Author Topic: sudden brake failure (Read 2921 times)

Davie70 · « **on:** 15 August 2017, 02:56:34 pm »

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.

Kenbob · « **Reply #1 on:** 15 August 2017, 03:36:59 pm »

Have you rechecked the fluid level in the reservoir to eliminate a leakage somewhere.

Davie70 · « **Reply #2 on:** 15 August 2017, 05:06:27 pm »

Yeah, fluid level if ok and I can't see any signs of leakage.

Fazerider · « **Reply #3 on:** 15 August 2017, 05:08:40 pm »

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.

Dustydes · « **Reply #4 on:** 15 August 2017, 05:50:36 pm »

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

Davie70 · « **Reply #5 on:** 15 August 2017, 06:03:59 pm »

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.

Dustydes · « **Reply #6 on:** 15 August 2017, 06:10:16 pm »

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.

Davie70 · « **Reply #7 on:** 15 August 2017, 06:13:25 pm »

Thanks. will strip it again tonight and double check, but fairly sure it could only fit one way.

Dustydes · « **Reply #8 on:** 15 August 2017, 06:29:43 pm »

It would be the seals Id check and condition of bore as Fazerider said
Good luck, keep us updated :-)

Davie70 · « **Reply #9 on:** 15 August 2017, 08:49:01 pm »

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.

unfazed · « **Reply #10 on:** 15 August 2017, 09:07:02 pm »

Are they standard hoses and what mileage is on the bike? Sounds like a dodgy hose

Davie70 · « **Reply #11 on:** 15 August 2017, 09:12:26 pm »

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 ?

unfazed · « **Reply #12 on:** 15 August 2017, 09:19:58 pm »

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.

Davie70 · « **Reply #13 on:** 15 August 2017, 09:31:07 pm »

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.

Kenyun · « **Reply #14 on:** 15 August 2017, 09:59:06 pm »

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.

Davie70 · « **Reply #15 on:** 15 August 2017, 10:10:36 pm »

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.

PieEater · « **Reply #16 on:** 16 August 2017, 06:30:46 am »

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.

Davie70 · « **Reply #17 on:** 16 August 2017, 07:33:12 am »

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.

unfazed · « **Reply #18 on:** 16 August 2017, 07:52:05 am »

Forgot to add in my last post, Check your wheel bearings also

NorthWestern · « **Reply #19 on:** 16 August 2017, 07:56:54 am »

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.

Simon.Pieman · « **Reply #20 on:** 16 August 2017, 09:34:58 am »

Try bleeding the brakes again but crack the banjo bolt next to the master cylinder instead of the caliper bleed nipple (put a rag underneath the cylinder of course). If the fluid splutters/spits when you pump then you've found the air bubble that can hide there. I do this everytime I bleed the brakes on my Fazer, sometimes there is air there, sometimes not.

Davie70 · « **Reply #21 on:** 16 August 2017, 11:53:30 am »

Guys a massive thank to you all for the helpful posts. Not 100% sure until I have replaced the offending part, but it looks like its the front wheel bearing. When I'm riding the pistons are being pushed back by the extra movement that the worn wheel bearing is allowing. So when I brake, the pads have more travel to reach the disk, hence no brake. Then when I pull the brake again immediately after they are working, coz the pistons are back where they should be. I will get a new bearing later this week and hopefully that will be the end of the problem

BBROWN1664 · « **Reply #22 on:** 16 August 2017, 02:36:30 pm »

depending on the hose layout, it could still be air in the system. Bleed each caliper separately starting at the one furthest from the master cylinder. Before you do that though, leave the bike overnight with the brake lever pulled back to the bar as far as you can and secured with a tiewrap to try and let any air rise out of the system. It will need a few pumps in the morning to get the pressure back though.

Davie70 · « **Reply #23 on:** 22 August 2017, 10:43:43 am »

Just to complete the story. I have changed the bearings and the brakes are now back to 100%.

I didn't feel the dodgy bearing whilst I was riding the bike, but I confess the handling is a bit tighter now. Would never have thought of checking a bearing to sort a brake problem. So again my thanks especially to Unfazed.

Dustydes · « **Reply #24 on:** 22 August 2017, 03:25:24 pm »

Good to know your up and running
Added to my mental notes for future ref: