'87 K100RT Scraping Noise

Paul_F · Sep 5, 2019

Went for a 250 mile ride today on my old K100. Upon returning home and parking in the garage, when rolling the bike in neutral, I could hear what I would call a low scraping noise from the back of the bike. Put the bike on the centre stand and rotated the rear wheel and no noise. Wheel had no wobble at 9 & 3 or 12 & 6. Could not see where the wheel might be rubbing against anything. Went for a brief ride a few hours later and when rolling the bike out of the garage, no noise. Upon returning from the ride, rolled bike in the garage and the sound returned. Splines were done about 30,000 miles ago.

Any suggestions as what might be the cause of this noise? :dunno

98lee · Sep 5, 2019

Paul,

Did you check your rear brake pads?

:dance

69zeff65 · Sep 6, 2019

OEM rubber brake lines?

If you still have the OEM style rubber brake lines on the bike it might be time to swap them out for new or stainless steel ones. Try bleeding the brakes and see if the noise comes back after a ride.

Paul_F · Sep 6, 2019

98lee said:
Paul,

Did you check your rear brake pads?

No I haven't but that would make sense, Lee. If it is the brake pads, what is the cause and of course, the remedy?

69zeff65 said:
If you still have the OEM style rubber brake lines on the bike it might be time to swap them out for new or stainless steel ones. Try bleeding the brakes and see if the noise comes back after a ride.

The front has stainless steel brake lines but not the rear. I'll bleed the rear and see what happens. Thank you for the suggestion, Zeff.

98lee · Sep 6, 2019

Paul_F said:
No I haven't but that would make sense, Lee. If it is the brake pads, what is the cause and of course, the remedy?

If they are worn down to the backing plates, that would make it metal to metal. Solution is replace brake pads before it damages the rotor.

Paul_F · Sep 6, 2019

98lee said:
Paul_F said:

No I haven't but that would make sense, Lee. If it is the brake pads, what is the cause and of course, the remedy?

If they are worn down to the backing plates, that would make it metal to metal. Solution is replace brake pads before it damages the rotor.

Click to expand...

This afternoon I'll take them off and examine them. If they need replacing, I have a pair in stock. If that is the case, I can do a bleed while I am at it, although they were bled in early April.

Thank you, Lee, from a non-mechanical Paul.

Paul_F · Sep 10, 2019

98lee said:
Paul,

Did you check your rear brake pads?

Thank you for the suggestion Lee as that was the problem. One pad was worn very thin. Replaced both pads and made the 200 km ride to our friends 75th birthday party. My wife would have been quite displeased if I had not shown up for the party.

The rear rotar has some damage but is still functional for now. I will begin looking for a reasonably priced used rotor , one with some life left in it.

98lee · Sep 10, 2019

Paul,

Post a photo of the rotor damage and the bad pad. Some MINOR grooving will not really affect a REAR rotor, as most of the braking force comes from the fronts.

:dance

Paul_F · Sep 17, 2019

98lee said:
Paul,

Post a photo of the rotor damage and the bad pad. Some MINOR grooving will not really affect a REAR rotor, as most of the braking force comes from the fronts.

Sorry to take so long to post the pictures, Lee. The right pad was almost worn down to the metal; hence the groove on the right side of the rotor. The left pad looked fine but I replaced both pads. As for the pictures of the pads, that is not possible as they were pitched before the request of photographs of them.

I definitely am on the lookout for a new, or preferably, a slighlty used rear rotor for my '87 K100RT.

98lee · Sep 17, 2019

Paul,

The rotor doesn't look all that bad (for a rear rotor). I would suggest that it is not urgent that you replace it. The pads should always be replaced in pairs on the rear or in fours on the front.

:dance

Paul_F · Sep 17, 2019

98lee said:
Paul,
The rotor doesn't look all that bad (for a rear rotor). I would suggest that it is not urgent that you replace it. The pads should always be replaced in pairs on the rear or in fours on the front.

I figure a replacement rotor will be due when the next set of pads are required. Since I seem to replace the rear pads less frequently than the front, the replacement will be quite a few miles down the road. That should give me enough time to find a replacement rotor. I like to have parts I am going to need in stock so when the need arises, I have what is needed.

Stainless steel brake lines are going to happen before a rotor replacement.

pglaves · Sep 17, 2019

Here is a very important point when replacing pads with the existing rotor. Even if not obvious there are ridges and grooves on the rotor. With the old pads you didn't notice because the pads had worn to match those ridges and grooves.

But with new pads they are contacting the rotor only on a fraction of the surface - the ridges. It takes some miles of braking before the pads conform to the rotor surface, and until they do you will have reduced brake effectiveness. The deeper the grooves the longer this process takes. Be careful right after changing pads.

8ninety8 · Sep 18, 2019

Don't forget to check what's left of the rotor thickness. Minimum IRC is .14 inch. Not that it won't work but guess it's a safety/design thing. I just changed my rear rotor, split/cleaned and renewed the caliper plus Spiegler, at .14". The drag was on the inside pad after 84k. Just regular maintainence. 84 KRS. All original parts.

Paul_F · Sep 25, 2019

PGlaves said:
Here is a very important point when replacing pads with the existing rotor. Even if not obvious there are ridges and grooves on the rotor. With the old pads you didn't notice because the pads had worn to match those ridges and grooves.

But with new pads they are contacting the rotor only on a fraction of the surface - the ridges. It takes some miles of braking before the pads conform to the rotor surface, and until they do you will have reduced brake effectiveness. The deeper the grooves the longer this process takes. Be careful right after changing pads.

Good to know, Paul. Thank you for the advice/warning.

Paul

8ninety8 said:
Don't forget to check what's left of the rotor thickness. Minimum IRC is .14 inch. Not that it won't work but guess it's a safety/design thing. I just changed my rear rotor, split/cleaned and renewed the caliper plus Spiegler, at .14". The drag was on the inside pad after 84k. Just regular maintainence. 84 KRS. All original parts.

Our riding season is almost over and I intend to replace the rotor over the winter, as well as installing Spiegler lines.

Thank you, 8ninety8

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