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73-87 Chevy _ GMC Trucks => Brakes, Frame, Steering & Suspension => Brakes and Braking Systems => Topic started by: Rattler12 on February 18, 2016, 06:22:28 pm
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Will JB3 rotors, calipers and pads on the front, JB3 drum brake components on the back mated to a JD5 master cylinder cause excessive pedal travel? The truck stops fine but the pedal is long and soft. Was just bled by a company long time in the brake business so I don't think it's air in the line but??????/
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do you have the hydro boost or vacuum booster? im not sure but i think the JD5 would use more power than the jb3 so in turn you should be over powering the brakes and maybe have a stiff pedal??? but this is completely a guess.
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Vacuum booster.........was the JB5 MC only used with hyd boost? JB3 MC has a 1 inch piston and JB5 1 1/8 ? I thought I might have had the pedal rod adjusted wrong but with the engine off and all the vacuum released from the booster I've got about a inch and a half to 2 inches free pedal and when I crank it up the pedal sinks to dadgum near the floor. I thought I was going to have a problem with the vacuum booster because if insufficient vacuum. With the cam I have in it it's only pulling 10 lbs at idle which ain't much
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New master?
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Yessir......and booster
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after thinking, there may be several factors at play,
first, push-rod is wrong length, for more free play then allowed, I think free play should be around 3/4 inch...it may be from booster to pedal, but I think master to booster would be different. WAIT!! what master again, you wrote JD5 in beginning, then changed to JB5 later. JB is vacuum, JD is hydro, if you have the vacuum master, then you may want to adjust the booster to pedal linkage to remove some free play
second, during the bleeding procedure the proportion valve may have activated resulting in low fluid going to rear brakes., it could also be because of an internally leaking master(being new it is unlikely but still possible)
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It's a JB5 MC.......If the prop valve is tweeked would it not be in the direction of the front brakes since they are bled last?
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I was hoping vile would jump in cause I don't know for sure I've read a few things jb5 being dual diaphragm booster and one page said jd5 was dual then another said jd5 was hydro boost. But jb3 was single and I think that might be the problem but I don't want to be posting bad info If I'm not sure. Bd might also have some knowledge on this also
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from the 1983 service manual,
JB3 single diaphragm
JB5 Dual Diaphragm
JD5 HydroBoost
I won't comment on compatibility, as I am not sure
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properly adjust the rear brakes.
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I was told that was done. The folks I took it to have a stellar rep for brake work but who knows? Maybe somebody was hungover......
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I've seen "stellar" guys put wheels on and leave the brake drum sitting on the ground. It's very easy to jack up the rear axle and check the adjustment.