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Discussion Starter #1
Just did a disc brake swap up front and then new drums on the back. Dual bowl, proportioning valve, 4 piston calipers, new brake lines, all that jazz.

They brake worse than they did with my old drums and only 2 of them were working out of 4.
Having 4 new brakes I thought they would crazy fast reacting. I live on a hill and drove down it and took it right back to my house cause I could barely stop to get to the bottom of it. Its just not safe. I got an alignment and paid the shop to go over my brake lines and make sure there were no leaks, we bled the brakes, and are going to do that again to see if that might help.

Brake pedal doesn't go all the way to the floor, but its not as much built up pressure as I think there should be..

Any ideas of what it could be? brake fluid is new and bowl is full. I am so frustrated its crazy. :/

All help would be appreciated! Thanks in advance!!
 

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With all the work done it could be a number of things. One common thing is the calipers are on the wrong sides up front. The bleed port should be at the top and there is likely a big statement to that fact in the directions.

Another is the length of the push rod. Is yours correct for your car?

With adding a dual bowl, did you plumb the lines correctly? Front bowl to rear, rear bowl to front.

And which 2 wheels were working?
 

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Discussion Starter #3
@Driveway, Calipers are installed correctly, the brakes bled through fine so the pushrod has to be accurate. I cant have it any shorter or longer or it wouldnt fit over my brake pedal correctly.
Front bowl is hooked to the proportioning valve then to the rear brakes, rear bowl is set to the distribution block then to the front brakes.
and I have no clue which ones they were, but every single item from the pushrod to the brake pads were changed. I did a 5 lug swap with everything brand new, so its not like I can have faulty items that need to be replaced.
 

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I read your statement as 2 of the new brakes were not working.

You do not say if it is a power brake system.

If yes, I would be checking the vacuum source, check valve for direction, etc. PBs make horrible manual brakes, which is about what you describe.


If not, it could be the glaze on the pads and rotors have not worn off and don't get a good bite. But, I would go over the entire install again and verify everything is right, and not just 'I'm sure that was OK'.
 

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Similar problem with my 65 in the past. Added vacuum pump, didn't really improve . Replaced the master cylinder etc and much better now. System is power brake system . Drums in the rear and disc up front. Car is a 289 with a RV cam , headers, 4bbl etc.
Check vacuum and then m/c.
 

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Discussion Starter #6
@Driveway, they are not power brakes. A friend told me he thinks since they are new brake lines, that it might be air in the line somewhere even though we bled them. So I am going to have a shop with a compressed bleeder redo that. and probably pay them to just fix it if thats not it lol
 

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My 70 had an electric vacuum pump. BTW, I had thEvsame problem as you. Bled the lines, changed the MS, finally completely changed the vacuum pump and system......still, no change. Finally changed the booster, that was the problem.
 

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You need to find out what the bore on the MC is. The bore has a direct effect on fluid pressure at the wheels and 13/16" to 15/16" are optomal. Also is the pedal a manual or power brake pedal as they have different ratios. some kits give you a big mc that moves a lot of volume but have no pressure to brake effectively and to me it sounds as the bore diameter is your problem. Do some research on the best pressure target for your car and get the appropriate mc, bleed and try it.
 

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Did you do a bench bleed of the MC? Really tough to get all the air out with the MC in the car. If you have air in the lines, a motive power bleeder should def do the trick. Don't give up yet...the discs really do perform better. You may want to consider a power setup since you've gone this far.
 

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You do not need power brakes on a light car like the early Mustang. With the right pads, the stock KH type front brakes work very very well. The best pads for street use are either the ebc redstuff pads, or the Porterfield R4- S pads. But ever the cheapest OEM pads will work better than you describe. Quit throwing complicated solutions like power brakes at the problem and find someone who knows how to work on these old cars.

Z
 

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Try backing the proportioning valve all the way out. If it feels like the fronts lock up if you sneeze on the pedal while not getting much brake force, then this is probably the case. Too much pressure to the fronts, almost none to the rear.
 
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