RABS issues??? - Ford Powerstroke Diesel Forum
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Old 05-07-2014, 05:31 AM
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RABS issues???

Alright guys so since i bought my truck ive had a wierd brake pedal. So i put all new pads, rotors, wheel cylinders, brake booster and master cylinder calipers and most recently i threw a vaccum pump at it. The pedal will go down about 4-5 inches before it grabs then it stops fine. IF i pump the brakes when its running the pedal will eventually get firm then the RED brake light will come on..soon as i stop pumping the brakes it will go off. This things got me stumped.
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Old 05-07-2014, 08:36 AM
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Quote:
Originally Posted by RushFORD View Post
Alright guys so since i bought my truck ive had a wierd brake pedal. So i put all new pads, rotors, wheel cylinders, brake booster and master cylinder calipers and most recently i threw a vaccum pump at it. The pedal will go down about 4-5 inches before it grabs then it stops fine.
That usually indicates air in the system. Did you bench bleed the M/C before installation? Did you bleed the system in reverse order of distance from the M/C (RR, LR, RABS valve, RF, LF)?

Quote:
IF i pump the brakes when its running the pedal will eventually get firm then the RED brake light will come on..soon as i stop pumping the brakes it will go off. This things got me stumped.
That's a red herring. You're just exhausting the vacuum reserve for the power boost when you do that. The firm pedal is from losing boost, not from gaining hydraulic pressure. The light is triggered by the sensor on the vacuum distribution box, sensing the loss of vacuum. When you stop pumping, and the engine continues to run, the vacuum reserve catches up and the light goes off.
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Old 05-07-2014, 09:51 AM
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My brakes were super soft for a long time on my 97. Tried everything, bled everything a million times. Ended up being the valve. I took the spring out pumped it once to push the rabs piston up and bang brakes were perfect.

I anything it's something else you can rule out and it's really easy to put the spring back in if it doesn't fix it.
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Old 05-07-2014, 10:51 AM
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Where's the rabs valve..is that the thing on the driver side frame rail?..I've only bled the pics out of all the wheels and yes I bench bled the master cylinder..
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Old 05-07-2014, 11:16 AM
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Yeah that's it. You can try to bleed it first too. It's basically a piston in there with a spring and when the truck senses rear wheels locked up it lets the piston go and it compresses the spring. Also when the valve is bad the piston just floats on the spring so every time you push the brakes you have that amount of pedal travel before fluid actually starts being compressed. I could be wrong that's just the way I understand that it works.

If I remember right there is a big 1" or so nut/plug on the front side of it (towards the front of the truck). Just unscrew it remove the spring some people put a bolt or something in there and put the plug back in.
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