Road bike mechanical disc brake advice

[aea730]

Folks. Ive lost all braking twice today on a 100 mile ride in wet weather. I’ve got Shimano mechanical discs. On the first failure I used the hex tool to turn the right hand pads inwards. This sorted it. The second time I was only 2 miles from home and just winged it with no brakes. Is feasible that the right hand threaded adjusters are winding themselves out while riding, can this/should this happen. I’m thinking of a drop of thread lock on the adjuster threads or just binning and going to hydraulic

Any advice ?

[bigdom]

When you mention no brakes, what sensation did you feel through the levers?

Really only two issues on mechanical. Either cable tension, or piston actuation. When was last time the pistons were cleaned, or fluid changed?

[millen]

That's disconcerting! Especially in the wet. Did you lose front and rear? I've never used Shimano mechanicals but ran TRP Spyres for 12,000 miles. They were OK-ish but needed very frequent adjustment, typically every 100-200 miles. I don't feel it can have entirely been pad wear, so like you I suspected the screw adjusters were slowly unwinding, especially as they became very loose to turn with an Allen key. I did resort to applying a couple of drops of thread lock which seemed to improve things somewhat.

If you look vertically at the caliper against a light surface you should be see if the pads are moving when you apply pressure. As bigdom suggests, perhaps one piston is seized. Removing the wheel should confirm.

Going hydraulic should make a big improvement, but you'll presumably need a new pair of shifters.

I eventually switched to Juin Tech hydro-mechanicals which I'm very happy with and mean you retain traditional cable shifters. Downside is there's I believe just one UK distributor https://www.edgesportsuk.com/store/components/disc... There was talk of a 4-pot caliper but it's no longer on their website.

Edited by millen on Sunday 3rd March 22:15

[aea730]

Thanks for your replies. The brakes are mechanical (cable) operated. They are spotlessly clean with good friction material. It seems with these that once set up the adjustment is limited to screwing in the inner pad. I wind it in until the pad contacts the disc then back it off a couple of notches. At that the wheel locks under hard braking.

For some reason and a few miles down the road all braking goes, I can pull the levers as hard as I can and nothing happens.

I’m fairly certain the pad adjuster is winding itself back out or whatever takes up the adjuster travel has reduced.

[mikecassie]

If it is Shimano, is it the type of mechanical disc brakes where you can only 'adjust' one pad, the pad furthest away from the wheel?
I had those type of calipers on a bike I have, horrendous is my description of them.

I think your inner pad is wearing down and when you actuate the brakes only the outer pad actually moves, this contacts the disc and then the disc deflects to contact the inner pad. Then you get the benefit of both pads working to squeeze the disc...

To adjust these correctly IIRC you need to slacken the caliper off, squeeze the brakes and then tighten the caliper down again. Then you adjust the outer pad with the hex screw you mention.

I changed to TRP Spyre calipers, a big improvement. These allow you to keep the cables and the way they work both pads move when you actuate the brakes to squeeze the disc.

[TwistingMyMelon]

Ive just bought a bike with TRP Spyres

I wasnt keen on cable disks, but these are good and real easy to adjust, as poster above says

You can adjust both pads and also realign the calipers in seconds if needed, been using mine offroad with no issues

[Johnny]

I swapped by Avid BB5s for TRP HyRd after years of st performance.

Huge improvement.

[aea730]

Thanks guys. I bought the bike with discs fitted. I certainly wouldn’t have another disc equipped road bike.

[Connectors]

aea730 said:

Thanks guys. I bought the bike with discs fitted. I certainly wouldn’t have another disc equipped road bike.

Hydro brakes don't suffer like mechanical ones, so don't tar them all with the same brush. I've never had the misfortune to use mechanical discs, mainly because I listened to the tales of woe about them and ran away!

I know that none of the above helps you, but I didn't want you to think that all brakes are created equally.

[Barchettaman]

aea730 said:

Thanks guys. I bought the bike with discs fitted. I certainly wouldn’t have another disc equipped road bike.

It does seem a very odd problem that you're experiencing.

Maybe you could mark the caliper and adjustment wheel with TippEx and see if it's really winding out whilst you ride?

I have Avid BB7 on my commuter which are finnicky to set up, but I do appreciate the better braking peformance in wet weather.

For an all-weather commuter rig I wouldn't go back to rim brakes; for a road bike however I'll stick with normal rim calipers.

[aea730]

I must say I have hydraulic on my MTB and they are tmendous. I just think these Shimano single movement piston units are just not quite up to it.

I’m looking at a set of Shimano hydraulics I’m going to put a post up about them

[mikecassie]

Road Hydros are ace. I've a set of Sram on another bike and they are good. The Spyres are a step up from the Shimano and the Sram are a couple steps up again.

Don't think all road disc set ups are as bad as what you've experienced.

[millen]

Thread drift, but useful video here about how to clean and lubricate piston seals to minimise 'sticky piston' syndrome. Applicable to both hydro-mechanical and full hydro calipers - typically the rear gets gunged up more than the front, especially with wet riding. Pure cable discs are less susceptible I think.
https://www.youtube.com/watch?v=vQXFFgRButo