Club 80-90 Forums

hi , i need to change my brake master cylinder and flush all the old brake fluid out does anyone know how much i need to buy to do this ? thanks jeff

Just buy a 5 litre can of Dot 4, you may have a bit left over.

Ian

If all the air bleeds out easily then normally one litre will be enough...however, if it's being a bit of a pig then you might need to break into another 500ml bottle.

Furthest from the master cylinder first (N/S/R on a R/H/D) working your way to the closest

Martin

better to use synthetic brake fluid as it never needs changing again as it does not absorb water so you brake parts dont corrode

OMG.... ...the poor bloke won't know which way to turn....


Martin

Different procedure for changing fluid as opposed to merely bleeding:

ive got to change the master and thought i might as well 'bleed' the old fluid out as i went along

ive got to change the master and thought i might as well 'bleed' the old fluid out as i went along

I was working on the principal of 500ml from each of the 4 (or more if 6) brake nipples and the long run to the clutch slave cylinder. It's often cheaper to buy 5 litres in one go than to buy 3 litres in 1 litre bottles and you have spare fluid to top-up with.

Dot 4 is what is recommended in the Haynes and Bentley manuals and is what the seals in the whole brake and clutch systems will have come into contact with from new.

Ian.

When you think about it...once the furthest rear has been bled then the fluid is fresh upto the rear split so very little fluid is needed to run the other rear clean, and as the resevoir is empty after fitting a new master cylinder, the fluid coming from the resevoir is also new (not old partly diluted with new.) So bleeding the fronts in turn doesn't take much to run clean and new.

You can put as much fluid through the brakes as you like but after a certain point you are just wasting fresh fluid.
Personally I don't keep any brake fluid for topups as by the time it is needed that fluid is already contaminated however well it is stored.
And besides...your brakes don't use brake fluid, the level just goes down as the brake pads wear, topping up only creates an issue when you fit new pads, with an overflowing resevoir. As long as the fluid remains a few millimetres above the minimum mark I would leave it alone.
Martin