Hydraulic Brake Maintenance Technical Advice

General cycling advice ( NOT technical ! )
phil_cordingley
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Joined: 24 Nov 2020, 12:58pm

Hydraulic Brake Maintenance Technical Advice

Postby phil_cordingley » 24 Nov 2020, 1:07pm

Hi,

I have quite a bit of bicycle maintenance experience (always done my own), but am dealing with hydraulic brakes for the first time and have just (successfully) fitted a new set of Clarks M2s to my hybrid and have a couple of questions:

I need to shorten the brake hoses. Can I use my Park cable cutters, which are designed principally for mechanical brake cables? The reason I ask is that the Clarks' video of the procedure uses what looks like a mini version of a copper pipe cutter
When it comes to bleeding the brakes, can I use mineral oil fluid sold for car braking systems, or should I buy something specifically for bikes, such as Finish Line? The reason I ask is that the Finish line product typically retails @ £7 or £8 per 120ml, and car brake fluid @ for £13 per litre. So Finish Line is the equivalent of c. £60 per litre

Thanks in anticipation.

Phil

Brucey
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Re: Hydraulic Brake Maintenance Technical Advice

Postby Brucey » 24 Nov 2020, 2:00pm

the brake pipes used on bicycles usually cut OK with a stanley knife. If the cut needs to be absolutely square with the fitting you are using, practice cutting before the final cut is made. Some cutters can crush the hose before cutting and this weaken it.

Re brake fluids; the two most common are

DOT4 which is Glycol based, (and is the common brake fluid used in most cars) and
'Mineral oil' (eg shimano)

Under no circumstances should you use the wrong fluid in your system. Most manufacturers use only one type of fluid so for example all shimano brakes are mineral oil type. Only one or two manufacturers of bicycle brakes have used more than one different type of brake fluid. If you want to buy a suitable mineral oil in the car spares shop, get some Castrol LHM. This is reputed to be compatible with all bicycle brakes using 'mineral oil'. For systems using DOT4, use DOT4.

cheers
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thelawnet
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Re: Hydraulic Brake Maintenance Technical Advice

Postby thelawnet » 24 Nov 2020, 2:32pm

hydraulic hose cutters are razor blades essentially. the idea is not to crush the hose. You can have a go with your cable cutters, if they are sharp they should be fine, and if you cut off a bit too little for practice, you can see how straight and non-crushed they are working. There are cheap hose cutters for about £2 on ebay but you can use a craft knife also.

You can buy hydraulic mineral oil for bikes in large quantities

e.g.

https://www.bike-discount.de/en/buy/mag ... oil-975379

https://www.chainreactioncycles.com/shi ... p-prod5620

about £20/litre seems to be the going rate.

Small quantities do work out very expensive per litre, but depends how much work you are doing if it's really cheaper to buy a whole litre and keep it for several decades.

The problem with most bike stuff is it's snake oil sold with vague promises and lacking technical information.

E.g., this is the pisspoor Shimano data sheet for their mineral oil

https://www.georgesbikeshop.com.au/wp-c ... il_Eng.pdf

'CAS registry number : Trade secret'
'Relative density: Approx. 0.83/cm3 at 15 ℃
Initial boiling point/range: Expected >200°C
Viscosity: Not available'


Here are apparently some test results from the Germans, who tend to not have such a terrible standard of bicycle journalism as the Anglosphere:

Image

As you can see, the viscosity (c St) of the two bike oils Shimano and Trickstuff is almost the same

Do ignore the Glycol (DOT) ones listed.

The hydraulic oils for cars listed there are mostly significantly thicker.

If you could find a cheap car oil with similar properties to the Shimano/Trickstuff there, you could buy that. But it might be just as well to stick with stuff intended for bicycles.

PH
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Re: Hydraulic Brake Maintenance Technical Advice

Postby PH » 24 Nov 2020, 3:14pm

Epic brakes have the clearest instructions I’ve seen, along with some videos. Their kits seems good as well, but as it’s the only one I’ve used I have no compassion.

Jdsk
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Re: Hydraulic Brake Maintenance Technical Advice

Postby Jdsk » 24 Nov 2020, 3:17pm

Brucey wrote:Under no circumstances should you use the wrong fluid in your system.

Yes. This isn't a place to ad lib. If you don't understand the possible incompatibilities between different fluids and between fluids and seals I strongly recommend following the manufacturer's instructions.

Jonathan

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willcee
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Re: Hydraulic Brake Maintenance Technical Advice

Postby willcee » 24 Nov 2020, 4:20pm

Was in a similar position last year, read all I could, asked on here, bought more kits than I needed ..had extra good hospital quality syringes, extra plastic tubing to fit and I had the same job to do as you, connect and shorten hosing, in my case with new unused STI'S and post mount calipers instead of the supplied flat mounts.. believe me I'm not a pilgrim at any job around any vehicle bike or car brakes or otherwise, this was a first for me and I was apprehensive enough to ask a good friend for his input, also a great teckie around any vehicle hydraulics electrics etc.. took us longer than we thought, the idea of back bleeding was strange, the awful design of Shimanos bleed ports and their far from hi teck way of sealing them but we prevailed and had a good result after bleeding perhaps 6 times, we recently added a GRX interrupter brake into the system, that had us scratching for a few minutes but it has proved itself on the road and is now an excellent addition to my E bike rear brake.. good luck, but in my opinion and that of an experienced mechanic its a 2 man job and off the bike if possible.. will

Tiberius
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Re: Hydraulic Brake Maintenance Technical Advice

Postby Tiberius » 24 Nov 2020, 5:33pm

PH wrote:Epic brakes have the clearest instructions I’ve seen, along with some videos. Their kits seems good as well,


+1.... :wink:

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Redvee
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Re: Hydraulic Brake Maintenance Technical Advice

Postby Redvee » 25 Nov 2020, 12:42am

I use an Epic Bleed Kit on my Shimano brakes, one syringe pushing fluid at the calliper up to the lever and bleed funnel. When I first had hydraulic brakes I took the bike ot the LBS for work on them but had time during Lockdown 1 to work on them at leisure and am now confident working on them and replaced a calliper then a hose with no issue other than it took longer than it should have on my first time fiddling with them. The complexity of hydraulic systems stopped me adopting them earlier, now I wonder why I held back.

tim-b
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Re: Hydraulic Brake Maintenance Technical Advice

Postby tim-b » 25 Nov 2020, 7:10am

Hi
Clarks have used DoT fluid in some of their brakes and mineral oil in others, so be careful when ordering a "Clarks bleed kit"
The M2s use mineral oil but I can't find a spec for it, your LBS or info@clarkscyclesystems.com should give you that
As far as value for money is concerned, 120ml should be enough to flush the whole system and will last you for a couple of years in use (at least) unless you change/damage the system. As an alternative it should be enough for three bleeds
Mineral oil doesn't absorb water like DoT fluid so it can be stored, but that doesn't stop water getting into the opened container over time (and a litre will last a long, long time)
Regards
tim-b
~~~~¯\(ツ)/¯~~~~

Brucey
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Re: Hydraulic Brake Maintenance Technical Advice

Postby Brucey » 25 Nov 2020, 8:38am

a litre of LHM will cost about ten quid.

cheers
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gregoryoftours
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Re: Hydraulic Brake Maintenance Technical Advice

Postby gregoryoftours » 25 Nov 2020, 7:19pm

To be sure what fluid you need, it's often written on the reservoir cap at the lever. Obviously don't use mineral oil in place of DOT fluid or vice versa. Also DOT 5 is silicone based and shouldn't be used instead of DOT 4 and 5.1 which are glycol based.