R9170 Dura Ace disc - constant readjustment required

Discuss light weight issues concerning road bikes & parts.
scale29
Posts: 79
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.

hkgmatt
Posts: 7
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.

by Weenie


scale29
Posts: 79
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: 76
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

Cemicar
Posts: 73
Joined: Mon Aug 21, 2017 7:40 am

by Cemicar

So have you ever replaced the caliper? You may go with the warranty claim, but I think you can just swap the front and the rear calipers, as they're apparently the same.

hkgmatt
Posts: 7
Joined: Sun Apr 08, 2018 9:17 am

by hkgmatt

I did replace the caliper, which did not change anything to the problem.

But finally I figured out what the problem was: the caliper mounts were not faced correctly. I finally took my courage in my hands and used a Park Tool DT-5.2 facing set with a hand drill driving the cutter. After the facing, the problem disappeared completely. In retrospect, I should have diagnosed the problem earlier after observing that the caliper pivoted inwards when tightening the bolts, which it shouldn't do on well faced brake mounts. This being my first disc brake, the learning curve has been steep.

I have to absolve Shimano and it's Dura Ace disc brakes of all blame, the rotor now stays true even after long braking sessions when descending, other than some pinging which goes away when the brake cools down again. It seems that if the caliper is mounted on uneven brake mounts, it bends the rotor much more easily.

But I'm seriously unimpressed with Legend (I have the TX10.0) who delivered a faulty fork which made me lose almost a year trying to get to the bottom of the problem, and the LBS that sold it to me and failed to fix it.

Thank you all for your very helpful suggestions.

sychen
Posts: 366
Joined: Thu Apr 24, 2014 1:06 pm

by sychen

Matt thanks for this post and thread.

While my 9170 have been great... Only the regular pinging after hard braking and howling in the wet, have learned much about setting up on less than ideal platforms and the need to have properly faced mounts.



Sent from my SM-G950F using Tapatalk


andreas
Posts: 59
Joined: Thu Jun 12, 2014 10:21 pm

by andreas

Holy shit, facing a $4000 frame sounds intimidating as hell... you basically get one shot? If you face too much the rotor will go out of alignment horizontally I guess?
The need for it plays into Hambini's observations on frame BB shell manufacturing accuracy, though.

spdntrxi
Posts: 2033
Joined: Sat Jul 20, 2013 6:11 pm

by spdntrxi

andreas wrote:
Sat Nov 24, 2018 9:35 am
Holy shit, facing a $4000 frame sounds intimidating as hell... you basically get one shot? If you face too much the rotor will go out of alignment horizontally I guess?
The need for it plays into Hambini's observations on frame BB shell manufacturing accuracy, though.

its not... with the park tool anyways. It's not a big deal other then the tool is pricey. You are basically making it super flat.. I would not call it a one shot deal.

moyboy
Posts: 219
Joined: Thu Aug 18, 2016 12:19 am

by moyboy

That park tool facing unit is bad ass. I've seen it before. not your home workshop quality tool.

BdaGhisallo
Posts: 2060
Joined: Wed Mar 17, 2004 1:38 pm

by BdaGhisallo

There's the new Var facing tool to consider too: https://bikerumor.com/2018/10/29/the-ne ... erfection/

Machoman
Posts: 2
Joined: Sun Nov 25, 2018 12:33 pm

by Machoman

Oh no - you don't have to go to that defacing tool yet - try this - i'm almost very sure my tip will work - you'll need three things:
1) Park Tool DT-3
2) Park Tool DT-3i.2 Dial Indicator Kit For DT-3
3) aluminium disk brake shim

You first need to true your disc, then you adjust the brake to fit perfectly between the trued disc.

With the park tool equipment i've been able to true my disc (so they are straight) - the DT-3i.2 dial lets me true them to within 1mm trueness !! It's a heavenly tool for the OCD - actually quite fun to use.

When the disc is trued - i'll loosen the bolts of the brake and place the disc with an aluminum shim in - squeeze the brake handle and then tighten the bolts on the brakes. The disc is now centred between the pads.

I've ridden in the mountains and still have perfectly trued disc - equal spacing between the disc!!!!!

Watch this for how the DT-3i.2 works: https://www.youtube.com/watch?v=WYNT9vLfL6U

mattr
Posts: 3907
Joined: Fri May 25, 2007 6:43 pm
Location: The Grim North.

by mattr

Machoman wrote:
Sun Nov 25, 2018 12:47 pm
the DT-3i.2 dial lets me true them to within 1mm trueness !! It's a heavenly tool for the OCD - actually quite fun to use.
I really really hope you are at least one order of magnitude out. 1mm "out" is pretty much fit for the bin. I'd expect closer to 0.1mm. Or less.
spdntrxi wrote:
Sun Nov 25, 2018 12:29 am
andreas wrote:
Sat Nov 24, 2018 9:35 am
Holy shit, facing a $4000 frame sounds intimidating as hell... you basically get one shot? If you face too much the rotor will go out of alignment horizontally I guess?
its not... with the park tool anyways. It's not a big deal other then the tool is pricey. You are basically making it super flat.. I would not call it a one shot deal.
Most facing tools will only take a skim off (usually just cleaning the paint off!) you can probably repeat the process half a dozen times with *most* frame/caliper/disc combinations. But if you are needing to do it more than once, maybe take it to someone who knows how to use the tool (they are remarkably easy to use if you read the instructions and use some common sense).

If you do over face, a 0,5mm washer can be used on each bolt to lift the caliper.

It is actually quite easy to face with a good file, steady hand and a something with a nice accurate right angle. I use an old stainless standoff from a CMM. Every angle on it is as near to 90 degrees as makes no difference. (And it has the actual dimensions machined into the relevant face.)
The issue is with cheap frames, where the actual bolt holes aren't a right angles to the axle. Need to start mucking around with concave washers and such like to get an even load. (On-One frames for starters!)

Machoman
Posts: 2
Joined: Sun Nov 25, 2018 12:33 pm

by Machoman

hey guys - we're not working on the hubble telescope here - you should have approximately at least 1mm on both sides of the disc free. So truing the disc within 1mm thereabouts should be enough.

How do you know your disc is straight without running it though the park tool disc truing tool?

Again - once you have trued your disc - use the metal shim method to center the disc between the pads and tighten the bolts down....you really should now have a trued and centred disc. Unless your disc warps permanently when used or heated up. Mine has stayed true so far.

by Weenie


mattr
Posts: 3907
Joined: Fri May 25, 2007 6:43 pm
Location: The Grim North.

by mattr

Machoman wrote:
Tue Nov 27, 2018 1:01 pm
How do you know your disc is straight without running it though the park tool disc truing tool?
With a DTI?

Even park suggest a tolerance of 0.3mm.

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