Tyres, Brakes and Suspension » Front caliper piston and seal replacement

Whilst I’ve had my front wheel out, to get a new tyre fitted, I took the opportunity to check and clean the brake caliper and pistons. Not that I think the brakes are bad but I don’t think they are as sharp (initial bite) as the used to be and I’m sure there is more lever travel than there used to be.

I took the pads out, cleaned what was exposed of the slave pistons (toothbrush and brake cleaning fluid) and pushed them fully home (re-seating), well re-seating all bar one of the eight, (but I come to that later) and then in pairs and singly I’ve inspected their behavior when gently squeezing the brake lever a few time before re-seating them to fully home, and try the next piston.

PistonsLocation.jpg - Bild entfernt (keine Rechte)


To identify the pistons see the above photo of the caliper with the red and yellow hand drawn markings. Each caliper can be said to have an outer pair of pistons, on the outside of wheel / rotor, (i.e. the Brembo writing side of caliper ) and an inner pair, those inside the rotor. Then you can say you have the pistons that ‘see’ the rotor first (when wheel rotating) the Red circled one and its inner partner, call them the lower pistons and you have the upper pistons (yellow ones)

On both caliper the pistons on the outside, both upper and lower, move fairly freely, are the first to move and can be re-seated fully home with light finger pressure. The Inner pistons are a different story. The right-hand side (when sat on bike) lower inner piston, is all but seized, requiring all the other three pistons in that caliper to be restricted from moving before it’ll move out at all and it takes more than full finger pressure to re-seat it (leverage on the piston face with a prising tool). The left side lower inner piston is similar but can just about be re-seated with all the finger pressure I can supply. The upper inner pistons in both caliper are slightly less seized than their lower inners, but still bloody stiff to move.

Even repeated pushing out, cleaning and re-seating didn’t improve the action of the stiff pistons.

And now to that that oddity piston that I didn’t fully re-seat, take a look at this second picture.

PistonDamage.jpg - Bild entfernt (keine Rechte)

The red circle shows where the piston has a nasty ‘dent’ on the sliding surface, on the outside end of the psiton (brake pad end), it is approx 3mm long and 4mm wide and has a lip I can catch my nail on, you can see the lip towards the seal side (the marks further in on the sliding surface are dust and muck I hadn’t cleaned off not scoring).

It’s almost as if something has hit it. It is the Right-hand side, upper/inside piston, and the damage is on the side facing the other (lower) piston. I didn’t push the piston fully home as this damage would likely tear the seal or scratch the caliper bore. Fortunately it appears that with everything in their operating position this damage doesn’t retreat back far enough to damage the bore/seals, but when I next come to fit new pads I’m not so sure.

So given this damaged piston and the ‘stiff/seized’ pistons, I’m thinking I might have to buy a brake piston and seal repair kit to try and return the brakes to how the where when I first got the bike, bike mileage is now 24,600+ and I do ride in the winter.

Has anyone else replaced seal and/or pistons, any hints or pitfalls to avoid?

Looks like there are kits available (kit BRA56200, second to last item on this page) which match the BMW part number from the microfiche I’ve found ( item 13 on here), and yes the price did make me wince, and haven't yet click buy...

Jason

Zitat von wessie im Beitrag #2

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Not sure for certain but I think one of the front pistons on each caliper is connected to the rear brake.

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