WhiteHorse

Hi All:

I'm going to replace my brake fluid and am also considering stainless steel brake lines. However, I'm looking at the Bentley Manual and it is saying that if I introduce air into the brake system (e.g., as I switch out the brake lines), I need to use the "BMW Service Tester (DISplus/GT1/MoDiC)" as a part of the bleeding procedure.

If I don't replace the lines, it appears I can get away with just using a pressure tank method.

If looked through as many threads as I can find on the subject but don't see any reference to the "tester".

Is the use of this gizmo a requirement when I replace the brake lines or is there another method I can use? I'd really like to switch the lines but I'm concerned about not having one of these tester devices.

Thanks in advance for your insight.

pmiranda

As long as you keep the master cylinder from running dry when you swap the lines it should be OK to just use a plain pressure bleeder. Basically you must keep air out of the system, and the two places it can get in are the lines at the caliper and the master cylinder.
From what I've read, you should fill up the master cylinder (to keep it from getting so low that air gets in) and put the cap on tightly (to prevent the ambient air pressure from pushing more fluid than necessary out the open fitting at the hard line when you swap the flex lines.
I'd swap one at a time and bleed each as you go to get the bubbles out ASAP, always keeping an eye on the fluid level in the master cylinder.

The great thing about the motiv-style pressure bleeder is that it keeps the master cylinder topped up with fluid. Do not have it pressured when swapping lines, though.. or you'll loose a ton of fluid.

EDIT: I should note that I haven't swapped lines myself, although I just bleed my brakes yesterday. Sadly I was almost done before I remembered that I had stainless lines sitting on the shelf waiting to go in.

WhiteHorse

Thanks for that! That makes perfect sense and I should have thought of it. I'll give it a go.

shadowman

I have as matter of practice also bleeded the DSC system which is part of the BMW process.

It is a simply process that can be accomplished within your shop.

The DCS motor (right front corner of the car) has a plug with 2 leads. As I recall on the motor said there is a red and a ??. I fabricated a simple push buttin (aka stater button) that I use to cycle the motor during the bleeding process.

I hope this helps.

pmiranda

Hmm... same motor runs ABS and DSC, right? What's the whole procedure? Flush normally, run motor, then flush more? Are they control leads you short together to run the motor, or do you need to supply power to one and ground to the other? If so, how much current does it use?

Very interesting!

shadowman

"Boy o boy", I was not very clear at all, sorry.

The red lead on the DSC pump/motor (you will see that the leads on the DSC pump/motor are red and black?? however the BMW harness wire colors leading it the DSC motor are something else) needs to be supplied with 12volts and the other black?? lead goes to ground. Hence the reason I assembled a small harness with a momentary push button and a pair of clips to attached to the battery and two small barrel type connectors to slide into the plug end attached to the DSC pump/motor.

Typically I completely bleed the system, right rear, left rear, right front, and finally left front. Once I am satisfied I cycle the DSC pump/motor several times and then bleed each caliper in the pattern, I repeat the cycling of the DSC pump/motor before I re-bleed each caliper. You will find that when you engage the DSC pump/motor manually that the brake pedal will be pushed all the way up and become extremely hard, release the button and the pedal will relax in much the same way as the system opperates in real time.....only you will be doing it slowly whereas under actual operating condition the pedal will pulse very fast. If you do not do this and air has gottne into the motor and associated lines that "only come into play" when this system operates you will have retained air in the system. As for a power source, I use a loose battery on a cart however you can use the jumper post under the hood as well.

I hope I was more clear this time.

FYI, the reason I adapted this practice is because when Super Charging M5's I relocate the DSC pump/motor. For most folks if all you are doing is swapping brake lines and calipers it may not be necessary but it is certainly piece-of-mind.....otherwise by some remote chance if air found its way into the system you may not know until it is to late.

Take care