I have a 90 Bronco. The rear brake line blew out while driving. The pedal went to the floor, brake light and rear abs light came on. I replaced the line and it was time for a front brake job so I replaced the front pads, calipers, rotors, and master cylinder. I bleed all four corners and the RABS valve now the pedal will be rock hard when the engine is off and will go to the floor when the engine is started, the abs light will also come on. I have bleed the brakes several times, bench bleed the master twice. I ran the truck on a hoist and the rear brakes don't work, they won't hold when the truck is in drive at idle. Is there something wrong with the ABS valve, or a specific procedure to bleed the rear brakes. Any input will be greatly appreciated.

 

Goose, im not sure if this will help you but here it goes. I'm sure one of the guys that works on these all day long will come along and offer some input. Most of my experience is gm and i will admit i dont know the hydralic controll unit or the combination unit like the back of my hand. I have however, run across some of the older combination valves and controll units for older gm and chrysler rwal vehicles where as they had a button on the side of them that needed to be depressed to allow fluid to be bled through that circuit.

The problem you described seems to be consistant with air in the rear circuit. If i were in your shoes i would bleed at the combination valve and verify a high pressure stream of fluid and no air. If present i would then bleed at the controll unit and verify the same. If either one lacked pressure like it had a restriction i would inspect it for a rubber dimple which normally covers that valve. The purpose on these was if there was ever a loss in pressure to a specific circuit this isolation valve would close so that there was not a total loss of fluid and pedal travel.

Last suggestion but its kinda lame. Any chance all is well but you also have a leak at one of the wheel cyls causing you to loose pressure?

Anyway, sorry i couldnt be of more help.