Brake Pedal soft
i ain't rite
Joined: Mar 2005
Posts: 65,548
Likes: 5,589
From: Marlboro Mental Hospital.
i made small cuts and cleaned it often.
since i only needed to clear 1/16 inch, i took half off the master and half off the booster.
1/32th of an inch can almost be done with rough sand paper. it is only 31 thousands of an inch
since i only needed to clear 1/16 inch, i took half off the master and half off the booster.
1/32th of an inch can almost be done with rough sand paper. it is only 31 thousands of an inch
i ain't rite
Joined: Mar 2005
Posts: 65,548
Likes: 5,589
From: Marlboro Mental Hospital.
i did the conversion on those trucks 20+ years go and used NAPA masters.
all my aftermarket parts are from NAPA, i have a very good store a few miles away from me with people that actually know what they are doing. .
all my aftermarket parts are from NAPA, i have a very good store a few miles away from me with people that actually know what they are doing. .
i ain't rite
Joined: Mar 2005
Posts: 65,548
Likes: 5,589
From: Marlboro Mental Hospital.
no idea. i only did the 88 to 91 trucks. i only has the 92 F-350 for 2 years before i sold it, and never messed with the brakes.
Senior User
Joined: Jun 2014
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Spongy pedal generally is air in the lines, or a leaking seal in one of the two brake circuits. When the tech did the brakes, compressing the caliper may have pushed some u-cup wear material upstream causing one circuit to bleed down.
First step IMO would be to bleed. Second would be to reseal or replace the master cylinder and rebleed.
I must be missing something with the SD master thing here. Larger bore MC would exert less force on the brakes from the same pedal force wouldn't it? I mean larger bore means more force to move the same fluid, but less pedal travel to make it happen.
First step IMO would be to bleed. Second would be to reseal or replace the master cylinder and rebleed.
I must be missing something with the SD master thing here. Larger bore MC would exert less force on the brakes from the same pedal force wouldn't it? I mean larger bore means more force to move the same fluid, but less pedal travel to make it happen.
Laughing Gas
Joined: May 2009
Posts: 854
Likes: 49
From: Maine
The OP probably has an actual fault, in addition to the stock design flaw.
i ain't rite
Joined: Mar 2005
Posts: 65,548
Likes: 5,589
From: Marlboro Mental Hospital.
a larger bore will move more fluid with the same amount of pressure, resulting in less pedal travel
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Senior User
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Sorry, but that ^ is partially incorrect. As a rule, a larger bore on the master end will move more fluid, but at a cost of more force required to provide the same fluid pressure.
Not to say it doesn't work better, but benefits from bore size are offset by drawbacks.
Is there a known design flaw with them? I've never had the old Ford one apart. I have seen design flaws though. For instance Suzuki Sidekicks use a master that has the seals on the housing instead of the piston, so even when brand new and perfect they have a tendency to leak down with gentle but consistent pedal pressure.
I just assumed they are conventional u-cups on sprung piston inside honed iron bore. Are they not?
Not to say it doesn't work better, but benefits from bore size are offset by drawbacks.
Is there a known design flaw with them? I've never had the old Ford one apart. I have seen design flaws though. For instance Suzuki Sidekicks use a master that has the seals on the housing instead of the piston, so even when brand new and perfect they have a tendency to leak down with gentle but consistent pedal pressure.
I just assumed they are conventional u-cups on sprung piston inside honed iron bore. Are they not?
New User
Joined: Sep 2005
Posts: 13
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From: Acworth, GA
Need help with diagnosis
I'm a firemean. Went in to work Sat morning no problem.... Truck sat in lot for 24 hours. Leaving the station this morning brake pedal was soft and almost didn't stop truck before entering road from station. Checked brake fluid and vacuum pump, full and functioning...
What else do I need to check? There were no warnings of this
What else do I need to check? There were no warnings of this
Laughing Gas
Joined: May 2009
Posts: 854
Likes: 49
From: Maine
No recent brake work, right?
No loss of fluid, right?
I would take a look at the rubber brake hoses (three of them) while applying the brakes to make sure they are not bulging. After that, I say internal master cylinder leak.
Roy
No loss of fluid, right?
I would take a look at the rubber brake hoses (three of them) while applying the brakes to make sure they are not bulging. After that, I say internal master cylinder leak.
Roy
New User
Joined: Sep 2005
Posts: 13
Likes: 0
From: Acworth, GA
I'll inspect the hoses. Thanks...
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