[cschuster1952]

Hello all.

Full of enthusiasm and optimism, I let the rear pads wear out and kiss the rotor. My bad, but not bad enough to change the rotor.

Now reassembling with EBC HH pads, I can't recall how the slightly convex, rectangular anti-rattle spring (34 21 7 663 749 Support Plate per the Max BMW online fiche) is supposed to fit. There is a tiny embossed triangle which might mean something but IDK. The fiche shows no obvious orientation. There's next to no room for the little thing, do I really need it at all?

Next, thought the caliper pins slide easily as does the caliper mount pin, the face of one piston is closed over with "something" while the other piston face is only partially occluded. Dunno what that stuff is or whether I should scrub it off, any ideas? The cylinder faces of each piston seem to be parallel, but the old pads wore out first in one corner (threw them out, don't recall which corner). I don't know what the piston faces should look like, are they "open" or hollow, or closed over?

The caliper is together and on the bike, the disk was scrubbed with the wire wheel, but I haven't ridden it yet. Still have to change the front TPMS sensor though I recently changed the front and back tires. Hint, tires go on/off a LOT easier with some soap solution on both the rim and tire bead. And a whole lotta patience.

 

[EricK1300GTSE]

The support plate with the directional arrow is needed to make sure the pads stay centred to the rotor. The arrow points in the direction of rotation of the wheel. The narrow tapered end slots into a mating recess in the caliper and you need to press it down then fit the pad retaining pin. The spring in the plate maintains the pressure on the pads and the pin keeps the plate in place.

 

[cschuster1952]

This is the plate or clip I'm referring to. The embossed directional arrow is barely visible at center. Does this clip go in the retaining pin end of the caliper or the other? No way it's retained by the pin, but I can't see it fitting in the other end either, where there is already a smaller, different metal clip.

Next, I want to scrape the brittle schmutz off the pistons so they bear evenly on the pads but the schmutz seems to extend into, and protrude above the ends of the cup-shaped caliper pistons. I've never see anything like this on caliper pistons before but this is my first rodeo with the K13 caliper(s). What is that stuff? Don't want to do something irreversible.

 

[Meese]

Does it go in the retaining pin end of the caliper or the other?

It goes at the other end.

See image below from Max BMW Online Parts Fiche for K1300GT.

Part #17 clips onto the inside end of the caliper carrier piece and sits between it and the end of the brake pads (the square protrusion end, not the round hole end). It allows the pads to slide freely against the caliper carrier.

Part #6 sits on top of the brake pads after they're inserted fully and before putting in the retaining pin (also part #6). That's the anti-rattle spring, and it should need to be slightly pressed into place to ensure good spring contact against the pads.

The schmutz on the pistons seems to be from the (probably original) Brembo pads

Note that some calipers use plastic cylinders slid inside the hollow caliper pistons so the hard plastic presses on the brake pads, not just the pistons themselves. I don't remember if the K13GT is like that, as it's been a long time since I've had the rear caliper apart. Sometimes, these plastic inserts can wear or deform over time, which could be the schmutz you're seeing. A pic would help here.

I will scrape it off so the pistons bear evenly on the pads.

Good idea to clean everything properly. Also, make sure the caliper slides side-to-side on its pins without stiction. If it sticks at all, pop the caliper off the pins, clean the pins well (steel wool or fine sandpaper works here), and apply a light coating of brake caliper grease to the slide pins. Don't let any grease get onto the pads or disk, of course.

If the caliper doesn't slide freely then it can't self-center, and you'll end up wearing one brake pad much faster than the other side.

 

[cschuster1952]

Thanks Meese, your response arrived while I was composing. Now I get the function of the metal clip.

Part 17 see the picture, seems to be in place but I've damaged the piston insert (yes my 2010 K13GT does have something over the piston ends, and it's brittle). I think I've passed the point of no return, the pistons in the present situation won't bear evenly and my only way forward would seem to further scrape out the insert so the circular piston ends bear directly on the pads.

Sometimes it seems that everything I think I know about fixing my stuff, has been learned by doing it wrong at least once. The lack of OE information on this subject doesn't help, either. The service DVD makes no mention of a filler on the pistons.

 

[EricK1300GTSE]

Sorry mate,I wrote my response from memory, thinking the rear clip is the same as the front. I have not seen those plastic inserts before, I think you do need to scrape that off or get the plastic pistons out. I can get you a photo of the rear caliper on my 09 GT for reference,if that helps. Sorry for any confusion.

 

[Meese]

Sometimes it seems that everything I think I know about fixing my stuff, has been learned by doing it wrong at least once.

No worries, we've all been there.

Sometimes, the best way to not screw something up is to just screw it up the first time...

 

[EricK1300GTSE]

As promised, photo of the same clip as per my 09 GT, the arrow points in direction of rotation.

 

[pedalmike]

Hello all.

Full of enthusiasm and optimism, I let the rear pads wear out and kiss the rotor. My bad, but not bad enough to change the rotor.

Now reassembling with EBC HH pads, I can't recall how the slightly convex, rectangular anti-rattle spring (34 21 7 663 749 Support Plate per the Max BMW online fiche) is supposed to fit. There is a tiny embossed triangle which might mean something but IDK. The fiche shows no obvious orientation. There's next to no room for the little thing, do I really need it at all?

Next, thought the caliper pins slide easily as does the caliper mount pin, the face of one piston is closed over with "something" while the other piston face is only partially occluded. Dunno what that stuff is or whether I should scrub it off, any ideas? The cylinder faces of each piston seem to be parallel, but the old pads wore out first in one corner (threw them out, don't recall which corner). I don't know what the piston faces should look like, are they "open" or hollow, or closed over?

The caliper is together and on the bike, the disk was scrubbed with the wire wheel, but I haven't ridden it yet. Still have to change the front TPMS sensor though I recently changed the front and back tires. Hint, tires go on/off a LOT easier with some soap solution on both the rim and tire bead. And a whole lotta patience.

Unfortunately, looks like you need new caliper pistons, seals, and a new clip to ensure that caliper functions properly. Buying a good used caliper and swapping it in might be a good option.