A year-old, a slight leak, and the fluid's getting darker. The big Katoom's front master cylinder reservoir has been leaking for ages. Shame on you Brembo for that design, and the KTM dealer for not fixing it at first service. Maybe it's how they sell more of their KTM-branded sweat bands.
Why should I change my brake fluid?
Brake performance is lost as the fluid degrades. Why? Moisture is sucked in out of the atmosphere, lowering the boiling point which, in turn, could cause brake fade or failure. Seals slowly break down as they move back and forth with the pistons, discolouring the fluid, and metal particles move in suspension with the fluid from contact in the bores of the master cylinder, or calipers. A regular flush will keep the brakes in tip-top condition, and they'll continue to feel great.
First job, wrap the reservoir in rag, and cover any painted areas. Brake fluid is great at taking paint off and not recommended on your nice shiny bike. Brembo, for some reason, use two screws to hold the plastic cap on. This one leaked from day one. The problem with a two-screw fixing is it distorts the cap, and allows the areas away from the screws to lift - allowing it to leak. Over-tightening is the problem, and when they leak everyone nips up the screws a little more. Big mistake.
The discoloured fluid. A syringe is ideal for emptying the reservoir. I like to drain it and clean it out with a fine, lint-free rag. That way the new fluid goes straight through the master cylinder and hoses.
The quick, efficient method.
Dry the sealing boot and cap completely with rag. You'll probably see moisture on this. In my opinion, the boot needs to be dry when it goes back in - it seems to help when sealing it later.
We're using Valvoline VR1 brake fluid on the big Katoom. It has a boiling point that 'exceeds 290°C', which is perfect for the upcoming track day, and it's also completely clear (they call it yellow).
To put it in context, normal brake fluid boiling points are as follows:
- DOT3 - 205°C
- DOT4 - 230°C
- DOT5.1 - 260°C
- DOT5 (silicone-based) - 260°C
There shouldn't be any fade under hard use now.
Hard to see it in the reservoir!
As we've covered this before I'll keep this to a minimum. Pump the lever a few times to get good pressure, release the bleed screw on the caliper and allow the lever to come back to the bar. Tighten the bleed screw and release the lever. Repeat six or seven times, always remembering to keep the reservoir topped up. When you're happy with that, and the lever still feels good, flush the other caliper. Top up the reservoir and refit the bone-dry boot and cap as per.
Refit the screws and make sure everything is sitting flush before tightening. If the boot is slightly askew, or the holes don't line up properly, it may leak.
Don't over tighten the screws, they only need to be nipped up. Happy to say that the reservoir hasn't leaked since the brake fluid flush so Davey's happy (well he's not moaning anyway).
It's a beautiful job!
The rear was done in exactly the same way and both brakes feel great. Loving the clear VR1 fluid!