help evaluate link design for HJ47 troopy (1 Viewer)

[arnott1t]

Hey Folks, Wanted to get some input/advice on a build of mine. Specifically I have a 1981 HJ47 that I’m making into a pretty capable camping rig. As it sits now it had a 1hdt with Gturbo (whizzy Australian turbo) H55 5 speed, NWF black box and split case. This is routed to the factory 40 series diffs open with 4.11 gear. Its all sitting on 37 x 13 cooper STT’s on Rock Monster bead locks. I love this truck… it’s my dream ride. The next progression though is to improve the axles and suspension. That is what brought me here.

My plan is for a comfortable ride with good off road characteristics and better than leaf performance at speeds. I liken it to a stock 80 series suspension in terms of performance and ride. I don’t need crazy articulation or travel but would like a well balanced functioning suspension that rides nice. I’ll be doing more camping and fire roads than hardcore rock crawling. Places I’ve been in other rigs than I would go in this are places like Hell’s revenge, Moab Rim and Turf and Surf. At some point I’d love to squeeze this bus down the Rubicon trail more technical trails. Not things that are buggy only but difficult trails none the less. My local trails are more a mud sand forest kind of mix. Nothing a locked truck with good tires can’t do. So again focus is on general handling and ride.


Here is the plan:
4 link kit from TMR with Johnny joints in the rear
Rear Air bags for adjustable weight capacity for a given ride height. In full camping hear I tip the scales at just over 7000lbs and can shed over 1000 in daily driver duty. Hoping to have air bags out back (firestone heavy truck 12” travel rolling lobe)
AAM 10.5” rear axle with TMR shave kit and truss. 68” wide
Outboarded shocks and some version of anti sway bar….
Aiming for 6” up and 6” down travel.


3 link kit from TMR in the front again with Johnny joints
80 series front coil springs
Some shocks….
Dana 60 from Dodge, rebuilt hubs and kingpins, currently has a new LSD
Aiming for 6 up 6 down but may be limited to 5 up…

The front design

Rear Above


Both should allow for 5-6” up travel. The front upper axle mount will be tricky. I needed to lower it to keep the top of the mount level with the top of my imaginary housing. This means I’ll need to weld the mount to the dana 60 center section or off a low profile truss. I’ll likely get a pro to weld in that after I tack it all together. To keep enough separation at the axle end I place my lowers below the center line. Centerlin of the axle should be 17.5” and center of the mount will be 15. This means bottom of the joint will be at 14 and bottom of axle tube at 15.5…. so I’ll have a 1.5” nub below the axle on each end. Keeping it as close to the tire as possible should help keep it out of harm’s way I expect.

 

[White Stripe]

Have you thought about just using the front control arms off of a 80 for your front end set up? They flex decent and are pretty simple. They also seem to hook up well on climbs.

Hey Folks, Wanted to get some input/advice on a build of mine. Specifically I have a 1981 HJ47 that I’m making into a pretty capable camping rig. As it sits now it had a 1hdt with Gturbo (whizzy Australian turbo) H55 5 speed, NWF black box and split case. This is routed to the factory 40 series diffs open with 4.11 gear. Its all sitting on 37 x 13 cooper STT’s on Rock Monster bead locks. I love this truck… it’s my dream ride. The next progression though is to improve the axles and suspension. That is what brought me here.

My plan is for a comfortable ride with good off road characteristics and better than leaf performance at speeds. I liken it to a stock 80 series suspension in terms of performance and ride. I don’t need crazy articulation or travel but would like a well balanced functioning suspension that rides nice. I’ll be doing more camping and fire roads than hardcore rock crawling. Places I’ve been in other rigs than I would go in this are places like Hell’s revenge, Moab Rim and Turf and Surf. At some point I’d love to squeeze this bus down the Rubicon trail more technical trails. Not things that are buggy only but difficult trails none the less. My local trails are more a mud sand forest kind of mix. Nothing a locked truck with good tires can’t do. So again focus is on general handling and ride.


Here is the plan:
4 link kit from TMR with Johnny joints in the rear
Rear Air bags for adjustable weight capacity for a given ride height. In full camping hear I tip the scales at just over 7000lbs and can shed over 1000 in daily driver duty. Hoping to have air bags out back (firestone heavy truck 12” travel rolling lobe)
AAM 10.5” rear axle with TMR shave kit and truss. 68” wide
Outboarded shocks and some version of anti sway bar….
Aiming for 6” up and 6” down travel.


3 link kit from TMR in the front again with Johnny joints
80 series front coil springs
Some shocks….
Dana 60 from Dodge, rebuilt hubs and kingpins, currently has a new LSD
Aiming for 6 up 6 down but may be limited to 5 up…

The front design

Rear Above


Both should allow for 5-6” up travel. The front upper axle mount will be tricky. I needed to lower it to keep the top of the mount level with the top of my imaginary housing. This means I’ll need to weld the mount to the dana 60 center section or off a low profile truss. I’ll likely get a pro to weld in that after I tack it all together. To keep enough separation at the axle end I place my lowers below the center line. Centerlin of the axle should be 17.5” and center of the mount will be 15. This means bottom of the joint will be at 14 and bottom of axle tube at 15.5…. so I’ll have a 1.5” nub below the axle on each end. Keeping it as close to the tire as possible should help keep it out of harm’s way I expect.

 

[mr jits]

Stick with the phenomenal input you're getting on that other site from some people who've been giving you some real world input (and have built many different link setups for a multitude of customers).
From what I've read in your other thread, you've had some pretty good numbers figured out, minus the upper link separation. Packaging is a pain with the 4x series frames so some concessions will be made.
Airbags won't be an issue, they come in all shapes, sizes, and lengths. Just be sure to get ones with an internal bump stop and have them air up separately from eachother or you'll have some exciting things happen in off camber situations.

 

[arnott1t]

Thread revival... Im in the midst of doing this project finally. Link numbers below:

Went with trailing arms and 2.5" Coil overs mounted ~12-14 inches up the lower arms. This helps the shock get out of the way of the tire so the frame and tube shouldn't have to be modded to much. That why the lowers are so long. 250 wall 2.5" with 2" alum bar inside should help keep them straight. TMR antiwobbles on one end....

 

[SuperBuickGuy]

Your instant center is going to make your rig squat on acceleration. Basically that means your axle will unload when you matt the throttle. Perfect IC is at the crank flange.

think of instant center as putting weight in optimal places. The twisting of the axle is transmitted through the control arms to a point.... put it in front of the vehicle and the rotation will pull the axle into the vehicle - which actually unloads the axle. Put it too far back, and you'll get separation where the axle moves forward but the vehicle doesn't.

 

[arnott1t]

My uppers on the frame side can come down alot to 24" or 26" so that would solve that. Essentially changes the "squat" value. Seem that I'm stuggling the most with roll axis angle. having oversteer vs under... but basically hovering around 0+-1*

 

[SuperBuickGuy]

outside of keeping your panhard bar equal length to your steering cross shaft... over/understeer really isn't a primary consideration on a flexy, lifted 4x4. By the time you get to a speed where that matters, you'll have other concerns. Not just that but the biggest contributors to scrub radii and O/U steering are hard to change because that change puts a bar way in front of the axle (making it more susceptible to trail damage). Add to all of those considerations that a locked rear differential pretty much makes it all understeer.