Brake Problem
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Brake Problem
1949 Mercury M47 (Ford F-1). Brake pedel slowly goes to full hard...have to open a wheel cylinder to release pressure.
Pressure does not dissipate when truck sits over night, pedel still at full pressure.
Unable to determine if the pressure build up is from brake usage or heat transfered to lines...cannot find any line close to heat source.
Have changed the check valve twice and still the same problem...could it be the master cylinder itself?
Pressure does not dissipate when truck sits over night, pedel still at full pressure.
Unable to determine if the pressure build up is from brake usage or heat transfered to lines...cannot find any line close to heat source.
Have changed the check valve twice and still the same problem...could it be the master cylinder itself?
Thread Starter
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Senior User
Joined: Jun 2003
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Brake problem
1949 Mercury M47 (Ford F-1). Brake pedel slowly goes to full hard...have to open a wheel cylinder to release pressure.
Pressure does not dissipate when truck sits over night, pedel still at full pressure.
Unable to determine if the pressure build up is from brake usage or heat transfered to lines...cannot find any line close to heat source.
Have changed the check valve twice and still the same problem...could it be the master cylinder itself?
also, bypass opening is clear
Pressure does not dissipate when truck sits over night, pedel still at full pressure.
Unable to determine if the pressure build up is from brake usage or heat transfered to lines...cannot find any line close to heat source.
Have changed the check valve twice and still the same problem...could it be the master cylinder itself?
also, bypass opening is clear
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after a few minutes the pedal is as hard as a rock...no play whatsoever. Sometimes after sitting overnight it will go back to having play, other times its still hard as a rock despite sitting for hours.
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its not the adjustment...theres plenty of play after bleeding and adjustment. Its after use/time that causes it to build/maintain pressure.
I have rebuilt the master cylender with the same results so I am questioning if the master cylinder may be defective...
I have rebuilt the master cylender with the same results so I am questioning if the master cylinder may be defective...
Lead Driver
Joined: Apr 2002
Posts: 8,813
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From: Littleton, New Hampshire
Merc,
Check the brake pedal rod and be sure that when the pedal comes up that there is no pressure on the rod. It sounds like the rod is not retracting enough to allow the fluid to come back into the master cylinder. I had this problem once and had to shorten the rod.
Vern
Check the brake pedal rod and be sure that when the pedal comes up that there is no pressure on the rod. It sounds like the rod is not retracting enough to allow the fluid to come back into the master cylinder. I had this problem once and had to shorten the rod.
Vern
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ok...adjusted the pedal rod to the minimum travel and max play...bled brakes, adjusted each brake and confirmed no line blockage...within 5 minutes of normal city driving she again went to full hard.
Totally frustrated!!!
Totally frustrated!!!
Posting Guru
Joined: Dec 2004
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From: Shasta Lake, Ca.
Do U have Disk/Drum, Drum/drum/ or disk/disk? U may have a stuck slave or caliber.. Or if U have power brake.. U maybe lousing Vac to the booster.. Need to know.. is there a lot of cam? or a bad Vac Loc on the Vac feed line?
Last edited by Madathlon; Jan 24, 2005 at 08:08 PM.
Lead Driver
Joined: Apr 2002
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From: Littleton, New Hampshire
Merc,
You said your brake lines are new,but what about your front and rear brake hoses? Are they new also? I have heard that brake hoses can become clogged enough to allow pressure through but since the return pressure isn't nearly as high, the fluid is retained in the wheel cylinders. This would be a pretty rare situation, but that's all I can come up with.
Vern
You said your brake lines are new,but what about your front and rear brake hoses? Are they new also? I have heard that brake hoses can become clogged enough to allow pressure through but since the return pressure isn't nearly as high, the fluid is retained in the wheel cylinders. This would be a pretty rare situation, but that's all I can come up with.
Vern