Hydraulic Disc Maintainance...on a new ride.

icbk · June 2007

I bought a brand new ¶œ649 Specialized Rockhopper this weekend and am loving it - I used to ride loads years ago so it's great to get back into it. Took it out for a spin and even rode it to work today.

Anyway, I'm a bit of a sucker for taking things apart to clean and service them and after removing the front wheel I noticed the pads of the disc brakes (Juicy 3s) closed in tighter so the rotor wouldn't actually squeeze back inbetween them.

I used a flatheaded screwdriver to gently rock them back and forth and open up the gap (the manual said this was OK!) enough to replace the wheel. Since then I've noticed that both the front and back pads are touching the rotors, resulting in a small amount of drag -- is this normal?

I also notice the manual says the brakes are 'self-adjusting' - how exactly do they self-adjust? If I want the action in my levers to be a little less squishy, how do I go about that?

Apologies if this is a nubish question but I'm completely new to hydraulics...

Other than the brakes, I absolutely love the Rockhopper and am glad I went with that rather than the Hardrock (which I was originally going for). The stock pedals suck though, so I'll be ordering some Gusset Incas asap! [:D]

ddoogie · June 2007

What you will have done is squeezed the brake leaver whilst the wheel is off. You now have to reset the pistons back into the caliper. Don't worry, its not as bad as it sounds!

Use the manual to work out how to take the pads out. Make sure your hands are clean and you put them on a clean surface. This will stop them getting contaminated. Once the pads are out you should have access to the pistons that push the pads onto the rotor when you squeeze the lever. Use the flat headed screwdriver or a tyre lever and push them so that they are plush against the caliper wall. Put the pads back together and then the wheels on as well. Squeeze the levers until you get the bite back.

They are self adjusting in that they accomodate for any wear that the pads sustain. As they do wear, the pads will have to move further to bite the rotor. The pistons accommodate for this.

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nicklouse · June 2007

read the manual.

are the discs being twisted as the brkeas are being applied? align the calipers.

yes the pads rub a bit from new or after being played with but the settle down after some use and bedding in. there should also be a reach adjust screw.

self adjusting yes they are. friction between piston and seal...... do you really want to know.

nick
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icbk · June 2007

<blockquote id="quote">quote:<hr height="1" noshade id="quote">Originally posted by ddoogie

What you will have done is squeezed the brake leaver whilst the wheel is off. You now have to reset the pistons back into the caliper. Don't worry, its not as bad as it sounds!<hr height="1" noshade id="quote"></blockquote id="quote">

Absolutely the answer I needed, thanks v much -- I'll do this when I get in tonight. And the self adjusting makes more sense now, cheers. [8D]

icbk · June 2007

<blockquote id="quote">quote:<hr height="1" noshade id="quote">Originally posted by nicklouse

read the manual.<hr height="1" noshade id="quote"></blockquote id="quote">

I've read the manual and indicated as much in my post...

<blockquote id="quote">quote:<hr height="1" noshade id="quote">are the discs being twisted as the brkeas are being applied? align the calipers.<hr height="1" noshade id="quote"></blockquote id="quote">

No, the caliper alignment is absolutely fine - as I said in my post, the pads themselves are the issue.

<blockquote id="quote">quote:<hr height="1" noshade id="quote">self adjusting yes they are. friction between piston and seal...... do you really want to know.<hr height="1" noshade id="quote"></blockquote id="quote">

Yes, I posted this question because I wanted to know the answer...[;)]

I'm pretty sure DD above has very helpfully pinpointed the issue but thanks for your reply also.
[|)]

nicklouse · June 2007

ok so if the disc are not being twisted by the pads the "squishy" feel will be the pads settleing down to where they want to be. Or the friction material still needs to bed in.

Ok so how do the pistons self adjust. the friction of the seals allows the pistons to retract at a given rate while the lever piston retracts at a different rate and when it passes over some drillings in the mater cylinder bore allows fluid to join the braking line from the resivoir. this also stops the pistons moving back any more. So over time the pistons are adjusted to the correct place. as the pads wear the distances are compensated. Just like a disc system on a car.

nick
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icbk · June 2007

Very clever and interesting, nick, cheers for the explanation. Yeah, I'm assuming the squishiness may well be down to the pads not being bedded in yet since it's only a couple of days old!

nicklouse · June 2007

and if you (re)read the manual Avid tend to say upto 100 aplications to allow the brakes to settle bed in etc. but not this is almost true for every time the brakes are disturbed by re-adjusting or sticking a screwdriver between the pads. (ok it does not take quite as long on minor adjustments).

but the biggest problem people have with brakes if they will not let them be.

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Hydraulic Disc Maintainance...on a new ride.

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