Curious about callipers.........

[polecat]

Having rebuilt my calliper recently I am curious if anybody knows why the calliper bolts have 4 o rings and two rubber boots on each one ?

I can understand the piston needs seals and a boot but the brake fluid stays behind the piston and has nothing to do with the bolts so why so many seals on them ?

would be really interested to know

[Tango]

So's the callipers can "float". Meaning that they can self adjust their lateral position to clamp on both sides of the disc equally. This movement needs to be protected from the elephants, hence the boots and O-rings.

I think that's what you are asking?

Bob

[megawatt]

Spot on Bob

[Tango]

One other thing....and opinion may be divided on this.....I tend to put a small smear of Copper Grease on these bolts too (as well as on the back of the disk pads).....just as added protection from corrosion. The callipers need to move freely or you can lose braking efficiency and possible damage to the disk (warping).

The o-rings on the bolts also take up some free play so you don't get squealing from the callipers.

Hope this helps,

Bob

[Stu]

One other thing....and opinion may be divided on this.....I tend to put a small smear of Copper Grease on these bolts too (as well as on the back of the disk pads).....just as added protection from corrosion. The callipers need to move freely or you can lose braking efficiency and possible damage to the disk (warping).

The o-rings on the bolts also take up some free play so you don't get squealing from the callipers.

Hope this helps,

Bob

 

as you probably already know your not supposed to put copper slip on the caliper bolts as they can come undone easier

but i always do it too never had one come loose

if a bike is maintained properly things like this should be checked every so often anyway

[polecat]

I used Red rubber grease on the seals and copper grease on the pins and bolts (keeping pads clean)

Thanks for the awnsers it kind of makes sence now and I only asked because I spent a small fortune on all these boots and wanted to know what I was getting for my money

[Tango]

Yeah....that's why a said the thinnest smear on the bolts. Never had one come undone yet either....but as soon as you mention Grease and Brakes in the same sentence people start moving away from you

Bob

[Colin the Bear]

A single piston caliper or a caliper with both pistons on one side moves on the bolts, so needs (a little) lubrication. The Seals keep lube in and weather out. I use silicone grease. I find a thread lock compound is more useful for the mounting threads on these bolts as it will keep weather out and so impede corrosion while stopping any losening from vibration. Copperslip is a legal must do in areas like the back of the pads where there is no weather protection and salt can cause problems. A smear will suffice. Less is more as far as lubricants and braking systems go. Better to apply little and often than risk any contamination and brake failure