Brake fluid replacement

[Glendonwyn]

Merry christmas
w203 c270cdi
Please does anyone know how many pumps of pedal it takes when renewing brake fluid to make sure all the old fluid is out. I have no desire to introduce air into the system.
Andrew

 

[BlackC55]

One litre for the whole system. More for the rears than the front as the pipes are longer.

 

[Merc Owner 2B]

Depends where you are bleeding from, front or back. Personally I use a vacuum device attached to each individual bleed nipple and run it until the fluid runs clear

 

[Paparazi]

Preferred method:

Bleed from the furthest away from the master cylinder first, so N/S/R (if it's a right hand drive), second O/S/R, third N/S/F lastly O/S/F. However, in the interests of ensuring that the system is 100% flushed I revisit the N/S/R again and just bleed out another 100ml as this receives a certain amount of old contaminated fluid with being the first calliper to be bled.
It is good practice to suck out as much of the 'old' fluid from the reservoir before starting (then top up), otherwise the first calliper receives just used fluid from the reservoir.

Yes....1litre....so around 200-225ml out of each calliper and a further 100ml from the first calliper bled (done at the end).
AND?
What about the clutch if it's a manual.

Martin

 

[Paparazi]

As for bleeding until it 'runs clear' that's all well and good for middle to high mileage vehicles where you can visibly see the fluid has darkened through work. However, a vehicle stood for 2 years without being driven will have perfectly clear brake fluid yet STILL REQUIRES it's brake fluid replacing because of water contamination.
Brake fluid is 'HYGROSCOPIC' (attracts water from the surrounding air) this moisture is drawn through closed caps/calliper seals and level sensor switches....just 3% of water contamination lowers the boiling point of the fluid by as much as 90 degrees. Dry boiling point for quality DOT 4 is around 230C however, wet boiling point (3% contamination) drops dramatically to around 155C.
If the brake fluid 'boils' the gaseous bubbles in the fluid are compressible which leads to 'Total' brake loss (foot to the floor job!) this is called 'vapour lock'.

Martin

 

[Dieselman]

If you are just topping up the reservoir you won't properly remove all the old fluid until a considerable quantity of fresh fluid has been through the system. It's better to suck the old fluid out of the reservoir, fill with fresh, then bleed as normal.
This guarantees a complete change with minimal fluid use.

 

[markjay]

There are basically two alterntives to the 'one man bleeding kits' (essentially a no-return valve of some description).

The first is a vacuum device that connects to each caliper bleeding screw one at a time, the second is a manual pressure device applied to the brake fluid resevoir (and topping it up as it does).

 

[Glendonwyn]

Now I will have to do it

Thank you for all the good advise. Now waiting for it to stop raining, so I can start.
Andrew