Sticky rear wheel on bike

shad_68

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Prelude: Yesterday evening I noticed that the brake light on the BMW was on the whole time. Apparently because the pedal was hanging a bit low, and thus constantly setting off the contact switch.
No big deal, I thought, and set out to readjust the pedal position this morning. After I had done that, I thought why not readjust the chain tension, since it was really loose.
Getting the nut holding the axle undone was a real fight, in the end I had to use a wrench and a hammer... getting it in the same position on both sides of the swingarm was a bitch too, but nevertheless after some time it was done, and I had it at the recommended 20mm of play.
Anyway, here comes the crucial part:
When I wanted to push it back to its place in the garage, I noticed that pushing was much harder than usual. So I put it up on the main stand, started the engine and put it in first gear. The wheel turned alright, but almost instantly after pulling the clutch it stopped, no freewheeling at all. :|
I then turned the engine off again and carefully touched the brake disk, and sure enough it was HOT.

So apparently the brake pads are constantly rubbing on the disk. Could anything I did with the rear axle or the brake lever have caused this? I tend not to think so, because I already had this problem once some time ago. Back then the wheel was turning fine again once the brakes had cooled down and didn't notice it again until now.
Ugh... <_<

-----

Oh crap, I really don't think that the disk is actually supposed to look bent like that...
100624DSC_3913.jpg


I have no idea what to do about that though. :(
 
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Spectre

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I saw your other post and was about to reply to it.

The kicker is the fact that your brake pedal was low and you adjusted it upwards. The problem isn't what you did to it, it's that the caliper has a sticking piston (or two) that isn't retracting all the way. Since the piston(s) were still extended, the pedal didn't come back up all the way. Quite common; you need to put the pedal back where it was and then rebuild your caliper. It could also be a sticking master cylinder but those almost never fail that way so it's only a remote possibility.

Edit: Well, the only way to find out if it is really bent is to take the rear wheel off and measure the disc runout. However, if your brake was dragging like that, it's completely possible to warp or even bend a disc, especially where the pad stayed in contact with the rotor after stopping. It could just be an optical illusion, though.
 
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shad_68

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Hmm, so what can I do about the sticking piston(s)?
 

shad_68

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Remove and rebuild the rear caliper.

Ugh, the brakes are something I really don't feel too confident about doing myself, and that sounds like a pretty involving job. (I don't even know where I could get a rebuild kit)

The Chain Gang said:
Problem#2: Caliper piston did not want to return to "home" position all the way into it's bore.
Reason: Lots and lots of dirt, sand, mung, pigeon excrement, and various other detritus indigenous to NYC stuck to exposed sides of piston not allowing it to recess fully into it's bore.
Solution: Take pads out, pump pedal SLOWLY and SLIGHTLY to expose piston a little more than usual. Spray profusely with lots and lots of highly toxic ozone-depleting brake cleaner spray. Let it dry. Then cram pistons back into the bore. Make sure that brake fluid reservoir is NOT overfilled at this point. Which could also be a reason why the piston would not want to recess fully into it's bore.
That sounds like it could help though.

Edit: Apparently the F650 is very prone to rear brake problems. http://faq.f650.com/FAQs/BrakeQuestionsMiscFAQ.htm#What about Sticky Pistons

Comment: Kawasaki got rear discs right in 1973, Honda in 1975... BMW? Eh, well..... :p :D :mrgreen:

Well, they're Brembos, so blame the Italians!
----

I just readjusted the pedal so that it's just at the point where it'll disengage the switch, but not further, and the wheel turns more freely again. Decent freewheeling time, and the disc didn't get hot when I let the engine run for a bit again. :?
The disc doesn't look bent like it did anymore either, but I'm not sure if its not just an issue of perspective or seeing-what-you-want-to-see.
 
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Spectre

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Rebuild kits should be available at your BMW motorcycle dealer. Nobody else seems to have them for the F650, though.

It's actually not very hard at all to rebuild calipers, at least not ones that were in regular service until being torn down. Just messy.
 
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Crazyjeeper

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Sounds like its time to rebuild the calipers, but don't fret, its not that difficult, especially when you only have one and not a set of two to do.
 

shad_68

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Well, I've taken off the brake pads and hosed the piston in brake cleaner at least.
But I've come across yet another problem:
100625DSC_2589.jpg


As you can see, that (completely useless btw) mudguard partly blocks access to the caliper. So if I want to do anything more - including pushing the piston back in or removing the caliper - I need to get that plastic bit off. Really annoyingly the head of the allen screw the red arrow points to is completely shot.
Fortunately a friend of my dad said he had the right tools (what's the name for those in English?) and would come by tomorrow to help me get it out.

After that, I'll see if cleaning the piston did anything (doubtful), and if not I'll have to go to the BMW dealer on monday and see if can get a rebuild kit or replacement caliper there.
 

Spectre

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Those are "broken bolt extractors" or "screw extractors" and that specific type is commonly known as "Easy-Outs" after the original brand that produced them here.

I know I am going to regret asking, but what is the German term for them?
 

shad_68

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"Linksausdreher", literally something like "left (handed thread) unscrewer".
Quite simple really, the name says what it is (a left handed thread) and what it does (unscrewing bolts). :D
 
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Spectre

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Hm, that's not so bad. I was suspecting it was going to be the equivalent of "The thing that goes into a fastener which holds down metal for the removal." :p You have to admit, German nouns can be weird that way sometimes. :D

How is the extraction going?
 
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shad_68

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No progress today, my dad's friend didn't show and when I tried to call no one was home. And I'll be gone most of the day tomorrow for a combined Formula1-BBQ-WorldCup event with my friends, but I'll try to get my dad to see if he can do the extraction with his friend then. It's 50% his bike too, after all...
 

shad_68

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Apparently, the proper way is overrated... <_<
So I spent most of today attacking the little **** with a barrage of creativity and improvisation.
Luckily, a bit of the screw stuck out at the end, so I filed away a bit of the thread to get two level surfaces I could use an adjustable wrench on. After that, the real battle had begun. Using a mix of pliers, allen keys wedged in the head, liberal use of penetrating oil, curses and other desperate measures, I finally got the :censored: out.

The Aftermath
100628CIMG1540.jpg

100628CIMG1541.jpg


Once again, man triumphed over machine. Or did he?

Because now I'm stuck with the caliper, and once again don't know what to do.

100628CIMG1539.jpg

100628CIMG1537.jpg


I think that you can rotate and access the caliper like that when it's still mounted, but to be honest I'm not sure. Or do I have to remove the rear wheel so I can take off the whole caliper and mount? I'm a bit hesitant to do that - can I just pull the axle out of the wheel? What about the wheel bearings and seals? :confused:
 
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Spectre

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I'm not that familiar with the F650, so I can't pull advice on it out of the air. You might want to try the F650 forums and/or your service manual, especially since when you go to torque it all back up I have no idea what your proper torques will be.

Can you get me a side on shot showing me all the caliper fastenings and mountings? I might be able to get an idea then.

Edit: Also, in the picture where you're holding up the dust boot to the caliper - that pin you have the red arrow pointing to looks like a stud. Are you not able to use the flats inboard of the caliper to turn it out?
 
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bone

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i say don't bother with the rotating, useful for changing brakepads, but you can't do anything decent to a caliper when it's still attached.

but to get it rotating, you will have to get that first bolt undone, and english wrench should be able to do the trick.

and can't get it loose doesn't exist. use a longer extention, or get a hammer :) (gentle persuading does wonders )
 

shad_68

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Here's a pic of the caliper and mount removed from the wheel:
100628IMG_0535.JPG


It's a floating caliper, so the mount sits on the axle, and an extrusion of the swingarm sticks into that cut-out left of the axle hole. The two small holes in the flanges at the bottom aren't used for anything on my bike.

About you edit: that was one thing I thought too, but since that pin is obviously not steel (and I don't know what material it actually is) I didn't want to just take a spanner to it only to discover that it's some soft metal I'd immediately ruin.

i say don't bother with the rotating, useful for changing brakepads, but you can't do anything decent to a caliper when it's still attached.

Right now it's just about getting the disc out of the way so I can at least push the piston back in.

and can't get it loose doesn't exist. use a longer extention, or get a hammer :) (gentle persuading does wonders )

Generally yeah, but it looks (and felt a bit) like the nut may be fixed to the caliper - in which case trying to force it off doesn't seem like sucha great idea. ;)

----------------

Oh, and a bit of research on the weekend revealed that rebuild kits for this caliper are apparently not avaible. BMW only sells the whole caliper, no parts. The same brake is used on an older KTM as well, and you can only get the whole caliper from them too. It looks as if Brembo has a very tight grip on these and doesn't allow rebuild kits to be sold.
 
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Spectre

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The sliding caliper pin is brass or cadmium-plated steel, probably the latter. Go get a flare nut wrench of the appropriate size - that's how that caliper will come off. I'm assuming the end is peened so you can't just slide the caliper off, right?

As for no rebuild kits - I'm just the cynical kind of guy who thinks that maybe that's why BMW chose them, so that you'd have to order a new one from them if you ever needed it. Just like their idiot $800 ignition keys.

That said, I believe someone on the F650 forum has sourced rebuild kits.
 
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shad_68

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Generally yeah, but it looks (and felt a bit) like the nut may be fixed to the caliper - in which case trying to force it off doesn't seem like sucha great idea. ;)

Nevermind, the "nut" is actually part of the pin, and I just managed to get the pin out.

Now I only need to (re)move the brake line out of the way to be able to rotate the caliper, and also see if the second pin is removeable as well, so I could get the caliper off without having to take the mount off as well.

This really comes at a terrible time... I fear that this'll take a couple more days to resolve, and I should concentrate on some work for uni that's due next week. <_<
 
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Spectre

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Don't forget to plug the brake line with something so that it doesn't completely leak out, and then seal it with plastic so that moisture can't get in. Also, remember to replace the sealing washers with new ones when you go to put it back together.
 

shad_68

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Anything in particular I should use for plugging? My first thought was a piece of cloth, a small plastic bag over that and tape around the opening of the bag.
 
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