Upgrading from 1/2 ton to 3/4 ton leaf springs

[Logan R]

Ok

Yeah those JB3 brakes are sketchy enough for stopping the truck alone, never mind towing 5-8k trailer. Then you probably don’t have a transmission cooler to go with (assuming 4L60)transmission, that seem to grenade even without added towing stresses! With enough money and time you could replace brakes, suspension, transmission and rear end though.

Ok I have a 700r4, trans. Sure it’s the same, haven’t looked if it has a trans cooler or not. Do you know where I could find an upgrade kit for the brakes? Maybe I’ll just worry about brakes instead of payload for a while

 

[Schurkey]

I looked in the glove box, seen a GU6,

3.42 gears. Very common on 1500s. That's what my '88 K1500 has.

and a JB3 code. So maybe I focus more on brakes then I do suspension at the moment?

AAAAHHHH!! The worst, weakest power-brakes installed on GMT400 trucks.

Maybe I’ll just worry about brakes instead of payload for a while

You absolutely need to deal with this before suspension upgrades. (Suspension REPAIRS are another story.)

And if so where can I find a good upgrade kit.

The nearest Treasure Yard that has a C1500 extended-cab, or a C1500 regular or extended cab newer than...'92, perhaps. Kinda guessing that a C2500 light-duty (6-lug) would be the same up-front, master, and booster. Check the SPID sticker in the donor's glove-box, look for JB5 or JB6.

You will need the rotors, calipers, master cylinder, and power booster. I have not converted a 2WD, I'm assuming that the wheel bearings and steering knuckle are the same on the C-trucks. The front bearings/hubs are NOT the same on the K-trucks. Maybe you wanna grab the steering knuckles from the donor truck, just to be sure.

Having converted the front from JB3 to JB5, you still need to deal with the rear. You have the 254mm (10") leading-trailing shoe drum brakes. What you want is on the upgraded axle, 11.x" Duo-Servo rear drums. Bigger, stronger, heavier; and not as sensitive to park-brake non-use as the leading/trailing design. Upgrading the front and the rear gives you the equivalent of JB6 brakes.

The "Kit" to replace my JN3 front brakes (plus a master cylinder and booster, not shown in this photo):

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K-series rotor difference: "3" rotor is narrower than "5" rotor. Diameter is the same.

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The caliper pistons are also larger on the "5" than the "3", which requires a bigger-diameter master cylinder, and a more-powerful booster. MAYBE you turn-in the Treasure Yard parts as "cores" for "rebuilt" parts...but be sure to take the Treasure Yard parts even if you don't plan to use 'em. I pulled the calipers and master cylinder apart, cleaned-out the sludge, dreck, garf and garfelderfarb, put 'em back together and they're in use on my K1500. I used the old disc pads (nearly worn-out) to clean the rust off of the rotors for about a week of use, then put new pads in the calipers.

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For ****'s sake, do not install an "NBS" GMT800 master cylinder on low-drag calipers (JB3, 5, 6)

There are aftermarket brake upgrades (be careful!) and there are upgrades from newer-generation pickups that I'm not really familiar with. What I've posted is cheap, available, OEM-verified, and effective.

Flush the brake fluid while you're in there. If you have an iron-body RWAL unit, it has a bleeder screw. If you have the newer aluminum-body RWAL, you'll need a scan tool to bleed it properly.

 

[Logan R]

ok sounds good, will definetly be looking then for all them parts, do I need to snag the a arms cv axles and all that other fun jazz too?

 

[Schurkey]

ok sounds good, will definetly be looking then for all them parts, do I need to snag the a arms cv axles and all that other fun jazz too?

I've never converted a 2WD truck.

Pretty-sure you won't need the control arms. You absolutely won't need the CV axles. You MIGHT need the steering knuckles.

 

[Logan R]

Ok

I've never converted a 2WD truck.

Pretty-sure you won't need the control arms. You absolutely won't need the CV axles. You MIGHT need the steering knuckles.

I've never converted a 2WD truck.

Pretty-sure you won't need the control arms. You absolutely won't need the CV axles. You MIGHT need the steering knuckles.

ok so I could get away with getting the JB6 pads, rotors, and calipers maybe? If not that’s fine if just like to make one trip and not have to get what I don’t need as I’m gonna replace more consumable things like pads, rotors and such on the junkyard parts

 

[HotWheelsBurban]

3.42 gears. Very common on 1500s. That's what my '88 K1500 has.


AAAAHHHH!! The worst, weakest power-brakes installed on GMT400 trucks.


You absolutely need to deal with this before suspension upgrades. (Suspension REPAIRS are another story.)


The nearest Treasure Yard that has a C1500 extended-cab, or a C1500 regular or extended cab newer than...'92, perhaps. Kinda guessing that a C2500 light-duty (6-lug) would be the same up-front, master, and booster. Check the SPID sticker in the donor's glove-box, look for JB5 or JB6.

You will need the rotors, calipers, master cylinder, and power booster. I have not converted a 2WD, I'm assuming that the wheel bearings and steering knuckle are the same on the C-trucks. The front bearings/hubs are NOT the same on the K-trucks. Maybe you wanna grab the steering knuckles from the donor truck, just to be sure.

Having converted the front from JB3 to JB5, you still need to deal with the rear. You have the 254mm (10") leading-trailing shoe drum brakes. What you want is on the upgraded axle, 11.x" Duo-Servo rear drums. Bigger, stronger, heavier; and not as sensitive to park-brake non-use as the leading/trailing design. Upgrading the front and the rear gives you the equivalent of JB6 brakes.

The "Kit" to replace my JN3 front brakes (plus a master cylinder and booster, not shown in this photo):

You must be registered for see images attach

K-series rotor difference: "3" rotor is narrower than "5" rotor. Diameter is the same.

You must be registered for see images attach

The caliper pistons are also larger on the "5" than the "3", which requires a bigger-diameter master cylinder, and a more-powerful booster. MAYBE you turn-in the Treasure Yard parts as "cores" for "rebuilt" parts...but be sure to take the Treasure Yard parts even if you don't plan to use 'em. I pulled the calipers and master cylinder apart, cleaned-out the sludge, dreck, garf and garfelderfarb, put 'em back together and they're in use on my K1500. I used the old disc pads (nearly worn-out) to clean the rust off of the rotors for about a week of use, then put new pads in the calipers.

You must be registered for see images attach

For ****'s sake, do not install an "NBS" GMT800 master cylinder on low-drag calipers (JB3, 5, 6)

There are aftermarket brake upgrades (be careful!) and there are upgrades from newer-generation pickups that I'm not really familiar with. What I've posted is cheap, available, OEM-verified, and effective.

Flush the brake fluid while you're in there. If you have an iron-body RWAL unit, it has a bleeder screw. If you have the newer aluminum-body RWAL, you'll need a scan tool to bleed it properly.

A 400 suburban would have everything you should need to change over. Your pickup is 2wd C1500, there are usually several C1500 Burbs in the wrecking yards.....

 

[Schurkey]

I could get away with getting the JB6 pads, rotors, and calipers maybe? If not that’s fine if just like to make one trip and not have to get what I don’t need as I’m gonna replace more consumable things like pads, rotors and such on the junkyard parts

Pads, rotors, calipers, master cylinder, power booster. Reasonable chance the rotors are usable as-is, or--like mine--needing only to scrub the rust off of 'em. I wouldn't buy new rotors "just because", but then I throw nickels like they were manhole covers.

Calipers and master cylinder are more tricky. I pull 'em apart for cleaning and inspection, and if I like what I see, I shove 'em back together and use 'em. Not everyone can or will do that. Rebult calipers and/or master cylinder might be worthwhile--but you need to turn in the Treasure Yard cores because of the piston size difference.

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Scraped the crust off of the square-cut seal with my fingernail. This one is partially-done.

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There are better brake hoses than this. I didn't know that at the time.

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Three-chamber master cylinder suitable for low-drag calipers. Note relatively huge piston/seal at rear, and stepped casting to house the bigass piston.

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I don't pull the booster apart, I install it and see if it works. If it doesn't, I'd either get another one from the Treasure Yard, or get a rebuilt, turning in the Treasure Yard booster as the core.

IF (big IF) you have to change steering knuckles, that's the perfect time to replace the control arm bushings and ball joints, or the entire control arm assemblies. MAYBE you want to grab the Treasure Yard control arms, rebuild them with joints and bushings, and then swap the whole works at one time. Or--just buy new control arms.

 

[Logan R]

Ok why is there a maybe on the steering knuckle? Is the clearance issues on some and not others?

 

[Schurkey]

The 4WD vehicles use a different hub/bearing assembly when swapping from the narrow "3" rotors to the wider "5" or "6" (same thing in front) rotors. I changed the entire steering knuckle rather than swapping hub/wheel bearing assemblies, because the whole project started as a steering knuckle replacement due to ball-joint failure. I happened to be scavenging parts from an extended-cab truck a few days away from being crushed. I didn't figure out I was getting bigger/better front brakes until I started comparing. Once I figured-out the brake differences, I had to race back to the Yard to grab the master cylinder and booster before they got squished.

MAYBE the steering knuckle/wheel bearings on the 2WD are different when rotors are swapped. I don't know.

 

[Logan R]

Ok sounds good thanks for the info, I will definetly see about finding such parts in a local junkyard, thanks!