How to bleed brakes?

[Anthony]

Hey all,
So I'm doing some serious maintenance to my bike now, and thought I should go ahead and replace all my oils (brake, engine, filter, etc.). I have no idea how to replace the brake fluid, all I know is that it might require to bleed the brakes, which I've never done before either. I will be also replacing the lens for the sight glass on the front M/C when I change the oil. So, how do I go about doing the brakes? My bike is a 1982 GS750E. Thanks!

[BiomedDR]

Flushing out the fluid is pretty easy. Just get a 2 foot piece of aquarium tubing that fits on the bleed fitting.

1. Break loose the fitting and connect the tube.
2. Loop the tube so air can be trapped, then put the end in an old soda pop bottle.
3. Fill the bottom of the bottle with a little brake fluid to cover the end of the hose.
4. Take the master cylinder cap off.
5. Loosen the fitting
6. Start pumping the lever and refill the master cylinder when it starts getting low.
7. Keep going until the fluid coming out is clean then tighten the fitting and top off the master cylinder.

If you have air in the master cylinder most of the time you can get it out by SLOWLY pushing in the lever then let it pop back out. I don't believe it is the proper method but I have had good luck with the method.

[Anthony]

Is there a way to empty out the M/C and clean the inside while doing the bleeding? Or would that interfere with the bleeding process?

[tkent02]

If it's been thirty two years, the whole system really should be disssembled and cleaned inside and out, lubed properly, checked for wear and pitting from rust. Everything rom the master cylinder to the caliper. You might need new rubber seals, or you might not. New lines, new fluid, new pads can't hurt either. You might get away with just changing the fluid, or you might not. That depends a lot on what maintenance if any all of the POs did since it was new. If you know for a fact the brake fluid has been changed faithfully every two years or so forever you can be fairly certain the system is fine.
If you don't know this, it's all a big crapshoot.

A wheel locking up out of the blue is not a good thing.

[Steve]

Is there a way to empty out the M/C and clean the inside while doing the bleeding? Or would that interfere with the bleeding process?

Oh, it won't "interfere" with the process, it will MANDATE it.

The process of "emptying and cleaning" the master cylinder will involve total disassembly, which means there will be a HUGE air bubble in the line when you re-connect the master cylinder. Once you get that bubble pushed down the line, you will have flushed the system and bled it.

.

[Grimly]

To make the bleeding easier, you could drop some bucks on a specialised vacuum workshop bleeder; or you could spend a single buck on a large plastic veterinary syringe and attach it to some plastic tubing which goes over the bleed nipple.
Suck the fluid down the way - bleed in two minutes, both sides, job done.

[tkent02]

Bleeding won't do anything to remove the chunks that can cause the brake to lock up.

[Grimly]

Bleeding won't do anything to remove the chunks that can cause the brake to lock up.

Indeed it won't and the owner should be careful not to blow chunks into the brake master cylinder.

[Anthony]

The fluid itself looks like a very light beer color, so I don't think it's been neglected, I just wanted to be safe and change the fluids.

[chuck hahn]

I agree that the entire system needs disassembled. inspected, cleaned, and all caliper seals replaced and pistons inspected. Brakes ARE NOT a place for short cuts or "guessing" whether the parts are okay.

And mosy auto parts have tool loaners and see if they have a mighty vac bleeder to use...youll be glad you did.

[chuck hahn]

BUT do you KNOW with 100% certanty when they were last fully rebuilt? Or if so, what was done and replaced??? See our concern here???

[GateKeeper]

good on the left and dirty/old on the right, what is yours like

[Brendan W]

I find I can get gravity to do the work. Pop a clear tube on the bleeder, maybe one or two pulls on the lever to get it started and keep topping the reservoir off until the fluid runs clear in the tube and then some. Avoid aggressive pumping as the seals can reverse. The bleed nipples will most likely be seized in the calipers and require penetrating oil a day or so beforehand. I mix 50:50 kerosene and acetone. Some may remain blocked after loosening and a small drillbit spun by hand can clear the crud out - they've probably lost the dust caps.

[Grimly]

I mix 50:50 kerosene and acetone.

Have you found a local source of acetone in reasonable quantity?

[tkent02]

Any store around here has it, hardwars store, auto parts store, paint store, even the evil Walmart. Bought a gallon last week for about ten bucks. Probably not available in Europe because it's a useful chemical.