Passenger brake dragging

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aaronswink

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WHICH "new calipers"???

If the calipers are for the original-to-the-truck brakes, or even the upgraded JB5 or JB6 brakes like the rotors, they're Low-Drag calipers and NOT DESIGNED TO WORK WITH THAT MASTER CYLINDER.

If they're the JB7 calipers, they're not "Low-Drag", and you could be OK.

Mostly, the newer-design master cylinder is bad advice from people who didn't know any better; and it's repeated endlessly on this forum by other folks who don't know any better. IF (big IF) it "crutches" a problem at all, it's because there was an underlying fault that was never identified, and therefore probably has not been corrected.

You didn't mention whether this was a 2WD or 4WD, but since I count only 5 lug nuts per wheel in the photo of your truck, I'm figuring it's a 2WD. The 4WD need different hubs/wheel bearings to work with the wider rotors, but I guess the 2WD don't, since the rotor and bearing assembly are together.


Can't be the master cylinder, or both front brakes would "hold".

MIGHT be the combination valve, MIGHT be the ABS, MIGHT be a partially-crimped brake tube--but most likely is the caliper or brake hose.


JN3/JB3 were the weakest power-assisted brakes installed on a GMT400-series vehicle. (JN1 had the same components, but without the power booster.)

Upgrading to the wider, 1.25 rotors from the JN5/6 or JB5/6 by themselves isn't much of a change. The real difference is in the calipers which have a substantially-larger piston for more clamping force on the pads. To go along with the calipers, the JN/JB 5/6 master cylinder needs to be installed, as it has a greater bore diameter than the JN/JB3; and is still compatible with the "Low Drag" calipers because it has the third, larger chamber to provide a high-volume, low-pressure "gush" of brake fluid. The newer master cylinders don't have that third chamber, they just have a huge bore with only two chambers--dangerous if the booster fails.

AND, to go along with the bigger caliper pistons which require a bigger Quick Take-Up master cylinder bore, the brake booster is larger also.

When you get the wider rotors, bigger caliper pistons, bigger QTU master cylinder, and bigger booster, you've essentially converted your truck from JB3 to JB5 brakes.

When you shitcan the pathetic 254mm (10") Leading-Trailing drum brakes in favor of the 11.x" Duo-Servo drums, you'll have the equivalent of JB6 brakes.

As far as I'm concerned, JN/JB6 is the minimum of what these vehicles should have come with as standard equipment. Heavier trucks may need the "7" "8" or JF9 brakes, probably with hydroboost.

I found the rear brakes to be a bigger improvement than the fronts. But tougher to do on a 2WD than on a 4WD due to the 5-lug axle shafts and wheels.
I’m pretty sure you solved my problem in your reply and I overlooked it. New master required me to flex my lines for them to line up. Pretty sure I crimped the line that goes to the rear port on master. Wonder if that’s the passenger side caliper????
 

aaronswink

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Apparently wasn't the brake hoses.




If you're saying that you installed the replacement calipers intended for JB5 brakes, they're not compatible with the "NBS" master cylinder you installed.
What issues would I run into??
 

Schurkey

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Pretty sure I crimped the line that goes to the rear port on master. Wonder if that’s the passenger side caliper????
The master cylinder is split front/rear. The split for left front and right front happens downstream from the master cylinder, usually at the combination valve.

What issues would I run into??
The low-drag calipers are designed to need a "gush" of low-pressure fluid to move the piston/pads up to the rotor surface. Then the regular high-pressure, low-volume part of the master cylinder actually provides the braking force.

The "NBS" master does not have a low-pressure/high volume chamber. Instead, it's (usually) got a bigger-diameter main bore than the correct master cylinder. The larger-diameter main bore creates less pressure but increases volume through the entire brake pedal stroke. If the booster fails, you'll need both feet on the pedal and a squirt of adrenaline to provide adequate pressure at the calipers because you don't have the hydraulic advantage of the smaller main bore to increase pressure. And you'd better hope your wife or teenage daughter isn't driving; they may be incapable of stamping the brake pedal hard enough to stop quickly.
 
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