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Sunday, 18 September 2011

Brake Caliper Rebuild + Stainless Brake Line Swap (Part 1)

Hello everyone!
I'm going to be doing a series of posts on how I rebuilt the brake caliper on this 18 year old machine, and swapped out the tired old brake line for a Galfer stainless steel line. Hope you enjoy it!

First thing I had to do is to get the brake caliper off the bike. Off with the mounting bolts. In no particular order, off comes the top one...

then the bottom one...
 Remove the cap that covers the pad pin.
Crack loose the pad pin bolt with an allen key.
On hindsight I would also strongly suggest that you also crack loose the screw that holds the brake hose onto the brake caliper. That screw is a tight one to remove, and if you try to loosen it after removing the caliper mounting bolts, you'd need a vice or it's not going to be easy.

Just crack it open a tiny bit so that it's easier to remove later, but not so much that the brake fluid is going to leak out.

Here I unscrew the pad pin all the way out.
And then you just pull it out.


You'll notice that the pad pin is badly encrusted with years of built up crud. We'll deal with that later. It's no wonder the brakes aren't working well, the pads can't slide smoothly over the pin when it's badly covered in crud.

And you just pull out the pads. These still have a lot of meat left on them, so I'm going to clean them and reuse them.
This is how the caliper looks. See how clean and shiny it looks.

See those two round things in the picture below? Those are the brake pistons. When you squeeze the brake lever, you transmit the force applied to the hydraulic fluid (that will be your brake fluid) that's in the master cylinder (that's the black boxy thing with brake fluid on the right side of your handlebar).

Since brake fluid is not compressible, it transmit that force down the brake hose and into the brake caliper. There are hollow chambers and passages cut out inside the brake caliper where the brake fluid from the brake hose can travel into, and it finally goes into two hollow chambers behind these pistons.

The brake fluid then forces these pistons to move out from the caliper body and push into the back of the brake pad, which then squeezes the brake disc which gives you the friction needed to stop the bike.
The normal way that you would go about removing these pistons is to use a hose attachment connected to an air compressor to pump air into the hole where the brake hose goes into, and that will force the pistons out.

If you're going to do that, make sure you put a piece of wood on the opposite end of the pistons to catch it, because it's going to come flying out at great force. Make sure no part of your finger is in there when you do it.

Since I don't have access to a compressor, and can't justify buying one just to do this job, I had to lie in bed many nights coming up with a plan. An evil plan.

I've heard of people using a grease gun to pump grease instead of air into the caliper to get the pistons out, but I really hated the thought of doing that. I can't imagine how I'm going to clean out all the grease from all the passages inside the caliper later on. That seemed an even more daunting task to me then the task of removing the pistons themselves.

You might be thinking to yourself, why not just use the brake lever and brake fluid to force the pistons out? The problem is that the pistons are not going to be forced out at equal rates, and once one piston comes completely out and the brake fluid faces no resistance in that chamber, it's all going to flow out from that chamber and you would lose all pressure in the system, and won't be able to get the other piston out either.

You will not be able to pull these pistons out by hand. Not a chance. Anyone who tells you that you can do that is either:

A) King Kong
B) Chuck Norris
C) Lying through his teeth
D) Parks his bike in a showroom and never rides it

Anyhow, there's no chance I'm going to have any chance pulling even a partially out piston by hand.

Well, after many nights lying awake in bed, I finally came up with a plan. As far as I know, I've not seen this done before, but I'm sure someone somewhere must have thought of it. Just that I haven't seen it anywhere on the web.

What is it? What's the plan? Let's find out in Part 2....(ducking and running)

3 comments:

  1. I feel your joy. I bought a 1996 in April 2010 and have been tinkering with it ever since. One of my biggest problems is corrosion. I was unable to disassemble the front forks because of it, and I dread removing any bolt or nut I haven't but a wrench to yet. Good luck on any of your other projects, look forward to part 2 of rebuilding the brake caliper.

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  2. I am anxiously awaiting your solution Pepper Crab! Great posts by the way.

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  3. So sorry, I got a new job and haven't even had time to read my personal emails nowadays. I'll use the holiday weekend to post up the rest of the pictures and steps.

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