Brake Fluid

[pretzladay]

Read owner posting elsewhere that he had replaced brake fluid with DOT5 and had eliminated that annual chore. Good idea, or bad? Also, anybody have experience with Speed Bleeders? Good investment?

[The Meromorph]

Speed Bleeders are excellent.

Using DOT5 fluid is a very bad idea...
First DOT5 and DOT4 should never be mixed, to the point where you have clean out the old DOT4 to the extent that there isn't any left. The crud they produce when mixed is nasty.
Second DOT5 is not hygroscopic, so the water in the atmosphere doesnt get absorbed into the brake fluid, but neither does it mix with the brake fluid. So the lesser amount of water that does get into the brake system, falls to the lowest point (that's your calipers!). Plain water boils at normal brake caliper temperatures, so when you do get a little water in there, you are likely to lose all braking suddenly! Far from avoiding the chore of bleeding the brakes, you should bleed them (a little) to get just the (little bit of) water out very frequently! (Every day would not be too often.) Or risk having no brakes when you need them...

[pretzladay]

Meromorph,
Thanks for the info, on both counts. Just bought an 04 R with 1800 miles, and I don't think the brake fluid has ever been changed, let alone bled. I'm 2.5 hours from the nearest BMW dealer, so you've been a big help. Thanks again

[The Meromorph]

With the DOT4 fluid (which you should continue to use), most times, bleeding the brakes exactly equals changing the brake fluid, because you bleed until only clean clear new fluid is coming out.
Occasionally (for example if you fail to tighten the bleed screw [DAMHIK ] ) you'll need to bleed only enough to get the little bit of air out.

Speed Bleeders work much better...

[OU812]

So what is the difference between 3 and 4?
Just asking and thanks for your posts!
Steve

[The Meromorph]

So what is the difference between 3 and 4?
Just asking and thanks for your posts!
Steve

DOT 4 is a significantly better formulation of the same basic technology.
You could use DOT 3 in an emergency, but it would get contaminated faster, and be more susceptible to boiling when it does. If I had to use DOT 3, I'd replace it with DOT 4 within 6 months. (Actually I'd replace it as soon as I could )

[OU812]

So I can flush DOT 3 out with 4?

[The Meromorph]

Yes.

[OU812]

Thanks for the info! Used DOT 4 on my 98' DR350 Off Road.

[omg1010]

DOT 4 and DOT 5 are not compatible. However DOT 4 and DOT 5.1 are. It is really confusing but the development was DOT 3 -> DOT 4 -> DOT 5.1. DOT 5 is a totally different stuff as this one is based on silicone and it is not compatible with the other DOTs because of the seals used in every brake system.

Best regards
Oliver