With all the options for the front, what’s the strongest front axle/IFS setup for a 89 1500?

[Burntoutaccountant]

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:

You must be registered for see images attach

JN5/6 left, JN3 right.

You must be registered for see images attach

Master cylinders are the same Quick Take-Up design, but with a 1/8 larger bore for the JN5/6 compared to the JN3.

You must be registered for see images attach

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.

Looks like I actually have the larger booster. Now I just have to figure out how to order the jb6 brakes and what not.

You must be registered for see images attach

 

[GrimsterGMC]

Looks like I actually have the larger booster. Now I just have to figure out how to order the jb6 brakes and what not.

You must be registered for see images attach

IIRC when the factory realised just how bad the JB3 brakes were they offered owners the option of having the booster upgraded as part of the regular after sales service. Mine was one of those that got swapped as well. The rest of the system is still the same though.

 

[Supercharged111]

There's not a whole lot of love for the 1500 front diff. The larger one bolts in different, different width, different length cv axles, 2500 uca's don't bolt on a 1500 frame, etc. The 8.25 is not known to hold up for extreme off road. No lunchbox lockers or LSD's that I'm aware of. Quite a few have tried but none have ever come back to say they completed the bigger diff swap or have been remotely successful that I'm aware of. Most serious guys skip the lift kits and go SAS.

From those who have done it the diff swap only sounds not terrible. There is welding involved.

 

[Hipster]

From those who have done it the diff swap only sounds not terrible. There is welding involved.

I haven't seen where anyone has had it fully worked out. Links? info? Most threads I've come across the guys have disappeared into the night before completing it .

 

[Supercharged111]

I haven't seen where anyone has had it fully worked out. Links? info? Most threads I've come across the guys have disappeared into the night before completing it .

Oh man you want me to jump in the wabac machine. It seems like yesterday but we're probably talking 5 years at this point. From what I think I recall, you needed the passenger bolt in frame mount and that was bolt in and go, then the upper driver's mount bolted in as well and you just needed to extend the lower driver's mount to get the diff in (welding). Next there were some minor differences in the shafts themselves, I don't recall exactly but I think the flanges were the same. One is longer than the other and there may be trimming involved on a bearing dust shield. I don't recall which shaft you run. Maybe the long one requires trimming and the short one spacers? That all sounds about right.

 

[Hipster]

Oh man you want me to jump in the wabac machine. It seems like yesterday but we're probably talking 5 years at this point. From what I think I recall, you needed the passenger bolt in frame mount and that was bolt in and go, then the upper driver's mount bolted in as well and you just needed to extend the lower driver's mount to get the diff in (welding). Next there were some minor differences in the shafts themselves, I don't recall exactly but I think the flanges were the same. One is longer than the other and there may be trimming involved on a bearing dust shield. I don't recall which shaft you run. Maybe the long one requires trimming and the short one spacers? That all sounds about right.

I remember having to use the 1500 cv's and having to have spacers for them made along with what you said. Think I'd swap in a 2500 frame, or do a front frame clip section before the hodge podge of parts begins. I'm sure it can be done but it's far from bolt in. Maybe the diff is narrower. I don't remember all the particulars.