ABS Modulator Replacement?

[David Greer]

Hi folks, I'm new to the forum but have owned my '99 Contessa since 2011.  Question is has anyone had to replace their WABCO ABS modulator on a Magnum chassis?  It's located on a shelf forward of the fuel tank just inboard of the right frame rail and looks impossible to get to the line connections without cutting a hole in the living room floor.

The reason for the question is that I have no brake fluid flow to the left front caliper now.  The problem was first discovered back in August when I was flushing with my homemade garden sprayer pressure bleeder.  No issues with fluid flow to both rears and the right front but nothing coming out the bleeder in the left front caliper.  Figured I'd try the old-fashioned way and had my daughter depress the brake pedal while I opened and closed the caliper bleeder.  (The pressure bleeder remained connected during this process--a possible goof.)  Pedal depressions provided good fluid flow for several depressions and then the flow stopped.  I then started the engine (mistake, shouldn't have done that) to build air pressure since we were down to less than 50 psi but that didn't make a difference.  To rule out the caliper, I disconnected the brake line from the caliper and still no flow.  That's where I am now, after attempting a 2nd pressure bleed.  I'm thinking the ABS modulator left front inlet valve is either clogged or stuck shut, or the outlet/dump valve is stuck open.  Corrosion.  No reason to suspect a line problem.  Last thought is to reverse flush the left front and see what happens and will do that soon.  And since I was way into this front brake thing anyway, I replaced the front calipers to get rid of the phenolic pistons in what I had and replaced with remanufactured NAPA calipers with metal pistons.

Thanks,  Dave

1999 Contessa Naples 40'
CAT 3126B (with new injectors and HEUI pump)
1987 Ford Bronco TOAD
   

[Gerald Farris]

David,
Before you replace the modulator, disconnect the brake hose to the LF wheel. ON these 20 year old brake hoses the inside lining can deteriorate and a portion of the lining can act like a check valve, allowing the fluid to flow in one direction only or partially restrict fluid flow in both directions. It is a lot more common than you would think with a hose of this age or older.

Gerald

[David Greer]

Thanks Gerald.  I'm probably in some sort of brake hose denial as the upper connection to the LF hose is inside the frame rail and have no idea how to get to it, and to compound the problem, there's so much corrosion to all the brake line fittings, especially as you get up into the line/hose nesting area near the modulator.   You're right and I'll figure out a way to isolate or remove the line. 

I also invested in the WABCO Toolbox software and a network bridge, mostly to bleed the modulator since I made the error of turning on the ignition during the bleeding sequence.  So far, I haven't been able to get Toolbox to talk to the module.  But that's another story.

Dave