Passenger brake dragging

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Caman96

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Strange the build sheet shows both.
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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.
It’s 2wd an has the jb5 master stock booster
 

someotherguy

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Quite a bit of unnecessary confusion going on here..

RPO codes get recycled over the generations. There's no way a 4L70E came in a 1991 model truck so you can stop worrying about that. 4L70E's didn't even exist in 1991.

The reason a manual-equipped truck has an automatic gear indicator in the cluster is because someone swapped the cluster out. 1988-1991 clusters aren't as durable as 1992-1994, in general, so someone likely had problems with the original and just grabbed another to throw in there.

My money on the brake locking up will be the flex hose, if they're original. Shoulda put new ones on both sides while you were swapping all the other brake stuff. Go ahead and do it anyway if you still have the old ones on there. If they're not bad now, they will be soon enough..

Richard
 

someotherguy

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I spent about two years looking for a 3.42-geared 14-bolt six-lug axle. Had to travel 750-ish miles round-trip to get it.

$300 plus gasoline, plus fixing the brakes that the previous owner screwed-up.

OTOH, it had the G80 locking differential.
I was surprised while parting out a 1994 K1500 w/F44 package that it had 3.42's in the 14 bolt, as well as G80. I can only imagine what not-fun it was driving a K1500 extended cab with a 5.7 TBI and 3.42's with the tall tires they had on it. Might have contributed to why the transmission was in pieces in the back seat area.

I understand people searching for a rear axle with gearing to match their front, to save money on re-gearing.. but I think if I had a lead on a 3.73 14 bolt I'd jump on it, then go ahead and spend the money to re-gear my front to 3.73's also. :)

Richard
 

HotWheelsBurban

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Quite a bit of unnecessary confusion going on here..

RPO codes get recycled over the generations. There's no way a 4L70E came in a 1991 model truck so you can stop worrying about that. 4L70E's didn't even exist in 1991.

The reason a manual-equipped truck has an automatic gear indicator in the cluster is because someone swapped the cluster out. 1988-1991 clusters aren't as durable as 1992-1994, in general, so someone likely had problems with the original and just grabbed another to throw in there.

My money on the brake locking up will be the flex hose, if they're original. Shoulda put new ones on both sides while you were swapping all the other brake stuff. Go ahead and do it anyway if you still have the old ones on there. If they're not bad now, they will be soon enough..

Richard
2X on changing the brake hoses! Had one collaps internally on the Burb 4 years ago; locked the right front brake up, almost ruined the rotor, and caught the brakes on fire. I ended up having to replace the hoses, calipers, pads on both sides,and the ABS sensor/backing plate($100 item then) on the right side. No truck for 3 weeks while I worked on it, but I found out the upper ball joints were worn out, so I replaced those as well. And the Burb got a set of cheap tires since the fronts were worn out in 6 months from the ball joints. And it handled and stopped lots better afterwards too.
 

Schurkey

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My money on the brake locking up will be the flex hose, if they're original.
2X on changing the brake hoses!
The sleeve that rides on the pins had dimples which didn’t allow them to slide freely, swapped out for old pins and works perfect!
Apparently wasn't the brake hoses.



It’s 2wd an has the jb5 master stock booster
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.
 

aaronswink

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Quite a bit of unnecessary confusion going on here..

RPO codes get recycled over the generations. There's no way a 4L70E came in a 1991 model truck so you can stop worrying about that. 4L70E's didn't even exist in 1991.

The reason a manual-equipped truck has an automatic gear indicator in the cluster is because someone swapped the cluster out. 1988-1991 clusters aren't as durable as 1992-1994, in general, so someone likely had problems with the original and just grabbed another to throw in there.

My money on the brake locking up will be the flex hose, if they're original. Shoulda put new ones on both sides while you were swapping all the other brake stuff. Go ahead and do it anyway if you still have the old ones on there. If they're not bad now, they will be soon enough..

Richard
Just put new flex hoses on today with jb5 master and bled. Now truck has no spark or fuel after upper radiator hose blew last night. Can’t even test the brakes! Smh
 

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.
I have stock calipers for my truck. I have 1&1/4 rotors with pads but I have a jb5 non hydro boost master. Havnt got to test after new flex hoses because no fuel or spark. No idea what the problem is now
 
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