Brake fade + vibration = Baws!

[wull]

I have this annoying problem with the road bike. The bike is a 2009 GSXR 1000 which for the road the brakes were fine, I had the standard set up with a set of GPFAX pads fitted.

I then took the road bike on track and that’s where it went wrong, I had no brakes after 5 laps and that was the 2hr open session ruined, I let them cool down, went back out and went at maybe 75% and had at least some fun for just under an hour.

I swapped out the standard lines for Hel braided lines, race set up. I swapped out the brake fluid for RBF660 and stole the wife’s RCS19 master cylinder and chucked that on.

During this time I had a leaking fork leg so I changed the oil and dust seals and stuck in the correct weight oil, no idea what was in it before.

Now this is the strange part, after this I started getting a vibration whilst braking but I can’t for definite say when exactly it started happening, I was so convinced I had maybe done something wrong with the forks but it was done to the book. It’s more than likely the discs but it was so strange the timing of it all.

Anyway, back for another outing on track, this time all day sessions and again within 5 laps or so I was getting brake fade, I adjusted the lever from 18 > 20 ratio which helped a little and also adjusted the lever to the furthest out position which also helped but my confidence was gone. Also the front end vibration at times was terrible.

The RCS19 was no more than a year old at that time so what’s the chances of it needing rebuilt? I know of a few that have had similar issues and that’s been the cause but where I differ to them is I experienced this brake fade problem with a different set up initially before fitting the master cylinder, there’s was already fitted when they experienced the problem for the first time.

You can’t purchase the kit yourself it has to be sent away but the cost is £40 iirc, I suppose that’s worth paying if it saves wasting another track day.

Any other ideas? I think I’ll rebuild the calipers just to rule them out also and replace the discs, do you think warped discs would contribute to cooking the brake fluid? Causing brake fade? But I didn’t have and vibration during the first track day so I believe the discs were good then, but of course standard set up might have been the main reason for brake fade that day.

I have also checked wheel bearings and head bearings which are fine.

[KungFooBob]

I'd say discs, however as you've had the front end apart, I'd loosen it all up bounce it around a bit and tighten it all back up again, just incase something was twisted when you originally put it back together.

[weeksy]

different manufacturers have different ways of doing it all, some want the lever pulled in and then the bolts tightened, some done, some want one set of bolts first, then the other etc... So that's as KFB says, where i'd start.

Where did you get the RCS ?
What fluid ? Who bled them ?

[DefTrap]

Vibration is normally knackered discs, you don't always get noticeable pulsing

[wull]

I'd say discs, however as you've had the front end apart, I'd loosen it all up bounce it around a bit and tighten it all back up again, just incase something was twisted when you originally put it back together.

Forgot to say, already done this. The manual for Gsxr doesn’t say to do the method with the brakes but I’ve tried that as well. I’ve tried it every which way.

Could warped discs cause brake fade? Overheating from the constant contact with the pads? Could be the first time round purely because the set up wasn’t capable of dealing with track riding but after the changes maybe the discs causing not?????

[weeksy]

I'd say discs, however as you've had the front end apart, I'd loosen it all up bounce it around a bit and tighten it all back up again, just incase something was twisted when you originally put it back together.

Forgot to say, already done this. The manual for Gsxr doesn’t say to do the method with the brakes but I’ve tried that as well. I’ve tried it every which way.

Could warped discs cause brake fade? Overheating from the constant contact with the pads? Could be the first time round purely because the set up wasn’t capable of dealing with track riding but after the changes maybe the discs causing not?????

Hmmm i'd say no. I had warped discs in JErez on my 750 and apart from the vibrations it was fine.

I'd say the fade is either fluid, air or the MC itself.

[wull]

I'd say discs, however as you've had the front end apart, I'd loosen it all up bounce it around a bit and tighten it all back up again, just incase something was twisted when you originally put it back together.

Forgot to say, already done this. The manual for Gsxr doesn’t say to do the method with the brakes but I’ve tried that as well. I’ve tried it every which way.

Could warped discs cause brake fade? Overheating from the constant contact with the pads? Could be the first time round purely because the set up wasn’t capable of dealing with track riding but after the changes maybe the discs causing not?????

Hmmm i'd say no. I had warped discs in JErez on my 750 and apart from the vibrations it was fine.

I'd say the fade is either fluid, air or the MC itself.

I’m confident the fluid is fine as it was brand new and RBF660 so for the sake of £40 I think I’d be as well sending the m/c away and having that rebuilt and that will definitely rule that out, then use fresh fluid again. Just a pity it had to be sent away, very sly of them not making rebuild kits available.

[weeksy]

Forgot to say, already done this. The manual for Gsxr doesn’t say to do the method with the brakes but I’ve tried that as well. I’ve tried it every which way.

Could warped discs cause brake fade? Overheating from the constant contact with the pads? Could be the first time round purely because the set up wasn’t capable of dealing with track riding but after the changes maybe the discs causing not?????

Hmmm i'd say no. I had warped discs in JErez on my 750 and apart from the vibrations it was fine.

I'd say the fade is either fluid, air or the MC itself.

I’m confident the fluid is fine as it was brand new and RBF660 so for the sake of £40 I think I’d be as well sending the m/c away and having that rebuilt and that will definitely rule that out, then use fresh fluid again. Just a pity it had to be sent away, very sly of them not making rebuild kits available.

Well you can diagnose it further by adding a standard MC for a day while the Brembo RCS is being rebuilt. That'll narrow it down completely.

[KungFooBob]

Warped discs push the pistons back, which means more lever travel to get them to bite, which could be mistaken for fade?

[dern]

My guess would be if you originally just had fade and no vibrations then that will either be fluid or you're exceeding the top of the temperature range of the pad but that shouldn't be the case with those pads.

You've now changed too many things at once to be sure of what the cause is so the first thing I'd do is measure the run out of the disc to see if in the current state they're warped. I'd then free up the bobbins to make sure the disc is floating properly and then measure the run out again. Vibration can also be caused by the pad gripping/releasing. Is there any possibility that you've contaminated the pads? The other thing that probably worth doing is take off the surface of the disc with garnet paper and try bedding them in again.

Given that the only consistent things before and after are the pads and the discs and you're sure you've bled the system then that's what I'd be focussing on.

[Le_Fromage_Grande]

Braking vibration is either, you've assembled the front end wrong, something isn't tightened up properly (there are huge forces involved in braking so use a torque wrench), warped discs or you can get a build up of pad material on the discs which feels exactly like warped discs, pattern discs are a lot more prone to this than genuine ones.

By brake fade, I assume you mean the lever is coming back to the bar with little braking effect, probably air in the system, if the fluid was getting hot and expanding you'd have the opposite problem, gradually less travel until the wheel won't turn.

Both your problems could be caused by poor brake pads, I've had the pad material pull away from the backing plate cause problems like you describe - the original pads Yamaha fitted on 98 R1s did this, Yamaha replaced them on mine for free.

[wull]

Warped discs push the pistons back, which means more lever travel to get them to bite, which could be mistaken for fade?

That sound plausible, I think I heard that elsewhere as well.

With regards to the standard m/c it happened with that set up before I swapped everything out and they are prone to needing rebuilt as well so not sure if that will make any odds and to save me having to bleed x amount of times I’m as well getting the Brembo serviced and fitting that when it gets back.

It got so bad towards the end of the season there that I was feeling fade or a softness in the lever from road riding.

[wull]

Braking vibration is either, you've assembled the front end wrong, something isn't tightened up properly (there are huge forces involved in braking so use a torque wrench), warped discs or you can get a build up of pad material on the discs which feels exactly like warped discs, pattern discs are a lot more prone to this than genuine ones.

By brake fade, I assume you mean the lever is coming back to the bar with little braking effect, probably air in the system, if the fluid was getting hot and expanding you'd have the opposite problem, gradually less travel until the wheel won't turn.

Both your problems could be caused by poor brake pads, I've had the pad material pull away from the backing plate cause problems like you describe - the original pads Yamaha fitted on 98 R1s did this, Yamaha replaced them on mine for free.

That’s not entirely true, fluid fade caused by it “boiling” giving you bubbles which are compressible hence the soft spongy lever, I’m not convinced it’s this due to using RBF660 but you never know.

It’s looking more likely that I’ll have to service the m/c, fit new discs and pads and service the calipers as well.

As for the front end everything is nipped up as it should be, I went over it all again just to rule any of that out.

[Mr. Dazzle]

The fact that the initial fade only happened after a period of riding suggests it's temperature related and hence down to the pad/fluid/disc combination.

If it's warped discs you may be able to tell just by pulling the lever very gently, you could feel/hear a squeak/pulse etc. Or even just by pushing the bike around and keeping your ears open - listen to the tssssskkk sound. Warped discs would also cause the bike to shake faster/slower depending on how fast you're going, whereas other problems might be less related to speed.

As above though, my bet would be wonky suspension in some way or another. Either literally wonky, or a loose/overtight bearing etc. Do the IT fix - turn it off and turn it back on again!

[Ditchfinder]

Floating discs? Are the bobbins seized maybe......?

[Le_Fromage_Grande]

Braking vibration is either, you've assembled the front end wrong, something isn't tightened up properly (there are huge forces involved in braking so use a torque wrench), warped discs or you can get a build up of pad material on the discs which feels exactly like warped discs, pattern discs are a lot more prone to this than genuine ones.

By brake fade, I assume you mean the lever is coming back to the bar with little braking effect, probably air in the system, if the fluid was getting hot and expanding you'd have the opposite problem, gradually less travel until the wheel won't turn.

Both your problems could be caused by poor brake pads, I've had the pad material pull away from the backing plate cause problems like you describe - the original pads Yamaha fitted on 98 R1s did this, Yamaha replaced them on mine for free.

That’s not entirely true, fluid fade caused by it “boiling” giving you bubbles which are compressible hence the soft spongy lever, I’m not convinced it’s this due to using RBF660 but you never know.

It’s looking more likely that I’ll have to service the m/c, fit new discs and pads and service the calipers as well.

As for the front end everything is nipped up as it should be, I went over it all again just to rule any of that out.

You need air for bubbles

[Yorick]

With warped discs, you will feel a pulsing through the lever. On my K9 and L3 it happened. It's not quite warping, more the bobbins sticking. I improved things by taking the disks off, then soak the bobbins in WD40 then give them a reet good twatting with the big 'ammer.

The best braking performance improvement is to use an Accossato Master cylinder. I used GSXR1000s on track 15 years and never had brake fade using the Accossato M/C.

I even have one now on my 2019 bike.

[Mr. Dazzle]

You need air for bubbles

What're the bubbles in this kettle made from?

Well actually that's a piss poor example, 'cause I'd bet those are actually air bubbles added for the photo But in a normal kettle, what are the bubbles made from?

[Le_Fromage_Grande]

You need air for bubbles

What're the bubbles in this kettle made from?

Well actually that's a piss poor example, 'cause I'd bet those are actually air bubbles added for the photo But in a normal kettle, what are the bubbles made from?

A gas, it's either that or a vacuum, you don't generally get vacuum bubbles.

Edit: Bollocks

https://wonderopolis.org/wonder/why-doe ... n-it-boils

[Yorick]

You need air for bubbles

What're the bubbles in this kettle made from?

Well actually that's a piss poor example, 'cause I'd bet those are actually air bubbles added for the photo But in a normal kettle, what are the bubbles made from?

A gas, it's either that or a vacuum, you don't generally get vacuum bubbles.

Edit: Bollocks

https://wonderopolis.org/wonder/why-doe ... n-it-boils

Steam.