Contaminated brake fluid

I pulled the cover off my rear master cylinder and the brake fluid looks like muddy water or chocolate milk. The question I have is, do I only need to replace the fluid and bleed out the brakes?
They seem to be working o.k. Just wondering if I need to pull the calipers off and check them. The bike is an 05 with 7k on it,any ideas what would cause this? As always thanks for the help!!!
Big Toe

sounds like you had some moisture in there, considering they are your brakes, I would go ahead and flush them out . but I would change the fluid

In 05' HD changed back to using DOT 4 fluid in the brake systems. DOT 4 is a glycol based fluid and is hydroscopic, which means it absorbs moisture. Prior to 05" HD used DOT 5, which was slilicone based, and would not absorb moisture.

The brown color your seeing is moisture in the fluid. You need to do an entire system flush and refill with clean fluid. To keep the system moisture free you should to a complete system flush every 2 years or 10K miles. Now, because DOT 5 doesn't absorb moisture, the moisture gets suspended in the fluid. This can cause a soft feel in the brakes, similar to having air in the system. So even if you have DOT 5 in your system, it should be flushed on a regular schedule also.

And remember, because of the different material used for the seals in brake systems, DOT 4 & 5 are not interchangable, and should never be mixed. If you mix them, you will end up with a nice thick syrup in your brake system. Then you have to replace everything.:gah:

just a follow up to some of the post. I used dot5 brake fluid and flushed the system out this morning. The top of the master cylinder calls for dot5.
How do you get moisture in the system? I thought it was a closed system.
Big Toe

Are you sure you had dot 5 in there, maybe someone replaced the master cylinder with a chrome one(aftermarket) that still said dot 5 I have heard of that on occasion The moco did indeed switch to dot 4 in 05. My 05 has dot4. Dot 5 is usually yellow or purple but normally does not get brown like dot 3 or 4 because moisture is what turns its color and like Ringo said it doesnt mix with dot5 just seperates. If you bought the bike new I wouldnt question it but if you bought it used you wouldnt have any way of knowing, I just know you dont want to mix brake fluids. I would check your owners manual or service manual just to make sure. Todd

you should be ok just changing fluid as it should be changed every 2 years you will notice a big improvement in your brakes
kev

water will get into anything closed or not, when it's cold and your bikes hot, bang moisture, your bike sitting out all night, a little frost, start your bike and it gets hot, bang moisture. same thing like milldew

If it is the stock master cylinder then use what it says on the cover. I would check your SM to make sure also. The moco changed to DOT 4 in 05', however, it wouldn't surprize me if they only made the change on a few models and then did the rest in 06" My brother has an 05 Road Glide and his SM and master cylinder call for DOT 4.

Even though the system is closed, it is not hermetically sealed. Moisture will get in. There is an old saying, "Water always wins". Moisture can get in just from the humidity in the air, when you take the cover off to add fluid. Remember, there is always a small air pocket in the master cylinder between the top of the fluid level and the bottom of the cover. If your fluid is low, there is more of an air pocket. As this air pocket heats and cools with temperature change, moisture forms.

If you fill from a bottle of fluid that is only half full and has been sitting around the garage for 6 month's, the moisture in the air in the bottle mixes with the fluid. Two things you shouldn't do is shake a bottle of brake fluid, it creates air bubbles, or use fluid that's been sitting around for a while. When I flush my system I always use a new bottle of fluid. I never by the big quart bottles. I buy the small ones, and after I flush the system, if I have a little left in the bottle I dump it in my dirty oil that goes to recycle.

What does the top of the front m/c have on it? In '05 HD went to Dot4 brake fluid. Dot4 and Dot 5 CAN'T be mixed. It could/probably be the wrong cover on there,like when I got my '03 it had "use Dot4" on the front m/c...it was the wrong cover. Check your service manual for the correct type. I'm pretty sure it's Dot 4.
I don't want to alarm you but mixing the 2 can cause brake failure(no brakes or lock up), The Dot4 and 5 react and turn to a gel. I don't know if flushing the system of Dot 4 and replacing with Dot5 will cause that,but I wouldn't take any chances with my braking system.
I would replace the brake lines and completely clean the master cyl and caliper with denatured alcohol,thoroughly dry em out and then refill with new fluid.

I have an '05 Heritage and the service manual calls for Dot 5. That is also what is on the top of the master cylinder.

Best to check the manual then to make sure, Dot5 will turn an amber color after a couple of years. Not a good practice for the MOCO to change some to Dot4 and leave some Dot5 in the same year(05) IMO. A mistake in using the wrong fluid could have serious consequences.