Tutorial: Changing Your Brake Fluid

[SpudRider]

The front brake on your motorcycle provides at least 70 percent of your braking power! 8O Therefore, it is vital to properly maintain your front brake. You should regularly inspect your front brake rotor, and brake pads. It is also important to change you brake fluid on a regular basis.

As with most liquids, brake fluid does not compress much under pressure. Therefore when you squeeze your brake lever, the brake fluid transfers the pressure generated at the master cylinder to the front brake caliper, compressing the brake pads against the brake rotor. However, unlike most liquids, brake fluid is a special liquid, designed with special properties.

Brake fluid is designed to have a high boiling point. When you apply the brakes, the friction between the brake rotor and the brake pads generates a lot of heat, and some of this heat is transferred to the brake fluid. When a liquid boils, it becomes a gas; unlike liquids, gasses will compress under pressure. :( Therefore, if your brake fluid starts to boil, your brake lever will become mushy, and you will not stop as fast. Besides having a high boiling point, brake fluid also contains anti-corrosion additives, and these additives help prevent your brake system from rusting.

Brake fluid deteriorates with time, and usage. The main culprit causing this deterioration is moisture. Brake fluid is hygroscopic, which means it absorbs moisture from the atmosphere. Over time, moisture enters the brake fluid via the permeability of the brakes hoses, brakes seals, the master cylinder cap, et cetera.

Water has a much lower boiling point than brake fluid. Therefore, old brake fluid contaminated with water will boil faster than fresh brake fluid. Also, water degrades the anti-corrosion additives in the brake fluid, promoting rust. :(

As brake fluid deteriorates, it changes color. Fresh brake fluid is clear, but contaminated brake fluid becomes progressively darker as the contamination increases. If you don’t race, you are probably safe changing your brake fluid once a year. However, a change in color is the best indication you need to change your brake fluid.

If you want your brakes to perform well, and not be damaged by moisture, you should change you brake fluid on a regular basis. The following link points to a PDF file containing a lot of interesting information regarding the properties of brake fluid.

http://www.mightyautoparts.com/pdf/articles/tt136.pdf

In my next post I will tell you how to change your brake fluid.

Spud

[SpudRider]

You can change you brake fluid manually, or you can employ a hand-operated vacuum pump. Either method will work, but the vacuum pump makes the job faster, and easier. However, the manual method works well, and saves you the cost of the vacuum pump.

Using the manual method, you don’t need a lot of tools. You can loosen, and tighten the bleed bolt on a typical Chinese brake caliper with an 8mm wrench. You also need about 2 feet of 3/16-inch, clear, fuel line; you can buy this fuel line at most auto parts stores. You can collect the used brake fluid in an old soda pop bottle, with a hole drilled in the cap to accommodate the free end of the fuel hose. Of course, you also need a Phillips head screwdriver to loosen the cap on the brake fluid reservoir.

Brake fluid is very corrosive, so you should cover your motorcycle with rags to prevent damaging your paint, or plastic. You should also have extra rags, and lots of water handy to clean up any spilled brake fluid. I change my brake fluid in my driveway, with my garden hose nearby. The following videos show you how to change your brake fluid manually.







In my next post, I will tell you how to change you brake fluid more easily, with a hand-operated vacuum pump.

Spud

[SpudRider]

I prefer to change my brake fluid with a hand-operated, vacuum pump. One popular pump is the Mity-Vac.

http://www.mityvac.com/pages/products_hvpk.asp#MV8000
http://www.amazon.com/Mityvac-Brake-...=pd_sbs_auto_3

Another popular pump, and the one I use, is sold by Harbor Freight.

http://ww2.harborfreight.com/cpi/cta...452&pricetype=

In addition to the hand-operated, vacuum pump, you also need the same tools you would employ with the manual method for changing your brake fluid. The following videos show you how to change your brake fluid using a hand-operated, vacuum pump.




Of course, after the job is finished, you need to properly dispose of the used brake fluid, the same way your dispose of your used motor oil.

Spud

[Wild_Alaskan]

Thanks a bunch for the well written guide! Should i be able to pull my brake lever all the way to the bar? of course i think the front wheel would be skidding long before i pull it that far but is it too mushy you think?

[SpudRider]

Originally Posted by Wild_Alaskan

Thanks a bunch for the well written guide! Should i be able to pull my brake lever all the way to the bar? of course i think the front wheel would be skidding long before i pull it that far but is it too mushy you think?

You're welcome, WA. No, if your brake fluid is in good condition, you should not be able to squeeze the brake lever all the way to the handlebar. If you can squeeze the brake lever all the way to the handlebar, your brake lever is mushy, and your brake fluid is contaminated. If your brake system is in good condition, the brake lever should stop short of the handlebar when you squeeze it as tightly as you can.

Spud

[Zongdawg]

You are the reason I am buying a sierra. I will post after I receive it. Thanks again.

Todd

[Weldangrind]

Originally Posted by Zongdawg

You are the reason I am buying a sierra. I will post after I receive it. Thanks again.

Todd

I'm glad that you're using your powers of influence for good Spud.

[Weldangrind]

IME, it's best to use a six-point socket or even the box end of a wrench to loosen the bleeder screw. The open end of a wrench can easily slip and ruin the bleeder.

[FastDoc]

I also use a Mity-Vac. Useful tool for diagnostics too. IIRC, it was all of about $40 and worth it.

I've used it for bleeding clutches too. Also changing differential fluid in my pickup.

[SpudRider]

Originally Posted by Zongdawg

You are the reason I am buying a sierra. I will post after I receive it. Thanks again.

Todd

You're welcome, ZD. Once again, welcome to these forums! Please do keep us updated regarding the purchase of your new bike.

Spud

[SpudRider]

FastDoc and WG; thanks for the tips. I hope others will also contribute the wisdom of their experience.

Spud

[Dahamaster]

I was wondering if anyone else has experienced this problem with their front brake. My problem is that there is so much pressure in the brake line, that the brake is always on. The brake lever becomes so stiff that you can barely budge it. The pads are engaging with no action from the rider.

I have to stop and do an emergency road-side bleed after or during every ride. Otherwise, the brake is on and I'm pushing a "snow plow." I have been bleeding the brake for the past year since this problem arose. I have replaced everything but the cable--caliper, master cylinder, pads. The last item replaced was a new caliper...about a month ago. No change. Wheel still locks up. I can loosen the two top bolts on the back, top of the caliper. It relieves the pressure on the pads and the front wheel will spin freely, but that's not a wise thing to do since I can't keep the bolts from backing out.

I just bled the brakes the other day along side the road and decided to let a little air into the line--allowing the lever to draw a small gulp of air in while pumping the lever and draining the fluid reservoir dry. That seems to have worked (for now). I have a much better feel and the brake isn't locking up. However, the pads squeal and squeek very loudly on braking. (which has always been a problem...I really don't care about that)

Fluid movement in the system doesn't seem to be the problem; it works just fine. There wasn't any air in the system (until I let it in). I just don't understand "where" all this pressure is coming from?

Other than allowing air back into the system so I can continue to ride, I don't have any clue what the problem is? Any suggestions???

[SpudRider]

I suggest you examine the brake fluid level in the master cylinder. When you apply the brakes they become hot, and transfer heat to the brake fluid, which expands. If the brake fluid level in the master cylinder is too high, the brakes will drag.

If your bike has the standard, Chinese brake caliper, the squeeking is caused by uneven wear on the round brake pads. You can stop the squeeking by using a hacksaw, or a Dremel tool to remove the raised portion on the rear of the brakes pads.

Spud

[Dahamaster]

Yeah, I've tried running at low fluid levels as well. Still locks up. I've got it half way in the window right now. It's been fine today (with a bit of air in the system to soften it up). I think if it locks up again, I'm going to bleed the system completely dry and start over.

Cutting the pads down sounds like a good idea; I'll give it a whack. Thx Spud.

[SpudRider]

Originally Posted by Dahamaster

Yeah, I've tried running at low fluid levels as well. Still locks up. I've got it half way in the window right now. It's been fine today (with a bit of air in the system to soften it up). I think if it locks up again, I'm going to bleed the system completely dry and start over.

Cutting the pads down sounds like a good idea; I'll give it a whack. Thx Spud.

You're welcome, DM. If your brake fluid level is correct, then you probably have some crud stuck in the brake caliper itself. :? I encourage you to disassemble, and inspect the brake caliper. The typical, Chinese front brake employs the same front brake caliper as the Hyosung GF125 motorcycle. Searching the internet I discovered the Hyosung GF125 Service Manual.

http://www.chinariders.net/transfer/...NUAL-GF125.pdf

Complete instructions for inspecting, maintaining and repairing the front brake caliper follow page 6-22 of this service manual.

Spud