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Jerry
Jerry, Auto Mechanic
Category: Ford
Satisfied Customers: 2948
Experience:  Mechanic with over 30 years experience with N.Y.P.D. fleet service division
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1990 Ford F350 4x4 has spongy pedal. new front brakes, lines,hoses,

Customer Question

1990 Ford F350 4x4 has spongy pedal. new front brakes, lines,hoses, calipers, master cylinder, new drums and new rear brakes adjusted. Still a spongy pedal with no air at any bleeders. Anti lock brake light is on. One flash when the switch is turned on and then it stays on. Any ideas? Will the anti lock brake system cause a spongy pedal?
Submitted: 5 years ago.
Category: Ford
Expert:  Jerry replied 5 years ago.

Hi the brake valve is a common cause of a sinking pedal on your model truck. I have replaced many of the valves for this problem. Here is an article that describes the problem and how the manufacturer recommends it be testedI have and alternate method that I leared at a brake clic some years ago. It requires a spare end cap, to use for testing,it has a small 1/8" hole drilled in it. I remove the end plug on the truck and install the test cap.I insert a rod in the hole until let it bottoms out,then apply the brakes,if the rod moves,it indicates the valve is bypassing internally and needs to be replaced.

Kelsey-Hayes rear wheel antilock (RWAL) systems have been gotten a bum rap in recent years. The RWAL system on 1991-96 Chevy S-10 and S-15 pickups, Chevy Blazer, GMC Jimmy, 1992-95 Chevy/GMC Suburban and 1990-95 Chevy Astros have been the subject of numerous "investigative reports" by various news media, the target of a class action lawsuit (dismissed in August '87) and an NHTSA investigation which found nothing (in spite of having received more than 7,000 complaints including 1,600 accidents and more than 500 injuries!).

The Kelsey-Hayes rear wheel antilock brake system was first used by Ford in 1987 on F series trucks, and was later added to the Ford Ranger, Bronco, Bronco II, Explorer, Aerostar and Econoline vans. Ford calls their version of Kelsey-Hayes EBC2 system "RABS" for Rear-wheel Antilock Brake System."

The GM RWAL version is found on '88 and later "C" and "K" full-size pickups, "S" and "T" series pickups, some "S" series Blazers, '89 and up Astro minivans, '90 to '92 "R" and "V" series light trucks and "G" series vans.

Dodge has also used the Kelsey-Hayes RWAL system since '89 on its "D" and "W" 150/350, Dakota and Ram pickups. Geo, Isuzu, Mazda, Nissan and Subaru have used the system since 1991.

Considering how many Ford, Chevy, GMC and Dodge trucks have the Kelsey-Hayes rear wheel antilock brake system, it's not surprising that a certain number of these vehicles would experience some kind of problem during their lifetime. NHTSA says there's no inherent defect in the system, so any failures that occur are the result of normal service conditions.

Pedal problems

One of the most unnerving failures that can occur with this system is the loss of pedal when braking. The problem may feel like a bad master cylinder, but it may not be the master cylinder. The real problem may be a bad Electro Hydraulic (EH) valve in the rear wheel antilock brake system.

 

Kelsey_hayes RWAL rear wheel   antilock brake hydraulic valve If a small piece of dirt or rust gets into the unit, it may prevent the dump valve inside the EH valve from closing. The dump valve will then leak fluid into the accumulator when the brakes are applied. The misrouted fluid allows the pedal to drop, and the pedal may go all the way to the floor without applying the brakes. No ABS warning light or fault code will be found either because the limited diagnostics on this system can't tell if the dump valve is fully closed or not.

Wagner Brakes recommends the following procedure to find out if the problem is a bad master cylinder or a leaky EH valve in the RWAL system. To rule out a bad master cylinder, disconnect the rear brake line at the master cylinder and install a plug to block off the port. Have an assistant depress the brake pedal about an inch to purge any air from the outlet, then tighten the plug while the assistant holds the pedal in this position. After tightening the plug, continue to apply pressure to the pedal to prevent damage to the primary cup in the master cylinder as the cup moved across the vent port.

If the pedal holds and no longer drops, it isn't the master cylinder that's causing the problem.

Reconnect the brake line to the master cylinder and block off the outlet port on the EH valve. Then apply pressure to the brake pedal again to see if the pedal drops. If the pedal goes down, the EH valve is leaking fluid into the accumulator. The EH valve needs to be replaced.

It's important to note that one of the underlying causes of EH valve failure is moisture-contaminated brake fluid. If the fluid is more than a couple years old, it may contain a lot of moisture. GM trucks do not have a recommended service interval for brake fluid, but most experts say that flushing the brake lines every couple of years for preventative maintenance can greatly reduce the risk of internal corrosion inside the brake lines and EH valve. But most people totally ignore their brakes until something goes wrong. So the best you can do is flush the system and replace the old fluid with new when the EH valve is replaced -- then recommend a fluid change every two years to prevent a repeat occurrence.

Air trapped in the EH valve can be another source of trouble with the RWAL system. Some RWAL EH valves (the smaller ones) do not have a bleeder screw, which makes the unit hard to bleed if air gets into the lines. The trick here is to loosen the brake line connections at the valve to vent air when bleeding the brakes.

Brakes can be bled in the usual way manually or with pressure equipment. The wheel bleeding sequence is RR, LR, RF, LF. If a pressure bleeder is used, the combination valve must be held open.

Customer: replied 5 years ago.
Just so confirm what you said, the ABS valve (RABS valve on Fords) is the unit attached to the frame w/ 2 inlets and an electrical connector? What is the process of bleeding this in conjunction with the other cylinders (wheel cylinders and calipers). You info has been helpful and I will try bleeding this first and if that don't work out I will test it and replace is required. Once I hear back from you I will accept this so you'll get paid. Thanks Jerry
Expert:  Jerry replied 5 years ago.

Hi,The valve is the part with the the 2 lines and the electrical connecter.If you had the problem before doing any work,I would not bleive air was the problem. If it started sinking after replacing the rear wheel cylindres or reak brake hose,you may have some air in the rear brake circuit that needs to be bleed. If the original problem was a sinking pedal,then I would feel confthat replacing the valve,and bledind the rear brakes will cure the sinking pedal.

. Some RWAL EH valves (the smaller ones) do not have a bleeder screw, which makes the unit hard to bleed if air gets into the lines. The trick here is to loosen the brake line connections at the valve to vent air when bleeding the brakes.

Brakes can be bled in the usual way manually . The wheel bleeding sequence is RR, LR, RF, LF. If a pressure bleeder is used, the combination valve must be held open.

Jerry, Auto Mechanic
Category: Ford
Satisfied Customers: 2948
Experience: Mechanic with over 30 years experience with N.Y.P.D. fleet service division
Jerry and 9 other Ford Specialists are ready to help you
Customer: replied 5 years ago.
<p>I have ordered a valve and will try your suggestions when it arrives. I plugged off the master cylinder export to the rear brakes as you suggested. The pedal did not go to the floor. If I understand you correctly this means the master cylinder is ok. How do I contact you in a few days if this doesn't cure the problem? Thank you for your help.</p><p>Greg</p>
Expert:  Jerry replied 5 years ago.
Hello Greg,if the master cylinder was defective,still bypassing internally,you would have still had a sinking pedal. Actually the best way to bleed and test a master cylinder is to block off both ports,fill and stoke slowly you should get a rock hard pedal if it is ok.Solves the mess of connecting short lines back to the reservoir when installing and blleding a new master cylinder.. If you need to come back to this question,it will be open for you,don't open a new one.
Customer: replied 5 years ago.
<p>Thanks you Gerry</p><p> </p><p>I'm a deputy sheriff in Maine (24 year vetran) mechanics is a side line/hobby and what I did before joining the force</p>
Expert:  Jerry replied 5 years ago.
I am glad to be able to help you out with the brakes. When this system first came out, we replaced a few master cylinders more then once until the valve problem was discovered. I believe the valve will fix the problem,Good luck,Jerry.

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Jerry
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