Hi all, could use some advice please.
I was riding home from having a new back tyre fitted, thankfully that kept my speed down. My front brake lever started to travel a little further each time I used it. After a few uses it failed completely, no pressure at all on the lever. I have relatively new pads which had been working fine. I have replaced the fluid and now have bought and replaced the master cylinder seals. I tried the brake and it felt ok again, admittedly with slightly more travel than it had previously. I went for a run and all seemed ok, even with the extra lever travel. Then the brake failed completely again. No pressure on the lever. I stopped and tried it again, and it was working fine again. There are no apparent leaks and the hose all look fine. I am pretty sure its not an airlock because they are not spongy. Any help would be very much appreciated. FZS 1000, 2003 model.
Have you rechecked the fluid level in the reservoir to eliminate a leakage somewhere.
Yeah, fluid level if ok and I can't see any signs of leakage.
Perhaps the spring is unable to push the master piston back reliably, did you replace it as well as the seals?
Otherwise it could be wear on the cylinder bore causing the piston to jam occasionally.
Sure ive read this before, piston seal was in the wrong way around, sticking closed. Not done seals on fazer before but sure I read it.
Try google see if it comes up
Was a complete seal kit. Spring, circlip, piston with seal pre-attached and the seal that goes between the piston and the spring. I am fairly sure that I put them in correctly. It did work and gave me a good brake for a few miles before it failed again. I have tried google but didn't get too much useful info. I have tried bleeding it again and have a good lever, but I still don't trust it. The kit was an after market one so I am tempted to buy a Yam one. The fact that it fails completely with no evidence of leaks makes me think it has to be the master cylinder itself or the seals in it. Will keep looking. Was just hoping someone had experienced something similar and could point me in the right direction. Thanks for the info.
Ive been looking on Google but cant find the post, might not have been an fzs?
Did notice spring is tapered worth taking apart and re checking, and if you didn't put seals on re check them does sound like master? sticking pistons you get a hard lever after a few pumps.
https://www.youtube.com/watch?v=njKRhPwHOaM
Thanks. will strip it again tonight and double check, but fairly sure it could only fit one way.
It would be the seals Id check and condition of bore as Fazerider said
Good luck, keep us updated :-)
completely stumped. Stripped, checked and cleaned. No obvious wear or damage to the bore, can see piston moving, and it moves freely and smoothly, seals all good and fitted correctly. Re-assembled it and its still not right. I can get the lever to touch the throttle grip, way too much travel. Tried pumping it in case there was air in the system but it made no difference. I have tied the lever back against the bars in case it has air in the upper section, but doubt it, as surely the lever would firm up if there was air in the system. Done all I can for tonight. Will check it tomorrow, perhaps a slow run.
15-08-17, 09:07 PM
(This post was last modified: 15-08-17, 09:07 PM by unfazed.)
Are they standard hoses and what mileage is on the bike? Sounds like a dodgy hose
bikes a 2003, I've had it for 10 years, think the hose have never been changed. Would that cause the lever to go completely slack and leave no brakes ?
The rubber hoses can bulge causing exactly what you describe, I have seen it happen on a few old bikes over the years.
They will eventually burst. Set the adjuster to 1 and get some one to operate the lever and go over the hoses with your hand mm by mm.
Difficult to see on the fazer as there is a cover over the hose but you will feel it.
Thanks for that, did have a look at the hose for leaks but couldn't see any, wasn't checking for stretching or bulging. Will have a look tomorrow.
I had this problem after fitting a pair of new looking second hand front brake discs. There was 1.25mm runout on one of the discs which caused the calliper pistons to be pushed back a tiny amount when the wheel was turned.Multiply 'a tiny amount' by 4 pistons and it was enough to lose the front brake altogether, until it was pumped back up at a standstill. Totally cured by brand new EBC discs.
Don't think its discs or pads. Discs are a few thousand miles old and genuine Yam items, pads were replaced 600 miles ago. Problem only started this week. Thanks for the thoughts though. Worth a look.
When it happened did you notice if one or both of the disks were hot, just thinking if the brakes are binding slightly enough not to be noticeable but enough to heat the brake fluid so it starts boiling that would explain the loss in pressure and why it recovers shortly after as the fluid cools down.
No, didn't notice anything on the discs, but then again never thought to check them. Don't think it is the discs though. The last time it happened I was just turning the bike and was only moving at a snails pace, the brake failed completely, then immediately started working again. So no real chance for the brakes toheat u[, or to cool down really. I am going to try looking more closely at the hose as Unfazed suggests. Failing that I will try another short run and see if there is any heat in the discs.
Forgot to add in my last post, Check your wheel bearings also
Are your caliper pistons all moving? The fact that it works then doesn't suggests that it is either the calipers having stuck pistons or the master cylinder diaphragm is at its full extension which will not allow the brakes to work correctly. It could be the hoses but IME a bulging hose gives consistent issues. Check that your hose banjos are not at tight angles, particularly at the master cylinder side where they can be knocked out of place.
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