Disc Brakes - How do they work?!

[Roggia]

I recently bought an old BMW e34 banger and decided a spot of DIY servicing was in order. (I know it'll end in tears but I just can't help myself!)

Anyway, I decided to inspect the rear disc brakes and was baffled by something. When I removed the rear calipers to get to the pads, I can see how the piston pushes in inner pad onto the disc and I think a clip which is attached to that pad returns it to its original position when the piston retracts.

However, the outer pad merely rests on a fixed bracket and I can't understand how the movement of the piston would a) force the outer pad onto the disk like it does the inner pad and b) return it to its original position!

Also, the pads, which have only 1cm of depth left and will need replacing soon, have no more the a 1mm clearance from the disc and I cant see any way of adjusting this clearance. So how on earth would I install a new thicker pads without driving around with the brakes permanently applied?!

I've known for many years that I have great stupidity within me but could someone point out how and why again?

[TheEnd]

The bit with the piston loops round to the other side, which holds the other pad

http://cgi.ebay.co.uk/FRONT-BRAKE-CALIPERS-FOR-GEN...

take a look at that pic, and you'll see the 2 parts.
The bit that crosses over the front of the piston in the pic is the bit that is bolted to the car, the actual piston housing bit is free to move forward and back, so when the piston pushes out against the inside of the disc, the piston housing is forced back as well, and this pulls the outside pad onto the outer face of the disc

[Roggia]

Thanks, that makes perfect sense. I'm off to ruin the car some more.

Much appreciated!

[HellDiver]

1cm of pad is practically new. Most don't come with anywhere near that much meat on them.

[Roggia]

HellDiver said:

1cm of pad is practically new. Most don't come with anywhere near that much meat on them.

Yes they've defintely still got some life in them. I not impressed with the stopping power of the e34 brakes so was hoping that replacing the pads might improve them.

However, the car might need a brake fluid change or better pads perhaps. To be fair I am comparing them to the drilled Brembos on my other car so I'm not sure if tinkering with them will improve them at all!

[Huff]

Standard e34 brakes are actually rather good (and not, like so many, over-servoed) so I'd definitely look at the fluid first (annd perhaps hoses while you'r eat it). Replaced the fluid on mine a few months ago and it made a very worthwhile difference to feel and control, esp. at speed.

[Roggia]

Huff said:

Standard e34 brakes are actually rather good (and not, like so many, over-servoed) so I'd definitely look at the fluid first (annd perhaps hoses while you'r eat it). Replaced the fluid on mine a few months ago and it made a very worthwhile difference to feel and control, esp. at speed.

Thanks for the advice - it was the braking at speed I was looking to fix.

I would do the hoses too but I don't plan to run the car for more than 6 months. It's already done 176k miles, has small spots of rust bubbling through 2 panels and also some random but harmless electrical gremlins. I know these cars can keep going for many more miles but I'm not sure the car I have is worth spending too much time or money on.

For £315 though, it drives beautifully. In fact, it feels far more connected to the road than my Alpina!