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Old 03-01-2016, 02:46 PM   #1 (permalink)
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1981 HJ47 Troopy Build

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…


I ran the link calculator and played with a tape measure last night...
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Old 03-02-2016, 12:40 AM   #2 (permalink)
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Love the look mate!

Last edited by andy3542; 03-02-2016 at 12:40 AM.
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Old 03-02-2016, 06:23 AM   #3 (permalink)
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Link numbers

Technical difficulty prevented me on this yesterday.... Please give me feedback on the link placement and numbers as you see fit.


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.
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Old 03-02-2016, 04:35 PM   #4 (permalink)
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Cool rig.

Rear looks really good, front not so much

You want roll understeer (which you have) in the front. That requires a little triangulation on the lower links but that looks like a bit too much. Your links are also way too steep. If you can flatten your links you can run less triangulation and still keep your understeer. You should also try for a little less side to side angle on the front upper link.
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Old 03-02-2016, 06:29 PM   #5 (permalink)
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Cool rig.

Rear looks really good, front not so much

You want roll understeer (which you have) in the front. That requires a little triangulation on the lower links but that looks like a bit too much. Your links are also way too steep. If you can flatten your links you can run less triangulation and still keep your understeer. You should also try for a little less side to side angle on the front upper link.
Thanks for the advice… I'll try getting the links flatter.

how does the anti dive look? To run flatter links I believe my anitdive will get closer to 100% as the upper link frame mount can come down easily enough. I can also straighten the top link out some but thought it was better angled for no good reason.

Is vertical separation as important on a front axle as rear. What is the lowest I can go to get the lower more level?

This seems to be a game of compromises…..
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Old 03-03-2016, 06:23 AM   #6 (permalink)
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So here is what I came up with based on the above advice.

I lengthened the lower link to flatten them out and moved the axle end up a touch. This reduced vertical separation to 6" which isn't as much as I'd hoped but does get me flatter links.

Next the upper was dropped on the frame side some more to get Anti Dive back to a target number around 50%. Still have a little roll understeer and can get more by widening the lowers id I think I need it.

I think I'd be able to add a 4th upper link to the other side with the space I have. This would make me more comfortable about running the lower axle separation as I'd have twice the joints fighting that axle wrap. Locations could be identical but I may need to drop the Z location on the the axle side on the new link an inch to keep my up travel target.
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Old 03-03-2016, 06:50 AM   #7 (permalink)
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Link angles look a lot better. 6" is not much for vert sep. What is preventing you from raising the upper link?
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Old 03-03-2016, 08:14 AM   #8 (permalink)
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Link angles look a lot better. 6" is not much for vert sep. What is preventing you from raising the upper link?
my desire for up travel. Even where it is now I may be limited to 5". Moving it up means I would need to raise the engine to keep the travel, raise the frame entirely(making steeper links)

Would the dual uppers make 6" more palatable. I don't have huge hp and am not racing but want a good suspension that behave well...
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Old 03-03-2016, 01:35 PM   #9 (permalink)
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Don't forget that you should be using 'sprung' weight COG in the link calculator. 36" sounds low to me on a full body car at ride height. Its always guess, but it does have an effect on the AS/AD/AL numbers.

Looks like it is going to be a really cool build.
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Old 03-03-2016, 03:21 PM   #10 (permalink)
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my desire for up travel. Even where it is now I may be limited to 5". Moving it up means I would need to raise the engine to keep the travel, raise the frame entirely(making steeper links)

Would the dual uppers make 6" more palatable. I don't have huge hp and am not racing but want a good suspension that behave well...
dual uppers with a panhard will bind on articulation. You can get away with it if you use some rubber joints but if you use all heims it will eat heims and constantly be trying to tear it's self apart.
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Old 03-03-2016, 05:23 PM   #11 (permalink)
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how can I tell if I have enough triangulation on the front to not need a pan hard?
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Old 03-04-2016, 02:12 PM   #12 (permalink)
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did more reading and now understand why i want a pan hard….

I'll spend a little more time on it trying to squeak more separation and flat links. The reading I've done on instant centres tells me they are ok where they are i think…

Thanks again for the advice...
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Old 03-04-2016, 02:40 PM   #13 (permalink)
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Why not work with am4x4 or 4wheelunderground to adapt one of their kits to your application. Or turn the Master of Toyota metal loose on that thing...
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Old 03-04-2016, 03:14 PM   #14 (permalink)
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If we send a $10,000 canadian truck to the US for $100 of modifications, we have to pay import tax on the entire value of $10,100 or whatever new value the border guard decides when we try to bring the truck back into Canada. Very cost prohibitive for us to get our trucks worked on in the US.
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Old 03-04-2016, 04:51 PM   #15 (permalink)
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No clue you guys were in Canada. Assumed you were in Cali by the places you wanted to wheel.
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Old 03-06-2016, 07:04 PM   #16 (permalink)
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having second thoughts on this entire setup. Mainly worried about the complexity of a 3 link and stability on road. Some friends and I were talking more about it today and discussed the simplicity of a stock 80 series radius arms. They work pretty well off road and and ride nice too. They also provide some sway control.... this obviously come at the cost of articulation.

Then I got to reading about some radius arm builds.... the metal cloak link that spring loaded to change length by 3/4" each way. So the theory is this thing is adjustable to be locked for on road and unlocked off road.... But then it feels like I'm bandaiding a lesser suspension....

time to read more on 3 links I guess....

Want this to work out well and not have to be redone...
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Old 03-06-2016, 08:02 PM   #17 (permalink)
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Everyone has their own opinions, and I am still learning just like you, but I like the combination of a 3 link up front and leaves in the rear. The rear leaf springs seem to keep everything in control. Also my lower links and panhard/drag link are almost flat at ride height. I have less brake dive and more control up front than I did on clapped out flat leaf springs riding on the bumpstops.

I am on my second 3 linked vehicle that sees street time and I feel more confident with each build.

This is why I suggested working with am4x4 or 4wheelunderground. You could get a system shipped to you that will work very well for your intended purpose. It would take most of the guess work out of the geometry and you would just have to focus gluing it all together.
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Old 03-07-2016, 01:40 PM   #18 (permalink)
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I think with 11-12" of shock you would be ok with most of the options.....3-link + panhard, 4 link + panhard, or radius arms + panhard.

3-link. You can end up with a little odd brake dive depending on what side and what angle the upper link is sitting on. The single upper link takes all the forces so it is better to overbuild it slightly.

4-link. A few million vehicles are running around with two upper links. As long as you have some bushing compliance and don't triangulate them too much you will be ok. Having two upper links to share the load is likely a good thing. Packaging can be a bit harder. I think emergency/panic brake performance is a little more predicable since the forces are even on each side of the frame.

Radius Arms. For 10-12" of shock travel I think they can work just fine. Again, a few million vehicles running around with them. You get some sway control as you mentioned. You will have to replace the bushings at the axle more often if you are really working them. One quirk I notice is that you may get a little more axle 'chatter' under power, especially as the bushings wear. I think this is generally just a function of force vs separation vs bushing compliance.

I took the easy way out on my new build....



I am just building an FJ45-esk body to fit on an complete FZJ80 ( actually an LX450 in my case ) chassis.
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Old 03-07-2016, 09:18 PM   #19 (permalink)
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well went with ordering parts for the 3 link front. Sounds like I may add a 4th link to share the forces. It will be something close to my last design on the front. That should net me a decent performing suspension. My goals for each are:
30-80% AS/AD by moving upper link mounting
Instant centres a long ways away to aid in wheel recession
Aiming for 0 to -2 understeering roll axis
lots of castor up front to help keep tracking straight 4-6*
3-5* max pinion change through travel
12" shocks

Parts ordered through TMR today...
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Old 03-08-2016, 05:13 AM   #20 (permalink)
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Very cool build, I will definitely be following along.

I have no experience with a true 3-link suspension, but lots of experience with radius arm and wristed radius arm(one radius arm, one single link) suspensions. I personally like the stability and predictability of the 80-series front suspension particularly for a rig that sees street time. It may not have the most flex, but it works very well IMO.

I am planning to link my 40 front and rear in the next year or so though, so I will be curious to see how you go about it and how you like the end results.
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Old 03-08-2016, 06:33 AM   #21 (permalink)
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I will also be following this thread! Great info on various suspension set ups so far. I'm having a 40 linked in the next couple of months and really want to know how and why it works well.
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Old 03-08-2016, 06:36 AM   #22 (permalink)
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http://www.offroadxtreme.com/engine-...n-inside-look/

I found this article online when I was looking up radius setups you mentioned. Kinda help explain a couple things for a newbie like me, might be useful....
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Old 03-08-2016, 10:59 AM   #23 (permalink)
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well went with ordering parts for the 3 link front. Sounds like I may add a 4th link to share the forces. It will be something close to my last design on the front. That should net me a decent performing suspension. My goals for each are:
30-80% AS/AD by moving upper link mounting
Instant centres a long ways away to aid in wheel recession
Aiming for 0 to -2 understeering roll axis
lots of castor up front to help keep tracking straight 4-6*
3-5* max pinion change through travel
12" shocks
If you can build some adjustment into the upper link frame side mount that will be a good thing.

Long instant center is good....and rather low also. A long instant center also seems to help indicate how AD/AL/AS changes through the suspension travel.

I would shoot more for -2 roll axis rather than 0. It will help with how much steering wheel input you need to give the vehicle....or rather how sensitive the chassis will be to input. I wouldn't be afraid of a little more either.

Lots of positive caster? As tire size increases, in theory, you need less. Running LOTS of caster ( which 4-6* isn't really ) was an old school patch to help with high speed stability and poor suspension geometry.

I wouldn't worry too much about pinion change...other than it's a good indicator of caster change. Both aren't THAT big of a deal. Most of the time the suspension is going to be operating in a pretty small window. We don't really care what happens too much on the edge of the window. It is pretty impossible to have almost no pinion angle change ( driveshaft relative ) while keeping caster change ( wheel relative ) in check.

12" shocks. Good. I don't see the need for more than that on most vehicles. I'd try to make room for 6" of uptravel from ride height if possible. Packaging that in a low ride height is always fun. I would try and get the shocks as close to the tire as possible. Having them mounted slightly wider at the bottom and angling in at the top will help the sway related motion ratio. Packing that will be challenging.
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Old 03-08-2016, 11:44 AM   #24 (permalink)
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great tips and comments again from everyone. I'm looking closer into running front coil overs now as and option rather than the 80 series stuff. Mainly for tight packaging and more tunabliity for ride height and frequency. aiming for 300-350 lb coils but will measure corner weights before landing those for sure.
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Old 03-08-2016, 12:11 PM   #25 (permalink)
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Have you read this by chance?

Suspension Encyclopedia/4Wheel Underground


My FJ40 ran a 175 over 200 which is a 93.3 lb/in primary rate. I know your truck is much heavier overall, but a lot of that is in the rear. I had 6" uptravel on a 14" shock.

Calculators are great for getting an initial plan, but I would get your link kit and start mocking everything up as well.
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