Front Brake Failure - Temporary

[HawaiiJ]

Today I departed on a 5 day trip with the intent of staying as close to the borders of Myanmar and Laos as I could without straying over the border and having a problem and getting shot at. As I was coming down from a mountain (1800+ meters) west of Fang Thailand I had been using the front and rear brakes heavily to prevent a certain crash. I had no other option but to lay on the brakes. About half way down, I stopped to put on the rain gear and noticed a smell. The front break disk is discolored from the heat and when I hopped back on to continue the decent I realized I had ZERO front brake. The front brake handle had zero tension and only came back after waiting about 30 minutes for every thing to cool down. It took me a few cycles of braking and rest to make the complete decent.

Very serious and scary situation. The roads here are extreme in some locations and I think I may need to rethink what the PCX can handle and plan better.

Anyone else experience hot brakes and no tension on the handle?

Pictures will follow in a few days when I get back home..

HJ

[JGC]

ALL brakes will behave in this manner when they are overused and get over heated (Unless they are of the ceramic variety)

Planned long decents carefully and try not to keep pressure on brakes for the whole time, or as you did, make frequent stops. No easy answer really.

[you you]

ALL brakes will behave in this manner when they are overused and get over heated (Unless they are of the ceramic variety)

Planned long decents carefully and try not to keep pressure on brakes for the whole time, or as you did, make frequent stops. No easy answer really.

Or alternate between front and back brakes to allow some cooling air over

Rare for scooter brakes to do this


I'd recommend change your brake fluid now it's been cooked. Go for the best quality stuff you can afford. It might cure, or at least alleviate the problem

[maddiedog]

The front and rear brake are linked on the right handlebar though. The left lever actuates two pistons in the front caliper, the right actuates the rear drum brake and one piston in the front caliper. Pulling both will actuate all 3 pistons in the front...

When I go on mountain runs, I don't use the brake the whole time -- I use it as infrequently as possible, and only hold it as short as possible. On long downhills, I coast, pulse the brake to slow, coast, brake, etc. I do the same thing with my car, you don't want to warp your rotors.

[you you]

It's got. A three piston calliper on the front?

[Taz]

.... The left lever actuates two pistons in the front caliper, the right actuates the rear drum brake and one piston in the front caliper....

Isnt it the other way round? The left is the combined brake lever and the right is the front only lever?

[gn2]

Yes, the outer two pistons are controlled by the right lever and the centre one is controlled by the left combi brake lever.
Which explains why there are two hydraulic cables and bleed nipples on the caliper.
There is a separate hydraulic reservoir for the centre combi brake piston which you can see through a small window to the right of the ignition switch.

[Woolley]

.... The left lever actuates two pistons in the front caliper, the right actuates the rear drum brake and one piston in the front caliper....

Isnt it the other way round? The left is the combined brake lever and the right is the front only lever?

I thought that too...

[HawaiiJ]

Thanks for the feedback. Like I said, I had little options other than to come down the mountain in the manner I did. One thing I should have done was take breaks and decent in stages until I reached the bottom or flatter stages where the brakes could rest while coasting. Lesson learned.

I think I'll get the fluid swapped today before I head out on the road, I'm a little concerned with the whole front brake caliper system because it got very hot and when I touched it with my wet glove it put off a little steam.

Anyone care to predict the cost of a break fluid swap might cost?

[Tristik]

~~
This actually interests me greatly as I know absolutely nothing about mechanics. OK, i know a little as I've owned a lot of beaters but...

I thought brake fluid was similar to hydraulic fluid? As in...in a car for example, when you push the brake, it puts pressure in the brake line putting pressure into the fluid lines, in turn putting pressure on the brake calipers initiating friction onto the rotors/drums. How does that work with the wire tension of cable based, handle brake systems? Is it straight forward like a regular bicycle where the cable tension directly impacts the caliper/drum tension? Or is there a system there where the cable pulls on a piston initiating a break fluid pressure into a piston kind of thing that works the breaks?

Hope that wasn't too confusing. I blame the boddingtons'.
~~

[gn2]

You are correct, brake fluid is hydraulic fluid.
The left lever's cable goes to a splitter, one half of which pulls on the rear drum brake cable, the other half pulls on a hydraulic master cylinder for the slave cylinder (the middle piston) in the front caliper.

[Tristik]

~~
I've always wondered about the CBS pressure split on the back brake, but never actually looked it up. You'd think if they perfected the ratio enough, there would be little reason to have more than one break lever.
~~

[gn2]

I reckon a single lever operating on both wheels would only work if there was independent ABS on each wheel.

[you you]

And you'd want a back up system?

[gn2]

Not really.
One lever, two hydraulic circuits.
Highly unlikely that both circuits would fail at the same time.

[you you]

I suppose that's what you rely on in a car. For me it would take some thinking about only having one lever

Mind you a cars split system works on a 2x2 system, front and back on alternative sides. You don't have this option on a bike

[gn2]

I had an old Lada that only had working brakes on one front and the opposite side rear.
In slippy conditions if I stood hard on the brakes the car would rotate so that the braked front and rear wheels were aligned with the direction of travel, when the brakes were released the car straightened up again.

[maddiedog]

The left is the combined brake lever and the right is the front only lever?

Oops, thanks for the correction. I've been riding my mountain bike too much, the brakes are backwards on it.

[louthepoo]

I've read that's common on a few american mountainbike forums! Over here the right is always the front brake, I'd probably be having some scary moments if I was to mix them up

[HawaiiJ]

Here's the front disk and the result of being overheated. I had no further issues with the brakes but I'm not completely comfortable without a bit of maintenance on the overall brake system.

I did a little research and this section of road is infamous for causing brake problems. I was near the top of Doi Angkhang and the problems started as I passed the security checkpoint on Thai Road 1249 headed towards Fang.