5th Gen Brake Question, shudder/pulsation

1998 VFR with Linked Brakes

Last year I swapped out my old brake line with a set of spieglers.

I bled them with a vacuum bleeder at all points listed, and in the order the directions said. I even turned the from caliper 90d to get any trapped air out.

I noticed it intermittently when I first started riding, but lately it has happened all the time..

Grab the front brake, good. Grab the front brake and then the back, good. Step on the back brake and I get a pulsation/shudder through all the brakes, as soon as I apply some front, it all stops.

I have re-bled all, even the proportioning valve under the seat and it won't go away.

Any ideas?

 

I think it has something to do with the Secondary Master Cylinder located on the left front brake caliper.

I recently did the same swap, putting in new Spiegler lines on a '99. I think I'm also getting a little of that pulsation/shudder that you're talking about. My thought was that it probably had something to do with the fact that at the same time I also put on new EBC brake pads and they aren't quite bedded or matched to the old surface of the rotors yet so there's a little uneven feel (especially in the front rotors which get more vigorous usage).

So when I initiate braking with the rear pedal the system goes into its linked braking routine, and with only the rear brake pressed the system only grabs the front rotors with the one small piston on each caliper which probably applies just enough pressure to really highlight that slightly uneven feel of the new pads being not so smooth on the old rotor surfaces, and that light pressure drags the left caliper (lightly and unevenly) up against its Secondary Master Cylinder (rather than firmly as it would with a squeeze of the front brake lever). So the slightly uneven braking of the new pads on the old rotors gets transmitted back to the middle piston of the rear brake.

Yeah, it's an odd feeling. I was betting it'll go away when the new pads settle in.

Although it is possible that this phenomena was always there but you (and I) didn't feel it until after putting the Spieglers on the bike because the Spiegler lines are so rigid. Maybe the old OEM brake lines would flex a bit and as a result they didn't transmit (or amplify) this odd system feedback.

 

Sounds like my idea of doing the delink just may be justified here. thanks guys, onward ho

 

Check all of your rotors. Maybe one is warped or loose.

 

Well, I guess I'm used to odd machinery, I fly Boeing aircraft for a living.

 

This isn't normal.

I did my lines with the shitty galfers and I have a GP lever feel -- half way to the bar and it's solid as a rock. The pedal has lots of authority up front and is solid. No pulsing no matter how I initiate.

One thing the directions never seemed to mention was the valve on the left front caliper. I manually worked that mini master cylinder a few times, to make sure it was pumping fluid to the back. That's a shot in the dark, though. I don't think it's your problem, but it is a weird item.

I'm guessing it has something is up with the back caliper. Did you pull the wheel and flip it on top so the bleeder was at the top when you bled it? And did you check all of the pistons to make sure they were free? If using the front stabilizes things, I am not expecting it to be a warped rotor, but a warped rear rotor might do that. I'd just expect to feel it through the center piston as well as the outers.

I wonder. If that little master cylinder has a bit of trapped air, maybe I'm wrong. Or maybe you have a hanger binding on a rotor? Floating rotors shouldn't ever pulse if they're straight, even if they're hot as hell and out of shape.

 

Thanks for that thought, it didn't occur to me to manually pump that secondary master cylinder when I was bleeding the brakes. That sounds like a good idea.

 

Let us know if it fixes anything. I'm genuinely curious. Especially since it's two people seeing the problem and, frankly, that's a weird little mechanism.

 

I didn't think about the little master cylinder on the front. I will attempt to bleed that over the weekend and see if that helps.

Thanks guys!

 

I was looking at the schematic in the maintenance manual after thinking about this. The idea behind tipping the left front caliper up is to get the air into that line so you can suck it out at the PCV bleed (behind the tank). I bet pumping this master cylinder will get that air untrapped more quickly. Still don't know if that's your problem, though.

Like I said, I don't know how this is happening, but it fascinates me.

The ONE other thing I can see causing this is the delay valve. The fluid from the rear goes to the valve in the front, where it is distributed to the right front through the delay, and to the left front. If something's wrong there, or even if there is air trapped at that valve, maybe it's opening and closing, which would shudder and, since it's also going to the left caliper the shudder might be amplified though that secondary master that goes straight to the rear brake.

Again, total conjecture, but I'm imagining how the tiniest bit of air or contamination at this valve could cause a pulsing behavior.

No solution to this, either, except bleed with clean fluid. I literally bought the litre bottle knowing I was going to waste a crapload and, after having charged the system and done an initial bleed I let it sit overnight. The next day I just kept going around the circle of bleed points until I got zero improvement in the lever 3 in a row. That last bleed didn't take very long at all, but I am glad I had a vacuum pump and speed bleeders because I used a LOT of fluid.

Good luck. Let us know how it comes out.

 

LOL what a freaking mess this read is.

 

Says the man with de-linked brakes....

(which I too have done).

 

And this comment helps how?

This is interesting. At least for those of us who kind of like working on their bikes. It's a weird symptom and I'm genuinely looking forward to finding out what caused it. It's a mystery for someone who doesn't have a television to entertain him.

The system isn't as complex as you think. It's just not normal, so some of us didn't understand it until we dug into it. And bleeding it isn't so bad once you know how. Especially with the speed bleeders, which are so helpful they should come stock.

I did the same thing with my 3rd gen and my GS. Steel lines all around, bleed the shit out of them, then bleed them more. Back and forth, back and forth, "wasting" plenty of fluid until the lever was firm and consistent, wait overnight, then do it again. Just with 3 bleeders instead of 7. That's what you have to do for perfect brakes, regardless. And you do it again at least every 2 years because the fluid doesn't last forever.


The linked brakes are a good system. I wouldn't put it on a race bike. I mean, beyond the ability to back into corners or other things that only happen on a track, there's a weight penalty. If you go to the ridiculous length of putting on UD forks to save a few ounces a side on unsprung weight, you want the simplest calipers possible for the same reason.

But around town the weight doesn't matter and it works a peach. Especially with the fresh lines so it's powerful and predictable. You can trail with the rear lever in a way I never could with my 3rd gen, and the way it squats then allows you to load the front progressively going into a fast corner is surprisingly good.

 

LOL its not suppose to help, more a case of relaying this forward so others know this isn't a cake walk when it comes to the VFRs linked brakes. As nice as some think linked brakes are , maybe when everything is working like it's suppose to, and even then, that's questionable. This thread tells how it takes little to upset the apple cart. Is what it is. All is good right?

 

How little? Both of these people added all new lines to 17 year old motorcycles, and at least one did a complete disassembly and rebuild of the calipers (and a lot more) in the process. And you're heckling them.

Literally disassembling everything down to individual component parts and reassembling... wow, that's not very much to do to make a possible mistake! These brakes must be SUPER delicate!

hey, I found a clip of you hanging around the garage while your friends work
[video=youtube;X6I_dKUYyI4]https://www.youtube.com/watch?v=X6I_dKUYyI4[/video]

 

Interestingly enough, in regards to linked brakes and racing, the current Yama R1 actually has them. They call it their Unified Braking System.
Video explanation: [video]https://youtu.be/2Z_s3k0jWNo[/video]

 

Cool! They take into account attitude and lean angle. I guess it's computerized. All the detriments of a purely mechanical system can be tuned out.

I was in automotive for a long time and remember the shit we had to do to get simple things to work just 15 years ago. What they can do with the processing power available these days absolutely blows my mind.

Motorcycle ABS systems are also insanely good compared to early automotive ones, and big displacement bikes are getting better traction control all the time, so it shouldn't surprise me.

 

I tend to ignore the haters/negative nellies. Everyone is free to have an opinion, even that douche bag!

 

I'm teasing. RVFR's awesome, and we all know it. But every once in a while I go looking for an excuse to make a Statler and Waldorf reference.

 

I'm teasing too. I've read a lot of good posts, and RVFR's rarely a douche!

I would consider de-linking if I hadn't spent the cash on Spieglers. Not to mention, I still need to install the DMR 929 rear and fork cartridges.