Shimano R517 Adjustment

[Padraic]

Hi everyone. I've done a lot of reading up on how to adjust the Shimano R517 brakes on my bike. I've given it a go and everything has gone to plan. I have a few questions that I'd like clarity on, so I'm hoping that someone here can help me.
Firstly these are the steps I took to set up the brakes, to ensure I done it right.

1. Removed caliper from bike to see how it works and how the pads are replaced.
2. Refit caliper, leaving the caliper mounting bolts loose enough to allow the caliper to be aligned with the disc.
3. Slide a 0.2 mm feeler gauge between the moving pad and disc.
4. Tighten in the fixed pad to align the caliper with the disc.
5. Torque the caliper fixing bolts.
6. Torque the cable fixing bolt.
7. Loosen the fixed pad adjuster to allow a 0.2 mm gap

Step 6 is where I'm unsure, with everything tight, the arm of the caliper has to be pulled 1-2 mm before the pad starts to move. Should I take up this slack before I torque the cable fixing bolt?
The next question I have is can I set the gap any tighter than 0.2 mm between the pad and disc? Or is this gap to allow for any disc expansion due to heat?
The final question is about the little screw on the caliper arm, how does this work?

Any help would be greatly appreciated.

Regards Padraic.

[Brucey]

most of what you need to know is detailed in the manual DM-BR0007-00.

[url]si.shimano.com/php/download.php?file=pdf/dm/DM-BR0007-00-ENG.pdf[/url]

IIRC you should be able to make the pads move earlier in the brake arm stroke if you adjust the small screw on the caliper arm. When you fit new pads this screw should be backed out as per the DM.

The golden rule with these brakes is that you should always set them up so that the brake arm has a full stroke available. This way you can safely adjust (using the barrel adjuster) with no tools mid ride; once you are back at base you can adjust the barrel adjuster back to where it was to start with and then adjust the caliper screws to restore the bite point (assuming the pad thickness is still in spec).

cheers

[Padraic]

most of what you need to know is detailed in the manual DM-BR0007-00.

[url]si.shimano.com/php/download.php?file=pdf/dm/DM-BR0007-00-ENG.pdf[/url]

IIRC you should be able to make the pads move earlier in the brake arm stroke if you adjust the small screw on the caliper arm. When you fit new pads this screw should be backed out as per the DM.

The golden rule with these brakes is that you should always set them up so that the brake arm has a full stroke available. This way you can safely adjust (using the barrel adjuster) with no tools mid ride; once you are back at base you can adjust the barrel adjuster back to where it was to start with and then adjust the caliper screws to restore the bite point (assuming the pad thickness is still in spec).

cheers

Hi mate, thanks for the information. I don't think I have a barrel adjuster on my bike??? Or should I?

So Instead of taking up the free movement of the caliper arm with the cable, I should adjust the small screw?

[Brucey]

Hi mate, thanks for the information. I don't think I have a barrel adjuster on my bike??? Or should I?

good point, I was thinking of a similar caliper model with one. If I had cable operated discs on a road bike I might fit an inline cable adjuster for mid-ride adjustments. If you always carry tools and/or don't expect to do any big descents in the wet (when the stock pads can wear pretty quickly), maybe you don't need barrel adjusters.

So Instead of taking up the free movement of the caliper arm with the cable, I should adjust the small screw?

provided there is no slack in the cable, (ie brake lever movement without brake arm movement), yes, I think that is the best way to proceed. Try it and see; you can always back the screw out if it doesn't work for you.

cheers

[Padraic]

Cheers for the advice so far, but I'm still a little confused.
When I aligned the caliper and set the pad clearance to 0.2 mm on each side, then I tighten the cable with no slack to the arm, I can see that for the first 1 to 2 mm of lever pull the pad isn't moving.
So in order to get over this I firstly moved the arm the 1 to 2 mm before tightening the cable.
Then instead of doing the above I just tightened the cable with the arm fully retracted, then tightened the small screw in order to overcome this free movement before the pad started moving.
But which is the correct method?
When i have this screw tightened in, do I loose some of the arm travel on the caliper?

[Brucey]

.
But which is the correct method?

the second one.

When i have this screw tightened in, do I loose some of the arm travel on the caliper?

no, I don't think so. You can verify this by dropping the wheel out and pulling on the cable.

cheers

[Padraic]

.
But which is the correct method?

the second one.

When i have this screw tightened in, do I loose some of the arm travel on the caliper?

no, I don't think so. You can verify this by dropping the wheel out and pulling on the cable.

cheers

I'll take the wheel off tomorrow and have a look. It's my first bike with discs so I want to get to know how they work and how to set them up myself.

[Stevek76]

Hello,

I have these brakes (well actually the CX77s but they're basically the same) on one of my bikes. The 2.5mm screw does not remove any arm travel, it just pushes the piston further round (and so inwards) relative to where the arm is (the end of the screw is what actually pushes the mechanism when you brake). The purpose of it is to provide adjustment for the outboard/moving pad, same as the 3mm allen adjustment for the inboard/fixed pad.

From what I've found with these brakes the total adjustment provided by the 2.5mm screw is somewhat limited so I'd actually advise not using it to take the slack up on the arm as you'll likely run out of adjustment before the outboard pad is fully worn.

Instead I would go with using the cable to take the slack, however that does come with some health warnings. You should avoid the situation where it's possible for the arm to hit the cable stop on the caliper before the brake lever hits your bars as if that happens it can be misleading as to when the brakes are in need of adjustment, until you find out when you try to emergency stop... - check with the wheel out if needs be. This will depend on your brake levers to an extent as they vary somewhat in how much cable they pull as well as if you're using a barrel adjuster.

Regarding the 0.2mm gap. I don't think there's any specific basis for that number, the rotors will not expand anywhere close to that even under heavy braking. However 0.2mm is pretty tiny, you're going to need dead straight rotors to go much closer with no rub. I usually just move them as close as they'll go with no pad rub.

[Padraic]

Hello,

I have these brakes (well actually the CX77s but they're basically the same) on one of my bikes. The 2.5mm screw does not remove any arm travel, it just pushes the piston further round (and so inwards) relative to where the arm is (the end of the screw is what actually pushes the mechanism when you brake). The purpose of it is to provide adjustment for the outboard/moving pad, same as the 3mm allen adjustment for the inboard/fixed pad.

From what I've found with these brakes the total adjustment provided by the 2.5mm screw is somewhat limited so I'd actually advise not using it to take the slack up on the arm as you'll likely run out of adjustment before the outboard pad is fully worn.

Instead I would go with using the cable to take the slack, however that does come with some health warnings. You should avoid the situation where it's possible for the arm to hit the cable stop on the caliper before the brake lever hits your bars as if that happens it can be misleading as to when the brakes are in need of adjustment, until you find out when you try to emergency stop... - check with the wheel out if needs be. This will depend on your brake levers to an extent as they vary somewhat in how much cable they pull as well as if you're using a barrel adjuster.

Regarding the 0.2mm gap. I don't think there's any specific basis for that number, the rotors will not expand anywhere close to that even under heavy braking. However 0.2mm is pretty tiny, you're going to need dead straight rotors to go much closer with no rub. I usually just move them as close as they'll go with no pad rub.

Thanks for the reply, now I'm getting a better understanding about them. I'll play around with them over the next few days. The bike is only new, just has covered about 100Km, but after my first go at adjusting them they feel a lot better.

Regards Padraic

[Brucey]

the pads are 2.4mm thickness when new. If you adjust the brakes using the cable alone (i.e by moving the brake arm round) shimano say you should ditch the pads when they are worn to 2.0mm thickness, i.e. hardly worn at all. If you don't, you can easily run out of travel on the brake arm and end up with no brakes. That is why you should use the adjustment screws, not the cable, to adjust the brakes as the pads wear.

Similar considerations apply to most cable-operated disc brakes; NB 'road' cable pull calipers often have brake arms with very restricted travel; in some models the arm will stop dead at what looks like about half the full travel, which is incredibly dangerous.

cheers

[Stevek76]

I'm not suggesting using the cable to adjust the brakes for pad wear and I don't believe Padraic was either. He appears to be talking about the small amount of slack at the beginning of the arms movement that results in no pad movement which seems to be something specific to the design of these R517/CX77 brakes.

It's not the easiest to describe and I really don't fancy extracting one of the calipers off my bike to photo the internals but essentially the arm pushes the piston around (and in). The contact point between these is the end of the adjustment screw. However, if the screw is fully wound out so its flush with the inside of the arm there's a gap of about 1mm between the internal mechanism and the arm when the arm is fully sprung back, this leaves a choice of either winding the adjustment screw or clamping the arm in a little. As mentioned, I prefer and use the latter option as the range of outboard pad adjustment provided by the small screw is really quite limited, if you use the former option you'll likely be in a situation were you've run out of brake lever before you've worn through a set of pads. Specifically for these brakes, using the arm to remove that small amount of slack will not later result in running out of travel: the arm does move all the way around until it hits the cable stop.

[Brucey]

I do see what you mean (it is similar with many shimano calipers) but anytime you have the arm started on its travel in the rest position, I would have said that you always have less (barrel adjuster/cable) adjustment left before the brake arm bottoms out, because the brake arm has restricted travel, rather than the piston, does it not? I guess if it is only a small amount it is not going to hurt much... it is also only of real concern if you ever experience rapid wear in a single ride without tools; given that you don't have barrel adjusters (I'd get some...) then you are in a bit of trouble anyway If you are ever in that situation.

Having said this, I don't think that you will be able to use the full pad life without doing this (ie starting the arm at rest) when the pads are nearly done. But when you are in that situation, you should be thinking (quite hard) about new pads.

cheers

[Padraic]

Thanks guys for the very useful information. I have setup the calipers, so I'll see how I get on on a cycle over the weekend. I will bring the required tools with me, just on the chance I'll need to adjust them.
But I'm happy so far that I'm getting the hang of them.