Mk IV Roadster ABS issue

[Racee75]

Ok... Here is a question for anyone with ABS experience. I have a MkIV that I am slowly progressing with using some donor parts and have been working on the brake system. Last weekend I finally filled the system and only fond a few leaks from loose fittings. Bleed the brakes as you would on a non ABS car and still had a pedal that went all the way to the floor.

Thinking that the master cylinder may be bad, I ran some hard lines to bypass the ABS module and confirm that the master cylinder was bad. This was not the case as once the ABS module was bypassed, I instantly had a firm pedal. I then swapped the lines back to include the ABS module and then lost the firm pedal. The ABS unit was out of a 1997 GT Mustang.

Any thoughts on what to look at or possible causes for this issue ?

[Sanford]

Could still be air in the ABS unit, some had special bleeding procedures but not sure of your model.

[2bking]

The ABS unit has air in it. Some units have a way to activate the pump through the test procedure. I was able to get enough air out of mine by pumping the pedal to generate some pedal resistance and holding it for several minutes and then rebleeding. After a few cycles of pumping and bleeding I got a hard pedal before the pedal hit the floor but was never able to completely purge it. I could activate the ABS unit by spinning the front wheels and applying the brakes (with the ignition on). That cleared the front circuits but I had to drive it to clear the rear circuit. It is easy to activate the ABS on a gravel surface. Once the air is out of the ABS unit and in the brake lines, bleeding will remove it.

There probably are easier ways to bleed it as others will offer up, but I enjoyed the challenge and had some fun trying different methods.

[Racee75]

Ok... Thanks for your input... I will try bleeding the system again and see what the results are.

[CraigS]

Nice Guy Eddie recently found that on his 2010 tacoma the trick was to have the key on while bleeding brakes. See his post in the off topic section of the other forum.