newbie front brake problem

pauls · Post by **pauls** » Fri May 03, 2013 5:55 pm

Def going to try single brake line when I get back on Monday. Wheel bearings and discs all seem
Good no play ect. Cheers

Corvus · Post by **Corvus** » Sat May 04, 2013 8:30 am

Merecat wrote:?....Still sounds like the pistons are being forced back in to the caliper for some reason. If this is on twisties it strengthens the argument for wheel bearing play. Have you had the front end off the floor and pushed and pulled it?
Is there excessive play in the disk mounting posts? Are the disks true?

Mick

Highly irregular this, but is it possible there is axial movement of the wheel. This would be the bearing outer races moving in the hub bores. I've never heard of that but if we're looking for explanations of how the wheel might move relative to the forks and yet not be detected by twisting the wheel (the usual way to check bearing wear) then that is one. You can't say I'm not trying....

Blackal · Post by **Blackal** » Sat May 04, 2013 8:51 am

I'll suggest the following:

A small amount of water in the hydraulic fluid.

* The water aglomerates in the lowest part of the system - the calipers
* You apply the brakes, and the calipers heat up. (The water does not evaporate yet, as the pressure is elevated)
* You release the brakes, but the residual heat in the calipers/fluid - now evaporates the water (no pressure).
* The increased fluid/vapour volume expands back into the reservoir.
*Next time you apply the brakes - you get a feeling of sponginess and the lever goes a long way back, until the pressure in the system - condenses the vapour and it returns to a single-phase system.
*Release the brakes again - and the water flashes off with the heat again.

*if you leave the bike for any length of time, the water condenses as the temperature lowers, but continued braking will return to the spongy state.

Al

slparry · Post by **slparry** » Sat May 04, 2013 10:42 am

Blackal wrote:I'll suggest the following:

A small amount of water in the hydraulic fluid.

* The water aglomerates in the lowest part of the system - the calipers
* You apply the brakes, and the calipers heat up. (The water does not evaporate yet, as the pressure is elevated)
* You release the brakes, but the residual heat in the calipers/fluid - now evaporates the water (no pressure).
* The increased fluid/vapour volume expands back into the reservoir.
*Next time you apply the brakes - you get a feeling of sponginess and the lever goes a long way back, until the pressure in the system - condenses the vapour and it returns to a single-phase system.
*Release the brakes again - and the water flashes off with the heat again.

*if you leave the bike for any length of time, the water condenses as the temperature lowers, but continued braking will return to the spongy state.

Al

With you on this Al, which is why I asked earlier if the hydraulic fluid was from a known sealed container as it's hydroscopic and will actively absorb moisture.

I assume it's the correct grade of brake fluid too?

pauls · Post by **pauls** » Sat May 04, 2013 11:53 am

Yes dot 4 I will drain calipers and put in new brake fluid when I try the single lines cheers

pauls · Post by **pauls** » Sun May 05, 2013 11:21 am

update, have tried it with only one line each side and it is slightly better but not much so got to be master cylinder? anyone know the cheapest place for master cylinder seals? cheers

slparry · Post by **slparry** » Sun May 05, 2013 2:17 pm

http://www.realoem.com/bmw/showparts.do ... g=32&fg=72

part 13 .... number 32727658464

Motorworks have them at £43.69

http://www.motorworks.co.uk/vlive/Shop/ ... 64&x=0&y=0

However, ask your BMW dealer if they'll match or beat that price, mine (Williams) do and in the process include free postage and BMW parts warranty.

pauls · Post by **pauls** » Sun May 05, 2013 2:56 pm

Ok cheers will ring up tuesday fingers crossed it is master cylinder?

pauls · Post by **pauls** » Fri May 24, 2013 9:02 am

Aahhhhhhhhhh put new master cylinder seal in yesterday it's still the same? So. Have now spent so far £200 and am no further forward?

slparry · Post by **slparry** » Fri May 24, 2013 9:08 am

Have you tried getting the system fluid replaced with one of the power bleeders that force it from the calipers up to the master cylinder?

Corvus · Post by **Corvus** » Fri May 24, 2013 3:07 pm

Hi

Did we eliminate water contamination from our list?

Whilst working on a mates r1100s recently I noticed that there is a manifold block tucked under the A arm (from memory). Could that be a source of air entrapment?

Someone earlier on up the thread suggested testing the calipers for temperature immediately after the symptoms occur. Have we eliminated that possibility? Again, on my mates bike, we found a build up of paint on the "turret" faces that the discs sit on, after the previous owner had the wheel powder coated, was affecting the way the disc expands and the amount of preload produced by the wavy washers. That one is probably not the case here I guess.

There have been some sound suggestions floated here. Have we ticked em all off our list? If we have then surely we must be narrowing down the possibilities to almost none!

Sincerely hope you get it sorted.

PS. By definition, if we've eliminated the obvious, then we're looking for something obscure. How about checking that the top hat shaped collars which allow the discs to expand are a)still there! b)working.

Cheers

timbox2 · Post by **timbox2** » Fri May 24, 2013 4:55 pm

pauls wrote:Aahhhhhhhhhh put new master cylinder seal in yesterday it's still the same? So. Have now spent so far £200 and am no further forward?

Ok, 3 things:

1), early on in your thread you said NO bubbles in master cyl when pulling lever. Do you get a mini jet of fluid spring up when pulling lever, (Mind the paintwork). You should by the way, if you dont then you may have crap in the bottom of the reservoir blocking the bypass bleed hole.

2) Clymer recommend bleeding the master cyl first by loosening the banjo then slowly bring the lever to the bars while holding rags etc around the banjo, and watching for any aerated fluid, then tighten banjo before you let go of lever.

3) And somebody else mentioned this, calipers. I had a similar issue once on my S and in the end I removed all the pistons and seals cleaned everything and put the seals back using the proper red brake seal grease, then bled it and that fixed it. My thoughts were that the outer seals were retracting the pistons too much because they were deforming when the brakes were applied owing to crud etc.

Out of the 3 the last would be my best guess.

Regards
Tim

Corvus · Post by **Corvus** » Fri May 24, 2013 5:59 pm

[quote="timbox2"] Do you get a mini jet of fluid spring up when pulling lever, (Mind the paintwork). You should by the way, if you dont then you may have crap in the bottom of the reservoir blocking the bypass bleed hole.

Surely the system wouldn't fill though?

timbox2 · Post by **timbox2** » Fri May 24, 2013 7:12 pm

Corvus wrote: Surely the system wouldn't fill though?

You may be right, Im just thinking through possibilties, my money is still on a caliper issue.

Corvus · Post by **Corvus** » Fri May 24, 2013 7:23 pm

timbox2 wrote:
Corvus wrote: Surely the system wouldn't fill though?
You may be right.......

I wouldn't put money on it! Hee Hee. Cheers mate.