Why do you need to change your brake fluid?

Most Classics run DOT 4 brake fluid. It is hygroscopic, which means that it absorbs water from the atmosphere. It takes about two years in the UK for the water content to get to a point where it is damaging the inside of your brake system.

As the fluid gets older the water content starts corroding the the inside of the master cylinder, servo and the pistons in the calipers. Two things eventually happen:

  • Initially the rust will break off and damage the seals as it moves around.
  • A little further down the line and one of the components will seize.

How often should it be changed?

When brake fluid is fresh it is a yellow colour, you want to change it when it looks closer to a bronze. At this point you can suck the old fluid out of the reservoir, top it up with fresh and
then bleed the brakes to get a firm pedal. When you are happy with the result top the reservoir up to it’s line and make sure the cap is clean before it is fitted.

How much does it cost?

The process is the same whether you own an MGB or an Aston Martin DB4 and costs £60 including labour, fluid and VAT.

If you have let the brake fluid turn black then it will be time for a very careful clean of your brake system before replenishing the fluid. This is more difficult to put a price on. Best case will be £195 including VAT, but you may need components rebuilding or replacing. We will be able to quote once we have seen your vehicle.

Is there a fluid that lasts longer and gives better performance?

Silicon (or DOT 5.1) fluid is available. When we scratch build a brake system then this is usually what we use. It is a ‘life’ product, has a higher boiling point and is not hygroscopic. You find it in all racing cars and a lot of performance road cars. However, for all it’s good points you have to be very careful using it in your car.

DOT 5.1 and DOT 4 brake fluid react with each. It only takes a tiny bit of residue and the fluid will congeal and stop your brake system working. We only recommend changing fluid on brand new or completely rebuilt braking system.

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