1987 Bronco xlt 302 spongy brakes

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Cr8or2

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I have an 87 Bronco XLT that is having some brake issues. About 2 months ago I had to replace my rear axle bearings and wheel cylinders, when I did I decided to replace both drum assemblys which eventually lead to me replacing the front calipers. After all that work my brakes were super soft, I have bled them 5 or 6 times using both gravity and traditional methods I have also replaced the master cylinder (I took the truck to a mechanic and that's what they said it was). The brakes are still soft, I have been working on the same problem for what seems like forever. I have watched countless YouTube videos and read a ton of articles on the subject and many say the problem is the master cylinder or the brake booster, I just recently found out about the possibility of the problem being the ABS module as well. I am out of patience, so I turn to you...the Bronco people of the internet, How do I tell whether the brake booster or the ABS module is the problem?

 

miesk5

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Yo Cr,

Welcome

Lets see if there any ABS codes;

RABS Self Test & Diagnosis Codes; "...The possible flashout codes are listed and explained in the Flash Codes Chart. Note that Codes 1 and 16 are not used.

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. RABS II modules have been designed with Keep Alive Memory to preserve stored codes during key-off, and are to be used to service all prior year RABS I systems, except for 1987 and 1988 Bronco II vehicles.

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.

To obtain the flashout code, locate the RABS diagnostic connector (with the Blackk/Orange wire), and attach a jumper wire to it.

RABS Self Test Diagnostic Connector Location pic in an 88; "...it is next to the brake pedal which this is a picture of and is C111; It has the one wire that is black/orange.."  Source: by Jem270

Momentarily ground it to the chassis. When the ground is made and then broken, the REAR ABS light should begin to flash. NOTE:

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..."

Post codes here.

Plus;

  • Hard or Soft Brake Pedal
Stuck shut isolation valve (hard).  

    Leaky dump valve (soft).

  Leaky isolation valve during RABS stop (soft).

  Stoplamps always on while driving.

  Hydraulic leak in rear brake tube or rear brake hose, fitting, brake master cylinder, rear wheel cylinder, or front disc brake caliper.

  Air in brake system.  

    Brake related concern:Little or no vacuum boost. Check vacuum hose to Booster.  Get a vacuum gauge and test vacuum  level, shoukd have steadt needle @ leadt at 15in

Stuck or inoperative rear wheel cylinder or front disc brake caliper.

Pinched or crimped rear brake tube or rear brake hose.

  • Brake master cylinder or power brake booster dash unit mounting loose.
  • TIGHTEN nuts and bolts to specifications
 
  • Front or rear disc brake caliper attachment loose.
  • REPLACE or TIGHTEN as required.
 
  • Worn or damaged self-adjusters.
  • REMOVE brake drum and CHECK rear brake shoe and lining for proper adjustment. REPLACE brake shoe adjusting lever. 
 
  • Brake pedal or support improperly mounted.

   damaged brake linings.

 
  • Brake drum out-of-round or front or rear disc brake rotors with excessive runout.
GL!

Al

 

Rons beast

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Hey Cr,

If the checks M5 advised don't correct the problem you may have a defective new master cylinder.  The quality of units has dropped dramatically recently.  It used to be one in 50 or turned out defective.  I recently had 2 out of 3 that would not hold pressure.  In both cases the supplier reimbursed me and didn't even ask for the defective parts back. A sign that they know the parts are poorly made.  I avoid anything from China and most of the part store brands. I have had a TRW unit that was defective too.  Just remember to properly bench bleed any master before installation.

Good Luck. 

 
OP
OP
C

Cr8or2

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The RABS light comes on when I start up the truck but doesn't stay on more then a few seconds and doesn't come on while driving. I am going to check if the rear shoes are adjusted properly as well due to that kinda escaping my mind for some reason.

Sorry for not replying sooner I have been super busy with work so this weekend is going to be the first time I get to work on it in awhile.

 
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Skitter302

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In some cases the Proportioning Valve can be a problem. It could be  made worse by flushing the brakes making the seals in it sloppy.

 

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