Working on my ABS, Part 3 (Original Post: Dec 3, 2012)

Some wise person once declared, "If you have something important to tell me, for heaven's sake, start at the end!" So.... It works!  It works!  It works!


In part 2, I told the story of the considerable effort required to replace my ABS pump and module, and how the error codes remained.  At the end of that post, I was wondering which of the two control modules in my possession I should send off for rework at www.ModuleMaster.com. I decided to send the one that came with the used pump, on the theory that they may be a matched pair somehow.

Module Master is in the middle of nowhere, apparently: Moscow, ID.  According to Wikipedia, which is never wrong, it has a population of 23,800.  Once the module was in their possession after a week on the road, they turned it around in one day.  I had paid an extra $5 to get new stainless screws to remount the module, but it turns out they didn't have the right ones for my module.  So, we agreed I would get 2-day return instead. Unfortunately, the package shipped the day before Thanksgiving, so it still took a week.

Once I had it in hand, I installed it, and... still had bad codes.  Different ones, but the ABS and DSC warning lights on the dash were still on.  Dejected, I decided to put the rest of the cooling system and engine back together so I could start it and test all the other work I've been doing. Once I started the engine (worked great - I'll do a full report later), the rest of the codes cleared! Success!

But, I was not out of the woods yet.  When I changed the pump, I very carefully bled the brakes using genuine BMW branded DOT 4 fluid, and ensured that no bubbles remained.  The brake pedal was still mushy, because of the air in the pump.  You have to be able to activate the pump to work that air out into the lines, and then re-bleed the system.

In part 1 of this saga, I detailed how my 1999 Z3 is "special" - it doesn't have the ABS relays that all the other Z3's and nearly all other modern BMWs have.  Thus, I couldn't use the standard hack of bridging two pins to activate the pump.  Of the other options to activate the pump, I chose this one: "drive" the car while still on my lift, and jam on the brakes to trigger the ABS.  Do it a bunch of times, and bleed all four brakes again.

I started the car, put it in gear, and let out the clutch.  The engine immediately bogged.  Of course, the computer was doing its job to keep the tires from spinning, even though they weren't even installed! I pressed the button to disable traction control (usually used in snow) and tried again.  I ran the car up to about 3000 rpm in 3rd gear, and then hit the brakes.  That ABS unit chattering away was music to my ears.

I did that process about 20 times, and then went to lunch.  After lunch, I did it 20 more times - surely, that would be enough to purge the air. Next step, bleed all the brakes using my BavAuto pressure bleeder.

When I ordered that gadget, I bought the full kit that also includes a hose and bottle to catch the fluid on the caliper side. That part was back ordered, so I had to improvise with clear tubing from Home Depot and a Coke bottle. When I initially bled the brakes after changing the pump, I was juggling that stiff hose and the bottle, which was a pain.  This time, both brain cells fired at the same time, and I used a longer hose and a couple of woodworking clamps to help out.

I saw more air bubbles at the second bleeding, and was rewarded with a good, firm brake pedal when done.  I used four 12-oz bottles of brake fluid, including the fluid remaining in the bleeder. I'll keep that around until I drive the car a while and force ABS engagement with all four wheels spinning, just in case I feel the need to bleed one more time. Then, the excess gets dumped - once brake fluid is exposed to air, it degrades very quickly.

Incidentally, on a car this age and especially, mileage, you are constantly running into signs that someone has been there before you. The bleeder screws on my brake calipers were three different sizes - 7mm, 8mm and 9mm. Here was one case where being old had its benefits - my 40-year-old set of ignition wrenches (small, slender wrenches for working on old point-and-distributor style ignitions) were perfect for opening the bleeders. I was surprised that Sears still has several sets for sale, even though modern cars don't have ignition systems that need them.  Here's one of mine to give a sense of the size:

If you will pardon the brake pun, I must say I'm "pumped" that I got this working!