Replacing the Brake Fluid
on a Suzuki GS500

Q: "What does it mean when the little glass window on the brake fluid reservoir is all dark?"
A: It means that it's way past time to replace the old fluid. (You're supposed to replace it every 2 years ... whether it needs it or not!)

Q: "But how do I do that? Isn't it hard?"
A: Well, there are simpler maintenance tasks ... but not many.

First, make sure that you have an UNOPENED bottle of DOT 4 brake fluid. Then gather up a Phillips screwdriver and an 8mm wrench, and figure out some way to collect the old fluid.

I used to use a bendable drinking straw, a paper cup and some Scotch tape. But this time I cut a length of vinyl hose and drilled a hole in the lid of an empty pop bottle. Fancy!

While you're getting, get some paper towels or rags too.

I recommend that you attach the drain hose to the bleeder valve before you do anything else. If you wait until after you remove the cover from the brake fluid reservoir (see below) you risk bumping the wheel while attaching the hose. That might send brake fluid everywhere, and THAT would not ... be ... good.
The whole idea is not only to get the old/bad fluid OUT of the system, but to get some new/good fluid IN. For the front brake, the brake fluid reservoir up near the throttle grip is as good a place as any to pour the new fluid in. (OK, it's the only place!)

So, remove the reservoir cover screws.

Underneath the reservoir cover is the diaphragm plate. It helps to provide a positive seal to keep air & moisture out of the system.
Under the diaphragm plate is the rubber diaphragm. It's the main barrier against external air and moisture, and it has a pretty clever design. Imagine that brake fluid has been leaking out of the caliper ever ... so ... slowly over time. If the diaphragm were stiff like the plate above it, air would eventually seep in as the vacuum in the system increased. But since it's flexible, the rubber diaphragm will unfold and get sucked down into the reservoir before it allows any air in. Hopefully you spot the low fluid level before the reservoir is ENTIRELY empty.
Pulling the diaphragm off of the reservoir, you finally get to see the brake fluid up close. Can you say "Eeeewwww!"?

Use a towel or rag to clean the diaphragm thoroughly before you set it aside. If you simply put the dirty diaphragm back on at the end of the job, the film of old fluid could easily contaminate the brand new fluid before its time.

Before you start pumping the old fluid out, you need to be ready to pour new fluid in. Remove the seal from the brake fluid container and set the container down where it is easy to reach (but NOT easy to knock over - brake fluid eats paint!)
Now it's time for the "manual dexterity" part of the process. The first step is to "crack" open the bleeder valve on the front caliper by loosening it about 1/8 of a turn. If you open it much further, air is likely to get past the loose threads.
With the valve open, reach up with your other hand and give the brake lever a good squeeze. Out comes some of the "yucky stuff".... Close the bleeder valve BEFORE you let go of the brake lever, so no fluid will be drawn back into the system. This is especially important until you can consistently pump out fluid with no bubbles in it.

Notice how the bleeder valve points upward? I think it's designed that way on purpose, to keep air from coming back along the drain tube.

If you see bubbles in the tube, you probably opened the valve too far. Open the valve a little less the next time and give the lever another squeeze.

As I hinted before, once you can pump fluid with NO bubbles there's no need to close the valve after each squeeze of the lever.

However, you must ALWAYS be aware of the fluid level in the reservoir. It's easy to get engrossed as you watch the "yucky stuff" come out. But if you pump the reservoir dry you'll regret it; air is a lot easier to KEEP out of the system than to GET out of the system.

When the reservoir is 1/2 to 2/3 empty, add some clean fluid and go back to pumping. (Rag not shown for clarity.)

Eventually you will find that the "yucky stuff" in the reservoir has all been replaced by clean fluid. But that's not good enough. You must continue pumping and adding fluid until the stuff exiting the bleeder valve is also clean, new fluid. This is one good reason to use a see-through drain tube. And don't worry about using up too much fluid. There's plenty in the bottle for both the front and rear brake systems, with about 1/4 bottle left over.

(Rag shown in place, to prevent spills. Remember ... DOT 4 brake fluid eats paint!)

With clean fluid in the tube, close the bleeder valve firmly. Don't torque it so hard that you break it off - that would turn an easy task into a much more frustrating one!

Manipulate the drain tube to get as much of the fluid as possible to run down to the collection container. Then remove the tube from the bleeder valve, clean off the valve with a rag, and replace the dust seal (if you had one in the first place).

Up at the reservoir, add enough brake fluid to bring the level up to the "fill line" molded into the interior walls. Replace the diaphragm, the diaphragm plate and the reservoir cover. Tighten the cover screws down nice and snug.

You're DONE with the front!

The process is much the same for the rear brake system (after you remove the seat):
  • Attach the drain tube to the bleeder valve...
  • Remove the reservoir cover screws...
  • Pull the reservoir cover and diaphragm (no diaphragm plate back here)...
  • Pump and add fluid until it comes out "clean".

I find that adding fluid is a little more difficult for the rear system, because of the cramped quarters and the smaller reservoir and the half-empty bottle. If I pour too aggressively, I risk a reservoir overflow. If I pour too gently, the fluid tends to run down the outside of the bottle and drip where it's not wanted.

I finally came up with an idea that seems to help (see the photo). Here I am using a trusty drinking straw to direct the fluid flow, but I have also used the same (clean!) Philips screwdriver that removed the reservoir cover screws.

Here is my collection bottle, containing ALL of the old fluid drained out of BOTH systems, along with a small amount of clean fluid.

Unless you have another bike that needs new fluid, it doesn't make sense to keep the rest of the clean stuff in the original bottle. Over time it will absorb moisture out of the air (which is pretty much impossible to prevent) and will become unsuitable for use. So, I just pour the "yucky stuff" back into the DOT 4 bottle and set it aside with my quarts of used motor oil. My local Checker and AutoZone stores accept both used oil and used brake fluid, so I save it up until there is enough to make it worth the trip.

Q: Now wasn't that EASY?
A: "Not just easy, but almost FUN!!"

Back to Kerry's General Purpose Home Page