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CNC Brake Help

#1
I have a 1450 Ranger with cnc 1” master cylinders, CNC 630 calipers and 14” rotors. After RATR we mainly had rear brakes and would have to pump the pedal 3-4 times to slow down. Since then I rebuilt both masters and replaced both 2psi residual valves. After getting some pedal back it was only locking up the front rotors with light pressure to the rears. I figured the balance bar might need to be adjusted, so I went and drove the truck down the street. First time I tried to stop, the pedal goes to the floor. After pumping a few times it slows down but the pedal will still go to the floor. I have since capped the masters to make sure they are not bleeding past and it had a rock hard pedal. Before throwing more parts at it, I wanted to see if anyone else has ever had a similar issue. Any input would be appreciated and thank you in advance.
 

osborne

Well-Known Member
#2
I have had a similar issue and after many many hours and $'s i figured out that rear axle flex was causing the rotor s to push the pistons back into the calipers just enough to have to pump the pedal to make em work. Are your calipers mounted to the top of your axle?
 
#3
I have a fabricated ruff stuff housing that is fully trussed. The calipers are mounted roughly 45 degrees off the top of the axle tubes. The issue I have right now was just driving down the street in a straight line and trying to stop.
 

osborne

Well-Known Member
#4
I could get firm pedal in the garage, but as soon as i drove the rear calipers would open up. Cap off front m/c and run it to isolate the rear. Then cap the rear to see if fronts work. Have to isolate the issue first then solve it
 

Dirtracer 619

Well-Known Member
#7
They are difficult to bleed properly. You can get a vacuum pump from harbor freight that works pretty good. Your master cylinders might be too big. I wood call CNC in san diego to walk you through it. They are pretty easy to deal with. Good luck


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desertspeed

Well-Known Member
#8
They are difficult to bleed properly. You can get a vacuum pump from harbor freight that works pretty good. Your master cylinders might be too big. I wood call CNC in san diego to walk you through it. They are pretty easy to deal with. Good luck


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They are very difficult to bleed. One trick is to get a spare reservoir cap and tap a schrader valve into it, and then pressurize with nitrogen (10lbs or so). You can then bleed the calipers, topping off the pressure as needed.
 

Kyle D

Well-Known Member
#9
Those calipers are terrible to bleed but check your rotors too. If they’ve gotten warped they’ll do the same thing as a bent or flexing axle housing and push the pistons back into your calipers while your driving.
 
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