Burntoutaccountant
Newbie
Looks like I actually have the larger booster. Now I just have to figure out how to order the jb6 brakes and what not.1. There are no "spindles" on a 4WD. You have a steering knuckle and a hub/bearing assembly on each side. The steering knuckle is the same. The hub/bearing assembly is different between JN3 and JN5/6. I took the entire steering knuckle/hub/bearing pair from the donor truck, since I had a damaged steering knuckle to begin with.
What I grabbed from the Treasure Yard:
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JN5/6 left, JN3 right.
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Master cylinders are the same Quick Take-Up design, but with a 1/8 larger bore for the JN5/6 compared to the JN3.
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2. JN3/JB3 brakes were discontinued for 1992, perhaps. After that, the base power brake system was JN5 or JB5. I think only the regular-cab pickups got JN/JB3. Extended-cab trucks got the JN/JB5. So use an extended-cab pickup, a newer regular-cab pickup, or a Suburban as a donor.
3. If you're using the 6-lug 2500 axle (be sure it came from a K2500, not a C2500--they're different widths) then you'll have the 11.x Duo-Servo rear brakes, and when you upgrade the front, master, and booster, you'll have the equivalent to JN6 just like my '88.
4. There's no limited-slip option for the 8.25 front differential that I know of. I've heard rumors that some Dodge limited-slip differential can be crammed in there, and there may be aftermarket options I don't know about.
5. You're upgrading the rear brakes via the axle swap. You upgrade the front brakes, the master cylinder, and booster to JN5/6 spec, you have a "matched set" front and rear. No problem with proportioning valve--should work as-is.
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