Floating Disc - Bobbin Play/Movement?

north_of_55

New Member
Joined
Sep 20, 2018
Messages
6
Location
Sudbury, ON, Canada
I have a 2013 with around 57K km on the clock.

Ever since I bought it (around a year and a half ago) it has had - it's hard to describe - what feels like warped discs in the front. But I don't really feel any feedback through the brake lever.

Rolling to a stop if feels like the coefficient of friction on one half of the front discs is higher than the other... so as I roll to a gentle stop under braking the nose of the bike is diving intermittently - as though I am squeezing and releasing the brake. At higher speed/harder braking it is not noticeable.

I have rotated the disc bobbins with brake cleaner, I have cleaned both calipers as well as the pads and discs. All of the pistons seems to move freely. The pads appear as new, the discs have no visible sings of wear, uneven contact with the pads or checking.

Over the coming days I plan to rig up a way to mount my dial indicator to my fork so that I can check run-out.

As a Professional Engineer and an experienced wrencher - I am a little stumped.

My main question at this point is about the floating discs. I have seen several forum posts about floating discs and the consensus always seems to be that the disc should be free to move slightly (axially and tangentially) if things are in good shape.

The discs on my ST seems very much rigid. The bobbins turn with light pressure on a wrench (with a 6mm bolt and nut snugged) but there is no way that they could be rotated with fingers alone (as I have seen several people suggest they should).

How much movement should the disc have with respect to the carrier on an ST? Are anyone's bobbins movable by hand?
 

cyclemike4

Well-Known Member
Joined
Sep 18, 2016
Messages
815
Location
ky
O.K. i know you are going to think this is crazy but on my bike i have the same issue. I checked everything just like i am sure you are doing. You are absolutely right about rotors having more friction at one point on the rotor than the other. I just do not think these rotors are made that well. It is almost like different metals that didn't blend well. When they get wet or dirty or some kind of contaminant gets on them you will feel just what you are describing. I cleaned mine well and took the bike out got into second gear and applied the front brake hard and kept the gas on to heat the rotors and pads. I let them cool and went through that cycle again. usually two or three times. Just like you would do breaking in a new rotor to clean it and seat the pads. Every time mine starts doing that i go through this and so far it has worked out for me.
 

WJBertrand

Ventura Highway
Joined
Jun 20, 2015
Messages
4,516
Location
Ventura, CA
I had my front rotors replaced under the YES warranty due to uneven thickness. Had the exact symptoms described by the OP. I think those bobbins are mostly to allow the rotor to grow radially as they heat up thereby preventing distortion where they would otherwise be hard bolted. The fit is probably a lot looser at operating temperatures.
 

tubebender

Active Member
Founding Member
2011 Site Supporter
2012 Site Supporter
2013 Site Supporter
2014 Site Supporter
Joined
Jan 6, 2011
Messages
656
Location
Oceanside, CA
Modern disc brakes come in 2 flavors – a floating caliper or a floating disc.

For instance, on my KLR the caliper floats on pins and the disc is rigidly mounted. It has a (1) piston on one side pressing on a brake pad and a bridge that holds the opposite brake pad. When pressure is applied, it presses one pad into the disc and pulls the opposite pad, and because there is a disc between them you get whoaed down. Any variance in the disc is absorbed by the caliper moving on the pins. Discs have an acceptable range of variance.

On the Tenere, the caliper is solidly mounted as it has pistons on both sides. When pressure is applied, it is pushing both pads into the disc. Thus, the disc has to be able to move about on its mount (the brake hat) to take up any variance. This is what the bobbins do. They allow tangential movement but not radial.

Any variance outside acceptable limits could cause various feedback issues, such as pulsing felt in the brake lever (or pedal), or grabiness (technical word) as the disc spins.

Further, maximum braking effectiveness is best when there is brake pad material deposited on a steel disc. Sometimes, there could be a buildup of more material in one spot on the disc and this could manifest itself as to thinking the disc may be warped. Improper bedding in of new pads on used discs can contribute to this.

Disc warpage is not a factor of heat, rather, it is a factor of uneven cooling after a heat cycle. In my personal experience, I have only experienced warped discs on one of my cars, but never on any of my bikes. I cured this by fashioning some cooling ducts for a Ford Taurus!

This is a bit of an oversimplification, but I think it explains the major points.

Years ago, I used to change a lot of pads and discs.

Brakes.jpg
 

north_of_55

New Member
Joined
Sep 20, 2018
Messages
6
Location
Sudbury, ON, Canada
The way it feels I would automatically think that it was a disc thickness issue - but the complete lack of feedback in the brake lever is what makes me try and explain it in terms of friction variation.

The only way I could see this being a thickness issue is if the ABS and/or linked braking system somehow reduces that feedback to the hand.

Maybe I'll take a micrometer and check thickness around the disc to see if that is the cause.
 
B

ballisticexchris

Guest
On the Tenere, the caliper is solidly mounted as it has pistons on both sides. When pressure is applied, it is pushing both pads into the disc. Thus, the disc has to be able to move about on its mount (the brake hat) to take up any variance. This is what the bobbins do. They allow tangential movement but not radial.
Thank you for that!! I did not notice pistons on both sides of the caliper. No wonder these brakes are so strong!!
 

WJBertrand

Ventura Highway
Joined
Jun 20, 2015
Messages
4,516
Location
Ventura, CA
Actually, a dual action caliper, like on our Ténéré’s, can work fine with a non-floating rotor too. Even under hard braking, the opposing pistons can move back and forth to follow the rotor. Since the fluid pressure is equalized behind each opposing piston they can move left and right in unison easily. So the use of rigidly mounted calipers vs. floating depends on the type of caliper, single or double action. Either type can accommodate floating or rigidly mounted rotors.



EBC Brakes believe axial float to be a bad thing.


So most references indicate that “floating” rotors are designed to allow radial expansion at operating temperatures, not axial float.


Sent from my iPhone using Tapatalk Pro
 
Last edited:

MattR

Well-Known Member
Joined
Nov 16, 2019
Messages
1,175
Location
North Hampshire UK
Sounds like the disks are warped to me. I had exactly the same thing with my zx14r after I had been using ebc hh pads. The Zx14r oem disks are cheap Chinese made disks whereas the S10 OEM are reasonably good quality Galfer disks but EBC pads are notoriously hard on disks. I changed my disks to PFM disks which are true floating disks that don’t have bobbins and don’t need cleaning


Sent from my iPhone using Tapatalk
 

jrusell

Well-Known Member
Joined
Aug 23, 2017
Messages
460
Location
Dartmouth, Nova Scotia, Canada
Uneven pad material transfer on the discs.

I have had the same issue with my 2013 and other bikes. As mentioned by cyclemike some hard braking drills like you would do with new pads will usually lay an even amount down and the issue will go away.
You can also clean the discs with a rotor hone or those foam sanding blocks to remove all the pad material that has been deposited over they years and start fresh.
If it was a warped rotor you would feel it at the lever at slow and high speeds.

Also any time you replace pads they should be cleaned with a rotor hone or sanding blocks before new pads are fitted. The only exception is if you are putting exactly the same pads back on. Different brands use different materials and you will be laying new material on top of old pad material. I know 99% of people never do this, but this is the proper procedure. Brake cleaner and a rag doesn't count.

My bike was doing this a lot last year. I did a light sanding to my rotors over the winter and haven't noticed it yet this year. Although I expect it will return at some point.
 

Drif10

Active Member
Joined
Jul 22, 2020
Messages
136
Location
Quebec
First ride tonight on my new-to-me 14, got back in my shop, loosened up the bobbins, still kind pulsing, a little search here and found the comments above.

Good to hear that I'm not imagining things, gonna give the rotors a little scrub in the morning followed by some braking drills, looks like that'll do the job.

Thanks for the tips, guys.
 

2daMax

Active Member
Joined
Jun 3, 2015
Messages
675
Location
Penang, Malaysia
You may want to try aligning the disks to the brake calipers. Usually after the front wheel is removed n reinstalled, there will be a slight misalignment. If u hv a jack, lift the front so that the wheel is free. Hand rotate it n on certain spots, there is more scraping. Uneven scraping.

Here is how to align them. Bike on double stand. Loosen 2 bolts that clamps the axle. Loosen the 4 bolts on the fender. Now get on the bike n push down on the handle about 3x. This will cause the front suspension to compress. Then hold the front brake n repeat the push down.
Hold down the lever either by hand or tie it with a glove n tighten up the 2 axle bolts. Release the brake lever. Tighten up the fender bolts. Now test it if u can.

If it doesn't improve, the lower triple clamp bolts needs to be involved also. Repeat loosening bolts as above and also loosen up the 4 lower triple bolts. Repeat the push downs n brake holding. Then tighten axle bolts, then lower triple bolts, then fender bolts.

I found that it improves by 1km/liter by just doing this. Discs are a lot cooler after a ride.
 

Kurgan

Well-Known Member
Joined
Dec 11, 2015
Messages
372
Location
SE Michigan
Uneven pad material transfer on the discs.

I have had the same issue with my 2013 and other bikes. As mentioned by cyclemike some hard braking drills like you would do with new pads will usually lay an even amount down and the issue will go away.
You can also clean the discs with a rotor hone or those foam sanding blocks to remove all the pad material that has been deposited over they years and start fresh.
If it was a warped rotor you would feel it at the lever at slow and high speeds.

Also any time you replace pads they should be cleaned with a rotor hone or sanding blocks before new pads are fitted. The only exception is if you are putting exactly the same pads back on. Different brands use different materials and you will be laying new material on top of old pad material. I know 99% of people never do this, but this is the proper procedure. Brake cleaner and a rag doesn't count.

My bike was doing this a lot last year. I did a light sanding to my rotors over the winter and haven't noticed it yet this year. Although I expect it will return at some point.
Exactly, there are sections of the disks with a bit more material transferred in, causing a different coefficient of friction. I first learned about this back in the 90's at the AMA Superbike Races. Al Ludington who was crew chief for Honda would have the disks bead blasted after every qualifying session and to prep before the race.

I even experienced this on a 99 Tahoe that I owned when living in the mountains of NC. That truck had tiny front disks and rear drums of all awful combos. Overheated brakes were common and I would have the pad transfer issue almost monthly regardless of what pad I tried from any manufacturer from OEM pads to severe duty ambulance/police rated pads to full on ceramics....just horrible.
 

Drif10

Active Member
Joined
Jul 22, 2020
Messages
136
Location
Quebec
You may want to try aligning the disks to the brake calipers. Usually after the front wheel is removed n reinstalled, there will be a slight misalignment. If u hv a jack, lift the front so that the wheel is free. Hand rotate it n on certain spots, there is more scraping. Uneven scraping.

Here is how to align them. Bike on double stand. Loosen 2 bolts that clamps the axle. Loosen the 4 bolts on the fender. Now get on the bike n push down on the handle about 3x. This will cause the front suspension to compress. Then hold the front brake n repeat the push down.
Hold down the lever either by hand or tie it with a glove n tighten up the 2 axle bolts. Release the brake lever. Tighten up the fender bolts. Now test it if u can.

If it doesn't improve, the lower triple clamp bolts needs to be involved also. Repeat loosening bolts as above and also loosen up the 4 lower triple bolts. Repeat the push downs n brake holding. Then tighten axle bolts, then lower triple bolts, then fender bolts.

I found that it improves by 1km/liter by just doing this. Discs are a lot cooler after a ride.
Front end alignment, we used to call it. :)
 
Top