Hydraulic disk brakes - what's wrong ?

[103Alex1]

Sorry to post this here but wondered if anyone can give me some guidance.... bought a bike with Shimano XT Hydraulic Disc Brakes (6" rotors) and derailleurs. I haven't dealt with disc brakes at all before and the few bits I've looked at on Youtube are mostly geared at mechanical disc brakes. The bike might get converted if I can get it running well.

The front brake is great but the rear one looks like it needs some adjusting. The disc rotor seems to be making contact with the pads because the wheel does not turn freely. I haven't dismantled them yet as I'm unsure how to / whether there are things I should know not to do or there's a simple explanation that can be tried first. Is there anything simple I can try first ?

The seller claimed the brakes had been serviced recently but the bike clearly hadn't been ridden in last couple of months. It otherwise seems in good nick for its age so would be good to sort this out if I can. I won't learn much by booking it in to the bike shop and will hopefully get to know and love the bike more once I do a bit of work on it.

On a related note ... I've cleaned and lubricated the chain ... should I also lubricate the cassette / derailleurs and if so are there any parts to avoid getting lubrication on ?

Thanks !

 

[benjy_a]

You have to reset the pads in the calipers, it's very easy if you know how. I'll try and explain but you'll be able to download the instructions online somewhere.

Take the wheel off, remove the split pin which holds the pads in. Carefully remove the pads but remember how they go back in.

Now you should be able to see the pistons in the calipers. I use a chunky tyre lever to carefully push the pistons back into the calipers. Now replace the pads and then the wheel.

Loosen the two Allen bolts which then allows the caliper to move from side to side. Squeeze the brake lever until the pads grip the disc, then tighten the caliper bots (without letting go of the brake lever).

That should be it, when you release the lever the wheel should be free and the brakes adjusted.

Ben

 

[103Alex1]

Thanks a lot Ben. I'll give that a go.

 

[benjy_a]

No worries, oh and don't get any lubricant on the discs or pads! Even oil from your fingers on the discs will reduce the effectiveness of the brakes. You can get special degreaser for the discs which works really well.

Good luck!

 

[Deleted member 4366]

Try this first.
Loosen the two upward (radial) facing screws. Hold the brake on. Tighten the screws. Let go of the brake.

 

[103Alex1]

Tried the easy option first - didn't work this time unfortunately, d8veh !

Ben - went through all your steps and wheel is running perfectly now and brakes are extremely responsive. The pads or caliper must have come out of alignment, or something obstructing the piston movement I guess.

Now know how to change the brake pads as and when needed which is a big plus . Took me an hour and a half but that's because it was all new to me. Should be a breeze next time.

Couple of other basic questions if I may (not had a derailleur bike before) - is the chain suppossed to be in contact with the outside edge of the front derailleur when riding the bike ? Makes an awful racket because of metal chain rubbing against metal derailleur !

Also when using the left shifters to test operation of the front derailleur the mechanism is noisy (to my ears anyhow) - there is no noise bar a light click when I change gears on the hub gear bike. This is more so when changing from high to low. Is that normal on this setup of bike ?

 

[Scimitar]

Couple of other basic questions if I may (not had a derailleur bike before) - is the chain suppossed to be in contact with the outside edge of the front derailleur when riding the bike ? Makes an awful racket because of metal chain rubbing against metal derailleur !

There are two adjusters on the front set - one for low movement limit, one for high movement limit.
Have a look on Sheldon Brown's site
Sheldon Brown-Bicycle Technical Information
Derailer Adjustment

 

[103Alex1]

There are two adjusters on the front set - one for low movement limit, one for high movement limit.
Have a look on Sheldon Brown's site
Sheldon Brown-Bicycle Technical Information
Derailer Adjustment

OK thanks - that's incredibly comprehensive. When I reset the chain on the middle ring (front) after sorting the brakes and the left gear was set to mid, the chain was pretty much bang on the centre of the front derailleur bracket and no clatter so looking hopeful. I can see why, now, having read through that. I keep forgetting that the gears cannot shift when the bike is stationary as they have to be pushed from cog to cog whilst the bike is in motion. Probably get the stand out tomorrow so I can just rotate the pedals forwards and test the shifting that way. Don't want to ride it again until everything is set up just right and nice and smooth.

There are clearly lots of tweaks that can be tried if shifting is not running smoothly (especially cable tension - which is very straightforward). The guidance on that is very good in those links.