Author Topic: Disc wearing into caliper - new K100 owner  (Read 5139 times)

Offline barnett

  • Curious
  • Posts: 5
Disc wearing into caliper - new K100 owner
« on: August 27, 2018, 05:56:55 AM »
I picked up a 1989 K100RS 2V yesterday, which was a bit of a gamble given this issue with the brakes and some other things I noticed but I thought I'd start with the brakes as it's rather a pressing issue.

on the front, the right hand disc appears to have worn the pad away entirely and begun wearing a groove into the caliper itself. When stationary it appears that the disc is touching the caliper on the right hand side, which you can just about see in the below pictures



I can only imagine this means the caliper isn't mounted correctly, but being new to bikes in general and brand new to this particular bike, I thought I'd ask the guys who know what they're talking about.

Has anyone else had this issue? What can I do to fix it as the front brakes are currently about as much use as a chocolate teapot.
  • Gloucester, England
  • K100RS, Triumph Bonneville Street Twin

Offline Scott_

  • Administrator
  • ^ Quintessential Motobricker
  • Posts: 2242
Re: Disc wearing into caliper - new K100 owner
« Reply #1 on: August 27, 2018, 06:59:43 AM »
It looks to me like the caliper piston on the right side is stuck, and has been for a while.
The calipers are bolted solid to the forks, so there is no real adjustments to it.
I'd suggest you consider a caliper rebuild-- cleaning, new seals, and pistons. Some seal kits come with pistons, some don't. Would be cheaper than a new one, and you risk the same problem with a used one.
  • My Garage
1995 K1100LT 0302044
2017 FLHTK Ultra Limited
1997 K1100LT 0302488 (R.I.P.)
1997 R1100RT ZC62149(sold)
"One who does not ask questions is ashamed to learn" Danish proverb

Offline K1300S

  • ^ Quintessential Motobricker
  • Posts: 1293
Re: Disc wearing into caliper - new K100 owner
« Reply #2 on: August 27, 2018, 08:20:22 AM »
either the disk has the wrong offset or something is wrong with the caliper mounting.  the disk should be centered in the caliper.  the pads look evenly worn, so i doubt it is a stuck piston problem.
Project Thread "K75s Midlife Refresh"
http://www.motobrick.com/index.php/topic,7810.0.html

Offline The Mighty Gryphon

  • Administrator
  • ^ Quintessential Motobricker
  • Posts: 6843
Re: Disc wearing into caliper - new K100 owner
« Reply #3 on: August 27, 2018, 08:38:53 AM »
Is the fork action correct with no binding?   Is the wheel properly centered in the forks?  Are the correct axle spacers installed in the correct places?  Are you sure the caliper is the correct one for the bike?

Worse comes to worse, you could shim the caliper out to center the rotor in the gap.
  • In my garage in Marilla, NY
  • '91K100RS White/Blue
Current:
'91 K100RS16V "Moby Brick Too"

Past:
'94 K75RT "Ilsa, She Wolf of the SS"
'92 K100RS16V "Moby Brick" (RIP, deceased in a vehicular assault)
'94 K75S Special Edition Dakar Yellow "Cheetos"
'89 K100RS Special Edition "Special Ed"

Offline Laitch

  • Faster than a speeding pullet
  • Administrator
  • ^ Quintessential Motobricker
  • Posts: 11299
Re: Disc wearing into caliper - new K100 owner
« Reply #4 on: August 27, 2018, 10:21:09 AM »
Moto disc brake calipers don't move. They hold the brake pads which clamp onto and retract from the brake disc by being moved by the hydraulic action of the pistons upon them that slides them along the pins (blue lines). Even with all the gravel road riding my moto experiences, my pad assemblies are not out of alignment like your example. Maybe the perspective of the photo is skewing things.

The pads should be stabilized in their positions by the spring (red line). The three pins (blue lines) should be parallel. The center pin creates the spring tension. There is a shallow channel in the center of each pin into which the spring should engage. In your image the spring appears cocked off center, not engaged in the center pin channel and the center pin also appears out of alignment with the other pins. The loop at one end of the spring appears disengaged in its channel located in the center of the lower pin in the image. The spring should be centered over the disc (yellow line) and equidistant from the inside walls of the caliper; it appears cocked within the caliper instead.


What is acting on these parts to move them out of position? Were they ever installed correctly? Is it an optical illusion? The whole assembly needs inspection and cleaning. The pads can be removed without removing either the caliper or the wheel. You might clean the crud off the assembly, to the extent possible. You could use a screwdriver blade to attempt moving the spring into alignment on the pins first. That might ease disassembly. You'll need a drift of suitable length to drive out the two long pins, starting at the hooked end of the spring. Do it slowly and prevent the spring from rebounding. Next, pivot the spring to remove the center pin, then remove the pin from the looped end of the spring. Poke the pads from their positions.

Try to learn how to use this site's photo software rather than posting via Photobucket then your photos will be permanent here. There is a photo posting guidance section at this site.

  • Along the Ridley in Vermont.
  • 1995 K75 89,000 miles

Offline barnett

  • Curious
  • Posts: 5
Re: Disc wearing into caliper - new K100 owner
« Reply #5 on: August 27, 2018, 12:14:12 PM »
Thank you all for your responses, they are each hugely helpful. Laitch in particular for the effort and detail you went into.

I have ordered a rebuild kit and will rebuild both front calipers. While I'm there I may as well install SS braided hoses and uprated pads.

Many thanks again.
  • Gloucester, England
  • K100RS, Triumph Bonneville Street Twin

Offline K1300S

  • ^ Quintessential Motobricker
  • Posts: 1293
Re: Disc wearing into caliper - new K100 owner
« Reply #6 on: August 27, 2018, 06:09:44 PM »
the issue has nothing to do with the pads,pistons or spring clip.  the issue is that the rotor is not aligned with the caliper.   is the other caliper in the same state?  gryph is on the right track.  gotta check all the "fixed" items which affect the rotor and the caliper.

the disk is attached to the wheel and the caliper to the fork.
Project Thread "K75s Midlife Refresh"
http://www.motobrick.com/index.php/topic,7810.0.html

Offline Laitch

  • Faster than a speeding pullet
  • Administrator
  • ^ Quintessential Motobricker
  • Posts: 11299
Re: Disc wearing into caliper - new K100 owner
« Reply #7 on: August 27, 2018, 07:40:29 PM »
the issue is that the rotor is not aligned with the caliper.  gryph is on the right track. 
That's an issue alright.
  • Along the Ridley in Vermont.
  • 1995 K75 89,000 miles

Offline barnett

  • Curious
  • Posts: 5
Re: Disc wearing into caliper - new K100 owner
« Reply #8 on: September 11, 2018, 03:36:24 PM »
So I rebuilt the calipers with new pistons, seals and pads, took the wheel off, discs off, discs back on and torqued up correctly, then I found that it was a bugger to get the spindle back through, so I realigned the forks by undoing the fork brace a bit to allow it to go back through smoothly.
Now the calipers are back on, minus the hoses as I'm waiting on a replacement set of braided hoses. Now the wheel seems to spin freely without friction from the pads or caliper, but the disc is still very close to the outside pad on the right hand side, while the left hand disc is right in the centre of the pads.
Does anyone know what else might be causing this?


  • Gloucester, England
  • K100RS, Triumph Bonneville Street Twin

Offline Laitch

  • Faster than a speeding pullet
  • Administrator
  • ^ Quintessential Motobricker
  • Posts: 11299
Re: Disc wearing into caliper - new K100 owner
« Reply #9 on: September 12, 2018, 07:58:20 AM »
Does anyone know what else might be causing this?
Replies #2, #3 and #6 have already indicated several likely causes. It is now up to you to compare the elements mentioned in those posts. It could be difficult because you have little motorcycle maintenance experience but what you will doing is analyzing the assemblies using a straight edge, measuring rule or tape and clear vision to find differences between commons elements on each brake assembly, each fork leg and the fork itself.

It's like that game where two drawings seem to show duplicate scenes outdoors or in a crowd but the challenge is to find elements in one drawing that differ from the other. Doesn't that sound like fun?
 :yippee:
  • Along the Ridley in Vermont.
  • 1995 K75 89,000 miles

Tags: