I've been looking around and I've only found one person who claims to have used 4.5" lift springs for a 66-77 Bronco for 5.5" of lift, but haven't detailed what what required to install them.

Going off of that info, I looked through the Moog catalog and found the Moog 580 coil springs. Same internal diameter as the Bronco springs, but longer length with the same stiffness as Terrafirma medium springs. I was about to pull the trigger until I had the bright idea to measure an extra spring perch I had. 4.5" in diameter.

Then how can this be? Bronco springs are a 4" ID, same as the Moog springs I spec'd out.

So, can someone shed some light? Anyone know if the guy that did it used stock perches? They wouldn't even work if the perches were flipped if my measurements are correct, though maybe springs are measured differently than I understand. I don't see how that would be true, though.

In the mean time, back to the catalog to try and spec some 4.5" ID springs. Would love any information if anyone has some.

 

RTE offers a 4" lift. Just order from them and you'll know it will work out of the box. It will require an HD driveshaft up front and some modification to the rear as well. Also, caster corrected radius arms and an adjustable panhard. There is a reason a 4" "lift kit" costs around $2000. It's a lot more than shocks and springs to make it right. If you go beyond 3" of lift be prepared to exercise your wallet. Good luck!

 

Yeah, I've talked to RTE. Too cost prohibitive for me. I'm on 3.5" now, but the rears are too soft for my uses and starting to sag.

Not true on the arms and driveshaft, btw. I've been perfectly happy with stock arms and stock style driveshaft. At 5" I would do all that, but not at 3.5" or 4". Only real requirement was extending the shock mounts in the rear, shortening g shock towers in the front, and converting to a rear panhard helped a ton.

 

I had steering issues and massive driveshaft vibrations even at 3". Caster arms and an HD driveshaft solved my issues. I was told I was one of the unlucky 20-30% that will have these issues even at 3" of lift. I was told most will have steering issues over 3". Consider yourself lucky! It was a large added cost to do the caster arms and GBR HD driveshaft. Drives like a dream now though.