Is this what binding does?

[adrianw]

Hello,

I was riding my R11S along thinking that something wasn't right, then I noticed a car flashing its lights behind me.

When I stopped I found that my rear caliper had 'popped off' and was missing the pads and pistons and was very hot. (Car driver said lots of bits had been falling off the bike - bits of hot disc as it turns out)

The entire edge of the disk looks like its been chewed by a large dog.

This all happened within 15 miles at speeds around 40/50 mph.

When I pushed the bike out of the garage, everything was moving OK.

I don't use the back brake at all, but could this have been the result of binding?

Adrian

Here is a picture of the caliper after the break down man tied it to the passenger foot peg.

[Jeff Heyerman]

Wow! But yes, my guess is that was a result of the piston not retracting when releasing the lever. Could be break line degradation, or calliper itself, or elsewhere in system.

[Noblehops]

Wow is right. My guess is you'll never figure out what it was as all the evidence is destroyed! Very glad it wasn't a lot worse, as in, you getting debiked or something.

N.

[SergioK]

Clearly that caliper got mad at you for not using it and decided to have a tantrum. I bet if you were to pull it apart you'd find a seized or VERY gummed up piston inside.

If your bike has ABS, then you do use your rear brake.

[Bob Hancock]

Seems unlikely to me that a non-retracted brake pad could do that.....rip the caliper off, I mean. So my guess is that the bolts holding the caliper got loose, maybe came out, things got crosswise and ugly's the only way it could go.

[adrianw]

Hi,

The pads and the pistons have disappeared, but the bolts were all in place and tight.

We removed the bolts and hugger and tied up the caliper, it was sitting on the speed cable (melted it), which explained why the speedo was fluctating wildly in the last 400 meters before I stopped.

At the time I was thinking I might have polished the splines on the output shaft (again) or that the rear diff had turned to slag (again)

The bike failed it's MOT (government stiplulated annual saftey check) about a month ago as the rear brake wasn't working (I hadn't noticed) , and the local shop had bled the system to fix it.

This was the first time I can recall riding the bike since then.

Thanks for your input,

Adrian
R11S 150500 miles
R12S 60500 miles

[smddanny]

Wow! Mountings must have come (been) loose...

[boxercup]

Originally Posted by Bob Hancock

Seems unlikely to me that a non-retracted brake pad could do that.....rip the caliper off, I mean. So my guess is that the bolts holding the caliper got loose, maybe came out, things got crosswise and ugly's the only way it could go.

Greetings Bob,

+1!

------

When I pushed the bike out of the garage, everything was moving OK.

Thank God you were not hurt adrianw - that looks frightening!

Must have been a light-show!

This speaks to safety: A good Pre-Flight Check is always in order every-time you go on a run.

Things do go awry!

[RBMann]

adrianw stated that when the tow truck arrived they removed the caliper. Looking at the the photos I see a lot of rust and corrosion. The side case mount that the caliper is strapped to looks horrid. Plus the bike has 150,000 miles on it. Can't tell from the photo but I had a rear disc get really thin once. If the pistons were really gummed up and corroded(not working a month ago) they could start to drag on the disc producing a lot of heat. If the disc is thin then at some point it begins to throw off chunks and one or more takes out the pads and pistons. There, that is my wild guess.

[lkchris]

Loose bolts related to hugger installation.

[adrianw]

Hi,

The two bolts that hold the hugger in place and the caliper onto the rear hub were on solid. (Part # 4)

The tow-truck man had to give it some welly to get them off (everything got hot).

So it was just the base of the caliper and the hugger mount left attached to the drive hub.

The caliper itself was hanging from the brake hose/speedo sensor cable - it got zip tied to the manky luggage retainer.

I think the disc itself would have been within specification, otherwise the garage would have offered to replace it when it was MOT'd as it would have failed the MOT.

I spoke to a Brembo dealer yesterday to try and find prices for the caliper, and he reckons that brembo have stopped making that caliper - I presume they still make them for BMW (fitted on R models till about 2000).

£40 on ebay, £90 pounds second hand with 6 month warranty Motorworks BMW Motorcycle Specialists - Home - haven't asked BMW yet but I'd guess about £250.

I think this could run to £500. (caliper + disc + pads + rubber boot for shaft as it got toasted)

Regards,

Adrian

[bradzdotcom]

if it wasn't loose caliper bolts, then there's an outside chance that a rock got up in there and hand-grenaded the thing for you. rock goes in, has no place to go.

i've seen it happen quite a few times on motocross bikes, and the end result looks familiar.

any way you look at it...that's ugly.

[Haggis]

Hi,
Bit of a mess that!
If the caliper is similar to the one on a 1200S (fixed pad on inside of disc and twin pistons on outside) and it slides on two pins as the pads wear then maybe one of the pins seized in its corresponding hole. I had exactly that on my 1200S and it caused the caliper to sort of ratchet in and it started binding and buckled the disc. It wasn't till the damage was done that I noticed it. Stripped off the caliper and the problem was obvious, one pin badly corroded in the hole in the caliper. emery cloth and and some moly grease sorted it but had to replace the disc.
Had it gone much longer potential for the damaged that occurred on your bike.
Easy to check, push caliper towards disc to push pads and pistons back, caliper should then slide back and forth on the pins freely. I check mine regularly now.

Cheers Haggis

[Noblehops]

Haggis' guess is the best yet IMO. Mine were crufty on my bike too, and I did the same. Cleaned them up and lightly greased them to restore good operation.

N.

[Sideshow_S]

FWIW, I've had a binding issue on my '99 and found another possible source of the problem. I had multiple times where the back brake would start to lock up. This happened once, so I cleaned the caliper up and moved on. Later that week it happened again. I pulled the caliper off and swapped it with a good spare.

The next week, it binded up again. Every time I fixed it by cracking the bleeder and letting off the fluid.

As luck would have it, the master cylinder on the rear was bad. Non-ABS bike, so nothing is linked. I reason that fluid leaked past the master cylinder piston, basically creating a solid system of fluid. The heat build-up caused the system to expand the fluid to freeze up the pistons to lock on the brake.

So it's possible the caliper didn't cause it, but I do question the quality of your pads, or the tightness of your lugs. I was going 60 when the tug of the rear brake was so obvious I couldn't go anywhere. That rotor was HOT!!!