Can Anyone Explain Brake Calipers?

[Foltan 0]

Hi, im fitting some 307 brakes at the mo, and after fittting one ive realised that the pads are touching the disc, which i imagine its not supposed to do, except under braking!! Im learning the workings of the car as i play with it however ive now realised that i dont exactly understand how the pads are made to grip the disc and, more importantly, how they return. particularly the outer pad. I havent fitted the hoses yet because im trying to get some braided ones, and so wont be trying the brakes out for a bit. Can someone help?! I need to have the brakes explained to me so that i can remedy my stuck brakes. Sorry if i sound like a bit of a cretin!!

[Rippthrough 98]

Hi, im fitting some 307 brakes at the mo, and after fittting one ive realised that the pads are touching the disc, which i imagine its not supposed to do, except under braking!! Im learning the workings of the car as i play with it however ive now realised that i dont exactly understand how the pads are made to grip the disc and, more importantly, how they return. particularly the outer pad. I havent fitted the hoses yet because im trying to get some braided ones, and so wont be trying the brakes out for a bit. Can someone help?! I need to have the brakes explained to me so that i can remedy my stuck brakes. Sorry if i sound like a bit of a cretin!!

 

 

They should touch the disc, just not with any real pressure. As for how they work, well the piston gets pushed out by the brake fluid, which pushes the inner pad onto the disc, and at the same time pushes the the caliper inboard on its sliders, which clamps the outer pad against the disc too.

Edited January 31, 2006 by Rippthrough

[allanallen 528 2 Cars]

yeah dont worry the pistons will be pushed out slightly you can prize them back in with a peice of wood if they are in the way but otherwise when you start the engine the vacuum will suck them away from the disc, hey presto

[M3Evo 0]

err, what vacuum?

 

There isn't any vacuum applied to the fluid in the braking system and therefore the calipers aren't subject to any vacuum.

Edited January 31, 2006 by M3Evo

[jackherer 543]

yep, def no vacuum

 

you can prize them back in with a peice of wood

 

when doing this make sure you open the fluid reservoir cap so the fluid can be pushed back, and keep an eye on the level while pushing the pistons in as the fluid can end up overflowing if its been topped up while the pads/discs have been heavily worn.

[Doof 11]

As for how the pads grip the disc, they just push bloody hard! Dont get your fingers in there while your mate presses the pedal

[Foltan 0]

excellent, thanks for all your help! Im glad no-one laughed at me!!

 

The only thing is, how do the pads return back when you stop braking? Is it because the loss of pressure sucks them back out? I can see a kind of spring loaded part on the yoke bolt but that would only make the outer pad return wouldnt it?

thanks again!

Ian

[C_W 3 1 Cars]

There's no suction they just sit against the disc. When you lift off the pedal the caliper just "relaxes" its grip on the disc.

 

The "spring loaded" part on the yoke is just a slider so as the pads wear the caliper can move.

[littlemike 0]

It's the shape of the seals inside the calipers which slightly pull the pistons back when you release the pedal.

 

The seals themselves are sqare, but the grooves that they are fitted in are slightly tapered/not square which makes one edge of the seal stick out more than the other (like a saw blade effect). When you press the brake pedal the highest edge of the seal flexes as the piston moves outwards, once you release the brake pedal the flex in the seal draws the piston back.

 

I'm not sure if that makes sense, but I know what I'm trying to say!

[Foltan 0]

hehe yeah thanks!! i think it makes sense!

[Pugnut 9 1 Cars]

the sliders allow the same to force to be applied by the piston onto both pads

[Rippthrough 98]

It's the shape of the seals inside the calipers which slightly pull the pistons back when you release the pedal.

 

The seals themselves are sqare, but the grooves that they are fitted in are slightly tapered/not square which makes one edge of the seal stick out more than the other (like a saw blade effect). When you press the brake pedal the highest edge of the seal flexes as the piston moves outwards, once you release the brake pedal the flex in the seal draws the piston back.

 

I'm not sure if that makes sense, but I know what I'm trying to say!

 

Unless you've got anti-knockback springs behind the pistons

 

The pads don't need to leave the surface of the disc - that would just result in extra pedal travel, they basically just work on pressure, and even a couple of pounds or so of residual pressure won't make much difference.

Edited February 2, 2006 by Rippthrough

[Foltan 0]

Aah good ok, im happy now. I was worried that i had done something wrong!