Antilock light on solid and rear brakes engage before fronts, HELP?

[autotech84601]

I'm green to old Fords so I thought I would give the forum a try and have had great success early on thanks to typ4 and icanfixall. I figure I should probably ask everyone else if they have seen a problem like mine since its something I've looked for in the forums and haven't quite nailed anything solid down yet so here we go. I've got an 89 F350 SRW where the rear antilock light is on solid and the rear brakes engage before the fronts. I have checked the fluid in the reservoir and have found it to be full. I recently installed new rear brakes and drums and new brake cables as the old ones were all shot and was hoping this would make a difference, but it didn't. I have worked on European cars for the last 15 years and rebuilt a 86 GMC from the ground up, but this has me stumped. I can't seem to find any good manuals to help so hoping you all can give me a hand. Thanks for replying.

 

[Bashby]

Most common cause of rears being grabby is contaminated shoes. Check for leaky axle seals or wheel cylinders.

 

[OLDBULL8]

There is an ABS sensor on the rear axle on the top of the punkin, pull it out, check that for metal chips.
Make sure the connector on the brake master cyl. is connected and clean.
Check connector on the RABS unit for corrosion.
To obtain a flash out code, locate the connector under the dash next to the brake peddle by the RABS module, it has a black/orange wire, with a long jumper wire connected to it so you can see the ABS light, momentarily ground out the jumper, the ABS lite will flash out a code. To start the flash out, the engine must be running and the ABS light on. there are codes from 1 to 16, code one and 16 are NOT used, the code starts with a number of short flashes and ends with a long flash, Example: 3 short flashes and the one long flash would be code #4.

There is a sensor connector under the hood drivers side next to firewall. You would have to put the truck on a lift and run the engine in drive about 5MPH, with a VOM set on the 2000 Mv AC scale, you should get more than 650 Mv, if not then sensor is bad.

Check the wiring to the sensor for chafing (grounding out). Check connectors for corrosion.

You could try this before retrieving the codes.
The dump plunger in the RABS valve may be stuck. Remove the large plug, remove the spring but leave the plunger in, replace the plug, start the engine and cycle the brakes several times, that will reset the RABS, install spring again, light should go out with engine started again.

There are too many codes to list here. Report back the codes retrieved. I'll go from there.

 

[OLDBULL8]

autotech84601

I see your looking. I made a couple of Edits to the post above. Might want to reread it.

 

[OLDBULL8]

I forgot about the proportioning valve on the rear, if it's stuck up,like the bed was fully loaded, that could cause the full rear braking.

 

[autotech84601]

The brakes themselves are brand new and not contaminated at all. I just checked them. I will pull codes as my best step to see what's going on there and report, thanks for the help oldbull8. Where would I find the proportioning valve for the rear? I think you might be on to something......

 

[OLDBULL8]

It's under the bed close to the rear axle, there is an arm attached to it, when the bed lowers for load, it opens the valve for quicker and more brake response.