I have a 1993 Ford F-350 dually with the 7.5 460 engine. My problem started one day with hearing a grinding noise very similar to front brakes metal to metal and it did it without pushing the brakes. Hard to pinpoint if it was coming from the rear or front but sounding like front brakes metal to metal I assumed that was my issue. I went to the store and just bought pads and new calipers and lol cause I'm assuming the worst with my luck. On the way home the Brie pedal goes to the floor and there is barely and brakes that work (luckily it's a manual transmission so I could downshift to slow down and get home a few miles away. I pull the front wheels and the front brakes have most of the bad left. The clippers were pretty nasty and felt a bit stiffer than they should when pushing piston in so I went ahead and replaced them and the pads. Get it all back together and still have the same issues with the brake pedal just going to the floor and brakes barely grab. So truck is 24 years old, has factory mastercylinder so I buy a new one and yes I bled it. After installing it and bench bleeding it I went around and made sure to bleed all the brakes. But the pedal is the same. So then I bled more and more and more because the pedal was the same like there is air in the system. I ran nearly a gallon of brake fluid through bleeding this thing. I read somewhere on here in a post that the abs hydraulic unit can cause these same issues with the pedal and I made sure it was bled. I read in the same post somewhere that you can pull the spring out of the unit and it would resolve the issue so I tried that but it is still the same and pedal just sinks to the floor. I ordered a new hydraulic control unit that will be in Friday some time anyways. The booster seems fine to me. I can not hear any vacuum leaks in the booster and sounds normal. A little more info about the brake pedal. I can get the brake pedal to firm up when the truck is off but as soon as I start the truck and try the pedal it just sinks to the floor. I don't see any leaks anywhere in the system and believe me several days under this thing this week I have exhausted myself looking for things. I'm stuck. Don't know what else to look for or know what else to try. Looking for any recommendations to help me find this problem so I can get it fixed. Oh I did test drive it to see if the grinding noise continued since replacing the calipers and pads and the grinding noise seems to be gone. Just a FYI.

 

i don't see where you have inspected the rear brakes at any point ... ?

 

I have not yet.

 

I'll see if I can find a place that does free brake inspections

 

it's easy enough to do yourself ... or are you outdoors in bad weather there ?

 

Chance of rain here plus I'm 3 months out of my 2nd back surgery and I'm also dealing with arthritis in my neck, both hands, both elbows, both knees and more. Stuff I have to deal with after being hit head on at 85mph because some jerk wanted to kill himself. I'm at a place right now that does free brake inspections. It'll save me a lot of physical pain.

 

Rear brakes are new including all hardware and they are in adjustment. No leaks back there either.

 

Just thinking out loud...

I had an old car once with similar symptoms. Turns out the previous owner had replaced some rusted brake lines. Where they spliced in a piece they used a compression style coupler instead of a flared type coupler.

It never leaked any fluid, but it did suck air back in. Must be a fine line between a crack big enough for air molecules and a crack big enough for brake fluid molecules.

After replacing the incorrect part with a more suitable part, the brakes worked great.


That was not an ABS vehicle, though.

 

I am really hoping it's not a hole in the metal line somewhere. I'll throw the abs hydraulic control unit on tomorrow when it comes in and I hope that fixes it. But if it doesn't I don't know what else to do cause I can't see leaks anywhere. I also did not see any metal lines that were spliced and repaired anywhere. It's still all original lines (metal ones). Truck only has 84,000 miles.

 

Did you check/adjust the push rod on the booster?

I had similar issues with my '94 F350 dually. Turned out to be multiple issues.

Here's the thread:

https://www.ford-trucks.com/forums/1...ir-thread.html

My rear brakes were afu and out of adjustment, the booster push rod was out of adjustment, and in the end I discovered that the booster itself was compromised.

Hope the input helps.

John

 

Ok. Update. I am still having issues. The same issues. The pedal does feel just a tad better after replacing the abs hydraulic unit. Only a tad. But looked at the ref brakes again and discovered some parts of the hardware kit in rear brakes were busted so replaced them with a new hardware kit which after making sure again brakes are adjusted the pedal is still the same. But now that same hardware kit is broken again on the rear driver side. So I'm puzzled. What in the world could be causing the hardware kit to break twice on the rear driver side?

 

What parts are breaking?

 

The spring on the front side about half way up. Short spring that's a bit thick.

 

Are you sure it's in the right spot? Backing plate and all that good, and you're 100% sure the rear is adjusted correctly?

 

yes I'm positive. It has been in 2 shops now and the brakes have been adjusted. They even tried adjusting them out far enough to where you can't even get the drums off and pedal still is spongy and goes to the floor.