Bike Brake Fluid same as Car Brake Fluid?

Hi!

Just had a go at bleeding my brakes last night and nearly emptied the ridiculously small bottle of fluid supplied. Is the fluid the same as car brake fluid as that seems to be better value for money!

Cheers!

same stuff just get the correct DOT

most brakes use Dot 4 which is the same as most cars.

Shimano use mineral oil ( a bit like Citroen LHM oil in the link below) which is not compatible and you can’t use Dot 4 in shimano brakes or mineral oil in brakes that use dot 4.

Some brakes may say dot 5.1 but this is compatible with dot 4.

http://en.wikipedia.org/wiki/Brake_fluid

Dot 5.1 is completely different and is silicone based.

Shimano brakes use mineral oil, but if you r brake use DOT4 or DOT5.1 then yes, same as car fluid

There’s a massive difference. Bike stuff is huigely overpriced.

Mineral oil for Shimano or Magura, so get a bottle of LHM fluid (unless your Maguras are within warranty, then you need to use their fluid.)
Dot 4 or 5 for others. Not worth buying anything bigger than a 500ml bottle mind you; it absorbs water once the seal is broken so will be useless by the time you bleed them again in 6 months time. (You may have Juicys though, in which case buy by the litre…)

Dot 5.1 is completely different and is silicone based.

DOT 5.1 is glycol based [the same as DOT 4]
DOT 5 is silicone based

They are Avid Elixor 3’s. Is Dot 4.1 the same as 4?

I had veggie oil in a set of shimano brakes for 6 months with regular use, bleed them eventually because I though I should no problems, and the oil looked good, no problems since either.
20p a litre 🙂

It was a mid ride emergency fix, I wouldn’t recommend it though.

Dot 4 or 5 for others. Not worth buying anything bigger than a 500ml bottle mind you; it absorbs water once the seal is broken so will be useless by the time you bleed them again in 6 months time. (You may have Juicys though, in which case buy by the litre…)

Not quite true.

Yes it absorbs water, but it’s not magic, if you keep the lid on it’ll last for years. Think about it, a half empty litre bottle contains ~500g of brake fluid and 0.6g of air of which 0.0075g will be water (assumed 15g/m3 absolute humidity, which is quite muggy). So if the fluid dessicates the air completely it will be 0.0015% water. The ‘wet’ specification for DOT brake fluid is 3.7% water, so you can open and circulate the air about 2500 times before it’s considdered ‘wet’. Car and motorbike system’s are often not even sealed at the top, just a plastic push on cap with a breather hole in the top! MTB systems only have a seal to allow them to be crashed and turned upside down.

They are Avid Elixor 3’s. Is Dot 4.1 the same as 4?

I think 4.1 is the designation given to brake fluid for car’s fitted with ESP? Basicly it’s super low viscocity so that the sensors and pumps can react quickly. It’ll work in a normal brake (probably), but not nececary. You want plain old DOT 4 or DOT 5.1.

Is Dot 4.1 the same as 4?

Can’t say I’ve ever seen 4.1

a half empty litre bottle contains ~500g of brake fluid and 0.6g of air of which 0.0075g will be water (assumed 15g/m3 absolute humidity, which is quite muggy). So if the fluid dessicates the air completely it will be 0.0015% water. The ‘wet’ specification for DOT brake fluid is 3.7% water, so you can open and circulate the air about 2500 times before it’s considdered ‘wet’.

THAT is the sort of answer that keeps me coming back here.

*sensible, restrained and polite applause*

Ok, cheers. Will be off to Halfords to get some more then!

Thanks for explaining that bud, I’ve been cautioned against keeping it in the past but thought about properly what you’ve said makes perfect sense. That’s my live & learn moment for today! 🙂

If you can get a trade card for Halfords (they will accept a business card for a mechanic as proof of working in the trade), then they do the small bottles of DOT 5.1 (250ml?) for just over a quid! 😉

Yes it absorbs water, but it’s not magic, if you keep the lid on it’ll last for years. Think about it, a half empty litre bottle contains ~500g of brake fluid and 0.6g of air of which 0.0075g will be water (assumed 15g/m3 absolute humidity, which is quite muggy). So if the fluid dessicates the air completely it will be 0.0015% water. The ‘wet’ specification for DOT brake fluid is 3.7% water, so you can open and circulate the air about 2500 times before it’s considdered ‘wet’. Car and motorbike system’s are often not even sealed at the top, just a plastic push on cap with a breather hole in the top! MTB systems only have a seal to allow them to be crashed and turned upside down.

HOW do you know this stuff?
It’s not like you had a day to go away and learn it all FFS.
Good work.

Nice sciencing, TINAS!

{returns to ep5 of Breaking Bad}

HOW do you know this stuff?
It’s not like you had a day to go away and learn it all FFS.
Good work.

A little bit of knowlage and a calculator.

Dot 5.1 is completely different and is silicone based.

wasn’t concentrating there and contracted myself. 5 is silicone based.

5.1 is like 4.

wasn’t concentrating there and contracted myself.

That sounds sore! Hope you were able to re-expand afterwards with no after effects. 😉

A little bit of knowlage and a calculator

Your “facts” aren’t welcome ’round these parts.

I say BURN THE MAN WITCH!

On a similar note mineral engine oil is fine in forks as well

not my day…contradicted myself

Edric – for the oil bath. not for the damping part.