How much fluid?

[quixoticgeek]

How much hydraulic fluid is needed to fill up a typical set of hydraulic brakes? How many times will a 100ml bottle fill the system?

J

[citoyen]

I don’t know how much it takes to fill from empty but for topping up/bleeding purposes, one full syringe (30ml) is more than enough for the rear brake.

Considerably less is needed for the front brake, obviously.

You could probably bleed both brakes 2-3 times with a 100ml bottle. Filling from empty might conceivably use up the whole 100ml bottle (complete guess).

[Paul H]

I replaced a hose on a rear brake when the original wasn't long enough - took less than 20ml, that was with some loss from the reservoir and calliper, but without draining them.  I'm pretty sure I've read that 50ml is enough to entirely replace the fluid in a pair, but haven't tested it and the type of lever, calliper and length of hose are all going to be factors.

[citoyen]

I admit I’m quite profligate with the oil when bleeding. Probably use a lot more than is entirely necessary. But I bought a 1L bottle a few years ago and still have loads of it left.

[grams]

Let's do some maths:

Prefilled Shimano brake kits are 1350+750mm long and either 2.1 or 2.5mm ID, which is 10.3 millilitres max in both hoses.

Pistons are 22mm diameter on each and travel maybe 4mm (?) and there are 4 of them in total, so 1.5 ml * 4 = 6 millilitres total.

There'll be a tiny bit more in the passages inside the lever and the calliper, and you'll need slightly more in the funnel/syringe to bleed it.

[Davef]

Let's do some maths:

Prefilled Shimano brake kits are 1350+750mm long and either 2.1 or 2.5mm ID, which is 10.3 millilitres max in both hoses.

Pistons are 22mm diameter on each and travel maybe 4mm (?) and there are 4 of them in total, so 1.5 ml * 4 = 6 millilitres total.

There'll be a tiny bit more in the passages inside the lever and the calliper, and you'll need slightly more in the funnel/syringe to bleed it.

Isn’t there a reservoir in the lever ? I suppose it cant be that big as there isn’t much space.

[Adam]

If you've got SRAM brakes, then you've got to push/pull the syringes to cycle the fluid through & then pressurize, so if you've got old contaminated fluid to start with, then that has to purged out first, so you'll end up using more than if you've got Shimano brakes.

If they are Shimano, then assuming no issues, then you should be able to fill at least 4 brakes from 100ml.

[quixoticgeek]

If you've got SRAM brakes, then you've got to push/pull the syringes to cycle the fluid through through, so if you've got old contaminated fluid to start with, then that has to purged out first, so you'll end up using more than if you've got Shimano brakes.

If they are Shimano, then assuming no issues, then you should be able to fill at least 4 brakes from 100ml.

I'm on Shimano. So looks like I can do this twice with one bottle.

J

[Paul H]

I'm on Shimano. So looks like I can do this twice with one bottle.
J

Yes, but I wouldn't normally do so, I think the recommendation is to do a complete fluid replacement every five years. I'm not even sure why that's necessary, it doesn't absorb water like DOT fluid, so as long as it's clean, I'm just going to check for air and top it up, maybe 10ml per brake and most of that is wastage.

[grams]

Isn’t there a reservoir in the lever ? I suppose it cant be that big as there isn’t much space.

There is, but it contains the fluid that fills the calliper piston at full extension, so doesn't need to be accounted for separately.

Although common practice is to brim the reservoir when the callipers are at working extension to push any air out, so a few extra ml required.

[rogerzilla]

You should discard an open bottle of glycol fluid after first use.  Given that the smallest bottle of DOT 5.1 is about 10x more than you need, this is terribly wasteful.  Mineral fluid is better for bikes, so I would choose brakes like Shimano's.

[quixoticgeek]

100ml of shimano oil arrived yesterday, and the rest of the parts arrived today. I am rapidly running out of excuses not to do the brake swap. Am more nervous about this than I was any other change on the bike...

J

[Paul H]

I'm more nervous about this than I was any other change on the bike...

J

You're not alone about that, I found the idea of it daunting, the reality is lots of bike jobs are more complex.  Plenty of good online guides, I've followed those from Epic which I found useful
https://epicbleedsolutions.com/pages/resources

[chrisbainbridge]

I feel the same way about mine. I bodged extra switches for my first di2 and do all the mechanical stuff but scared stiff of touching the hydraulics. Strange.

[Davef]

I think everyone is the same to start with as it is so alien. I now feel I can muddle my way through now but I feel you need about four hands.

Out of interest is it hydraulic TT brakes or are you moving to drop handlebars and conventional levers ?

[quixoticgeek]

I think everyone is the same to start with as it is so alien. I now feel I can muddle my way through now but I feel you need about four hands.

Out of interest is it hydraulic TT brakes or are you moving to drop handlebars and conventional levers ?

Dura-ace hydraulic TT brakes.

J

[Davef]

I think everyone is the same to start with as it is so alien. I now feel I can muddle my way through now but I feel you need about four hands.

Out of interest is it hydraulic TT brakes or are you moving to drop handlebars and conventional levers ?

Dura-ace hydraulic TT brakes.

J

Do post a picture once fitted.