Coil sprung SAS

109-0971_img.jpg (68694 bytes)After many years of resisting the urge, I finally got to the point of wanting to do a Solid Axle Swap.  The IFS worked well for many years, but I was to the point of wanting to do tougher and tougher trails and the IFS just wasn't gonna give me what I wanted.

Several Zu'ers have done the SAS, most in just the last couple years.  With the exception of a couple high-dollar, coil-over setups, they have all been done with leaf springs and all have ended up sitting higher (some much higher) than I wanted.  This wasn't a spur-of-the-moment kind of decision.  I've had ideas rolling around in my head for a couple years and what I decided on was to use coils with radius arms and track bar.

Cleaned up and painted with new axle seals inside.Finding a suitable axle took a while to decide on, but what I picked was an FZJ-80 Landcruiser axle.  Mine came from a '97 with about 70k on it..  Why this one? I didn't want a Dana 44 as it's not all that strong of an axle without about a grand in CTM u-joints and alloy axles.  A Dana 60 is far bigger and heavier than I want.  I really wanted something with a 3rd member. A Toy mini truck axle is too narrow and the birfs too weak, although the Longfields are supposed to be performing pretty stellar and would work well. It's still too narrow though. I even thought about something custom using a spare rear 12 bolt diff I have with Dana 60 knuckles, but cost would be absurd. Not to mention needing custom axle shafts.

The FJ-80 axle is about 63" WMS to WMS and it's about 2" wider overall than my IFS was with the 2" wheel spacers I used for several years. It's the perfect width that I wanted.  It's also got a 6 lug wheel pattern, although it does appear to be hub-centric rather than lug-centric.  The hub, rotors and calipers are also huge and wouldn't even come close to fitting the stock Isuzu 15" wheels.  The aftermarket 15" AL wheels I have though just fit with a little grinding on the calipers so I'm good there.  For the back, I'm still running the 2" wheel spacers for now, but I've picked up a 12 bolt from a 2nd gen Trooper (62" wide) that I'll swap in soon and get rid of the spacers.

The -80 axle's got a high pinion diff and I'm running an ARB and Precision Gear 4.56 gears to match my rear axle.  I was originally supposed to be getting the factory electric locker as well, but the junkyard screwed up big time and what I got was the locker-less diff.  They couldn't locate a locking diff for me, but they did refund some of my money and I'm happy with an ARB in front since I already have the rear ARB with it's wiring harness and an on-board air system hooked up to it.  All in all, it was still a pretty good deal for this axle, although not the smoking deal I thought it was when I was buying it.  It also came with the springs and radius arms which I wasn't expecting, but I ended up making custom arms anyways.  The springs I am using though.

This axle uses full-time drive flanges in the hubs, but I've swapped out for manual Aisin lockout hubs from a pre-85 solid axle mini truck and I carry the flanges for trail spares.  The spring pads place the coils outboard of the frame rails with about 2" clearance, which works just about perfect.


18 Jan 04
New Bilstein 5150's
37's mounted
Testing radius arm flex

2 Nov 03
Re-built my upper coil spring mounts.
Getting ready to mount new tires.


Axle Specs

'97 FJ-80 Landcruiser axle.
High pinion, 8" Toyota diff.
Precision Gear 4.56 reverse cut gears.
ARB locking differential.
Aisin lockout hubs.
"Mar-tacked" axle shafts.
Stock FJ-80 brakes.

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I did not re-build the knuckles, although I did clean, sandblast and paint the housing, re-packed the knuckle and wheel bearings and put in new inner axle seals.  The stock radius arm brackets were cut off and new ones made to work with my radius arms.

Axle Placement

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The axle is pushed out forwards about 5" over stock IFS location.  I had previously moved the rear axle back about 1/2" from the stock location and total wheelbase is now 98", up from 92.5" stock.


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Coils are stock FJ-80 coils.  Longer coil on driver's side.
Upper mount attaches to shock/coil hoop using a rod end.
A sliding mechanisim allows the coil to drop away from the mount.
Stock FJ-80 track bar is being used.
The spring is retained at the bottom on the axle tube, and to the large plate at the top.  The sliding mechanism allows me to insert spacers in there pretty easily to add lift.

Radius Arms

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The radius arms are custom I-beam type arms.  They mount up high inside the frame rail and splay outward to where they connect to the axle.  The center is cut from 3/16" steel and the caps are 3/8" top and bottom.
The arms connect at the front and rear of the axle housing, running over the top of it for ground clearance.
Rear connection of the arms are Rubicon Express spherical bearings.
All 3 bushings on the arms form nearly a strait line to give the best flex possible when articulating.
The rear flange on the driver's side is over-sized, allowing me to pull that bolt out for trail use if I want and still retain the bushing.  This is an alternative to wristing the arm.
Caster was originally set at 6 but I got a (very) bad wobble around 30mph when I went to the 37's.  I re-did the axle tube mounts to set caster to about 3 to get rid of the wobble.
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With the axle pushed out forward, the steering box had to go and was replaced with an IH Scout II Saginaw box.  This mounts outside the frame rail and uses a forward facing pitman arm.
The pitman arm is from an early 90's or so Caddy from the junkyard.  It's perfectly flat and 6.75" long.  The car had a standard Saginaw box mounted against the firewall, the pitman was forward and the steering arms were behind the axle.  Scab plates were used to mount the box (3/8" outside and 1/4" inside the frame rails) and the new holes were sleeved.  My stock steering shaft is 3/4" and I used a weld-on u-joint from AFCO racing to connect to the box.

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The draglink is stock FJ-80.  The steering dampener uses a u-bolt bracket on the drag link side.  For the frame mount, I used the mount from the FJ-80 dampener.  It's a plate with a tapered insert in it and uses a tie rod end.  I cut the TRE off and welded to my dampener and used the bracket with it.  The tie rod is stock FJ-80, but I am planning a HD replacement for it.

I've also got most of the parts for hydro assist, and the scout box is pretty easy to drill for it.  That will be added in a bit later on.

Drive shaft

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One headache other SAS folks with leafs and a D44 have had is the front driveline.  Between the low-pinion and leaf springs, getting a driveshaft with enough angularity and travel is a real problem, and many haven't really got it 100% yet.  Pushing the axle forward helps a lot, as well as giving the needed firewall clearance for bigger tires and giving a better approach angle.  With my setup, I have had no driveline issues to speak of.  The high pinion 80 series diff help a lot with the initial angle, and I don't need much travel in the shaft because the radius arm suspension keeps the length pretty constant throughout axle travel.  The stock IFS slip joint in the driveshaft gives more than enough travel.

The u-joints for Isuzu and what Toyota uses are very similar.  They are the same design and size in the critical areas.  I was able to use my Isuzu drive shaft and u-joints and fit the flange from the FJ-80 joint onto the Zu joint.  All it took was to open up the Toy flange about 100 thou between the ears so the clips would go on.

I'm using my stock Isuzu front drive shaft, cut and extended with sch 40, 1.5" pipe.  It is not balanced, but doesn't need to be for trail use.  I'm working on a dual transfer case and will get a proper shaft made when that's done.  There has been no binding in the upper u-joint, and with the radius arms, the stock slip joint is more than enough.  Total slip is less than 1".


In all, it took about 6 months for me to do taking my time.  I did waste a lot of time going down certain roads and changing my mind because I didn't like how it was turning out.  I started out modifying my stock cross-member and used the stock FJ radius arms for example, but really didn't like the compromises I had to make so I built the new arms.

I finished it and took a few test drives, then headed off to Moab 3 days later to wheel for a week at MoabZu VI.  It made the 500 mile journey both ways and a week of trail riding with zero problems.  I couldn't be happier with it.  

Trail performance is phenominal (remember, I'm an IFS guy) and the flex is much better than I was expecting.  We had a ramp there (20 deg) and I ran up it for an 1133 score.  I never did bother to pull the rear bolt out of the driver's side arm cause it flexed so well.  Body roll is minimal and it doesn't feel tippy like some of the coil-over guys I know have been fighting.  My low height has a lot to do with that I'd imagine.

Some trail pics of the first off-road testing.


I did find some things to tweak though.  Running up the ramp showed that my shocks are a bit long when the axle is twisted to the extreme.  I bought some cheap Pro-comp stuff initially and will get some of the new Bilstein 5150's now that I know for sure the size I need.

I still want to re-build the knuckles on the axle.  New seals and bearings, and get new rotors, calipers and wheel bearings while I'm at it.

Shave and armor the axle housing under the diff.

I did manage to hit the tie rod and put a very slight bow in it.  I'll be getting a heavier duty tie rod for replacement.  The radius arms over the top are great for ground clearance, but they do leave the tie rod more vulnerable.

I'm looking for a spare set of axle shafts and birfields, but they're not cheap.  Once I do, I'll send them off to Bobby Long for his treatment then keep the un-treated ones for spares.

When the driver's side is stuffed hard, the coil spring bows inward enough to hit the u-joint in the steering shaft making steering notchy.  I need to put in a guard of some sort between them.  The bowing in isn't an issue, but I want to keep it off the steering column.

I need to do some more fender trimming towards the front, including completely removing the stock bumper mounts and building up something with a lower profile.  My old, worn-out 33's clear fine, but I will be moving up to 37's soon and will need the room.

I want to get my hydro-assist steering hooked up and put a new seal kit in the steering box while I'm at it.

I want rock-lights.  A small group of us made a night run up Moab Rim and I had a blast.  I want to get lights for some night wheeling here in AZ.


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Created by: Dan Houlton
This page was last updated on 14 Apr 2004