Breaks?

[cd75hors]

I have a 75' Bronco with drums all the way around. Last time I took it out the breaks got rock hard on it. When I was driving down roads and what not the breaks were fine. But a little after getting on the trail, and slow speeds, the breaks hardened up to the point they weren't there. I could practically stand on the pedal. Then a few minutes after I got off the trail and back on the road they were back to normal, no problems. I replaced the master cylinder a while back and bled it out and what not. I have aftermarket exhaust headers, could the heat from them be effect the master cylinder and break lines that are right above? Any ideas?

[Hypoid]

But a little after getting on the trail, and slow speeds, the breaks hardened up to the point they weren't there. I could practically stand on the pedal.
The pedal does not go to the floor? Air in the lines, or boiling the fluid would cause the pedal to go to the floor.

Are these power brakes with the vacuum booster? Sounds like you are losing the power assist from the booster.

[cd75hors]

Actually they are not power breaks, no booster, just the master cylinder. I'm planning on getting a break booster hoping it will help. However, hasn't done this before. Just gets stiffer than hell.

[Hypoid]

Hmmm, the only time I've lost braking and kept a hard pedal was when I got the brake drums wet.

[cd75hors]

Hmm... I didn't think about that. There was quite a bit of water involved that day. I need to get it on a trail again. I don't run it that often and I've been a little hesitant to because of the whole "no breaks" thing. I remember coming down a long steep hill without the breaks. All was well until the T-case popped out of gear. That one renewed my passenger's faith in Jesus.

If there are any other ideas, please throw them out.

[84broncoII]

I have had a condition where My brakes got real touchy like locking up with even the slightest touch caused by a leaky wheel cylinder ,The master cylinder gets a little low and then touchy brakes .I also had a almost locking brake condition due to air or contaminatoin in the lines when the brakes got hot the water air would boil inside the lines and lock up the peddal also made the brakes real touchy had a bad rotor one time that over heated the brake fluid near that wheel did the same thing .I had a drum that needed to be turned but it was to close to specs for the guy to turn i couldnt get a drum so drove on it anywhay and the same thing happened the surface was too rough and cused too much friction and heat on that brake antd it would overheat the fluid and lock the system

[Doug F]

I am thinking you had the brakes over pumped. Can't say that I have had it equal no brakes, but the rock-hard pedal feel...
Did you look it up in your service manual?

[shawns 64 F100]

There are several issues you could have with anything being from wet brake shoes to heat fade. Manual drum brakes, (no power) the culprit sounds like wet shoes. I know this from years of driving my 67 mustang (4 wheel drums with no power assist) usually letting the shoes dry out after fording a creek will help. I used to just ride the pedal to warm them up so they would dry out from heat.

Heat fade is when the brakes are hot enough that the friction transfer becomes "ineffective" so to speak. If your driving down the highway for a while then come off the highway on the off ramp and slammed on em pretty hard and then just hit a trail, you could have heat fade.

If you need any brake work let me know I can get that for you at a reasonable price. :thumbsup:

[84broncoII]

Really dirty brake fluid in the master cylinder like black is usually contaminated fluid cn cause braking problems like locking up
I corected the problem once with no tools at a safeway parking lot went inside got Me a turky baster and some new fluid I simply sucked out the dirty fuid from the master and put in new fluid .

[shawns 64 F100]

Contaminated brake fluid is a VERY serious issue. You can not just bleed your system out. you have to do a denatured alcohol flush of the entire system. All components that have rubber seals or hydraulic control valves have to be replaced. Contaminated is when the wrong type of fluid (generally it is petroleum based products such as engine oil, power steering fluid etc etc). Brake fluid also accumulates moisture naturally. It is best to have a properly working brake system with a well sealed master cylinder cap to prevent moisture accumulation.

Your brake hydraulic fluid should look like a light beer or apple juice. The dark coloration you see after years of not being bleed out as a preventative maintenance is the rubber seal deterioration. When your fluid is at this point there will be a lot of sediment in the calipers master cylinder and wheel cylinders. When the system ages and the rubber components deteriorate it becomes tiny particles that float throughout the brake system. Those tiny particles work as a lapping compound and will grind through the other components until catastrophic failure of a brake component occurs. Generally the wheel cylinders and brake calipers will begin to stick, then leak, then if it ages long enough the master cylinder itself will fail.

Brake fluid should be bleed out on a regular basis. I suggest every 12 months or 12,000 miles as a preventative maintenance. Justl ike changing your engine oil or transmission fluid.