Brake Mystery: New MC, fresh bleed, still no brakes!
 

Hi everybody, I had what started off as a rotted brake line in my 2003 X5 4.4i and it's turned into a nightmare. One of the hard brake lines under the drivers door had rusted though and started leaking. I cut out the offending part and patched in a new piece of factory hard line there. I tested it and it worked fine, other than the pedal traveled way to far before the brakes engaged.

I took it to my local German shop here in the Detroit area in hopes that they could put it into "bleed mode" on their computer to get out any air bubbles that may have worked their way in to the DSC unit. They were unable to get the pedal hard, and couldn't figure out why.

Frustrated, I replaced the master cylinder, because what else could it be? Between the shop and myself, we must of ran a gallon or two of fluid though there.

Master cyl replaced and the brakes are worse. I took it back to another German shop in the area and they say that I have good pressure coming out of the Master cyl, but hardly any coming out of the DSC / ABS unit. Only the front brakes are working and the rears are doing nothing. They are now claiming that it's the DSC / ABS unit (part #3451676545) and I can either get a rebuild kit for $2,500 or a new unit for $3K.... madness for a 10-year old car with 100K!

So I did some research and I found a used one that's been tested and warrantied for a year for a few hundred dollars, so I'm having that shipped to the shop for them to install.

Sorry for the novel, but that's my history. Now does anyone have any thoughts? This makes sense I suppose, and we'll find out once they replace the pump, but I think they're just guessing at this.

I'll let you know if it was indeed the pump, but anyone else ever experience something like this? Any one have a similar problem of the brakes just not being able to be bled?

Have you tried bleeding them with car running?

sorry for your troubles. Where did you take it?

I've got a motive pressure bleeder, but I bet thats not it. have you thought about looking further down the line, like new calipers? Have you tried pressurizing the system externally and seeing how long it holds (like a leakdown test?).

You can replace your ABS module, but unless its LEAKING, I cant imagine why that would cause your issue.

MC compresess fluid, compressed fluid enters ABS, Exits ABS to lines, lines to calipers.

The only real way to get a soft pedal is air in the lines. MC replaced, lines replaced. Could be the ABS. See if they/you can fab up some jumper lines, and jump the ABS module (direct from the MC to the Calipers (If that can be done?) should solve that pretty quick.

My money is on air trapped in the ABS module. There is a specific procedure to,follow to cycle the ABS valves while bleeding, using a computer. Before replacing the ABS module, I would try another mechanic at another shop, one who has done that procedure. Cheaper as a first step, should cost a few hundred.

JCL- would that be the case for all brake bleeding on E53? to utilize a computer? or is it just in this circumstance ( as a guess to what possibly happened)?

thanks

I had something similar happen on a old Camry I was working on. Try checking the adjustment of the plunger going to the master cylinder. When bleeding the brakes the plunger went down too far and is now letting fluid pass into the system all the time ... I had to redo the adjustment .. Hope that this helps..

Any time, if circumstances allowed air to become trapped in the ABS module. There are dead-ends that trap air, and cycling the ABS module valves and actuators with the computer while bleeding is the only way to bleed the system then.

I have come across this issue several times especially when brake lines have rotted. When the brake maste cylinder becomes empty, most often times the brake hydraulic unit has air trapped inside of it. To make the brake pedal hard again, this is what you must have done to correct this concern.

Attach a pressure brake bleeder device to the vehicle. Here are some tools you will need.

Blue Point Brake Bleeder - BB100C QTY 1
Blue Point Pressure Cap - YA8925 QTY 1
BMW Brake Fluid DOT4 - 81220142156 QTY 4
Catch Pan for brake fluid and or Gatoraid Bottle with vaccum hose.
11mm and 13mm Combo Wrenchs

Assuming you have already bled the RR, RL, FR, and FL circuits sucessfully. The next step is to bleed the master cylinder. Gain access to the brake lines coming and going to the master cylinder, and carefully brake open the lines for a few seconds each. If you see bubbles coming out, then that is a good sign.

Next you must move on to the brake hydraulic unit. Gain access behind the drivers headlamp. It may be easier to remove the headlamp and or 3.0 Airbox. Do the same for the brake lines coming and going from the hydraulic unit.

Now the brake pedal should feel firm, and no longer fall to the floor after starting the vehicle. If however this does not correct the issue. You must attach the BMW DIS/ISTA D to perform service function to cycle the solenoids in the ABS module. This should free up any trapped air bubbles. You can leave the pressure bleeder on the vehicle while is it being performed. After this procedure, perform a regular brake flush again.

Thanks for all the advice guys. Both the shop and myself had used a Motive pressure bleeder, and the shop has a GT1 computer and while they bled the brakes, they had the computer set to bleed mode which ran the abs pumps to get any air out.

I didn't bleed them with the car running, as I didn't think that made a difference, but maybe I should have tried that. If the shop had it on the computer, then they must of at least had it on at that point.

I also let it sit with the pressure bleeder on and it held at 10lbs for 2 hours, so I have to rule out other leaks or bad calipers.

Also when I installed the master cylinder I bench bled it before I installed it, and then after I installed it, I cracked the lines where I did get some air out, so that was good. But the pedal is still bad. Worse than it was before I replaced the master cylinder.

I already purchased the used DSC / abs unit, so we'll see if that was the culprit. The one thing that was mentioned was the master cylinder not being installed correctly.

I did it myself and I'm by no means a pro, so maybe I screwed something up... Although it seems pretty straight forward. I just put the rod into the booster and lined it up with the piston on the master cylinder and then bolted it in. Who knows. If this dsc/abs unit doesn't work, I'll have them reinstall the master cylinder for me.

One thing that was mentioned was to open the lines before and after the pump to manually bleed any air out. I did not do that, and I think it would have been a good idea. But wouldn't just bleeding it normally with the computer set to bleed mode accomplish the same thing?

The shop it's at is Auto Europe in Birmingham, MI. They come VERY highly recommended so hopefully they can help me figure it out without sending me to the poorhouse.

Very frustrating! I'll keep everyone in the loop as things progress in case other have this challenge. Wish me luck, and if anyone has any other ideas, let me know.

Did you bench bleed the master cylinder?