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My daughter's rockhopper has Shimano Deore disc brakes. Recently, the rear brakes performance deteriorated. It brakes a bit, (stops the wheel with no load) but with a load, the wheel still spins. Hope I'm being clear. Any ideas about the problem? Does the bike need new pads? I think they are mechanical disc brakes.

Also, I have the Avid Elixer brakes on my Pivot 429. The rear brake is really noisy. Any ideas on how to reduce this screeching noise? They work fine. I've read this is a common problem with this braking system.

Thanks for any assistance. I'm changing from long distance running to placing more of an emphasis on mountain biking.
 

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Vaginatarian
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could be several things
start with the easiest
clean the rotor with alcohol or acetone, pull out the brake pads , check for oil on them, while theyre out check the pistons and inner area for oil. clean it all up with whatever you used on the rotor. now for the tricky part
gently apply the rear brake without the pads. be carefull not to let the pistons come out too far just about 1/4" or so. take a qtip and clean around the pistons. then lightly oil the sides with a qtip and mineral oil. push the pistons back down and repeat

re assemble

if that doesnt do it

spin the rear wheel while looking down into the caliper , watch the brake pads as you apply the brakes . do both pads come out the same or does one come out more (watch the rotor if theyre coming out uneven the rotor will push to one side.)
if they are uneven you will need to adjust the caliper so the rotor is exactly in between the pads

if that doesnt do it it will either need a bleed or new pads
heres a link to a bunch of tech sheets that explain how with pics.
http://bike.shimano.com/publish/content/global_cycle/en/us/index/tech_support/tech_tips.html

shimano brakes use mineral oil. do yourself a favor and stick with brake mineral oil
the screeching can be alot of the same things, dirty rotor/pads, miss aligned. you could try different brake pads (organic vs. metal)
 
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