ABS and Traction Control

The ABS light problem posted recently brought this nagging question to mind that I thought I would run by the forum.

Last year I did the rear brakes on our van at about 116,000 Kms because of excessive pedal effort and because the rear shoes were glazed. The front pads and rotors had been replaced at 60,000 Kms; the pads still had about 60 per cent left.

The van has both ABS and Traction Control so there are two control modules within the brake hydraulic system, each with a bleeder screw.

I bled the brakes using the 'furthest away' method starting with the RR wheel. Some air (and dirty fluid of course) came out at each wheel. By the time I was finished bleeding I had used about two liters of new brake fluid, so I know the system was purged and running completely new fluid. When I had finished, the pedal felt firmer, but still seemed a little spongy. I assumed this was due to the rear shoes being new and not seated yet.

The van now has about 10,000 Kms since the rear brakes were done, but the pedal still seems a bit spongy and requires more effort than I think necessary to bring the van to a stop. The rear shoes are now seated and the swept area on each shoe is in full contact with the drums.

The vacuum booster is working fine; - I tested it by plugging the vacuum line and depleting the vacuum in the booster. Without the booster, it takes a heck of a lot more effort to stop the van.

DON'T try this at home, but in an empty parking lot with LOTS of room to stop! Reconnecting the vacuum line to the booster made a big difference, but the pedal was still spongy (didn't think this would change after the test either).

Reasoning that in bleeding the system you are moving closer to the master cylinder with each wheel, I wondered if each control unit should be bled as well relative to their individual position to the master cylinder. I know I have asked this question previously, and the advice was to leave them alone.

If I do decide to bleed the brakes again, (including the two modules), is there a specific method for doing so?

Must each unit be 'activated' in order to allow fluid to be cycled through it?

Think I'm looking for a brake technician on this one....
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I think I found the source of my spongy brake issue, thanks to the help of a couple of experienced followers on this board.

Seems that the order I bled the brakes in the first time was not right. I should have known this after doing the brakes on our Isuzu (which is 'almost' a GM!).

I used an old-timers method; - furthest away followed by next furthest or (RR, LR, RF, LF).

Should have done it in this order; - RR, LF, LR, RF.

The design of newer dual piston master cylinders is different than of those built before 1980, although it was pointed out there are still variants between manufacturers too. Took a while to figure out what was 'wrong with this picture'.

I also found some good info on AutoZone.com that helped to clarify a few things.

Based on what I've been told and what I have researched (all of it consistent, I might add) there is no need to open the ABS or monkey with anything downstream from the master cylinder other than each bleeder at each wheel.

Too cold to do it today (was -14C this morning!), will have to wait for another day.

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