When was the last time you changed your brake fluid? DOT 4 glycol-ether brake fluid absorbs moisture and should be flushed through with new fluid at least every other year. The longer you leave the fluid, the more moisture is likely to be absorbed, which can lead to a reduced boiling temperature and corrosion in the lines. With a lower boiling temperature comes an increased risk of vaporisation during strenuous use causing brake fade.
Refreshing the fluid is a simple DIY job,but a syringe will really help matters. Avoid pumping out the old fluid with the pedal, as you risk damaging the master cylinder rubber seal(s) with excess force. Easy bleed kits can speed up the bleeding process whe you are working alone, but they can introduce air to the system if the fluid level drops too low and you haven’t noticed, so be careful. Have an assistant gently pump the pedal and keep an eye on the fluid level.
You can use Automec DOT 5 silicone brake fluid to refill the system. It’s not hygroscopic (moisture absorbing) like DOT 4, so unless you need to drain the system at some point, it’ll never need to be changed again. We’ve heard of cars still using this fluid successfully after 15 years. It also has a high boiling point of 260 degrees C, is less flammable than DOT 4 and will not damage your paint. You just need to ensure the DOT 4 is thoroughly flushed through, as any traces remaining in the lines could offset the benefits of using the more expensive DOT 5.
With a ring spanner on the bleed nipple, place a clear tube on the end, undo the nipple and use the syringe to suck out as much fluid as possible. Be very careful as as the nipples are very easy to round off. KAD alloy callipers have twin bleed nipples.
Here’s the fluid we’ll be using. It’s purple in colour rather than yellowish, so you’ll soon tell once the old fluid has been flushed through each part of the system. One litre will be plenty enough.
Check in a manual for the correct method of bleeding your particular set-up. There are several options. Fit a ring spanner to the bleed nipple at the brake furthest from the master cylinder. With a clear rubber tube fitted, release the nipple until fluid passes through.
Continue the process for the remaining three brakes – right rear, left front, right front - and repeat all round if you like for peace of mind. And that’s it – tighten everything up, replace the master cylinder reservoir cap and take the car for a test run.
by Stephen Colbran