How Bleed Brakes w/4WABS??

[David40]

Hi Gang, I have been getting an intermittent ABS light on my 96 E-350 for years. I finally got a code reader that works on these systems and got a
C1206 error code which is a rear isolation valve problem. I traced out the problem following the the factory pin point tests and it comes down to one of two problems. I either need a new ECU (Electronic Control Unit/ABS control Module), or there is air trapped in the HCU (Hydralic Control Unit) specifically the Rear Isolation Valve. I'd like to try bleeding the brakes before I plop down $400 bucks for a new ECU. Is there a way to manually bleed the 4WABS wihtout spending a thousand bucks for the T90P-50-ALA adapter and EEC-IV breakout box to do the proper bleeding of this system? I'm open for any and all ideas.
Thanks

[bigcountrysg]

Welcome to the Org.

There is two ways to bleed brakes.

1st way is the buddy system. Have a buddy sit in the driver seat. You take a wrench that fits the bleeder valve on the brake cylinder. Ooops make sure your master cylinder is full. Ok now I prefer a line wrench for bleeding brakes. It fits tighter on the bleeder valve. Ok what you do is crack open the bleeder valve. Have your buddy push the brake pedal down and hold it there. Once the brake pedal is down, tighten the bleeder valve. Then have your buddy release the brake pedal. Keep repeating this process until you have all the air out and have a steady flow of fluid at the brake cylinder. I suggest you do this to all four wheels starting at the passenger rear, then driver rear, passenger front, then finishing with drivers front. When you complete one tire recheck the mastercylinder under the hood to make sure it is full. Refill the mastercylinder as needed.

Now the 2nd way is with a vaccuum pump. You place the wrench on the bleeder valve of the brake cylinder at the wheel. Then attach the vaccuum pump to the brakecylinder bleeder valve. Then pump the vaccuum pump up so you have sufficient vaccuum. Then crack open the bleeder valve. You should see the vaccuum gauge on the pump move slowly back to zero. Keep repeating this proccess until you have all the air out and a steady flow of brake fluid.

Syptom of air in the brakelines, usually the pedal will feel spongy if you have air in the brake system.

[David40]

Thanks for the reply. I am aware of bleeding regular brakes in this way but with the 4 wheel ABS there is a special proceedure that must be followed because of the loops and feedbacks in the ABS hydralic unit. The special "bleeder box" and breakout box cycles the internal valves while running the electric hydralic motor to push air out of that unit. Regular bleeding is not enough and I believe when I had my brakes worked on the last time they did not perform this necessary proceedure. Few shops have the equipment to do this job the way it's supposed to be done even places that are supposed to be "brake experts". All those special tools do is allow you to manually control the system to simulate how it would operate while driving so I figured there must be a way to connect up some wires and do the same thing if I could understand exactly what needs to happen and in what sequence. It may end up being easier to just bring it to the dealership and let them bleed it.


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[bigcountrysg]

I know this I have done my brakes on my truck everytime they had to be done myself. I have even replaced the calipers as well. I have never had a problem with bleeding the brakes the way I described.

[David40]

I would agree that if you are only doing the brakes themselves I don't see how any air could get up in the HCU unless you let the reservoir run dry. On mine they did the master cylinder and the fronts calipers so I'm sure lots of air got in there ahead of the hydraulic unit and got sucked right in there when they did a conventional bleed on them. In any case I need to be sure cause I'd hate to spend the big bucks on a new control module and still have the same problem.
Thanks

[jramsey8]

There is a $5,000 computer required to blee 4 wheel ABS, it can not be done with the buddy system. The computer hooks to the 54 pin harness and takes the whole system through a 5 minute bleed cycle, opening and closing all the little valves inside the HCU. If repairs are made downstream from the HCU you may be able to bleed conventionally but if you were to replace the master cylinder lets say, you have to take it in to have bled.

[David40]

I've had my eye out for a used bleeder box for quite some time now. I've even run across home made versions that have buttons to let you do the routine manually. Basically the computer controls the valves and the pump motor in a particular sequence, so if you know the sequence of events you can do it without the computer. I'd take it in to the dealership but my experience is that they rarely have any idea what they are doing and that is why I try to do all my own repairs. My guess it that they would just disable the ABS lite and charge me $500 bucks for doing nothing. Finding a good mechanic is like finding a needle in a haystack.

[David40]

It's been a long time, but I just had to tell everyone that after all these years of searching I finally found that damned T90P-50-ALA 4WABS tool to properly bleed my brakes. Just happened to accidentally find it on eBay along with the breakout box and cable.