Brake disc buttons

[Gio]

Just replaced my rear tire and so was doing the usual obvious things whilst wheel was off (shaft lube, bearing check, pad check / caliper service etc) and got to wondering about the buttons that attach the disc to the carrier ... not so much for the back but am planning on checking the front brakes next.

 

This is something that I must confess to have not paid much attention to in the past ... I did some searching and came across some cautionary discussion of penetrating oil, appropriate lube (dry) and also docc's mention of using a mallet to ensure the buttons are free and the disc centred on the carrier in his checklist.

 

Just how much discernible play should there be in the buttons I wonder? In the case of the rear, I could not detect any. I would be more concerned about the front than the rear ... healthy front brakes are a good thing!

 

Thoughts /advice anyone?

[gstallons]

Are you referring to the caliper pistons? You will have to remove the caliper (leave the brake hose attached) to inspect these. After ypu get the caliper free from the rotor , remove the brake pads , push one piston in and this should push the opposite piston out . If it doesn't presss the brake pedal a couple of times to extend the piston. Stop when you see a clean surface on the piston.Use Brakekleen to remove all dust,etc. from this piston.You can use a shop towel to wipe off dirt.  When you are satisfied with this , push that piston back into it's bore til it is bottomed out . Do the same to the opposite piston.

  I do not use ANY petroleum base products on brake parts. It is a good idea to look at the pads to see if they need replacing. Make sure the friction material of the pad is facing the rotor.   When you are reinstalling these parts, make sure you are doing this correctly and tighten all fasteners. Try your brakes on the bike stand and not on the road. You do not want to hear the sound of parts falling off your bike !

[Gio]

Actually no - am quite familiar with caliper / piston maintenance (but thanks for the reminders!) ... I was referring to what I call the "buttons" that attach the brake disc to the carrier ie the things that make the discs "float" - my understanding is that it is these that allow the discs movement as required, but have never really given any thought as to any maintenance that may be required to keep them "floating" ..?

[docc]

The rear disc does not float, the rear caliper slides on a pin which should be kept clean. Some say lube it lightly (I use a thin coat of waterproof grease), others (BMW owner's manual for the 325i auto) say no lube on the pins.

 

The front rotors are "semi-floating" so there isn't any play in the buttons (sometimes called spindles). The rotor will shift on them under force which is why I use the rubber mallet to bump it around a bit. Using a spray solvent will help get the gunk out. I've used a little BreakFree CLP on each in the past, but even the slightest amount will try to sling out onto the braking surface. Very much of that and you're half way to a bad day!

[Gio]

Hi Docc,

 

I was thinking more in terms of the front discs, but on closer inspection the "buttons" on the rear are indeed just direct bolts to the wheel so have that covered with just regular caliper service.

 

When you applied this CLP stuff (and assuming negligable throw off onto the braking surface) ... did it affect the performance of the front brakes ..?

[gstallons]

The best thing is to use a dry film graphite lube spray from NAPA , LPS , etc. on this setup . Clean these pins and spray on them allowing them to dry before reinstalling.

[docc]

Good advice there from Gene on the best lube. And yes, when the rotors can "center up" there is less judder. It's one of the sources of what many would say are "warped rotors." The other two are sticking caliper pistons and uneven impregnation of pad material onto the discs.