Some random thoughts:
1. Why leafs?
Well, leafs are cheap, simple and reliable. Leafs suspend and
locate the axle, killing two birds with one stone. Some will argue leafs are old technology, and they're right. However, old is not necessarily bad, but is tried and true. Leafs can be “tuned” to some degree by anyone (however this tends to be more true with rear spring packs than the 2-leaf front packs that are most common in SAS’s). Examples of “tuning” (and I don’t mean “tuners” like sport compact cars) could include adding leafs, removing leafs and/or shaping/cutting leafs. Shaping and cutting leafs is perfectly acceptable but be careful about re-drilling the center pin hole.
Walk out to your Bronco and take a look at the rear suspension. Pretty simple. Which leads me to:
2. How difficult is a leaf SAS?
. A leaf SAS is arguably the easiest SAS, provided that your donor axle came with leafs from the factory (78/9 F250/350s and 86-97 F350s are your best candidates). This is because a leaf suspension is very simple, and is comprised really of just three parts:
-front spring hanger (one per side)
-rear spring hanger (one per side)
-shackle (one per side)
One spring hanger interfaces directly with the leaf eye, the other spring hanger acts as pivot for the top of your shackle. The eye at the other end of your leaf goes into the bottom of your shackle. The shackle swings and allows your leaf to change length, which naturally occurs as the suspension cycles up or down.
You need only find a way to anchor your spring hangers securely to your frame, and over the half the battle is won. Beyond this are smaller things like shock mounts, brake lines, and steering but I won’t touch on those much because if you can’t handle that stuff you probably shouldn’t be considering an SAS.
3. Where do all the parts come from?
There are many ways to do a leaf SAS. I’ll just cover one possible way here, which is the method with which I’m most familiar, and seems most common among those SAS’s which I linked to above.
Front spring hanger:
I used a front hanger for a late ‘70s F250, it’s a very simple piece and is pre-fabbed for you. Also it bolts onto the F250 from the factory, so removal at a junkyard is simple:
We also discovered that 4” square tube with .250 wall thickness works great if you wanna build your own:
Rear spring hanger:
Factory Ford stuff can also help you out here, look for this hanger on ’80-97 F250s or F350s. Yes, even tho F250s of this era used TTB, it was leaf-sprung TTB and the hanger is the same from F250 to 350.
You will find this hanger at the rear
of the front
springs on your donor truck, the same position in which you will be using them. Unfortunately they are riveted on at the factory, so removal can be problematic. Be nice and approach yards when they’re not busy; they may torch them off for you at minimal cost; I’ve had hangers cut off for $10 per side.
Note that this hanger is not as simple as it appears, primarily because it positions the leaf eye about 2/3 under the frame and 1/3 outboard (that’s a VERY rough guess). Thus, trying to build this hanger will be somewhat time-intensive and will require some trial and error. But the positioning on this hanger is perfect if using 36” center spring perch spacing (more on that later), so I recommend looking for the original piece.
I used stock rear shackles, ie walk to the back of the your Bronco as it sits now and you’ll see the shackle you need. Fullsize Fords from the early to mid ‘70s all the way thru ’97 should provide a suitable shackle, just be sure it takes a 3” spring as some 80’s F100s used 2.25 or 2.5” rear springs. You might also consider buying new shackles; it’s common for them to be sold complete because when the molded-in rubber bushing wears I suppose it can’t be replaced per Ford specs, ie the average consumer can’t mold more rubber in there. However, if you get some used shackles with trashed bushings, don’t fear as suspension.com will sell just the shackle bushings in poly which basically push in by hand and cost less than $20.
I recommend plating your shackles sooner or later as you can see they endure considerable twisting forces in uneven terrain.
: I’ve always used a main leaf from an ’86-97 F350. Under that I’ve tried a couple different lower leafs to soften the spring rate some, even tho the stock F350 spring pack really doesn’t flex or ride nearly as bad as one might suspect. Under my main leaf I’ve tried a very thin leaf from a rear spring pack, which proved to be too unsupportive and was arched too much causing it to want to curl at the ends – I broke an F350 main leaf up front with this setup. I’m currently running a 2nd leaf from a ‘99+ SuperDuty, it’s a bit thinner than the pre ’98 lower leaf but the arch more closely matches. In any case, I recommend starting out with a stock leaf pack and modding it later if you choose.
You can also use ’80-97 F250 front packs, but they’ll have a bit of negative arch, so plan on slightly less lift and **maybe** a slightly harsher ride.
: ’86-97 F350 steering is a direct bolt-in for your TTB Bronco
4. I have an ’80-’91 Bronco. Do I have to weld?
Yes, you’ll probably need to weld at least a little. If this is a problem, you can do what I initially did before I owned a welder:
Step 1: make a cardboard template to box your framehorns and then transfer that onto 3/16” plate which you can (with patience) cut with an angle grinder:
Step 2: take that to a friend who can weld it in place for you. At the same time you may want to install some tube to run bolts thru for the front spring hanger, but there are MANY ways to anchor your front spring hangers to your frame, and this is probably the weakest method (you’ll have to browse thru photos above for other ideas):
From here everything virtually bolts on.
4.b. I have a ’92-96 Bronco. Do I have to weld?
YES! Go take a look at your framehorns. Behind that ugly, tinny excuse for a front bumper you’ll find a bunch of ripples, known as crumple zones. Your front spring hangers will place quite a load on these as the framehorn will now be supporting at least part of the weight of the truck – something it was never meant to do. You’ll need to find a way to box these in to provide additional support. Note the crumple zones are much like a sippy straw, ie they could conceivably fold in any direction. For the purposes of your SAS this means they might not only fold UP, but could also fold SIDE to SIDE as sidehill, driving and cornering forces impose various loads on them. Point being not only do you have to plate them, but you need to run a crossmember to tie them together and help keep everything square.
I have outlined the various swaps that are of specific interest to crumple zones above, so take a good look at the pics and decide if you want to do this and/or can do this. You are technically defeating a safety feature of your vehicle here, so do so at your own risk and consult your insurance agent if you wish.
5. What’s the deal with spring perch spacing?
This is measured from center of one spring perch to the center of the other spring perch and is pretty important to your swap. There are basically two numbers you need to know here: 32” and 36.25” (approx). Any leaf sprung 4x4 from the late ‘70s will be 32”. This worked great for the framerails of that era which were essentially straight. However, if you look at the framerails of your ‘80+ Bronco when kneeling in front of the vehicle you’ll see that the framerails go in and out, particularly around the coil tower/shock tower.
’86+ (the year which Ford returned to solid axles – Dana 60s- on it’s F350s) is based upon a 36” center to center spacing to accommodate the wider, wackier frame. Note that for the most part every ’80-97 Ford truck, Bronco thru F350, used basically the same frame from the framehorns to the firewall.
*In my opinion* if you’re working with an ’80 Bronco and you want to do a leaf SAS, it is easier to use 36” spring spacing (otherwise the hangers I mentioned above will not work for you). This means if you find a donor axle with 32” spacing, you can simply move the spring perches out to the wider spacing. This what we did with Beerman’s
swap. If you are using an ‘80+ frame and want to run the 32” spacing, you will need to build a custom crossmember up front, see Bronco Boy’s
swap for an example of this.
You should also read this:
6. Other options for springs
: while the ‘86+ front F350 leafs work pretty well, they’re somewhat rare and can be difficult to work with or modify aside from ordering custom spring packs. A better option might be front Chevy leafs (no moaning about your short-sighted brand loyalty please) as they are readily available from the aftermarket and are 2.5” wide which might theoretically allow for more flex, but may require different spring hangers and perches. Also, they’re intended for a half-ton truck and will almost surely be softer.
Do some research if you wish, but remember most springs have unique characteristics – primarily width of the spring, center pin location, and length from eye to eye – which all affect how you build and position your spring hangers.
7. I heard all trucks with solid front axles ride rough. Won’t it be even worse if I’m running F350 front leafs?
The bottom line is this: your ride will stiffen some, yes. Is it bad? I wouldn’t say so. “It rides like a truck” is the most common conclusion from those who have completed a leaf SAS. Expect a firmer ride but a more responsive feel with a slightly crisper feel to the steering wheel and less wandering. Nonetheless, this is old-school, basic technology and it won’t handle like a sports car. However, do not go ride in a stock ‘80+ F250 or 350 and think your truck will ride so poorly because:
8. Ford put the shackle up front on ‘80+ trucks. Why did you put it at the rear?
Generally speaking a shackle mounted at the rear of your leafs will make for a smother ride. This is because 99% of the time you’re driving FORWARD at speed; as your wheel encounters bumps it must move up. As the wheel moves up the leaf spring flattens & lengthens a small amount. With a front-mounted shackle, when the spring lengthens to absorb a bump, the axle shifts forward just slightly, shoving your axle INTO the obstruction. With a rear-mounted shackle the axle swings back slightly, moving your axle away from the obstruction; a much more natural movement while driving forward.
This is only one explanation and some will disagree.
9. What is a track bar and do I need one with my leaf SAS
? In simplest terms a track bar is a rod which runs from one framerail at an angle down to your front axle. It helps to locate your front axle (or rear axle in some cases) laterally under the vehicle, ie it prevents the axle from shifting side-to-side. In most cases a track bar is not required with a leaf SAS, provided your spring hangers and shackles are strong and securely attached to the frame, along with proper u-bolts, etc. If you should find that your axle is allowed to shift side-to-side, a track bar may be required but it is unlikely at best unless you are running heavily arched lift springs, very narrow leaf springs, or Revolver shackles or similar.