brake issues again please help!
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Junior User
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brake issues again please help!
Hey guys have a f150 1978 4wd I've replaced master cylinder booster lines calipers pads and everything in between I still have hardly any pedal when a fire the truck up what do I do??
Moderator & parts slinger
Joined: Feb 2007
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From: S/W Missouri, Polk county
Did you "bench bleed" the master cylinder before installing it? Are you bleeding the brakes correctily?
If you did not bench bleed the m/s take it back off and do that and then when bleeding the brakes start with the far R rear to L rear to R front to L front.
Never let the m/s get empty, old fluid out till new fluid out. If you are trying this alone get a "pedal monkey" aka wife or sober friend, or some speed bleeders. lol
Have you read about the little pin on your proportional valve you are either suppose to push out or hold in depending on the GVW of your truck?
Do you have a basic Chilton or Hays maint manual? Its in there under the brake section (about the pin direction) I am not no where near my book (BTW I'm 6000 miles away from home) or I would look it up for you.
If I remember right the new m/s should of came with directions about bench bleeding and 2 plastic caps or it might be covered in the manual?
If you did not bench bleed the m/s take it back off and do that and then when bleeding the brakes start with the far R rear to L rear to R front to L front.
Never let the m/s get empty, old fluid out till new fluid out. If you are trying this alone get a "pedal monkey" aka wife or sober friend, or some speed bleeders. lol
Have you read about the little pin on your proportional valve you are either suppose to push out or hold in depending on the GVW of your truck?
Do you have a basic Chilton or Hays maint manual? Its in there under the brake section (about the pin direction) I am not no where near my book (BTW I'm 6000 miles away from home) or I would look it up for you.
If I remember right the new m/s should of came with directions about bench bleeding and 2 plastic caps or it might be covered in the manual?
Senior User
Joined: Oct 2012
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From: Dublin CA
Take a look at the old master cylinder. Theres a chance that the brake push rod coming out of the booster will need to be adjusted. In back of the old master, measure the depth of piston (measure all the way down in the center where the push rod goes into) to the top edge of the piston bore. Measure the new master cylinder the same way. It should be the same. If not, subtract the difference of both, and turn out the brake push rod that amount.
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Junior User
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I did bench bleed the mc but the plastic caps didn't stay in very well when I did so I just had friend plug holes with his finger if you can do that. I'm not sure about the pinion depth though I think I put it all back right but can't remember I was thinking maybe my booster is just bad? Cause ive bled them multiple times and even brought it to my mechanic and he said it was the best he could do with the booster and mic?? What does the mean?
Senior User
Joined: Oct 2012
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From: Dublin CA
Pump the brakes with engine off. Pedal should come up and get hard 
If pedal sinks, its not the booster. You can also clamp off each brake hose at a time to see pedal gets hard. You can narrow down if you have a faulty caliper or brake hose that way
If pedal sinks, its not the booster. You can also clamp off each brake hose at a time to see pedal gets hard. You can narrow down if you have a faulty caliper or brake hose that way
Cargo Master
Joined: May 2011
Posts: 2,388
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From: Northern California
X2 on the plunger... 1/4 turns extending until it feels right.
Also check your bench bleed. A bunch of guys on here told me that the plastic plug and pump method is crap. They advised to by the little hose and fitting kit where the hoses loop back into the fluid in the reservior. Youtube bench bleed.
Also check your bench bleed. A bunch of guys on here told me that the plastic plug and pump method is crap. They advised to by the little hose and fitting kit where the hoses loop back into the fluid in the reservior. Youtube bench bleed.
Cargo Master
Joined: May 2011
Posts: 2,388
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From: Northern California
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Junior User
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I can pump it up but not as hard or high as I should u think a need to bench bleed mc again??
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MSEE
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From: Austin, TX
This likely did not work. When you were bench bleeding, how far where you able to push the cylinder into the bore when you were "done"? If you could push it in any farther than 1/8 inch, it is not bled through.
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Junior User
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OK bench bled the mc last night but I could push it farther than the 1/8in you talked about I actually bought a kit to do it right but still the pedal goes to the floor it stops a little better but not like it should you think a leaking wheel cylinder could put air back in the whole system??
Fleet Mechanic
Joined: Feb 2007
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From: Middle TN
Most often over looked.
Before you do anything else, adjust the rear brake shoes.
This means adjust them as tight as you can (locked-up), then stick a small screwdriver through the slot to release the adjuster arm and back the adjuster off until the wheel starts to turn with very light drag. This centers the brake shoes.
This will change the pedal height when pushed.
Before you do anything else, adjust the rear brake shoes.
This means adjust them as tight as you can (locked-up), then stick a small screwdriver through the slot to release the adjuster arm and back the adjuster off until the wheel starts to turn with very light drag. This centers the brake shoes.
This will change the pedal height when pushed.
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