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Spongy Brakes, Early 90's F250, F350 & E-Series Vans ( Solved !! )


a31ford

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Greetings All,

Recently my 93 F-350 got really bad in the spongy brake department (was Never good even when I bought it 10 years ago), it needed Pads & Shoes, and all the rubber hoses where crap, and one rear drum was starting to show signs of a Slave Cylinder starting to leak. Turns out that the slave leaking was due to the last person installing one piston cup the wrong way around (both where facing the same direction.

After replacing all the parts needed (including both rear E-brake cables, (the ones that connect to the rear drums), Bled all four corners, in the correct sequence (Pass Rear, Drivers Rear, Pass Front, Drivers front, brakes where still spongy (Better, but not great), Did some research into this, and here is the solution.

These Fords of this era use RABS (I) or (II) (1 or 2) and there is a thing under the drivers foot-well, on the inside of the frame rail called an HCU (Hydraulic Control Unit) which is controlled by the RABS computer (NOT the ECM) the RABS is one of 2 places, behind the glove-box, OR above the fuse panel left and above the Brake Pedal.

The HCU is a Fluid Accumulator, it will close the port to the rear brakes if needed (so the rear end doesn't fish out to the side when stopping, AND/OR do the "auto tap, tap, tap, thing like modern ABS does, however, one does NOT feel it being done in the brake pedal, like newer ABS systems.

The HCU can develop an air bubble (just like the rest of the hydraulic brake system can...) SO, to fix the spongy brakes...........

IN THIS EXACT sequence... (TO THE LETTER)

make sure rear brake shoes are correctly adjusted (Tighten adjusters till firm, then back off 1 full turn)
Use a container (with a fitting lid, a plastic bottle with a cap, OR a dog treats container with a screw on lid, (You get the idea) make a hole in the cap or lid large enough to accept a rubber hose somewhat firmly (you want the bottom of the hose to stay in a small amount of brake fluid (preferably new) place the BOX end of a wrench on the bleed fitting (wheels are 3/8", HCU is 5/16") and attach the hose to the nib, on the bleeder, open the bleeder screw about 1/8 to 1/4 of one turn, pump the brakes once or twice, HAS the fluid level in the reservoir under the hood gone down? if so, top it up with NEW, CLEAN (From a jug with a closed cap) brake fluid. KEEP the RESERVOIR as full as you can (And keep it full during the bleed process), if it goes EMPTY, you will have to start the ENTIRE Process ALL OVER AGAIN !! once there are no air bubbles, tighen the bleed screw and move on to the next item on the list, and repeat, do ALL 5 points, IN the EXACT SEQUENCE.... (HCU is after rears, BUT before fronts).

BLEED the ENTIRE brake system in the following order, Passengers rear, Drivers Rear, HCU the bleed screw is a 5/16 wrench, Passengers Front, Drivers Front.

Move the container to each wheel one at a time, the HCU is done exactly the same as a wheel, There should NO air Bubbles flowing into the container at any bleed port, if the system is bled correctly.

Brake feel 100%,

P.S. I've seen some videos on you tube, about people calling it the RABS, and doing strange things like removing the end cap, and changing the entire unit, when all it needed was to be bled...... Cheers !

Greg
 
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19Walt93

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My credo
If you don't have time to do it right will you have time to do it over?
Or you can use a scan tool to put it in bleed mode per the manual.
 

a31ford

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For OBD-II systems ? never heard of one for OBD-II
 

franklin2

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Or you can bypass that whole mess with a line coupler. What are you going to do when the electronic module goes bad? I bet it's not cheap if you can even find it.
 


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