My brakes wont build pressure properly

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123456
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Joined: Wed Aug 01, 2018 10:28 pm

My brakes wont build pressure properly

Postby 123456 » Wed Aug 01, 2018 10:49 pm

Hi everyone, new to the forum. I'm having some trouble with my brakes. I have a 1967 wagoneer with 1978 chevy half ton axles. 10 bolt front 12 bolt rear. I have stock front calipers new. And 80-85 Cadillac Seville calipers in the rear. I have a vacuum booster out of a 1991 grand wagoneer and a master cylinder out of 1979 trans am that is for disc/disc systems with a 1 inch bore. I have a 4.33:1 pedal ratio. And 3/16 th line throughout the system with an inline adjustable proportioning valve to the rear brakes.

My problem is that I can't get a good pedal. It will consistently go to the floor and no matter how or how much I bleed the system and get nothing but fluid the pedal is very soft. And at. Idle the booster makes it feel like nothing is there. I have the rear calipers adjusted well enough I think and have no leaks in the system.

Paul_Soccio
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Re: My brakes wont build pressure properly

Postby Paul_Soccio » Thu Aug 02, 2018 5:32 am

Had the same problem. It was the proportion valve.

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REDONE
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Re: My brakes wont build pressure properly

Postby REDONE » Thu Aug 02, 2018 6:34 am

My intuition says it's a bad master cylinder. If you've got all the air out of the system, the calipers are all dead ends. Once they are full of fluid, the pedal should stop. If the pedal keeps moving down, the fluid must be slipping past the piston(s) in the master cylinder, back into the reservoir.
79 J-10 (The Money Badger) KE0LSU
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4" front spring drop, 5" rear shackle flip
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cmaje72
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Re: My brakes wont build pressure properly

Postby cmaje72 » Thu Aug 02, 2018 7:24 am

Ahhh caddy calipers. I have almost the same setup (just a different axle) in my CJ7 and the exact same problem. Been fighting them for years. They are either out of adjustment or have stopped working correctly. I did a little experiment where I switched to regular calipers without the parking brake bled the system and got plenty of pedal and the brake system worked much better. Cleaned, reset, reinstalled the caddy calipers and the problem came back.
I have also been told that the seville calipers are designed for a 1" thick rotor and since I'm using a 7/8" thick CJ rotor that extra may be causing part of the problem. I have not tried shimming the pads but at this point there are a few vendors selling dedicated parking brake calipers so I may just ditch the caddys and go with that. Its on the backburner though since I have been spending most of my money and time on the FSJ. As it should be.
79 Cherokee 5.3/4l65E/NP241C
79 CJ7

SJTD
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Re: My brakes wont build pressure properly

Postby SJTD » Thu Aug 02, 2018 8:27 am

What REDONE said.

Fluid has to go somewhere. If it isn't leaking out it's getting past the piston.

Unless you've got the caliper upside down with the bleeders on the bottom???
Sic friatur crustulum

'84 GW with Nissan SD33T, early Chev NV4500, 300, narrowed Ford reverse 44, narrowed Ford 60, SOA/reversed shackle in fornt, lowered mount/flipped shackle in rear.

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Stuka
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Re: My brakes wont build pressure properly

Postby Stuka » Thu Aug 02, 2018 9:17 am

Some good info above. I also say make sure the calipers aren’t upside down. The bleeder has to be facing up or there will always be an air pocket.
1981 J10 AMC 258 with HEI and Weber 32/36 DGEV Carb, T176, NP208, D44/M23 with 4.56 gears and Detroit Locker, 6" lift, 33x12.50 Cooper STT's, BJ's Offroad Rear Dozer Bumper.
2017 JKU Rubicon Lifted and stuff
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123456
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Re: My brakes wont build pressure properly

Postby 123456 » Thu Aug 02, 2018 11:14 am

The calipers are on with the bleeders up. This is my third master cylinder with the same problem. When I bench bled it I did the plug in the ports method and the piston wasn't sinking.

I was wondering if chevy front calipers would bolt up to the brackets. Maybe I have defective caddy calipers?

Paul_soccio what type of proportioning valve were you using? Mine is the knob type that you twist

SJTD
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Re: My brakes wont build pressure properly

Postby SJTD » Thu Aug 02, 2018 11:51 am

Caliper pistons extending but then retracting rather than staying out?
Sic friatur crustulum

'84 GW with Nissan SD33T, early Chev NV4500, 300, narrowed Ford reverse 44, narrowed Ford 60, SOA/reversed shackle in fornt, lowered mount/flipped shackle in rear.

123456
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Re: My brakes wont build pressure properly

Postby 123456 » Thu Aug 02, 2018 1:56 pm

Yes the rear calipers are retracting. Does that mean that the ratchet system is not working on the caliper?

SJTD
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Re: My brakes wont build pressure properly

Postby SJTD » Thu Aug 02, 2018 8:40 pm

I mean maybe one or more of the piston seals are kinda stuck to the pistons so the piston is getting pulled back instead of staying out "against" the disc.
Sic friatur crustulum

'84 GW with Nissan SD33T, early Chev NV4500, 300, narrowed Ford reverse 44, narrowed Ford 60, SOA/reversed shackle in fornt, lowered mount/flipped shackle in rear.

cmaje72
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Re: My brakes wont build pressure properly

Postby cmaje72 » Fri Aug 03, 2018 7:32 am

123456 wrote:I was wondering if chevy front calipers would bolt up to the brackets. Maybe I have defective caddy calipers?

Get a set of front calipers from the same 85 seville. They should bolt up and even use the same pad. Just no parking brake.
Thats what I used.The only reason I stuck the caddy calipers back on was because I need them once a year to pass safety inspection.
79 Cherokee 5.3/4l65E/NP241C
79 CJ7

123456
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Re: My brakes wont build pressure properly

Postby 123456 » Fri Aug 03, 2018 8:10 am

That's what I'm going to do, thanks for the help

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Stuka
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Re: My brakes wont build pressure properly

Postby Stuka » Fri Aug 03, 2018 3:33 pm

BTW: you can get parking brake functionality with a line lock. Just know they typically don't hold for extended periods. But handy if you have a manual trans and need the vehicle held while idling or something.
1981 J10 AMC 258 with HEI and Weber 32/36 DGEV Carb, T176, NP208, D44/M23 with 4.56 gears and Detroit Locker, 6" lift, 33x12.50 Cooper STT's, BJ's Offroad Rear Dozer Bumper.
2017 JKU Rubicon Lifted and stuff
Pevious Jeeps: 1975 Cherokee, 2008 JK, 2005 KJ, 1989 XJ


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