Most TTB application lift springs are way too stiff and short for good offroad performance since they are trying to cover up the deficiencies in the stock steering geometry that are magnified with soft springs and lots of travel. For a full size, I imagine a spring in the 300-350Lb/in range would probably work pretty well. Most TTB application lift springs are around 500Lbs/in.
really good information in just 4 pages here. I wish I read it back 2016 when I bought a TTB swapped E350. Modified and with sagged factory springs, It was a straight up handful on highway compressions and braking. The conversion dropped the mounting points by 2” but did not use a drop pitman I assume because the common 4 and 6 drop versions were too much. This increased the steering links angles and combined with sagged springs resulted in big toe changes during travel changes.
Spooked by the factory overly soft springs and wanting some lift, I of course went heavy. CC880s springs gave 1” lift (13” installed height). It was still a little darty wanting to get the links parallel to the TTB arms I added a 4” drop pitman. This brought the linkages parallel to the TTB arms and solved the dynamic toe issue.
The other issue was a loose lower radius arm bolt that allowed the TTB arm to rotate slightly changing caster. This created a crazy pull to the ditch. Everyone was telling me bushings. I’ve since read this lower bolt loosening is a problem. Replacing and properly torquing solved the issue for me.
The combination of the two problems made for fun times after hitting a compression at hwy speed, tires toeing out darting left or right, panic hit the brakes and then a hard pull to the ditch. The previous owner had given up and was planning a SAS but decided to dump it.
As a hwy cruiser I’ve been happy with it for a few years now … but performance even mildly rough roads especially washboard is horrid. This kind of defeats the purpose of the rig.
The moog cc880s springs I put in are quoted at 652lbs/in however they are variable rate and I suspect the lower coils might be higher rate. The design of the springs use upper coils that are intended to fully collapse (lower rate) and then ride on the top of much firmer coils. The manufacturers intent is to improve hwy driving and for that they are great.
However I would really like better rough road performance and would like to better use the limited wheel travel available. To do this a constant rate spring seems like the answer … but since I don’t know what the actual rate of spring I have now is, getting the right rate is not straightforward.
The CC880s specs are 652lbs/in and 16.6” free. The current installed height is 13”. This surprisingly lines up well with the rate. Moog quotes the load as 3006 lbs at 12” which is 653 lbs/in. At my installed height the 653 x 3.6 = 2350 lbs which I think is a little high, closer to corner weight vs sprung weight. Again the top 3” of the coil is collapsed to nearly bind (by design).
I think sprung weight is ~2000lbs per corner.
(it’s a D44 with D50 knuckles and 8lugs. I am right at the axle weight rating … this was one of my TTB discoveries. The work was done by the shop that did the 4x4 conversion. I’m watching wear items, it sees very light use. still … I know. I do like longer D44 arms, if I have a problem I’ll need them up)
Ok back to it … based on the recommendation above I am thinking I might try a 3”-4” lift spring. If they are too firm for a bronco/f150 might be perfect for the E350.
Does anyone know the rates for common lift coils?
Skyjacker
182 2?”
184 4”
186 6”, 623 lbs/in, 20-1/8” free
Any other coil recommendations, targeting high speed off-road.
This was the best and most recent TTB info I have found in years, thanks