[DouglasM]

Hi all, a friend has asked me to sort the brakes on his 1000 mile CF550 after a mobile mechanic failed to fix them The symptom is, as he was riding, the brakes just failed completely, front and rear. We can find no leaks and trying to get the system bled we are struggling to get pedal pressure. In fact when you pump the foot brake pedal the front brake master cylinder hisses and fluid even forces it's way out of the reservoir. This leads us to believe the front master is shot. Also, pumping the front brake gives us hardly any fluid pressure when we crack a bleed nipple while pumping the rear pedal gives us a nice stream when we crack a bleeder.
Before I spend my mates money on a new front master cylinder I would like some advise or suggestions if we are heading down the right road.

Cheers,

- Douglas

[NMKawierider]

I was under the impression that the front calipers were dual-feed as indicated with the separate lines from each master cylinder. That means there are two separate chambers within them to take pressure from either master cylinder separately as the masters will not stop or hold pressure from the other in their open position. So from what you are saying, that means at least one of the calipers has a breach between the two chambers. All it takes is one small hair-line crack to connect the two systems. I don't know how to tell which one but I would start there first before a master cylinder...unless each master cylinder has a check valve inline somewhere...if so it would take both of those to fail but look anyway.

[doug80638]

This isn't likely to be helpful but ...

My experience with the brakes on my Z8 has been puzzling as well. I removed my calipers so I could check the slides for binding (based on input I got in this forum). I had compressed the calipers in the process.

When it was all reassembled, I pumped the brake pedal knowing it would be soft until the pads reached the rotors. The problem was that the pedal would not firm up no mater how many times I pumped them. I couldn't imagine what was wrong because I did nothing to the brake lines or master cylinder, and the master had plenty of fluid in it.

I walked away for about 15 minutes to think about it, and when I returned, the pedal was back to normal; high and firm. I did absolutely nothing in between. It was very odd. There is clearly something I don't understand about that setup.

The slides were fine BTW: Others have said the slides need to be kept lubed, but after 3 seasons, they were all still like new.

[DouglasM]

Doug, that doesn't surprise me... one 'trick' we often use when bleeding bike brakes is to clamp the brake on and leave it overnight... this works out any residual air... This might be what happened in your case. So we'll try bleeding both bleed nipples on the callipers now that we understand the way the split system works and we'll report back. The question I'd really like answered is if the hissing sound from teh front master when pumping the rear is normal...

- D

[ctdls]

These brake systems are a nightmare, I've never so many problems with something that should be simple. The ATV's add another level of unnecessary complexity combined with so so components.

Seemingly impossible to bleed because the MC flat out refuses to pump up. I will share a trick I learned from another off road power sports tech 

Tie the brake handle to the bar after you pump several times, same with the foot pedal MC's. Find away to hold them down......then leave them for a few hours or overnight. This will push the air out & they will pump up, you can try to bleed & see if they hold pressure.

As far as the 550 hoe, I had a mystery unit that would loose pressure. In the end in it was the handle bar master cylinder, you could not identify the problem by normal troubleshooting techniques....it was trail & error.......junk

[NMKawierider]

As I look ate the brake system on the 500, I see what is called HYDRAULICDISTRIBUTIONVALVE that both systems are tied to. This may well be your problem. It's #38 in this pic:

[DouglasM]

Does anyone know how this hydraulic distribution valve works? If it fails does it commingle the front and rear systems? This I think is the main problem, either the one way valve in the front master is shot or this distribution valve has failed. I also like the suggestion of the crack in a calliper but with the volume of fluid going from back to front I kind of doubt it...

- D