Chatter

[Cash Dereszynski]

I have determined that my front forks are the source of my chatter. Using a tie wrap to measure the range of compression on a trip on Hwy74 which I'm very familar with now.
On the return home I just passed a line of 6 cars on a clear straight of level road. When I pulled back in at about 80 mph and started braking for the coming bend it happened again, chatter. Duration of maybe a couple of seconds.The forks completely bottomed out. I released the front brakes and the chatter stopped. Gathered myself and continued. I also noted no rear brake was used, typical of my riding. My modified front forks are from a R1 with stock springs. While on the rally with the fast guys most had stock fork set ups and I would guess resprung to be correct for weight and riding style. I would do like everyone else and select the proper set up from RPM and be done. But NOOOO, I had to go with USD R1 type, so my question is,what is everyone using for spring rates ? And oil viscosity ?

Regards

Cash

[simi_ed]

Cash, a good place to start for your custom build would be RaceTech.  They can spec springs and custom damping stacks for your forks, for your 'as installed' weight.  Specific spring weights included.  Oil is almost always 5w for your damper stack front end.
I did this with my YZF600 front end. It's one of the better plans to get you where you wanna be!

Ed

[giantkiller]

Check your steering stem tightness. Slightly loose will cause brake chatter. It's a fine line between too loose and too tight. Too tight will cause low speed wander.

[giantkiller]

I think USD forks because they are so much stiffer,with better brakes. Amplifies stuff. It could also be a bent rotor. Will's rim repair. Besides fixing bent rims also straightens bent rotors. But  if your fork's are bottoming out. You have other problems. That's why I chose 2007/2008 gsxr 1000 forks. They are notorious for being over sprung stock. I didn't have to respring them.

[Pat Conlon]

Hey Cash, yep, you need heavier springs.

The weight of the FJ exceeds the weight of the R-1 by over 100 lbs. It is necessary to know what year R-1 your forks came from..... On the newer version USD's they use a big piston KYB design has the compression spring on one fork and rebound on the other fork. IOW you might need one compression spring, not two.

I checked the Race Tech website and I see several different stock spring rates for the Yamaha YZF R-1 http://racetech.com/VehicleSearch

For example on the YZF R-1:

1998-2001:  .750 kg/mm
2002-2003:  .816 kg/mm
2004-2006:  .930 kg/mm
2007-2008:  .950 kg/mm
2009-2011:  .920 kg/mm

To give you an idea, Dan's (giantkiller) 2007-2008 GSXR 1000 forks have stock .976 kg/mm fork springs.

Therefore, I would look at .950 kg/mm fork springs, which is what I use on my new YZF 750 USD fork set up.

Again, you need to know what year forks you have.....Ed's advice is spot on....call the pro's at Race Tech. Chances are, if you have the '98-'01 forks with the soft .750 kg/mm springs, you will need to revalve your forks to control the heavier .950 kg/mm springs.

Springs control the bike, the valves control the springs.

Race Tech can help you with this.

Like Dan said, check your stem bearings.... Chances are you have a mildly warped rotor. To find out which one, take one rotor off,  zip tie the caliper up out of the way, ride and see if the chatter goes away. If it does, that's the rotor you need to replace...if not, replace the rotor and take the other rotor off, repeat....see  what happens.

Cheers lad....stay cool you poor sod.

[Cash Dereszynski]

Pat

  Staying cool by the cement pond.

  Cash

[Cash Dereszynski]

Check your steering stem tightness. Slightly loose will cause brake chatter. It's a fine line between too loose and too tight. Too tight will cause low speed wander.

Checked the torque settings on the stem all correct. Rotors straight, pads good . Springs at Race Tech just down the road, making appt. for upgrade.


Cash

[red]

Checked the torque settings on the stem all correct. Rotors straight, pads good . Springs at Race Tech just down the road, making appt. for upgrade.
Cash

Cash,

I would still want to check the rotors with a screwdriver blade clamped to one fork, with very little clearance from the screwdriver blade end to the rotor face.  Then make the same check, on the other side.  Remove the brake pads and chew through any glaze layer on the pads with sandpaper, by hand only.  Clean the rotors with brake cleaner and paper towels, twice. 

Tapered roller bearings are a fine upgrade for any steering head.  Mine are okay for now, but I will replace mine at the first excuse, using tapered roller bearings.  Torque values alone may not be telling the tale, there.

Cheers,
Red

[ribbert]

.... take one rotor off,  zip tie the caliper up out of the way, ride and see if the chatter goes away.......

Pat, have you actually ever done this?

If the caliper is off, why remove the rotor? Why not just push the pads back off the disc? Why not just do it in the garage by one of the many ways to check for run out like everyone else and without sailing down the road without brakes?



Noel

[Tuneforkfreak]

Hey man some guys use screwdrivers some just take off one caliper at a time and test run it. I think if you wanted to get really critical you could use a dial indicator, that's probably what i would use in such a case.

[ribbert]

 ....Remove the brake pads and chew through any glaze layer on the pads with sandpaper, by hand only. 

Cheers,
Red

This is a good idea but they need to remain flat, difficult if you are rubbing the paper over the pad. A good tip for this is to put the sand paper or emery on a piece of glass and rub the pad over it (glass is perfectly flat) If you don't have a piece of glass, do it against a car or house window.

This is also a good way to dress flanges you have gouged with a gasket scraper. You can even "surface grind" small heads this way.

Noel

Noel

[Pat Conlon]

Yes, you are correct Noel, no need to remove the rotor, just the caliper. One at a time obviously so you do have a front brake.

On the rotor removal, I was recalling when I deglazed my rotors. When de glazing I use a Flex Hone brush with my cordless drill. Makes work easy.


I lift up the front end, spin the tire and zip zip, the outside face of the rotors are done in short time.
To do the back sides I then have to take the front wheel off, remove the rotors, flip them around, put the wheel back on, spin it and zip zip the inside face.

Red's point is a good one, sometimes chatter can come from an uneven buildup of the pad transfer layer on the rotors.
When I went from organic pads to HH pads, I had to remove all the old transfer layer.

Bead blasting the rotors works well also. 

[racerrad8]

Yes, you are correct Noel, no need to remove the rotor, just the caliper. One at a time obviously so you do have a front brake.

Pat, if doing this wouldn't you also need to insert something between the pads to act as a sort of stopper for the caliper pistons on the disconnected caliper? I am seeing someone doing this riding down the road and POP out comes the pistons of the disconnected caliper. There goes the brake fluid and your front stopping power as well.

We simply jack up the front end and check the run out of the rotors with a dial indicator.

Robert

[Pat Conlon]

Hey Robert, depending on the pad thickness...I suppose so...When I did mine I had new thick pads.
Yes, on the unused caliper they squeezed together but I had no problem with the pistons popping out.

Did you get back the box I sent with the '91-'93 collar tool ?

[racerrad8]

We have had more than a few calls of people that were doing some kind of work on their calipers where the piston had come out just far enough to get stuck or where one side was already stuck allowing the other side to come far enough out to allow the piston to pop out and leak out the fluid. We have never had this happen here so it is good to know with new pad the pistons with not come far enough out to do this.

Yes, sir box in hand. Well not exactly anymore as the box itself was recycled, but the tool is indeed here.

Robert