front discs are hanging up.

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mikepasquale1

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I cant figure it out. Everythiing is brand new; rotors, calipers, pads, lines. When i put the pads on the first time. They were extremely tight. I sanded them down and they moved freely. Test drove a few times and they get tighter and tighter. Highway driving the pedal gets kooser. Building up a ton of brake dust on the wheels. Even the wheels are way to hot to touch. sanded off more pad material, they freed up and then gave me the same issue after about 5 - 10 minutes of driving.

Local mechanic told me even though the calipers are new, they are rebuilt. I bought them years ago from an ebay store that sold me a conversion kit. I never heard of nor have seen the company advertised anywhere after that. They also do not have ford stampings on them. They have that companys part numbers on them, but are identical in appearance. If i remember correctly the company stamping was "MBR".

The pads came with that kit.

The rotors that came with the kit did not fit the small dust shield on the spindle so i had to get new ones from advance auto.

The lines all came from LMM.

What do you guys think? Its weird, when the pads rub, the rotors heat up and the pedal gets really hard. When it cools it returns to normal.

Last week picked girl friend up. On the way to her house, they were rubbing giving me the stiff pedal. Cooled down and drove on highway for an hour and had a good pedal the whole way to a car show.

Sorry this is so lengthy. Just want to cover details.

 

mikepasquale1

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Unable to confirm since i cannot locate any info on manufacturer. Where did you get yours? Yes they are on correctly. Didnt think you could put them on wrong actually.

 
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the alarm bells would've rang for me if I had to shave the pads to fit. As long as the rotors can free spin a little with the engine off, they shouldn't bind. If they stick with engine on, maybe the peddle travel needs adjusting? Just throwing ideas out there?

 

midlife

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Any chance that the Master Cylinder is not plumbed correctly? IIRC, there's a valve to provide residual pressure for the rear drum brakes; if the chamber for the rear drum brakes is used for disk brakes, you'll get exactly what you're describing: an increase of caliper pressure on the disk.

 

mikepasquale1

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Im not sure. I do know that the rear bowel is plummed to the front discs. The small front bowl is plummed for the rear. Does that sound right or do i have it backwards?

 
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Im not sure. I do know that the rear bowel is plummed to the front discs. The small front bowl is plummed for the rear. Does that sound right or do i have it backwards?
That is the way it should be plumbed...does it have an adjustable portion valve? it should not have factory one if converted from drum to disk. I have seen that happen when an inner line gets weak and won't let fluid return, are you sure all lines are clear of debris?

 
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mikepasquale1

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Yes all lines are brand new and clear. Getting excelle.t flow uoon bleeding. This was not a conversion. the car originally had front disc brakes. I am using the original brass proportioning valve. which was recently replaced do to a blockage in the old one. the conversion kit that I was talking about that I bought a long time ago was for a 70 - 73 mustang that was meant for another project which i ultimately used fir this car.

 
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Mike, It could be the adjustable rod in the booster is set too long. That would produce exactly the symptoms you describe. The adjustment requires precision and the fabrication of a sheet metal depth gauge and + or - .010 makes the difference between right or wrong. The procedure is in the Ford Shop manual. Leave the lines attached to the master cylinder and unbolt the MC from the booster and pull it forward and to one side. You'll see the rod sticking out of the booster. It just pulls out and will have a rubber seal that comes out with it. If you don't have the gauge you could try shortening it .010 at a time, could take a while. Chuck

 

mikepasquale1

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Hmm. Makes sense. I hope thats not it cause im not good with small numbers lol. I do know what your talking about. The brake booster came off of another car and thr master cylinder is new but the rod is from my old booster. Wonder how ford matched those things up with eachother.

If the rod is too long, how is it that the brakes work fine after they cool down? If after driving for about 5 to 10 min they start rubbing.

 
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Hmm. Makes sense. I hope thats not it cause im not good with small numbers lol. I do know what your talking about. The brake booster came off of another car and thr master cylinder is new but the rod is from my old booster. Wonder how ford matched those things up with eachother.

If the rod is too long, how is it that the brakes work fine after they cool down? If after driving for about 5 to 10 min they start rubbing.
As you use the brakes everything gets hot and expands, causing the drag. When not used they cool down and contract, no drag. Chuck

 

mikepasquale1

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Ok. So when i replaced that booster, inserted the rod and put the master cylinder in, should i have felt any resistance at all when pushing the master cylinder into place? because i did. And if so how can i adjust and measure. I do not have the manual to follow the procedure

 
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here's what happened to my Jeep (same master cyl setup). The 'C' clip that holds the plunger in broke. The pieces would end up next to each other (stacked). This would keep the plunger from returning all of the way and keep brake pressure applied. You might take a quick look. You can just unbolt it from the booster and with a small mirror you can confirm it isn't broken and/or there isn't something else that slipped in there.

 
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Ok. So when i replaced that booster, inserted the rod and put the master cylinder in, should i have felt any resistance at all when pushing the master cylinder into place? because i did. And if so how can i adjust and measure. I do not have the manual to follow the procedure
With a different Booster and rod, and new master cylinder it is likely the rod needs to be adjusted. Assuming the rod was seated completely in the booster bore, and the lines were not connected, you should not have felt amore than 5 pounds of resistance. This may help. Chuck

Scan 121810001.pdf

 

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mikepasquale1

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Yes that hekos alot. I still have my original booster, the one thats matched to the rod. Do you think by taking measurements from the old one with the rod in place i could be able to then match that to the new booster by adjusting that rod?

Get the proper length with the old one

Adjust the rod to match that measurement for the new one


Yes that helps alot. thabk you. I still have my original booster, the one thats matched to the rod. Do you think by taking measurements from the old one with the rod in place i could be able to then match that to the new booster by adjusting that rod?

Get the proper length with the old one

Adjust the rod to match that measurement for the new one.

Im still just thrown on why its ok on highway but not on slower non freeway roads. Higher RPM on highway creating more vaccum maybe and pulling the rod back further?

 
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I've always adjusted my boosters to just start to need to push on the master to bottom it on the booster surface. Seems to make a good balance between drag and long pedal travel before engagement.

 

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First GIANT red flag for me = modifying new brake pads to fit.

Big no-no in my book.

Maybe the calipers aren't wide enough or pistons aren't retracting enough.

I'd compare the new components to old ones before proceeding. Master, booster, pads, calipers... everything. Hopefully there is only one out of spec measurement. Two or more would make the problem even harder to diagnose.

 
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