R9170 Dura Ace disc - constant readjustment required

Discuss light weight issues concerning road bikes & parts.
scale29
Posts: 61
Joined: Sat Jun 04, 2011 5:40 pm

by scale29

I had issues when 1st setting up my flat mounts on 9170 160mm discs, mainly due to the shape they arrived in inside the box, not at all true.

I spent a good 1/2hr truing the rotor and setting the clearances properly (centre the caliper on the rotor then adjust the pistons, not hold lever and do up bolts!).

Mine have remained true now despite some VERY heavy braking, I’m a reasonably big guy at 93kg currently and been stopping down some steep slopes in the Pyrenees, with only a little rub post braking for a few seconds then back to silence.

I will NEVER return to caliper brakes and was firmly in the “not on my watch” camp a couple of years back. I own a ‘nago C60 rim brake bike that I’ve not ridden since getting discs on my other bike, for next season I’ll have a carbon disc bike once I’m back to my fighting weight.

by Weenie


hkgmatt
Posts: 6
Joined: Sun Apr 08, 2018 9:17 am

by hkgmatt

You've been incredibly helpful, thank you for your time contributing with your experience.

What I'm taking away from your responses is:

1) Disc brakes can be very difficult to set up properly - using facing tools or diagnosing a faulty piston that is not retracting properly (thank you for the tip @Delorre) is not something that I expected having to do when I got disc brakes; and some of the LBS I've used don't seem to master this either.

2) It may be worth experimenting with other disc rotors and possibly calipers.

3) When properly set up disc brakes seem to work well for a majority of people, apart from some pinging for a bit after braking which I'm not bothered with.

I will have the LBS that mounted the brakes take a look at the caliper / piston and disc mount facing issues to see whether that gets me where I need to be. Meanwhile I'm doing my gran fondo tomorrow on my trusty rim brake bike.

scale29
Posts: 61
Joined: Sat Jun 04, 2011 5:40 pm

by scale29

Yes, I agree that a degree of tinkering was involved at 1st, happy that I was an early adopter on MTB and Cross too so I have quite a lot of experience with them, so maybe what I take for granted with discs is a real PITA for new road adopters.

My 1st Shimano caliper had a cracked piston which was returned under warranty and the shape of the rotors when new was a disgrace for such an expensive product, no one should have to true up new out of box products.
Now they’ve settled in though they’re very much worth the initial trouble.

numberSix
Posts: 73
Joined: Sun Sep 23, 2012 1:53 pm

by numberSix

15+ years of wrenching mtb disc brakes, and motorcycles as well.

If the pistons aren’t retracting, the rubbing is also heating the rotor. Causing more warping issues.

IMO the main cause is bubbles still in the system, or crud in/around the pads and pistons.

Bleeding: think bubbles in a soda glass. There will be bubbles stuck to the pistons’ cupped inner surfaces. Only vibration, and careful tilting will get them to migrate to the bleed fluid path. With the caliper dismounted, tap on it with a plastic handle or small plastic hammer, while tilting so the bubbles can rise to the hose fitting. As you push the brake fluid into the bleed fitting and siphon off the excess at the master cylinder, do the same tilt and tap steps for the master cylinder hose fitting and piston. A careful eye will see the last few bubbles rise out. One more bleed cycle to be sure and it’s ready.

Cleaning: the pads just rest in the caliper body, and when enough brake dust and road crud get in there the pad spreading spring can’t overcome it. I take the pads out to prevent contamination (especially important for mineral oil systems) which is a good time to scrub the exposed piston sides and pad tab areas on the caliper. Soapy water and a small toothbrush usually work. Rinse the pads too, you might need to use a scraper to get deposits off of the tabs.

Simple, right? For mtb the aggravation is worth it, I really don’t miss V brakes. Still on rim brakes for road as we don’t ride have to ride in the rain that often here.

Hope this helps
6

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