Hello,
I have a 76 F100 4WD, 390, manual trans, 9" rear end, short bed. I want to upgrade the rear suspension so I can haul more and I am wondering how to do it. Can I just add leaf springs? Or do I need to replace the entire leaf spring bundle? Is it possible to use F250 leaf springs? I am wondering how much I can beef up the leaf springs before I am pushing the limit of the rear axle and other components. Any advice/insight would be greatly appreciated.

Thanks!
Matt

 

I ordered some F250 leaf springs when I replaced them on my F150, they had a 1950# capacity compared to 1450# the F150 springs were rated at if I recall correctly. The 77-79 F250 springs are 3" wide like the F150 and bolted in place.

Prior to 77, the "highboy", the springs are only 2.5" inch wide as I recall and won't work without some modifications.

The bigger issue you may see after increasing capacity is the rear end itself. Ford 9" are great for handling power and can be built really stout for that purpose but they are not the best axle for hauling heavy loads. More than one person has had the axle walk out of the housing due to the semi-float design. If you're looking to haul heavy loads frequently or for long distance you should really consider upgrading to a full-float axle like a D60 or Sterling from an F250/350. Then you'll need to worry about upgrading front axle or at least the outer assemblies so you have same bolt pattern for wheels front and rear.

I assume you have the D44 front end, if you can find a donor heavy duty D44 from a 78/79 F250 you can swap steering knuckles out onto your D44 so it still mounts with your radius arms but has 8 lug bolt pattern.

When it is all said and done you might be better off just getting a rig that already has what you need to haul heavier loads.

 

I put an overload spring pack mounted above the existing spring pack thus retaining my nice highway ride.

Look at some pickups mostly the one-ton's and in the early '70's thes were common on the F350-with duals. That's where I scarfed mine for my now soft-ride F350. Mine being a CrewCab, and a '77, it has the narrow 2.5" spring leaves.
I pulled rear spring packs from a F250 short box 2wd, and installed them in place of the Stout harsh-riding F350 rear's.
The Ford setup on the early 1-tom duallys, is a cast 1" spacer block that separates the main-pack from the overload-pack, and then there is the Looonger U-bots to hold it all together. You'd like it, being able to utilize your existing soft-ride springs. Yep.

The "catch" to the set-up, it you will need to source the frame perches for the overload springs to push against.
I used the perches from a late '80;s Ford F250 with the poly bushing for sound deadening upon contact with the spring leaf.

Just a thought, as this can all be found at a local Recycle yard, and all OEM.

 

Just add a leaf.

I've used old JY spring packs, took them apart, cut the end eyes off, smoothed the ends for a smooth slip action, inserted under main leaf, piece of thin plastic or poly between, or just grease ... works nice. I did not do it with my '77 F-150 though, just was/is no need. Truck has OEM 3" wide leaves, 4 and that thicker lowest short helper.

A maybe 13 year old picture, it actually looks better now. I did lower the rear a couple years ago, but maybe the picture helps.



This below was near 10 years ago too, hauling a load of fifty 40 pound bags on a pallet home for my pellet stove, the Co-op guy used an extra pallet to push this one to the front of the bed on the drop in bed liner, for better weight. distribution. I measured on my level carport floor at home, it still had a rake. I once did hand shovel a bit of gravel into it, then the guy at the scale house had me at hair over 3,000 pounds heavier than weigh in. I was sweating too, glad I had a cooler in the truck with ice and cold water that day. I also once did haul seventy five of these 40 pound bags home from a sale after a buddy helped me load, but it had a fiberglass shell on it that time, but no heavy oak pallet. I got greedy I guess. I let the Co-op deliver these days, $10 a ton fee.



Even lowered a little, I think it would still do the job. I should have measured the front before / after, but it didn't move much at all. Always, when loaded, I kept her under 50, even 45 mph. I've seen rear axles walk out, like with cord wood piled 2 feet higher than the cab going down 501 one day (watched that happen as I was behind him in my work car), but his axle housing was bowed too. I recall was a early 9" with welded in tubes, old bumpside I believe, no extra gusseting like the later 9" rears have. I always have made sure the rear tires were at max inflation as stated on sidewalls before loading "heavy", fronts usually 5 psi less.



My FIL made himself a 3 or 4 leaf overload set up springs on top of stock spring pack, welded up his own slapper tabs to bolt to the frame sides, but his was a '77 F-250, he hauled some big loads of steel or firewood, etc. It had the Dana 60.

 

Thank you all for the info! I think the best thing for me to do is to add a leaf to the spring pack. That way I will increase the capacity a bit for when I am hauling firewood or lumber, but not making the springs so stout that the axle could get overloaded. I'm not hauling real heavy loads, just want to be able to load the truck with a decent amount of firewood and not worry about it.

Has anyone purchased extra leaf springs? That might be the easiest for me. Ive had my F100 for 23 years, but these trucks have become so popular lately that junkyards near me are pretty picked over!

Thanks,
Matt

 

Just a thought, why not just install Firestone universal kit helper bags? Allows you haul heavier loads and when not loaded it will ride like it does now. Once you start beefing up springs most of the time the ride quality will suffer.

 

I was under the truck looking at the leaf springs and noticed a couple things- there are only 4 leaf total, I thought there were supposed to be 5 total on a 76 F100 4wd? Also the bottom spring is shifted see Pic. Is this a problem?

 

I don't think a littleshift is "bad" but you might could tap it back, maybe add a spring clamp to keep it aligned? Mine is a '77 F-150, 6150 GVWR rating. Might be why has that extra thicker helper. My springs are 3" wide.

If clamping, just measure width and get simple rectangle clamps at Tractor Supply Co. or Lowe's. They don't have to be super tight, and you can double nut or use lock nuts on them.

Good read ....... I think I'll add some too. Leaf Spring Clips III - EATON Detroit Spring
My '07 has them OEM but I don't recall them on the '77?

 

I put Deaver soft ride springs in mine. Was able to completely get rid of the factor spacer and it lifted the back of my truck like another 1/2” to 1”.

My truck is a 77 SB 4x4.

I can go look up the receipt but pretty sure I bought them thru Jeff’s Bronco Graveyard.