Rear mechanical disc brake adjustment on a bike with horizontal rear dropouts

[John_S]

Hi All,

I have just carried out some maintenance on my bike, a 2014 Genesis Day One Alfine 8, and having put it back together and taken it for a quick spin tonight I'm not overly happy with the performance of the rear disc brake.

I wonder if someone could offer me some pointers with where to start on checking through things to work through addressing any problems plus I also wondered if something that I have done when putting the bike together has had an impact.

Now it's a bike with a Shimano Alfine 8 IGH and it has horizontal rear dropouts. When putting things back together I thought that the chain looked a bit slack, perhaps due to chain stretch over time, and so in order to tension the chain I pulled the wheel back in the horizontal rear dropouts so that the chain is taught. On the subject of the chain I do get in changed once per year by the LBS, if not sometimes more regularly than bang on 12 months. Anyway I just wondered if the result of pulling the wheel back in the dropouts could change the position in which the disc rotor sits in the caliper and therefore where the pads grip the rotor possibly causing issues? If this is not a factor then I'll treat this is a red herring and concentrate on other things.

I also noted that the rotor on the rear brake seems to flex more when the brake is applied when compared the front disc rotor and I wonder if this indicates an issue related to the positioning on the rear wheel and subsequently the rotor in relation to the caliper.

The brakes on the bike are cable operated Hayes CX Expert post mount mechanical disc brakes with 160mm rotors. Prior to taking the bike apart working on the IGH hub issue I wouldn't have said that I had a big issue with the brakes. The last time that I'd taken the bike to a LBS I had asked them to have a look at the brakes including pads and rotors to check & advise if anything needed replacing and I was told that they didn't

However now that I don't think that the braking performance is as good as it could be I need to work through some steps to check things and then address them if any issues present themselves.

Now I've never changed the pads on the bike before because I've always asked a LBS to do it but are there general easy to follow steps to follow through for all mechanical disc brakes are all models of brake so specific that they all have their own ways of getting into them and getting the pads out of the calipers to check them? I did take a look at the calipers one time when I had the wheel out and on quick glances I couldn't see an immediate way to get the pads out without knowing what you're doing & what steps to take but at the time I was tackling another job and so I didn't focus on it.

Having found the post/thread below on the topic of adjusting rear brakes I appreciate that the cable may well be the guilty party in this. However is that the best place to start to rule in or out various possible issues?

https://forum.cyclinguk.org/viewtopic.php?t=122688

However I don't know whether I'm best to firstly replace the pads and then see how I go and if the braking performance doesn't improve then move onto replacing the brake cables or is there a better order to do this in or other diagnosis steps that I have missed that I should also try in a particular order?

Also am I right in thinking that pads are quite specific to each brake type? If so do I need to do a search on the internet for specifically "Hayes CX Expert replacement disc pads" or are things a bit more generic than that?

Thanks to everyone for any thoughts and tips!

John

[John_S]

Oh and further to the above just in case it is of relevance to know the caliper is mounted on the seat stay of the bike.

Thanks again for any help & advice!

John

[Brucey]

almost certainly the cable is bad by now if you have never changed it. Setting up mechanical disc brakes is not very difficult if you go about it in the right way. Hayes official procedures here

https://hayesdiscbrake.com/wp-content/uploads/sites/5/2018/08/45-20182L_Mech-Brake-Install-2page.pdf

There are dozens of different brake pad fittings; they are manufacturer-specific. These are the pads you need for CX-expert brakes;
https://www.discobrakes.com/?s=0&t=0&c=7&p=730&

if you search for Hayes MX2 pads you will find most for sale in this fitment. Cheapo ones on ebay too.

cheers

[John_S]

Hi Brucey,

Many thanks for the advice and links which are much appreciated!

I've ordered myself the brake pads today and so hopefully they arrive soon.

Thank you,

John

[mattsccm]

I have a single speed MTB with track eds like you. Moving the wheel back does of course put the disc in a different place and thus I guess the pads are in a different place in the arc of the disc. Surely wear is in a different place and it might be that this has left high spots etc.
I would at least check that the pads are making contact properly and maybe stick some new ones in. Cable will be good or bad irrelevant of this.

The above is needed when the wheel is moved if I swap gearing for example.

[squeaker]

...and so in order to tension the chain I pulled the wheel back in the horizontal rear dropouts so that the chain is taught.

OT, but personally I like to see a small amount of slack in such a chain.

[Brucey]

^ me too. It (quite unnecessarily) beats the transmission up if you take all the slack out.

cheers

[Brucey]

the rear brake/mountings have changed on Genesis Day One models, almost yearly;


2017 model with Promax DSK-300 caliper


2016 model with Promax render caliper


2015 model (singlespeed) with TRP Spyre; note one-year-only dropouts. 2015 models were the first built with so-called "Mjolnir" tubing instead of Reynolds 520


2014 Di2 Alfine model with Hayes CX brakes (note weird photo orientation). This model cost £2200 RRP....


2013 model (with Alfine hub and BB5 caliper) 2014 model similar but fitted with Hayes CX disc brakes

Singlespeed models use the same frameset as the Alfine models. 2011 and 2012 models are similar to 2013 models but have BB7 brakes.

The 2015/2016/2017 model requires a ( fairly easy) brake adjustment every time the wheel is moved in the dropouts. Just make sure the wheel is properly centred between the chainstays (this is more important than the exact chain tension) then slide the caliper in the slots until it touches the disc, then move it forwards by about 1mm. Fine tune the pad to disc clearance as necessary.

The 2013/2014 model does not require that you adjust the brake every time the wheel is moved but the adjustment is different. In theory (if the slots are arranged correctly and the caliper is correctly mounted to start with) it ought not to be possible to get it wrong but it doesn't always work out as planned.

Because different brake calipers have different shapes for the brake pad friction material, discs have different track widths, and it is essential that no part of the friction material overhangs the edge of the disc, the tolerance of caliper alignment will vary with the parts used.

cheers

[John_S]

Hi Brucey & Squeker,

Thanks for your messages above and I'll make sure that I don't take all of the slack out of the chain.

Also just following on from Brucey's messages above with photos of the various Genesis Day One rear brake/mountings I thought that I'd add to it with my 2014 Day One Alfine 8 model. Although please accept my apologies because the photos are nowhere near as good as the ones in Brucey's post and due to my rear rack being in the way the photo from the non-drive side isn't great I'm afraid.

Thanks,

John

[John_S]

Hi again,

Following on from the above my plan is the replace the brake cable but I'm wondering whether or not to replace the brake pads at the same time or to keep using the current ones for a bit longer? I have ordered new pads which have arrived but I've just taken the old ones out and I wonder whether or not they need replacing yet?

My apologies for having to ask the question but I've never replaced the brake pads, or the brake cables for that matter before, because in the past this would always have been a job I would have asked a LBS to check and replace if necessary when doing a bike service. However now that I'm trying to do more things myself I'm just not sure whether or not the pads need replacing yet.

I've tried to take a photo of a current pad (the two current pads have almost identical wear) next to one of the new pads. However due to a combination of my lack of photography skills, the camera itself and it's ability to macro focus or the fact that the old pad is a bit dirty the photo is pretty much near impossible to see much detail on.

Anyway on the brand new pad the pad itself is clearly thicker than the backing plate.

On the old/current pad I would say that it's an even thickness all over and the thickness of the pad is (from looking at it with the naked eye) just about exactly the same thickness as the backing plate itself.

Therefore I don't know whether or not the pad has reached a point whereby it needs to be replaced now or whether there is more life left in it yet and I can reinstall the pad in the caliper?

Thanks very much for any thoughts and advice on this question!

John

[squeaker]

Given the relatively small cost of brake pads, and how far you have got with changing them, I'd just bung the new ones in and put the old pair in a 'come in handy' box for when I forget to check the pads and find they are down to the backing pads and I need to use the bike. Others may have different views

[John_S]

Hi Squeaker,

Thanks for your message and advice about the pads.

At the moment I'm just trying to replace the cable and can I ask for any advice about the next step to take because I've got stuck.

I've rolled back the rubber hood on the brake lever and I've unwound the bar tape to the point at which the brake lever is secured to the bar. This shows that the brake cable outer then goes into the plastic cashing of the brake lever.

In order to carry on with this job do I need to completely take the brake lever off the handlebar or can I leave the brake lever in place and somehow both remove the old brake cable inner & outer before installing the new brake inner & outer cables?

I've tried to attach photos below to show where the outer cable goes inside the brake lever. According to the original specs of the bike the levers are Tektro RL-340.

Thanks to all for any thoughts & advice on where I go next from here!

John

[John_S]

Hi again,

Actually don't worry about the post asking whether or not I need to remove the brake lever from the handlebar in order to replace the cable.

I've just found the following info in the link below and so the way I'm reading it I can replace the cable with the lever left on the bar where it is.

https://www.tektro.com/upload/Product/F_20150915101997SS8z8t.PDF

Thanks,

John

[LinusR]

Hi again,

Following on from the above my plan is the replace the brake cable but I'm wondering whether or not to replace the brake pads at the same time or to keep using the current ones for a bit longer? I have ordered new pads which have arrived but I've just taken the old ones out and I wonder whether or not they need replacing yet?

My apologies for having to ask the question but I've never replaced the brake pads, or the brake cables for that matter before, because in the past this would always have been a job I would have asked a LBS to check and replace if necessary when doing a bike service. However now that I'm trying to do more things myself I'm just not sure whether or not the pads need replacing yet.

I've tried to take a photo of a current pad (the two current pads have almost identical wear) next to one of the new pads. However due to a combination of my lack of photography skills, the camera itself and it's ability to macro focus or the fact that the old pad is a bit dirty the photo is pretty much near impossible to see much detail on.

Anyway on the brand new pad the pad itself is clearly thicker than the backing plate.

On the old/current pad I would say that it's an even thickness all over and the thickness of the pad is (from looking at it with the naked eye) just about exactly the same thickness as the backing plate itself.

Therefore I don't know whether or not the pad has reached a point whereby it needs to be replaced now or whether there is more life left in it yet and I can reinstall the pad in the caliper?

Thanks very much for any thoughts and advice on this question!

John

Those pads look fine to me. I would clean them by rubbing them on some clean sandpaper and be careful not to touch the pad surface with your hands afterwards. Keep the new ones for spares. Your original problem probably occurred because the pads were contacting the disc rotor in a different place. The rotor would have some wear and there would be a slight "step" in the surface as the pads bit against the rotor in the original position. Then when you adjusted the wheel in the drop out the pads bit onto the original "wear track" and also part of the disc that is not worn and this would have caused a very slight gap between pad and disc rotor. As well as the pads you should also clean your disc rotors with pure alcohol or a special rotor cleaner. Then test the brakes thoroughly by riding and braking hard in a safe area. Happy fiddling!

[Brucey]

pads are usually about 4.0mm total thickness, with ~1.6mm backings and ~2.4mm friction linings. In the owner's manual it should tell you how much wear to accept, and IIRC you will find that when the total thickness is ~2.5mm then the pads are definitely worn out. If the friction material is slightly thinner than the backing then you probably are at about 3.0mm total thickness which means the pads are about 2/3rds worn. I'd fit new ones and keep the old ones as spares in case you have an emergency of some kind.

Normally it is not necessary to do much more than loosen the brake lever on the handlebar (not even that with some brake levers) to get enough access to change the outer cable. In point of fact I'd fit a new inner (with lots of lube on it) to the old outer and see how that feels first; if it is OK then you can avoid having to untape the handlebars or replace the outer. However if the cable feels rough or draggy with a new inner fitted then you need a new outer too.

BTW you can learn a lot from the state of the old inner cable when you pull it out; you may well be able to see where it is dry, dirty, rusty, worn etc and this may tell you if the weather has been getting in either end and/or alert you to the part that needs most attention in future.

cheers