Ask Dave About Brake Fluid

bisbee

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Well it doesn't seem to have a section so it's here

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Load of shite. Brake fade is nothing to do with moisture in the brakes that causes vapour lock. In fact if you filled up the brake system with water it would work except for a few things like coroson boiling point and lubicration. In fact any liquit would work to a point. Please dont try it. The one thing I discoverd quite by accident is that brake fluid is highly flamible. Dont ask how I know but I found out the hard way. Question for you as in anybody who wants to answer if brake fluid soakes up so much water how come the level never rises? dosent even stay the same to compensate for wear. Its got to be soaking very little. JJH
 
Load of shite. Brake fade is nothing to do with moisture in the brakes that causes vapour lock. In fact if you filled up the brake system with water it would work except for a few things like coroson boiling point and lubicration. In fact any liquit would work to a point. Please dont try it. The one thing I discoverd quite by accident is that brake fluid is highly flamible. Dont ask how I know but I found out the hard way. Question for you as in anybody who wants to answer if brake fluid soakes up so much water how come the level never rises? dosent even stay the same to compensate for wear. Its got to be soaking very little. JJH

As brake linings wear fluid level drops and we are only talking 3 or 4% by volume of moisture so you would not notice by eye However that would be enough to lower the boiling point causing the fluid to be less efficient in a number of ways imho

Additionally most of the bikes I have ever bought had really dark fluid including ones from dealers So it looks like few folk bother to change their fluid but then that's also true of fork oil
Just my 2p
:beerjug:
 
I agree but every 90 days? I submit sir that more harm would be done by people trying to do their break fluid change than was ever done by old stale fluid. JJH
 
Agree with JJH fear mongering bollox.

My experience, when i first got my GSA the local dealer recommended my bike needed a service also stated that the fluid needed to be changing as it hadn't been done in 2 years. So i had them change it. since then i have serviced the bike myself.

2 years later i flush the fluid expecting it to come out discoloured and also expecting a difference more sharper braking the fluid that came out was the same as the new going in and no change to the braking performance.

I decided to give it a four year gap which was done about a year ago when i last serviced my bike. the fluid that came out was only slightly discoloured.
Again didn't notice any difference to braking.

My bike is garaged, every year i do trips to the Pyrenees and Alps where the brakes get heavily tested, i have never felt any brake fade I have done 40K on the bike since 2011

I wont change my fluid for another three years.
 
How does the brake fluid absorb water in a sealed system with minimal air gap in the reservoir?

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I've bought secondhand vehicles where the brakes weren't great. Just changed brake fluid and they were perfect afterwards. Changing fluid is important, but every 90 days is a load of nonsense.
 
How does the brake fluid absorb water in a sealed system with minimal air gap in the reservoir?

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Are they sealed? Reservoirs usually have a breather for starters...... The moisture comes from the air in contact with the fluid as brake fluid is hydroscopic. The moisture can then evaporate off when hot leaving air in the fluid.

At least, that's how I understand it?

Andres
 
Are they sealed? Reservoirs usually have a breather for starters...... The moisture comes from the air in contact with the fluid as brake fluid is hydroscopic. The moisture can then evaporate off when hot leaving air in the fluid.

At least, that's how I understand it?

Andres
Brake reservoirs that I have seen have a tiny hole in the cap that allows a (sealed) diaphragm to move with fluid level.
So, how does fluid absorb moisture in a sealed system?

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Agree with JJH fear mongering bollox.

My experience, when i first got my GSA the local dealer recommended my bike needed a service also stated that the fluid needed to be changing as it hadn't been done in 2 years. So i had them change it. since then i have serviced the bike myself.

2 years later i flush the fluid expecting it to come out discoloured and also expecting a difference more sharper braking the fluid that came out was the same as the new going in and no change to the braking performance.

I decided to give it a four year gap which was done about a year ago when i last serviced my bike. the fluid that came out was only slightly discoloured.
Again didn't notice any difference to braking.

My bike is garaged, every year i do trips to the Pyrenees and Alps where the brakes get heavily tested, i have never felt any brake fade I have done 40K on the bike since 2011

I wont change my fluid for another three years.

The 2 year figure is a conservative one based on the fact that some bikes might live outdoors in a wet climate.
If your's is garaged, then 3 years is probably fine. That's how often I do mine.
You can get an inexpensive moisture tester to check the condition of the fluid, but its easier just to change it. Gives you an excuse for a good hard look at the whole system while your on at it.
 
Brake reservoirs that I have seen have a tiny hole in the cap that allows a (sealed) diaphragm to move with fluid level.
So, how does fluid absorb moisture in a sealed system?

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Ah ok, I thought the diaphragm was there to stop shit getting in not to make the system 'air tight/sealed'? Surely if the system was properly sealed then as the pads wore down so you'd introduce a vacuum into the system and I'm not sure that actually happens?

Andres
 
Andres thats what the diaphragm is for - to allow fluid movement in the reservior while seperating air from the fluid

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Here is a pic from one of my bikes.
Diaphragm sealing brake fluid from air and the inderside of the plastic former with pin prick hole and res lid with air cut outs that allow the diaphragm to move up/down with fluid level.
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DOT brake fluid is hygroscopic by nature which means it absorbs water from the environment
This could be via seams worn or cracked seals leaky banjo bolts/washers pin holed diaphragms etc and microscopic pores in your hydraulic lines especially rubber ones
I agree about the 90 day comment but Dave Moss is a professional race track bike tuner
I'll change my fluid every year after all it costs very little when 128 horses need stopping ;)
 
Brake fluid becomes darker because of particles of the seals carried in the fluid and moisture. Normally when changing brake fluid, the dirtiest is in the reservoir from the master cylinder seals and in the calliper from the calliper seals. When changing brake fluid it is best to change the fluid in the reservoir first so that clean fluid is pumped into the system rather than dirty old fluid.

Don't be tempted to use DOT5.1 in a system that normally has DOT3 or 4. DOT3 and 4 fluid has more lubricity than DOT5.1.
 
Bisbee,
Brake fluid must be amazing stuff if it can suck water out of the air through a high pressure hose.

128bhp.... Do you brake while keeping full power?

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I have changed the brake fluid on my car and it makes a difference, no doubt about about it...... pedal firmed up again like a new car.
 


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