Got a bit of a problem with my VFR that even my mechanic can't seem to figure out whats going on.
Not to long ago I had to have the front discs replaced as they were both warped, so that along with new brake pads for both the front and rear. About a month after that my bike started to show a shudder in the front end when using the back brake at low speeds around about 6kmh. At first we thought it was the Proportionary Control Valve, but after replacing the valve the problem appeared again and has gotten quite bad. The next thing we are going to try is replace the rear master cyclinder.
But the actual problem is when applying the rear brake only, you get a shudder from the front end of the bike as the front brake vibrates/pulses, however if you use the front brake lever, the shudder doesn't show. When test riding it the mechanic can see the vibrations in the front brake caliper on the left side, its like its pulsing or something.
Details of the bike are:
VFR800 2006 model
braided brake lines
I would say the problems is when using only the rear brake it activates the LHS caliper center piston. The problem is that caliper is also the master cylinder for the front brake system to activate the single center piston on the rear caliper. I would say they have done this so applying rear brake only you end up with all 3 pistons rear caliper applying force.
The problem is your LHS caliper is probably modulating on the caliper mounted master cylinder, so what you have front end is only clamping force on LHS rotor with the caliper modulating for what ever reason which would cause a shudder.
Things to look at would be there is no air in that system which feeds caliper master cylinder & rear caliper center piston, The proportional valve for that circuit isn't faulty. The caliper mounted master cylinder isn't faulty.
I don't think your rear brake master will be problem I guess it's air in caliper mounted master cylinder circuit, the center rear piston maybe sticking & needs over haul, caliper mounted master cylinder needs over haul or the caliper mounting bushing on fork leg has allot of play. I ruling out warped rotor as you have had them changed.
I've had the same problem with my 2002 model, so has member Auspanol. It's worse in the hot weather.
Since you're in Melbourne, I'm happy to get together and compare notes.
Also, you're not the Craig Thomson from Fulcrum are you??
Sorry not the Craig Thomson from Fulcrum you are thinking of.
What did Auspanol and your problem end up being with the VFR, I'm assuming you have have figured out what caused the shudder ?
I would say the problems is when using only the rear brake it activates the LHS caliper center piston. The problem is that caliper is also the master cylinder for the front brake system to activate the single center piston on the rear caliper. I would say they have done this so applying rear brake only you end up with all 3 pistons rear caliper applying force.
The problem is your LHS caliper is probably modulating on the caliper mounted master cylinder, so what you have front end is only clamping force on LHS rotor with the caliper modulating for what ever reason which would cause a shudder.
Things to look at would be there is no air in that system which feeds caliper master cylinder & rear caliper center piston, The proportional valve for that circuit isn't faulty. The caliper mounted master cylinder isn't faulty.
I don't think your rear brake master will be problem I guess it's air in caliper mounted master cylinder circuit, the center rear piston maybe sticking & needs over haul, caliper mounted master cylinder needs over haul or the caliper mounting bushing on fork leg has allot of play. I ruling out warped rotor as you have had them changed.
Thanks, will need to talk to my Mechanic to see if he has checked those things as well.
I had the same problem for a while years ago and it was usually when it was hot outside. I replaced the front and rear pads and I haven't had a problem with it since.
When it would start to shudder like that I would just use the front brake lever. Since we have linked brakes it activates the rear anyway but with no shudder. At such low speeds it just wasn't worth throwing money at since I never had a problem any other time. But like I said, I changed out the pads and have been good to go since. Of course I also changed out the brake fluid and bled the lines really good at the same time so maybe that helped.
At least I know I am not crazy. My 07 does the same thing but only when applying light pressure to just the rear brake. If I brake harder and or apply front brakes the vibration goes away. Figured it was due to LBS but am not concerned enough with it to investigate. My bike was a left over new 2007 and only has 8000 miles added since I bought it Oct. 2011.
Looks like it's a feature of the model. Neither me or Auspanol worked out the root cause, but it's one of those things that does appear to be fixable with things like changing pads.
Mine didn't do it much the past summer, but then the rear disk I have on there right now is grooved to buggery and squeaks like mad. Maybe that stopped the front vibrating. :-P
Last year I had the same problem on my VFR800A8. When using the rear brake only at a very low speed, the front end suddenly started to shudder. It disappeared
immediately when additionally pulling the front brake at little bit.
All those little tricks as cleaning the pads, changing the pads, cleaning the disks, bleeding the system etc all cured the nasty effect only for a short time, i.e. some 500-1500km. My Honda-Dealer even changed the secondary master cylinder on left of the front fork. The result was all the same.
Finally I got rid of the problem, by VERY carefully bleeding the complete brake system, strictly according to the rules to be found in the maintenance manual.
The CBS, at least as implemented in RC46, isn't really a robust system, obviously
its behavior may change heavily of behalf of minor parameter changes.
End of thread · 8 posts recoveredWayback Machine snapshot 26 Dec 2012