Teaching the Principle

This is the first in a series of tech articles from Jeff Bryson at The Bike Room. The underlying theme here will be “teaching the principle, not the procedure”. Regardless of brand, most bicycle components share the same fundamental qualities and we hope this series might help demystify some of the usual suspects.

---

“Teaching the Principle, Not the Procedure”

With the Bikeroom just opening I’ve really had to refine the way I teach mechanics. My second student – local DH racer Jack Casey – is better learned than most, taking in everything I throw at him. First he completed the Bikeroom wheel building course with flying colors, and now, half way through the Bikeroom Disc Brake Systems course he needed a challenge. I put forth the challenge of rebuilding a set of 2003 Hayes Mag Brakes. I overhauled the rear brake and he overhauled the front.

I already had my thoughts on Mineral Oil vs. DOT but this rebuild just solidified my thoughts.  Almost ten years old and all the rubber parts in the brake were perfect! DOT fluid back in the day was designed to be “hydrophilic”, meaning it absorbs water. Now this may sound like a bad thing but, as no brake system is fully watertight, DOT is made to handle intruding water with little to no loss of performance. As it absorbs the water in the system it prevents corrosion and vapour affecting the system; when water gets into the system it’s absorbed into the DOT fluid.  This makes sure the moisture doesn’t pool in areas corroding the system from the inside out and it also prevents the moisture from heating up and vaporizing in high heat braking conditions. When moisture becomes vaporized it becomes gaseous and it is the gases which can then be compressed to cause brake failure.

When moisture enters the system, as it always will in any system, through the piston seals, lever seals, and so on, the boiling point of the fluid is lowered. DOT is designed to take on a relatively large amount of water before this boiling point affects braking performance. This gradual lowering of boiling point means you will have a longer period between service intervals bleeding the system to get the water out.

Mineral Oil is not hydrophilic and needs to be bled on a more frequent basis to rid the system of the moisture. Mineral oil also swells most seals and in my opinion this breaks down the seals over time. My Uncle use to always say, “Never put a “Stop Leak” engine or transmission fix in your car”. He said it would help in the problem immediately but over time the seals would swell and degrade to nothing making the problem worse. Mineral Oil brakes use a different rubber for their seals but over time the seals become porous, expand, and don’t seal as well.

In the spirit of teaching the principle – not the procedure, we went through the brakes from lever to caliper pulling every bit apart we could.  Brakes haven’t changed since the invention back in the early 1900’s.  The Mag brake along with my 1950 Chevy pickup uses the exact same system; only the Chevy’s brake system is way bigger.

I know the bike world has fairly divided views on the Hayes brake group. Hayes was on top of the heap for many years but a few production and R&D issues have put them behind the 8 ball for the last few seasons. That being said I have never stopped loving them. As a mechanic, you can always get them to work great. Overhauling these old Hayes Mag brakes, a lot of the parts from their newer Trail brakes are compatible and work great!

After pulling the brakes apart and putting them back together it was time for a bleed.  We couldn’t find a bleed procedure on Youtube specifically for the Hayes Mag brake so we followed the procedure for the Hayes Trail brake. It worked perfectly. Youtube is great! There are so many procedure videos for all different products, makes and models.

After fitting the brakes onto my new carbon Rocky Mountain Altitude all I have to do is bed in the new pads and I am ready to ride! All pads have a bed in period until they are at full power. Get up to speed and brake hard about 10 times and you will notice the power get better every stop. I like to douse the pads with clean water when doing this; it helps speed up the process. Don’t ask how.

I will let you know how they go!

bryson

This article is brought to you by the Bikeroom, a Bicycle Mechanic Training Facility for everyone located right here on the North Shore. Visit us at bikeroom.ca or on facebook.

---

Have you ever pulled a caliper completely apart? Did this article help your understanding of braking systems? Join the discussion below…