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Help diagnosing air in brakes

859 views 5 replies 4 participants last post by  Arisley 
#1 ·
Truck is a 99.5 F-250 Super Duty Diesel. Has 160K miles. Stock master, Aftermarket flex lines, bleeders are Russell Speed Bleeders.

I have been having a continuing issue with a mushy brake pedal, pedal firmness changes all the time, sometimes its firm, other times its soft. I figured it was just air in the system. I got around to bleeding the brakes a few weeks ago. Didn't have any issues until I got to the right front wheel, where I found air in the lines, it was mainly small bubbles nothing to be concerned about. I ran out of brake fluid before I could finish completely bleeding that wheel so I had to stop.

I tried bleeding the brakes again today, didn’t have any issues until I got to the front. This time both front wheels had air in the lines as I bled them, never seemed to get any better or worse as I bled. Some decent sized bubbles, but really just a lot of small bubbles suspended in the break fluid. I went through about ¼ a gallon of fluid doing the bleeding today.

I never let the master cylinder get below 1/2 full, so I doubt I introduced air into the system. I checked around and didn’t see any evidence of fluid weeping from the distribution blocks, lines or master.

Anyone have any ideas? Do I have a bad master cylinder? Any help/comments/suggestions are appreciated.

Thanks,
Dave
 
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#3 ·
had similar problems on my 01 ended up being front calipers on both sides. replaced once with fords 40000 later same thing went with napa no problem yet only been 20000 tho
 
#5 ·
had a small leak but it was hard to see until i had it all taken apart. second time had same symptom no leak, squishy pedal bled and bled it would work fine for awhile then go to hell so i just replaced second time. i think they are only like 70 apiece. i had checked all connections for leaks changed fluid with no luck so i took apart front end and found a small seapage around piston seals on both sides. not sure how it took in enough air to give me problems but it did
 
#6 ·
Any air is a problem. Even a tiny bit. Air is a lousy hydraulic medium. It also will cause the brake fluid to heat up.
 
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