Brake pedal goes almost all the way to the floor.

[BroncoJoe19]

Today we are getting hammered with a two foot snow fall. I decided to bring the '90 bronco home. It started right up after sitting for about 8-10 weeks.

I stopped for gas, and then to Dunkin Donuts for coffee, just in case I got stuck in traffic. The parking lot was on a pretty steep incline, but in 4x4 it was not a problem. When I backed out, my brake pedal went nearly to the floor, before it stopped.

I was in a blizzard, wouldn't be going over 30 mph, and still had my cable operated E-brake, so I continued on.

I stopped at a supermarket near home and popped the hood. The brake fuid in the master cylinder was on the low side, so I bought a container of DOT 3, and put about 9 ounces in.

Both my RearABS light, and RED Brake light, came on.

The engine is running fine, and idling fine, so I don't suspect a failed vacuum booster, (also red brake lights mean hydrolic system). I suspect one of two things,

1. with low fluid, and on a steep grade, I pumped air into the system when I backed out of Dunklin Donuts.

2. I have a failed master cylinder

3. There is a reason for low fluid level, (like maybe a leak somewhere)

Questions:

1. Would a failed master cylinder cause the rear abs light to come on?

2. If I replace the master tomorrow, the rebuilt one should be bench bled. How does one do this?

3. If I just let air into the system, through the master cylinder, how do I bleed it out? Will it just work its way to the top?

 

[Seabronc]

Today we are getting hammered with a two foot snow fall. I decided to bring the '90 bronco home. It started right up after sitting for about 8-10 weeks.

I stopped for gas, and then to Dunkin Donuts for coffee, just in case I got stuck in traffic. The parking lot was on a pretty steep incline, but in 4x4 it was not a problem. When I backed out, my brake pedal went nearly to the floor, before it stopped.

I was in a blizzard, wouldn't be going over 30 mph, and still had my cable operated E-brake, so I continued on.

I stopped at a supermarket near home and popped the hood. The brake fluid in the master cylinder was on the low side, so I bought a container of DOT 3, and put about 9 ounces in.

Both my RearABS light, and RED Brake light, came on.

The engine is running fine, and idling fine, so I don't suspect a failed vacuum booster, (also red brake lights mean hydrolic system). I suspect one of two things,

1. with low fluid, and on a steep grade, I pumped air into the system when I backed out of Dunklin Donuts.

2. I have a failed master cylinder

3. There is a reason for low fluid level, (like maybe a leak somewhere)

Questions:

1. Would a failed master cylinder cause the rear abs light to come on?

2. If I replace the master tomorrow, the rebuilt one should be bench bled. How does one do this?

3. If I just let air into the system, through the master cylinder, how do I bleed it out? Will it just work its way to the top?

Joe,

Sounds like a leak in the rear brake line. Could be anywhere from the MC back.

If you do have to change the MC, definitely bench bleed it. You need a way to plug off the out ports while doing that. I have an old set fittings with a Short stub of pinched off line for that purpose. Anyway, put it in a vise, plug off the ports, fill it with fluid, and then use something like a large screwdriver to press in on the piston, (careful the process will squirt fluid up in the air for a while so just keep the cap setting on top). At first you will be able to push the piston in about a 1/2 inch. Keep repeating the process, (press in and hold, then relax for 10 to 15 seconds, if you repeat it too fast you will create a zillion bubbles in the fluid), over and over. Shortly it will only go in less than 1/4 inch, (you are not done yet). Watch the rear reservoir for air bubbles, keep up the process until you don't get a single bubble and then do it a few more times to make sure.

When you are sure it is completed you can then mount it on the booster. Get yourself a large can of brake fluid and if you can find one, a brake bleeding kit to catch the fluid in. After mounting the MC, you will have to bleed all air out of the system. Start with the furthest brake cylinder (Right rear), bleed it till you are sure there is no more air in that line. Then go the the (Left rear) and repeat the same. From there to the (Front right and then the front left).

Don't reuse the old fluid you are bleeding out.

The answer to Number 3 is the same as above without the MC replacement. I don't think I left anything out, but if I did, someone please jump in.

Also, it is possible if the fluid was low enough that you introduced air then, but then why was it low? Possibly badly worn pads or shoes? A leak?

Good luck,

>-

 

[BroncoJoe19]

Thanks Fred,

Two years ago I replaced the pads and calipers, last year the rear shoes and wheel cylinders. Not enough miles on her for wear, but the brake hoses are probably as old as the truck. Oh... and it was parked near an oak tree and a zillion squirrels.

They had a party on the fuel line to my camper a few years ago... so I guess anything is possible. OTOH... If I didn't refill the reservoir after replacing the rear cylinders, that could also explain low fluid, but I doubt it. I agree... most likely a leak.

 

[miesk5]

yo Joe,

I just lost a page full when the power took a dive, again.

So here is a condensed version with just the pertinent info Links

First, RABS-II Troubleshooting & Some info on symptoms;



by Ford via Stebe83

Flashout Codes

Whenever the yellow REAR ABS light comes on during normal operation, a flashout code may be obtained to aid in problem diagnosis. If the vehicle is shut off before the code is read from a RABS-I module, the code will be lost. In some cases, the code may reappear when the vehicle is restarted. In other cases, the vehicle may have to be driven to reproduce the problem and, if the problem was associated with an intermittent condition, it may be difficult to reproduce. Therefore, whenever possible, it is recommended that the code be read before the vehicle is shut off.

WARNING: PLACE BLOCKS BEHIND THE REAR WHEELS AND IN FRONT OF THE FRONT WHEELS TO PREVENT THE VEHICLE FROM MOVING WHILE THE FLASHOUT CODE IS BEING TAKEN.

NOTE: If the red BRAKE light is also on, due to a grounding of the fluid level circuit (perhaps low brake fluid), no flashout code will be flashed and the REAR ABS light will remain on steadily.

NOTE: If there is more than one system fault only the first recognized flashout code may be obtained.

Obtaining the Flashout Code

A flashout code may be obtained only when the yellow REAR ABS light is on. No code will be flashed if the system is OK. There are certain faults (those associated with the fluid level switch or loss of power to the module) that will cause the system to be deactivated and the REAR ABS light to be illuminated, but will not provide a diagnostic flashout code.

Before obtaining the flashout code, drive the vehicle to a level area, and place the shift lever in PARK for automatic transmissions and NEUTRAL for manual transmissions.

Notice whether the red BRAKE light is on or not (for future reference) and then apply the parking brake.

Keep the ignition key in the ON position so that the code will not be lost.

WARNING: PLACE BLOCKS BEHIND THE REAR WHEELS AND IN FRONT OF THE FRONT WHEELS TO PREVENT THE VEHICLE FROM MOVING WHILE THE FLASHOUT CODE IS BEING TAKEN.

To obtain the flashout code, locate the RABS diagnostic connector (with the Bk/Or wire), and attach a jumper wire to it. Momentarily ground it to the chassis. When the ground is made and then broken, the REAR ABS light should begin to flash.

NOTE: If the red BRAKE light was on (as noticed before the parking brake was applied), the problem may be with the low fluid level circuit and, in this case, no flashout code will be flashed and the light will remain on steadily.

The code consists of a number of short flashes and ends with a long flash. Count the short flashes and include the following long flash in the count to obtain the code number. For example, three short flashes followed by one long flash indicates Flashout Code Four. The code will continue to repeat itself until the key is turned off. It is recommended that the code be verified by reading it several times. In addition, the first code flashed may be too short because it may have been started in the middle. It should be ignored.

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RABS-II Components

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RABS-II Codes

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RABS Valve pic - this is referred to as da Electro Hydraulic (EH) valve in next article

--

Chilton has the complete test and I lost all the C&P when power blew; I believe you have a Haynes or Chilton. El Kabong tried to C&P it all to FSB but never finished it; Jem did so too--->RABS Codes 2, 4, 5 & 9 (incomplete) Pin-Point Tests in an 88; & Self Test; Click NEXT to view all pages; miesk5 Note; for all Resistance tests, battery needs to be disconnected; remove Negative cable at battery: by Jem270 at SuperMotors.net

-------

Now to the symptoms;

RABS - KELSEY-HAYES RABS Overview (87-92), Faults & Troubleshooting (Rear-wheel, Nonintegral)- 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." Source: by Larry C CarleySoftware.com via aa1car.com

Excerpt;

"...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. 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.."

--

Next 2 reiterate above.

RABS Fading Brake Pedal in 87-92 Source: by Jeff B at Indentfix via asashop.orgRABS Low or Sinking Pedal, Ford; "...Contamination may be holding the dump valve portion of the Anti- Lock Braking System open, allowing the brake fluid to bypass into the accumulator and create a low or sinking brake pedal..." Source: by CARDONE® cardone.com

 

[BroncoJoe19]

Thanks guys.

Yesterday, I topped off the reservoir, and drove a mile home. This morning took my son to work a mile away, and popped the hood. The reservoir is only 1/3rd full, so I definitely have a leak. Unfortunately for me, my mechanic is too busy to take it in, so I may tackle it myself. OTOH... I may wait a week and let him take care of it.

 

[BroncoJoe19]

Well, it looks like the bronco is going to get to be the first one in the driveway for a couple of weeks.

I crawled underneath and took a quick look. There is brake fluid on the frame rail near the left rear rubber brake line. I couldn't easily see where it was coming from. I assume that it is the rubber hose.

I took it to the nearest shop for them to put it up on a lift, ID what part/s are needed, so they can order them and do it in the morning, or as soon as the parts come in. They didn't bring me into the garage to show me, but they claim that the metal fuel lines are all rotted out, and that they should all be replaced. A job that they won't do, because it may open a bag of worms.

I see that broncograveyeard has a set of metal lines for an '87. Are they the same for a '90?

Looking at that set, it would be quite challenging to bend your own, unless you are only going to do a couple.