Occasional Curvy brake problem

Hello Bretheren,

Have tried a search but nothing seems to match my symptoms.

Past six months or so I've experienced a really odd, very occasional unpredictable problem on my SV650S '03 but last of the curvy K2's.

The bike would start to labour as if wanting to stall. Wasn't instant, I could feel it gradually coming on, getting to it's worst after about 10seconds. I thought it could be something in the fuel filter but if I dipped my clutch, the engine went immediately back so healthy revs, but the bike rapidly lost speed rather than coasting. Clearly a brake issue.

If I just dipped the clutch a little to stop it stalling, but gave it a bit more revs, I could 'fight through it'. After about 30 seconds of this, it would loosen off, and be completely back to normal.

I say occasional. Most often it would happen on the first ride of the week, or the return journey. Some weeks never at all. Always at lower speeds (between 25 & 40mph). Most noticeably, when it did happen, it would often be after riding a downward incline. Oddly though, not steep hills. I ride lots of them and it's only cropped up back on the main roads. Despite a couple of standard commute routes, it has never happened in the same location.

Fluid reservoir level fine. No leaks on driveway. Lines not snagged when inspected (but who knows what's happening in motion). I say again, 99.5% of the time the bike's absolutely fine. This has happened maybe 10 times which accounts for less than 1 mile out of the last 3,000. I had a service booked for next week. EArlier in the year than usual but I wanted this looking at before a trip South.

Why's he talking in past tense? Well it happened again today on my way home. First rains for a while so greasy road surface. With the erratic power delivery, the back end went and we had a little slide at about 25mph.

So now I'm nursing my bruises and considering my options. I don't want to go to the expense of fixing up the cosmetics* if this fault can't be diagnosed and rectified. I hate taking the bike to the garage only for it to behave nice for them and not demonstrate any fault.

You guys pegged my last odd fault (freaky instruments & spark = badly corroded starter relay). Does this new manifestation sound familiar to anyone?

Ta muchly,

Jim
Trough of Bowland.

*need upper right fairing for sure.

brake fluid overheating problem possibly. Not too sure though, are the brakes completely free when the bike is not in use?

Originally Posted by warrenhewitt10

brake fluid overheating problem possibly. Not too sure though, are the brakes completely free when the bike is not in use?

Hi there and thanks for the quick post.

The bike seemed free to roll and coast. No brakey squeals or whines. I have to back it over an incline to park it on my driveway, and it feels no different to any other day.

I don't think it is an overheating issue because as soon as the fault dies back down, the bike is absolutely fine for the remainder of the ride (say 15miles average). I think if it was o/h, it would get progressively worse, rather than just flash in the pan and bye.

Nice idea though. Ta.

[NedSVS]

Sounds like siezed brake pistons to me. Potentially very dangerous, so I wouldn't ride it again at all until you have checked it out.

if the fluid is boiling, which I will agree is very unlikely as it has an extremely high boiling point, it would cause the pistons to lock on effectively, then when it cools they will release. Like I say thats only an idea

But as NED says there above, if its been a while since the calipers have been cleaned and the seals changed that would be a great place to start, Last time I did mine I had a huge build up of salt behind the dust seal and was causing one of the pistons to seize

Well my only ride will be to the local garage, less than a mile away.

As for the seizure, I'd be inclined to agree if it did it immediately after braking, i.e. sticking on. It could happen fully pronounced when I haven't touched the brake lever for 5 minutes.

[yorkie_chris]

I have some fairings for sale, what colour you need?

I would strip and clean brakes, also master cylinder, possibly change lines too.

I've managed to source the upper RH, which is the essential one to be able to re-mount the indicator. However I'd be interested if you have the RH lower, or even the pair (upper & lower). Colour is candy grand blue.

That sounds like the problem Mad Tony had on the track last year. He shimmed the front brake master cylinder with washers so his lever wouldn't come back as far when he braked. Unfortunately, this meant that the master cylinder wasn't returning all the way and the more he braked the tighter the pads got. he locked the wheel solid on the second straight.

So things to check. Are the front and rear levers returning all the way to fully out when you release the brakes? or are the pivots tight and causing the cylinder to pump up? Next time this happens, get off the bike and check the master cylinders for the mechanism binding and bake sure they are returning all the way out.

a little piece of toot or grit in the master cylinder might also do this. The cylinder must return all the way out to release the pressure.

and if you can identify whether its front or back or both (unlikely) then you can isolate the problem to one or the other.

I don't think its sticking pistons as that would manifest itself more often. But its worth checking anyway.

I think you have a problem with your master cylinder(s)

and I'd bleed the brakes too just to make sure there's no air in there that can expand when heated and cause this too. Just to make sure.


Oh and next time it happens (quickly and lightly) touch both front discs (don't burn your finger). If one is hotter than the other, its calipers, if both are as hot as each other, its master cylinder.
C

[Biker Biggles]

If your recent off was caused by the rear stepping out and you are sure this was the same old brake problem then it must be the rear brake that is sticking on.You may be unknowingly touching the brake lever with your boot causing it to come on and it may then be sticking due to a sh&gged caliper or corrosion in the linkage or brake lever pivot..it may be worth getting it up on a stand and trying to replicate the issue.