Bronco 2 brake issue

  • 1988 FORD BRONCO
  • 6 CYL
  • 4WD
  • 139,000 MILES
1988 Ford Bronco 2 with 4 wheel drive, the trouble I am having is with the brakes. I can drive it for about 6 to 12 miles, then all the brakes lock up tight, and the pedal cant be moved. If I let it sit for about 20 minutes then it is fine for another 6 to 12 miles. Is this a bad brake booster or just vacuum? I did replace the master cylinder recently like 6 months ago but the trouble now has just started. Thank you
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have the same problem?
Tuesday, November 23rd, 2010 AT 1:39 AM

1 Reply

First, when the brakes lock up, unbolt the master cylinder just enough to move it away from the booster. 1/8" is plenty. If the brakes release, you either have a push rod that is out of adjustment, (some are not adjustable), or the brake light switch is misadjusted and holding the pedal down a little. Ford used to use a weird type of switch that couldn't cause that; don't know if they still are using that design.

As an alternative, crack the steel lines open at the master cylinder. If fluid squirts out and the brakes release, it's the master cylinder that is holding the pressure. A common cause is brake fluid contaminated with petroleum product. That will cause the lip seals to swell and grow past the fluid return ports, blocking them off. In that case, cracking the lines will release the brakes but unbolting the master cylinder will not.

If the fluid is contaminated, the rubber seal under the reservoir cap will be ballooned up and mushy. The contamination can come from pushing that seal back into the cap when you have grease on your fingers. The ONLY proper repair for contaminated fluid is to replace every rubber part, including metal parts containing rubber seals and o-rings, and to flush and dry the steel lines.

If the brakes do not release when you crack the lines open at the master cylinder, open the bleeder screws on the front calipers and see if that works. If it does, look for a metal bracket crimped around the rubber brake hose. Rust can build up inside that crimp and constrict the hose. That will affect just one wheel first, not both, but it will cause a high and hard pedal.

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Tuesday, November 23rd, 2010 AT 2:47 AM

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