I’m having this really annoying persistent problem with the front brake of my bike. I’ve had 3 mechanics look at it now, and the system’s been bleed about 4 times, but I still don’t have a fix.
Basically, when I got my bike, it came with a Brembo Radial MC for the front. Same ratio as the original yamaha lever, but as it’s a Brembo Radial, much more powerful and should have been better.
The problem I had/have is that the system looses pressure while braking, but only slowly and when the bike is moving, and it builds up straight away after the lever is released.
So, basically, when the bike is standing, I can pull the lever, firm or not, all day happily and there is no loss of pressure whatsoever. When I ride the bike, and feather the brake very slowly (e.g. when approaching a traffic light and slowing down very slowly), then it looses pressure gradually and completely until the lever is against the grips, but it builds up again as soon as the lever is released.
I cannot reproduce this when the bike isn’t moving.
All the mechanics I have spoken to don’t understand it and usually say it must be air in the system, but it’s been bleed so many times now.
When I put back another lever, standard non-radial, I couldn’t really reproduce the problem either. That made me think it was a faulty MC. However, it’s been back with Brembo twice now and they say nothing is wrong with it.
So the only think I can think of is that the extra pressure of the radial MC would cause the problem. Initially I thought maybe it’d be a calliper seal or something, but people say it’s unlikely because I would be able to reproduce the problem by just pulling in the lever hard when the bike is standing still.
So, I’m completely out of ideas now. Any suggestions?
I’m putting up a reward of a crate of beer (or similar) for whoever makes a correct diagnosis and can point me to a working solution.
BTW. The caliper is a basic Brembo 2 pot that comes with the bike as standard.
I know the problem…woo hoo crate of beer (hopefully)
It’s the lever mate (i think). I’ve had exactly this before in a race and had to pull off. It turned out the lever had been ever so slightly compressing the MC the whole time which in turn overheats the brakes and gives a total loss of pressure. Then after a few moments sat still it will return within the fluids operating temperatures and be fine.
You saying this doesn’t happen with the standard lever only reinforces what I think it is. I only ever buy OEM levers now as a result of this issue.
We solved it by filing down the part of the lever that hit’s the hammer on the MC to give it 1mm of play rather than compressing it slightly in the return position. We didn’t change anything else other than taking a tiny bit of fluid out of the system, and went from having no brakes at all to winning the next race
I may well be wrong…I could certainly sort it if I had it in front of me.
Thanks for the suggestion.The first time it was back with Brembo they replaced the seals. Last time they openned it up and said there was nothing wrong with it (obviously, I don’t know for sure, I can only take their word for it, but I trust the guy who sent it off to Brembo).They have a bleed nipple, and the system has been bleed through both (MC and calliper).
Thanks for the suggestion. I’m not sure if I understand well. Is it that there is simply too much fluid in the reservoir so it’s applying pressure all the time?
I’ll certainly try to take a bit fluid out, but I’m not convinced it’s the same issue. You say you had it during racing, I assume you’ll have made the brakes work hard. I get this when I’ve just set of, feathering the brakes a little. Also, the pressure comes back the second the lever is released. Would it have time enough to cool down in that case?
Anyway, thanks a lot of the suggestion, I’ll take a bit of fluid out and try again. If it works, let me know which beer you favour and the crate will be on its way
If not and you want to have a second go at it, let me know where you are and I can come by, including beer
Adivce being it sounds like the lever has been produced incorrectly. So even when the lever is released it’s putting a small amount of pressure on the system. Take off the lever and file down the part of the lever that pushes on the hammer of the MC until there is at least 1mm of free play.
If the fluid level is slightly below max then don’t bother taking any more out.
had same problem with a zx9 when standing had good lever presure,soon as u rode up the road the lever went back to the bar.bleed bleed no better.what it was,the disc carrier bent and pushing the brake pads back ,thus having to pump the lever to get the piston back out.will only happen when the wheel is turning,but u don`t feel no judder through the lever,hope this helps.
Seb#43, I checked the fluid level and it’s about midway through min/max.
The lever has been on another bike and apparently worked then, but I have no way of being sure of that (just taking somebody’s word for it).
I’m not sure how I would file down the lever? It’s one of those adjustable levers.
car eater, that sounds like very similar/same as mine. I had another “play” around with it now, and I can easily reproduce it now. When I push the bike and feather the lever very lightly (approx at the point just before it’ll “bite”) I can gradually pull the lever to the bars. If I pull the lever firmly or quickly, there’s loads of pressure.
So what’s the “disk carrier” and how did you fix it? (sorry, as you will notice, technical I’m not very ;)).
If you have a disc carrier, it’s the bit between the hub, the bit in the middle of the wheel that goes round, and the brake disc. Some bikes, like most cars, just have the disc bolted directly to the hub so don’t have the “disc carrier” in between. Don’t know about your machine.
Assuming the whole brake fluid has been changed by now and the system is not now full of a mix of fluids, sure sounds like something that is making the brake disc wobble a little.
Assuming you have not stoked it into something recently, sloppy wheel bearings, a distorted disc carrier (if you have one) or a distorted disc are the most likely candidates but…
Only after you have made sure the brake lever is not keeping the brakes part on. That’s the cheap fix, so always start with that. Swap to the original equipment lever again. If there is no problem then, it’s the replacement lever that’s at fault in some way.
Seb#43, I checked the fluid level and it’s about midway through min/max.
The lever has been on another bike and apparently worked then, but I have no way of being sure of that (just taking somebody’s word for it).
I’m not sure how I would file down the lever? It’s one of those adjustable levers.
car eater, that sounds like very similar/same as mine. I had another “play” around with it now, and I can easily reproduce it now. When I push the bike and feather the lever very lightly (approx at the point just before it’ll “bite”) I can gradually pull the lever to the bars. If I pull the lever firmly or quickly, there’s loads of pressure.
So what’s the “disk carrier” and how did you fix it? (sorry, as you will notice, technical I’m not very ;)).[
new disc or u can hit the carrier in the right place with a thin bar it may take the bend out,i did it and got away with it,a beer i think.
good call car eater…this bit is the rotor, its basically holds the disk…
if it doesnt run true (straight) it will push the pads away from the disc. The first time you pull ya lever it’ll be pushing the pads out to meet the disc, rather than giving you braking…
(hopefully)
![Motorcycle-Brake-Disc-Rotor-045-[1]--8589653219010693308.jpg](https://londonbikers.com/uploads/default/original/2X/0/0c3c0b4e568de92ef63e990be9183cf67e91c53c.jpg)