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Discussion Starter · #1 · (Edited)
So here I am cruising to work tired and half asleep. Go to slow down turn into my job and the peddle is floored but wouldn’t you know it just kept on cruising like the truck had its own agenda. Checked the lines and appears to have no cracks or holes. Brakes are nearly new. Rotors are fine. Fluid is full. It’s just like the brakes are on vacation and have decided not to clock in this year. Anyone have any advice what I should do or check next before I go pull my life savings and 401k out to get a brake check at the local shop? Thanks in advance.

edit: 89 f250 7.5l c4 3 speed
 

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Discussion Starter · #6 ·
By any chance have you mixed synthetic and petroleum based fluids when adding to the system? Will cause really weird brake response. If so, the entire system needs to be flushed with the correct type for your vehicle until all of it has been replaced.
Bought it off my dad and he is pretty good about all that stuff. Still I could ask and make sure
 

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Discussion Starter · #8 ·
Check under dash at brake pedal for any sign of brake fluid at master cylinder push rod . If so , master cyl will be pulling in air and need replaced
Ok I’ll check that when I get off work.
If it’s the caliper wouldn’t it leak all over the wheel. I ruled out the caliper because I didn’t see any leaks anywhere
 

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I would start with replacing your master cylinder if you haven't found any leaks around the calipers, lines, wheel cylinders. New way for you to start bleeding brakes which is a hell of a lot better than the old fashioned way of having someone pump up the pedal while you crack open the bleeder. Get a plastic clear bottle and fill it half way up with brake fluid. Find about a 2 Ft piece of hose that fits snuggly over the bleeder nipple. Put the hose on the bleeder nipple, the other end in the brake fluid in the bottle. Crack open the bleeder and have someone gently pump the brake pedal and you'll see bubbles going into the bottles. When all the bubbles stop and only fluid is going through the line tighten the bleeder. Do all four wheels this way. Best trick I've ever been taught
 

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I assume that you are not losing fluid. This is an 89 F250 7.5L? BTW, that can't be a C4, must be a C6. How many miles? What section of the country? Does it have either Rear Antilock Brakes or full 4 Wheel Antilock Brakes?

Master cylinders can "bypass" when they wear out, causing this issue. They can be pumped up, but the issue will recur. It can be intermittent. In addition, the solenoid valves on the antilock brakes have springs that have been known to rust out and fail, causing the pedal to bottom. This is particularly true if the brake fluid has not been flushed and replaced. It is important to note that brake fluid is "hydroscopic" (absorbs water), especially the old type 3 fluid. Another possible issue is fluid boiling due to overheated brakes. This will also cause bottoming of the brakes. Overheating can be caused by a seized caliper, dragging, misadjusted drum brakes (set too tightly) failure of drum brake shoe return springs seized parking brake cables, etc.. So Bottom Line, change the master cylinder and carefully inspect the ABS,

Most US vehicles call for DOT3 Fluid. Most mechs believe that DOT4 can be used as an upgrade. DOT4 has a higher boiling point. The DOT 4 fluid is compatible with DOT3 systems. Synthetic DOT5 Fluid is NOT backwards compatible. There is a new designation, DOT5.1 which may be compatible with DOT3 and DOT 4.

I have a 91 Ford Aerostar that had the Bendix "cartridge" type master cylinder and Kelsey Hayes "RABS" Rear Antilock Brakes. My worst accident, I got cut off on the highway, lost brakes, swerved and lost control at 45 mph, hit or got hit by 2 cars and hit the Jersey barrier. Fortunately, and thank GOD no injuries to anyone else, but major damage to other driver's 1 year old car. The 3rd car left scene without stopping. I actually was able to save my Aerostar which otherwise would be totaled. After the accident, I found out that the RABS valve is known to fail in old, high mileage cars. At the time, my car was 23 years old with 187K city miles. I plumbed the RABS Valve out, and still had the issue. Replacing the Master Cylinder eventually resolved the issue. Interestingly, Ford stopped using that style cylinder and a "replacement kit" with a standard design Master Cylinder and proportioning valve was specified as a replacement.
 
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