next however many miles you ride, with a perfect feel to the lever every time I use the brakes.

The next time I use the bike I will try the rear brake first to see if this is just a front brake issue as I don't believe it is, if anything it must be an ABS issue surely given that they are linked.

 

[B33fys]

Hi Guys, a couple of times, when I am taking the bike out the garage, reversing down drive, there is no pressure at the lever, it's almost at the handlebar to stop, happened this morning again, however, when started up and before moving the pressure is resumed, is this normal or is the system faulty?

Cheers

to be clear, could you keep squeezing the brake lever all the way prior to starting up the bike and it was still not building up pressure until after you start the bike up? If it's just once or twice and then lever becomes hard even without engine started, there's 100% air in the system I would say.

 

[Frank-RR]

Hi Mick, yes exactly as you describe I contact the 2 motorradd dealers in Scotland, neither gave me a good enough reason why it should happen, with no servo assistance the brake lever should remain firm all the time, like I said, I bled mine on Saturday and I did get some air from the left side calliper, so I hope that was the problem

 

[Frank-RR]

Hi guys, I have removed the rhs calliper to start cleaning I have noticed, it's only the rhs pistons coming out no movement on the left and the top right piston comes out at a different rate and not came out as far

any suggestion

 

[alex]

Clamp the pistons that do move to hold them in place. It should be possible with fingers...but you may need to get creative with clamps. The others should pop out and allow you to clean them, which should see them all return to good working order. If they don't and are properly seized then you have a bigger issue...

 

[Frank-RR]

Thanks Alex, will give that a go, was beginning to think it was the same a car brake, only one side moves