Strange brake behavior - R1100RS

This new-to-me R1100RS has pulsing sensation on the rear brake pedal when applied. Fronts behave normal without pulsation.

No ABS error lights(they do light up at start), brake fluid flushed recently and wheels turn freely front and back. ABS function normal on sandy surface using only the front(I didn't think of testing the rears at the time).

Can anyone shed light on if this is normal or there is some check I can do?

This new-to-me R1100RS has pulsing sensation on the rear brake pedal when applied. Fronts behave normal without pulsation.

 

No ABS error lights(they do light up at start), brake fluid flushed recently and wheels turn freely front and back. ABS function normal on sandy surface using only the front(I didn't think of testing the rears at the time).

 

Can anyone shed light on if this is normal or there is some check I can do?

Afternoon TonyRS

That sounds a lot like a warped, bent, or distorted rear brake rotor.

Or possibly a bad rear final drive crown bearing.

Any signs of rear rotor damage when you look at the brake rotor?

Grab the rear wheel at top & bottom then front & rear then give it a wiggle to see if the rear wheel has a LOT of wiggle.

Can you tell us exactly when the problem started? If after the last tire change then maybe the brake rotor was damaged during the tire change.

Or glazed patches. A good rear disc inspection is in order.

Andy, DR,

Thanks for the quick replies. How best to inspect for rotor issues?

I did shake the wheel at 9 & 3 position as well as 6 & 12. No looseness. And I did rotate the rear wheel and didn't feel uneven drag but it was in increments not continuous rotation. I'm hoping I don't have to disassemble to inspect if possible.

I noticed this shortly after I bought the bike this summer. As I used mostly front brakes this wasn't a priority but nonetheless is on my list.

Andy, DR,

Thanks for the quick replies. How best to inspect for rotor issues?

 

I did shake the wheel at 9 & 3 position as well as 6 & 12. No looseness. And I did rotate the rear wheel and didn't feel uneven drag but it was in increments not continuous rotation. I'm hoping I don't have to disassemble to inspect if possible.

 

I noticed this shortly after I bought the bike this summer. As I used mostly front brakes this wasn't a priority but nonetheless is on my list.

Afternoon TonyRS

Hopefully a little more info can help us help you find it.

Do you feel the pulsation in the brake pedal itself or is the pedal solid but the bike pulsates as you stop?

DR, the pulsation is felt on the pedal when rear brake is applied. It's hard to say whether the bike feels jerky or not from memory. Another excuse to go riding tonight:)

DR, the pulsation is felt on the pedal when rear brake is applied. It's hard to say whether the bike feels jerky or not from memory. Another excuse to go riding tonight:)

Afternoon TonyRS

Then that points more to a bent, warped, thickness variation, or damaged brake rotor than to rotor glazing or rotor staining (oxidation).

Without a dial indicator and/or an caliper it is going to be difficult to find the root of the problem.

With bike on center stand maybe try prying the rear brake pads back a little (so rear wheel spins easily) then spin rear wheel & hold a screwdriver tip close to the rotor.

By judging the distance of the screwdriver tip to the spinning brake rotor maybe you can see a wobble or bend.

DR,

I checked the rear rotor by pushing back on brake pads and checking for warped rotor. As you suspected the rotor was warped

Can the rotor be 'turned' like car rotors? Or is a new rotor the only answer?

'No', to turning or grinding the rotor. It is just not cost effective. Replacement 'used' items from Beemer boneyard or other bike breakers is one way to go. However, new ones are not that expensive.

What is curious is how it got warped. Maybe badly handled during a tyre change?

DR,

I checked the rear rotor by pushing back on brake pads and checking for warped rotor. As you suspected the rotor was warped

 

Can the rotor be 'turned' like car rotors? Or is a new rotor the only answer?

Morning TonyRS

Can it be turned?--yes,

Should you turn it?--NO,

The brake rotors on most motorcycles are pretty thin to begin with (non vented) so there just isn't enough material to machine much off.

Even if you could machine one, a bent or warped rotor would need WAY too much material machined off to make it turn true again so a new or good used rotor is about the only option.

More than likely yours got bent during a hurried or incompetent rear tire change.

DR, Andy,

Thanks for that information. I will get the rotor replaced.

The rear brake was like that from the get-go for me so I can't tell what caused it. It's too bad as there seem to be plenty of rotor left.

I see rotors for sale need the ABS ring transferred from the old one. Is this straightforward process or are there know-how involved?

I see rotors for sale need the ABS ring transferred from the old one. Is this straightforward process or are there know-how involved?

Pretty straightforward. See below:

[RS] Removing and installing rear brake disc (attached to rear wheel drive)

• Remove the brake caliper.

• Remove rear wheel.

• Heat brake disc retaining screws (1) to 120 °C/ and remove.

Note:

Mark the installed position of the brake disc, so that

vertical runout of the sensor wheel does not change.

• Install in the reverse order of work.

• Degrease the brake disc before installing.

Caution:

[ABS] Check sensor gap and adjust with spacing

plates if necessary.

[ABS] If the brake disc and therefore the sensor

wheel are renewed, the disc’s vertical runout must

be determined/marked.

Sensor gap:.. 0.45...0.55 mm (0.0177...0.02165 in)

Tightening torque:

Brake disc to rear wheel drive

(clean thread + Loctite 273)............. 21 Nm

I have everything ready to go except for the ABS ring from the old rotor. I tried heating it with propane torch but no go.

Is there a step I"m missing or another way to this?

(I've been using only front brakes to slow down until I got to replace the warped rear rotor.)

Can I clarify.

Are you saying you can't get the bolts out?

If that is the case, can I make sure it is the bolts that you are heating up? Are you getting them to at least 120 °C.

Hi TonyRS

Have you definitely got those rotor bolts up to 120 degrees C.

They would normally be no major problem once the Thread locking adhesive has softened.

I have everything ready to go except for the ABS ring from the old rotor. I tried heating it with propane torch but no go.

 

Is there a step I"m missing or another way to this?

 

(I've been using only front brakes to slow down until I got to replace the warped rear rotor.)

Morning TonyRS

On the early 1100RS ABS rear brake rotor the ABS tone ring is serviced as part of the brake rotor so no real defined removal procedure.

You will probably need to get those bolt areas quite hot & as close to the thread areas as you can (maybe heat a few times then as it cools try to get some penetrant into the thread area so the cooling tries to pull the penetrant in farther).

It might take lots of heat plus using an impact driver (not air impact wrench but hammer driven impact hammer).

I guess worst case, you might end up drilling the bolt heads off then trying to find replacement bolts (I don't believe that BMW services those bolts)

Okay I applied more heat and the ABS ring finally moved! It's all ready for reassembly tonight and a test ride.

I will report back after the test ride.

(I had no issues with any of the fastener btw)

After the reassembly I took it for a ride and it's great! The vibration at highway speeds is gone and the braking power increased as expected.

As mentioned earlier the original rotor probably got warped during a tire/wheel change. How do I avoid this in the future? The rotor/ABS ring assembly stays on the bike with the wheel out so I don't know what the pitfall is.

Do you change the tyres yourself?

If so, maybe ensure that the disc sits inside another smaller tyre.

If it is done by a professional, then make them aware of your concerns. most of them use a similar method as described above.

After the reassembly I took it for a ride and it's great! The vibration at highway speeds is gone and the braking power increased as expected.

 

As mentioned earlier the original rotor probably got warped during a tire/wheel change. How do I avoid this in the future? The rotor/ABS ring assembly stays on the bike with the wheel out so I don't know what the pitfall is.

Morning TonyRS

Just be careful to not drop the rear of the bike on the brake rotor & careful to not to bolt rear wheel up with anything trapped between wheel brake rotor.

Do you change the tyres yourself?

If so, maybe ensure that the disc sits inside another smaller tyre.

If it is done by a professional, then make them aware of your concerns. most of them use a similar method as described above.

The R1100RS (and RT) rear rotor is attached to the final drive. Tire change should not involve the rotor.

The rear caliper guide pin could be corroded or gunked up (technical term) and hanging up the pad that is supposed to move away from the rotor. Or, the caliper itself has two pins that the two halves slide on. If either of those pins has become corroded the caliper will not easily slide away from the rotor when the rear pedal is released. These could leave brake pads pressing on the rotor and overheat the rotor which could warp it. It would also cause very fast wearing of the rear brake pads. If you remove the rear caliper from the rotor and squeeze the two sides together you should feel or see them push back out again. If you don't see/feel that then you need to separate the two parts and clean and grease those two slide pins.

Andy: I don't diy the tires. And from what I saw the brake rotor stays on the bike with the wheel/tire removed. So I was puzzled how the original rotor got damaged.

DR: When the time comes to refresh the rear tire, I will take the wheel off myself so I can be sure the bike doesn't get dropped on rear rotor.

The original warped rotor was 4.9mm thick. Too bad I had to change it.

PS: Michael, I took the opportunity to change the pads and to clean and grease the two pins on the caliper.

Aha, yes the disc mounting is different to the 1150 that I was thinking about.