o/t Disk brakes for mountain bike

[woodfell]

Hi,

 

I have problems with my Rockhopper front disk brake - it is a Shimano m525. Since I bought it over a year ago I have never been happy with it. Firstly, oil leaked out of the bottom of the Manitou shock and contaminated the pads. I fixed the fork leak and replaced the pads, cleaned the rotor and bled the brakes. However, the stopping power is still poor as I can push the bike forward with the brake applied hard. The brake lever is firm and is the same as the rear brake lever. I have swapped over the rotors/disks front to rear and the pads and I still have the same issue.

 

Any ideas please?

 

Thanks.

[caterhamnut]

No expert I am afraid - but did you bed the pads in - can make a big difference. May be worth a completely new set of pads (superstar components do sensibly priced non-branded ones) and a thourough wash of the discs using brake cleaner...

This is assuming the brake lever isn't bottoming out, and the brakes are bled - which you say they are...

Not much help I'm afraid...

 

Angus's Adventures in Sevenland

[Old Git]

Any hydraulic disk brake set up should practically send you over the handlebars with very little effort - but I don't have much idea as to why yours are so poor. Are the levers firm when you apply the brake or do they go down when you hold the pressure? Do the brakes squeal when the rotor goes through them?

 

Tim N

[taffyracer]

mine sent me over the handlebars on monday, damaged cruciate!

 

 

[Tonycaterham]

If you bled the brakes did you use special brake bike fluid?

 

I used car brake fluid then had problems similatr to yours. To save a couple of £'s I had wrecked all the seals and it cost me nearly £200 to replace the entire braking system

 

Tony

 

L7 EVL

 

 

[bobt]

Really! Mine says to use dot 4 fluid.

[captain chaos]

My Maguras were a bugger to bleed..felt spongy until i got them bled properly. Sounds like you may still have bubbles to me...

 

gary

 

[oilyhands]

You either have air in the system or the pads aren't bedded, mine are certainly capable of chucking me over the handlebars.. (Avids.)

 

Oily

[DohNut]

 

Shimano systems use oil, most other systems Hope etc. use Dot4/ 5.1 etc.

 

You may try jigging the bike/lever around so the caliper is the highest point of the system and re-try bleeding.

 

N

[Tim Smith]

I've had a similar problem with mine due to contamination. You really do need to get the discs properly clean using brake cleaner or the most aggressive solvent you can lay your hands on. I used methylene chloride which is the finest degreaser known to man.

 

Bed them in by riding down a good long hill with the brakes dragging to get the maximum possible heat into them to burn off any remaining contamination.

 

Tim

[jason liddell]

If it's just the pads need bedding...

 

Just sluice the pads/callipers with lots of tap water and then ride up the street repeatedly braking hard. Sluice again and repeat the process until he pads are well-bedded (should only take 3 or 4 goes if bedding is your problem).

 

 

 

^{(Mainly ) Scottish Motorsport/Trackday Pics Here.}

[myothercarsa2cv]

Manipoos 😔

Shimano disc brakes 😔

 

Make sure the disc mount surfaces are faced (most forks still have paint on the mounts ), and properly spaced so the caliper is central over the disc. If the disc is warped, bend it back, but not after a ride - they get hot!

THEN bleed the system, even without the pads bedded in the force applied to the disc should easily be plenty to lock either wheel.

Then scuff up the pads, rinse, and do some heavy braking. Don't use brake cleaner - it doesn't really heat up enough to get rid of it.

 

That should give you some fairly decent braking.

 

 

John

_________________________

 

Bugsy: '82 2cv6 (Back on the road!!! 😬)

Talloulah: '08 1.6K Classic (Grubby )

[woodfell]

Thanks for the suggestions.

 

The front brake is working well now since I attacked the rotor with wet n dry paper and rotor cleaner.

[myothercarsa2cv]

Nice little trick I was taught by some trials riders was to buy a can of coke, and pour it on the braking surfaces - the extra stickiness proved essential when balancing precariously on the rear wheel on the side of a bridge over a railway line.

 

John

_________________________

 

Bugsy: '82 2cv6 (Back on the road!!! 😬)

Talloulah: '08 1.6K Classic (Grubby )

[7 wonders of the world]

Why were you bleeding the brakes when simply doing a pad replacement ?

 

Pads - Clarks brand are very good and offer both organic and sintered material options the UK distributor is Fisher Oudoors and most bike shops will deal with Fishers, the OE Shimano organic material is fantastically soft and I've gone metal to metal on XTR in under 1 hour 😳 - though Shimano were little naughty in the way they made their pads opting for indented lugs in the backplate to secured the material as opposed to using spigots though the backplate this may not sound too relevant but it effectivly halfs the amount of material available before you go metal to metal

 

Brake fluid: Shimano and Magura use a 5wt mineral fluid LHM meets this requirement, most others Hope Avid Hayes etc use DOT 4 or 5.1 NOT DOT5 though.

 

Bleed kis are available for most brands however you do not always need these as most can b bleed in conventional top to bottom fashion magura and avid do not always offer a caliper bleed nipple therefore you can bleed the bottom to top with a syringe, if your on Hayes certain models benefit from using the push in plastic cone in order to catch the displaced fluid from around the bladder - not essential but VERY messy without it!

 

Bed in 20-30 stops starting light then slowing increasing in speed an power, disc should be clean isopro is fine as it will evapourate in seconds deglazing where necessary, caliper alignment should also be checked, ISO mounts usually benefit from being faced to ensure correct pad contact, coke on ths disc yes this works as does applying little abrasive sloppy mud to the discs, both these were used on older style pads to encourage more rapid bedding in, most newer pads are either scourched on their top layer to make them more brittle and aid the bed in process or surface ground with small groves akin to a record again to reduce the surfce area an so encourage a rapid bed in and pad to disc conformity.