Replacement for HyRd disc brakes - suggestions?

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Brucey
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Re: Replacement for HyRd disc brakes - suggestions?

Postby Brucey » 9 Jan 2018, 12:20pm

'Napier' kindly sent me the failed caliper to have a look at, and I've spent about ten minutes examining it. It didn't look to bad to start with but a closer examination revealed a surprising number of problems.

1) One of the pistons was sticky. This alone would make the brake not self-adjust correctly and/or drag on one side.

2) The pushrod locking grub screw was not tight, meaning that the correct pushrod adjustment could not be maintained.

3) The pushrod adjustment was not correct. It was wrong by about 1/2 turn, which meant that the piston(s) would (almost) self adjust on the way out, but it was difficult to push the pistons back, (i.e. the lip of the MC piston was acting almost like a one-way valve). If the 'tight' piston was pushed back, the other one would be pushed out, rather than brake fluid be pushed back into the reservoir.

4) There were signs of oil loss from the caliper, eg there was oil around the MC area

5) once the pushrod was correctly adjusted, the brake still didn't work correctly, in such a way as suggested that there wasn't enough fluid in the system

6) once the reservoir was opened up, there indeed wasn't enough brake fluid (mineral oil) inside

7) the brake fluid was dark brown and murky (opaque in fact) as if it were badly contaminated with rust

8 ) the brake fluid was also very clearly contaminated with water. {NB oil floats on water, so when there is water in the MC reservoir, it suggests that there is a load more in lower parts of the system].

Hydraulic pistons can become sticky in any event; this is not uncommon with this model of brake IME; they commonly need fettling when new pads are installed. However once the piston(s) is/are sticky, the result can be a negative pressure in the hydraulic system when the brake is released, such that any water sitting on the back of the MC pushrod may get sucked into the system. Obviously there is very likely to be water pooled there with this model of brake if the caliper is mounted on the chainstay; water can simply run down the pushrod past the rubber boot and then it will just sit there. A similar problem afflicts the brake cable in this installation also.

Once there is water in the system, there will be corrosion in various places and this greatly increases the chances that seals will be damaged and oil will leak out, making more room for water and the whole thing descends into an evil spiral of doom. I'm actually amazed that this caliper offered any resemblance to a brake at all, the condition it was in.

The takeaways from this are severalfold;

1) a chainstay mount is to be avoided with this model of brake, unless you envisage use in dry conditions only

2) it seems that very small issues (such as the pushrod being 1/2 turn out of adjustment, or one piston being a bit sticky) can precipitate a very evil chain of events with this brake system

3) In common with a lot of other hydraulic systems, when the system is failing, there are few external signs of what (if anything) is going wrong.

The last of these alone is sufficient to cause me to make the recommendation that, unless you are prepared to invest time and effort in detailed inspection and maintenance (proactive rather than reactive) of systems of this type then they are best avoided. By contrast if you maintain a cable operated caliper on a more reactive basis, there are only a few things that will bite you badly in the bum (such as cable problems or the possibility of a seized FPA in a BB series caliper, for example).

The other thing is that I'd say is that both in conception and execution (esp placement on the frame) this shows all the hallmarks of a 'typical modern bike design' in that it is really meant for folk that ride on the weekend and don't often get the bike wet, rather than all weather riding, leave alone a claggy daily commute. That is what happens if you leave you design work to a bunch of Californians.... :roll:

cheers
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gloomyandy
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Re: Replacement for HyRd disc brakes - suggestions?

Postby gloomyandy » 9 Jan 2018, 1:55pm

Brucey wrote:'
The other thing is that I'd say is that both in conception and execution (esp placement on the frame) this shows all the hallmarks of a 'typical modern bike design' in that it is really meant for folk that ride on the weekend and don't often get the bike wet, rather than all weather riding, leave alone a claggy daily commute. That is what happens if you leave you design work to a bunch of Californians.... :roll:

cheers


I hadn't realised that 531Colin had moved to California, his Elan like many other touring bikes with a disc brake have the mounting in this location.

Brucey
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Joined: 4 Jan 2012, 6:25pm

Re: Replacement for HyRd disc brakes - suggestions?

Postby Brucey » 9 Jan 2018, 5:32pm

gloomyandy wrote:
I hadn't realised that 531Colin had moved to California, his Elan like many other touring bikes with a disc brake have the mounting in this location.


The comment was more about the brake designers than anything else. The chainstay disc caliper mount just leaves the cable to worry about with a cable disc, and conventional hydraulic calipers are just more difficult to bleed out if they are in that location; the way they work is otherwise unaffected. The HyRd is different to that; because of its design there arguably isn't a perfect angle to set it at, in that the transfer ports inside the caliper body are only angled favourably for self-bleeding internally when the pushrod is angled so that it will be working in its own little puddle of rainwater (or worse). It is a bad combination to mount a HyRd on a chainstay mount.

If you look at the bits that you can buy, the vast majority of new-ish road bike parts originate with designs that come from and are meant for a leisure market that gives only lip service to foul-weather use. Road disc brakes (and their mountings), electronic shifting, A-head headsets, STIs, External BB systems, various stupid bikes that won't even accept mudguards, and a few others besides all originate in this way.

If you are designing a modern audax/touring bike, you can realistically only design it around bits that you can buy at a reasonable cost, i.e. commoditised parts. If you design the bike so that it won't accept a whole load of modern parts/groupsets (no matter how good or bad they actually are) then you will end up losing a lot of potential customers before you start; so many people will have made their minds up (rightly or wrongly) that they must have such and such on their bikes before they start.

I do not envy the task of designing a 'modern bike' that is both likely to work well and be durable in foul weather and at the same time appeal to the typical modern cyclist....

cheers
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Brucey
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Re: Replacement for HyRd disc brakes - suggestions?

Postby Brucey » 10 Jan 2018, 2:08am

this shows the state of the MC reservoir;

Image272.jpg
uhh... the horror....


The dark coloured blob to the RHS is water. The oil would have started out transparent and typically tinted either red or green depending on the brand used.

What I couldn't see until I drained the (almost opaque) oil out was that there were flakes of aluminium lurking in the bottom of the reservoir. I suspect these had been in there from when the caliper was manufactured. Needless to say it is pretty amazing that the thing ever worked in the first place, and didn't fail to a catastrophic leak before.

cheers
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RJC
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Re: Replacement for HyRd disc brakes - suggestions?

Postby RJC » 11 Jan 2018, 11:47am

Hi Brucey,

Thanks for the report.
Do you think the Juin Tech/Acor hybrid disc brakes are any better? Not many of these about I imagine so not much anecdotal evidence to go on.

Brucey
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Re: Replacement for HyRd disc brakes - suggestions?

Postby Brucey » 11 Jan 2018, 12:37pm

RJC wrote:Hi Brucey,

Thanks for the report.
Do you think the Juin Tech/Acor hybrid disc brakes are any better? Not many of these about I imagine so not much anecdotal evidence to go on.


Image

These brakes are similar (in that they are a cable operate hydraulic), using mineral oil but then again as I understand it they are also completely different; they use a closed hydraulic system, not an 'open' system like the HyRd. This means that

- the brakes are not self-adjusting as the pads wear; you must turn an adjusting screw (that looks as if it might easily seize up in our glorious winter climate) to adjust the brake to allow for pad wear. This is much like having to adjust a mechanical caliper, except with any hydraulic one if one of the pistons becomes sticky, you will have to move the caliper body sideways or resolve the stickiness problem to stop the brakes from rubbing.

- the bite point of the brake can be adjusted so that (unlike the HyRds) it can be very close if you wish

- if there is the slightest air or water in the hydraulic system, (or the brake is set to have a very close bite point) the brake will come on by itself when the caliper gets hot. This (along with the lack of self-adjustment of pads) is the main reason 'closed system hydraulics' dropped out of favour.

- unlike typical MTB closed system hydraulics, there is no adjuster that is accessible from the handlebars, so you have to dismount to adjust the brake, should the pads wear on a long descent or the brakes heat up and come on by themselves.

- the Juin caliper has an equally unfortunate cable/pushrod orientation should the caliper be mounted on the chainstay at the rear; I anticipate similar problems with water ingress, in UK winter use.

BTW in fact I did not find much water in the slave pistons of Napier's HyRd caliper. We'll never know for sure, but this leads me to suppose that the water might perhaps have somehow leaked into the MC reservoir directly, i.e. from the top, e.g. due to an ineffective reservoir seal. The other explanation is that the water entered at the pushrod, but somehow ended up only in the reservoir, perhaps because of the porting from the space between the pushrod seal and the main MC seal.

BTW I am pretty sure that there were flakes of aluminium that had migrated as far as the slave pistons in Napier's caliper, too; one of the pistons manifested a hard jam at the very end of the piston stroke only, that improved markedly once I had worked the piston back and forth a few times whilst the caliper was inverted. I think this may have flushed the flakes of aluminium through the transfer ports (which were more favourably angled for this to happen with the caliper inverted) to the reservoir.

With any of these brakes there are inherent (i.e. conceptual) flaws, but in addition there are flaws that are purely there because of poor execution, too. Unless you are prepared to be somewhat proactive in terms of preventative maintenance, (which is difficult with tiny parts of a delicate little hydraulic system) you would be hard pushed to be certain that you were not going to fall victim to the latter.

cheers
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Brucey
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Re: Replacement for HyRd disc brakes - suggestions?

Postby Brucey » 11 Jan 2018, 12:51pm

following on; has anyone tried simply mounting a cover of some kind over a vulnerable caliper of this type? It ought to help to avoid water ingress along the pushrod into the hydraulic circuit, as well as with the cable itself.

cheers
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keithb
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Re: Replacement for HyRd disc brakes - suggestions?

Postby keithb » 11 Jan 2018, 7:10pm

I'm sure I remember some sort of stretchy caliper cover being around years ago intended for mtb's, possibly before mtb brakes became sufficiently robust, so many years ago!

Can't find a reference on Google now, and it may be from before Google...

Edit: and they never took off, so may not be findable!

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Redvee
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Re: Replacement for HyRd disc brakes - suggestions?

Postby Redvee » 12 Jan 2018, 1:29am

RJC wrote:Hi Brucey,

Thanks for the report.
Do you think the Juin Tech/Acor hybrid disc brakes are any better? Not many of these about I imagine so not much anecdotal evidence to go on.


I've had them on my dike since November 2016 and the adjustment screw hasn't given any issues when I've needed to turn it. Only issue I've had is more down to the calliper location than the actual calliper and that's crud getting into the end of the cable and stopping the inner cable moving freely. The front one is adjusted so that it squeals when applied at a certain pressure which is handy when approaching pedestrians on shared use paths.

Brucey
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Re: Replacement for HyRd disc brakes - suggestions?

Postby Brucey » 12 Jan 2018, 10:41pm

one of the potential/theoretical advantages of hydraulics over mechanical systems is that of caliper MA. However this entirely depends on how the caliper has been designed. The caliper MA can be calculated by knowing

1) the dimensions of the lever that works the MC
2) The MC bore
3) the slave piston diameter

Given that there is always a dead portion in the lever stroke of (correctly adjusted) HyRds it is possible that, by comparison with the Juins, some of the HyRds caliper MA has been traded away just to get enough travel in the slave pistons to ensure an adequate running clearance. It is possible that the Juins have some combination of higher MA/ more running clearance than the HyRds, but with the Juins being non-self adjusting, some of the Juin's lever stroke should be put aside for pad wear purposes I suppose.

cheers
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Brucey
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Re: Replacement for HyRd disc brakes - suggestions?

Postby Brucey » 13 Jan 2018, 2:07pm

keithb wrote:I'm sure I remember some sort of stretchy caliper cover being around years ago intended for mtb's, possibly before mtb brakes became sufficiently robust, so many years ago!

Can't find a reference on Google now, and it may be from before Google...

Edit: and they never took off, so may not be findable!


It wasn't a 'lizard skins' product was it? They have tried all sorts of variations.

cheers
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keithb
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Re: Replacement for HyRd disc brakes - suggestions?

Postby keithb » 13 Jan 2018, 5:10pm

Someone on singletrack suggested fitting a cable oiler like this on the caliper end:
https://www.sjscycles.co.uk/cables/jtek ... ck-3-pack/

Obvious potential problems include overspray of lube onto disc/caliper, and another break in the outer cable creating a higher chance of spongiNess in the cable.

It may offer a limited solution with careful installation and use?

napier
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Re: Replacement for HyRd disc brakes - suggestions?

Postby napier » 13 Jan 2018, 5:20pm

That looks like a really good idea but I guess the cable will need removing and outer cutting in order to fit? It'll be interesting to see what others on here think.... If its positive I may well get one and give it a try.

Brucey
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Re: Replacement for HyRd disc brakes - suggestions?

Postby Brucey » 13 Jan 2018, 6:02pm

re the cable oiler; I reckon this won't do much harm and might do some good. In point of fact it may give the housing an easier time of it by simply allowing a point near the low spot in the cable run at which any water (that enters the cable at the caliper) to drain out.

In a similar vein, I have considered fitting a V-pipe to the caliper, and cross-drilling the ferrule between the V pipe and the housing to allow a drain/lube point.

In either case the last few inches of housing (which is invariably the worst bit with a chainstay mounted caliper) can be slid off the inner cable and fettled if needs be.

cheers
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gloomyandy
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Re: Replacement for HyRd disc brakes - suggestions?

Postby gloomyandy » 13 Jan 2018, 10:59pm

Brucey wrote:
In either case the last few inches of housing (which is invariably the worst bit with a chainstay mounted caliper) can be slid off the inner cable and fettled if needs be.

cheers


Looking at the OP it seems to me that this bike (like many others) uses a single continuous outer from the levers to the caliper, so I'm not sure how easy it would be to fettle anything.