Coil vs Leaf for 4x4 Conversion?

[vandiesel]

https://youtu.be/Jb_miPZzrbM

This guy knows a few things. Love the Trail Mater.

[deserteagle56]

Originally Posted by motovan_mn

Does the radius arm or 4-bar linkage used in coil systems allow the solid axle to move more easily than an axle constrained by a leaf spring?

One thing is for certain, from my observations over the past 40+ years. Coil suspension are more prone to "death wobble" than with an axle sitting on leaf springs. All those bushings the coil suspensions pivot on - track bar and locating links - get some wear and tear on them and that's when problems happen.

My first 4x4 van, leaf sprung, I drove for 32+ years. My current 4x4 van I've been driving for 15 years and the front end sits on coils. Can't say as I could tell any difference in ride between the two. But I never had any front end problems in the leaf-sprung van. I've had to change out the track bar and bushings in the current van...went into severe death wobble after hitting some rough pavement on I-15 in the Virgin River canyon a few miles southwest of St George, Utah. I thought I was going to end up in the river before I got it stopped and under control.

Ford went to coil suspension on the front ends of the Superduty in 2005, I believe. Before that, reports of death wobble were rare. Very common after the change to coil suspension.

[b. rock]

Originally Posted by vandiesel

I have had both and currently have a deaver leaf sprung SMB 4x4. Leafs ride like a plush cadillac for me and that is because the springs are progressive rate and have a lot more travel that coils. My quadvan 7.3 rode fine on the road and fairly well off road. I'm not sure you can really go wrong either way if both are properly setup and have tuned springs and the right shocks that are valved correctly for the van. Turning radius is something not to be overlooked either. My van turns on a dime now and is MUCH better than stock 2wd which I have also. Come drive mine anytime in Portland.

what kit/conversion do you have? usually leafs limit turning radius since they sit further outboard than the radius arms on a coil setup.

worth noting - the most recent personal van of the owner of UJ is coil front/rear it's not really mentioned, but 10 seconds looking at the pics very clearly show control arms on both ends. probably a fairly high end setup however, not a run of the mill short arm 4 link or radius arm up front, probably a 3 link or long arm 4, and guessing triangulated 4 in the rear? but who knows

[h.grenade]

You guys are amazing! Thanks for all of the insights. It sounds like as long as it's done right, it shouldn't really matter. My preference is highway handling as we plan to tour longer distances and then find back roads to setup camp. I doubt the cats or my furniture would want to do any real overlanding!

I wonder if the weight might determine which one is better. I assume that a diesel is heavier than the 5.4 so maybe leaf could be better with the extra lbs. I am leaning toward coils because I had a RAM 1500 that was coil and it handled like a car.

Thanks for the links too. I will have to do more reading. My current plan is just to get a locking rear dif, a good winch and a shovel/recovery gear for now. I am trying to find $20k, I swear I put it somewhere : )

[Lilnuts2]

As far as weight concerns go, my 2016 F-350 dually diesel has a GVWR of 14,000, and it is a coil spring front end.

Properly setup either one will get the job done with very similar results. As b. rock stated coils offer a tighter turning radius, which in a big van I think is important. A coil conversion is generally cheaper for both parts and labor and uses newer "up to 2016 at least" standard Ford parts. The Leaf spring design generally uses Ford axles that are 2004 and older with smaller brakes. Ujoint does have a bigger brake option but it's not cheap.

If the geometry of the coil setup is not well engineered or has worn out parts death wobble can happen. However, there are many thousands for Ford trucks out there with coil springs that don't have issues. Jeeps seem to be always in the death wobble spotlight because so many have poorly designed lift kits with massive tires that magnify any flaws in the system.

A leaf spring system is a more basic system with a more simple geometry and less moving parts. The key to a great leaf spring system is the springs themselves. There is so much adjustability in building a leaf spring. From the thickness of each leaf to the number or leaves, the length of those leaves and how they interact with the other leaves and the amount of arch all have an affect. I think Chris at Ujoint has done enough of them he has the leaf springs for the Ford vans pretty dialed in.

One aspect I have an issue with regarding the leaf springs. The Ford van frames are designed for trailing arm design (read coil) suspension and the forces the go with that design. The leaf spring design changes the forces on the frame and moves the stress to areas of the frame that are not engineered for them. In addition to that, the leaf spring design places the front spring mount in front of the "crumple zone" and the rear mount behind that zone. While that my never be an issue, I personally don't like the leaf spring design for the above reasons.

It boils down to a matter of choice. Both can be made to get you stuck in the back country lol.

To the OP you might reach out to Michael @MGmetalworks (member here) his shop is about 3 hours from you. He is one of about 3 people that know more about Ford van 4x4s then anyone else on the planet.

[deserteagle56]

Originally Posted by h.grenade

I wonder if the weight might determine which one is better. I assume that a diesel is heavier than the 5.4 so maybe leaf could be better with the extra lbs.

You would assume correctly! About 500 lbs for the gas engine, about 1000 lbs for the diesel. That's a huge difference over the front axle.

[motovan_mn]

Still, shouldn't a spring be a spring, whether it's coil or leaf?

A coil spring can have a higher or lower spring constant to support different weights.

[Lilnuts2]

A leaf spring has many more variables as I mentioned above. With a coil you can only adjust the rate with a different spring, or get a progressive wound spring with different rates. But honestly, there is not that many spring profiles made for the vans and ford trucks that will offer much tuning, besides overall rate.
It's my understanding that a coil spring releases it's energy at more consistent rate then a leaf spring, which is why most people regard a coil spring as riding smoother.

[vintageracer]

I have had both front coil spring and front leaf spring 4WD van conversions over the last 30 years from all the different converters. This includes E Series Ford vans, GM Express vans and earlier 1995 back GM Uni-Body Vans.

My observations are pretty simple when it comes to ride and driving of a 4WD "converted" van:

Coil spring conversions ride much better overall on the highway, ride far better on rough terrain and also have lot's of issues with Death Wobble at speed when you least want it to happen. Most all commercially available Death Wobble Solutions for 4WD van coil vans are now and were back then band aids at best when trying to eliminate Death Wobble. Handling and performance are adequate.

Leaf spring conversions typically ride worse overall, on the highway and particularly over rough terrain. "I" have never a Death Wobble issue with a leaf spring 4WD converted van. When properly built and aligned a leaf spring converted 4WD van is rock solid when it comes to handling, cornering and performance. The only real limitation I have noted is the reduced turning radius. The new style front axles help immensely with that issue.

The newer conversions with the much better front axle options available today continue to get better and better with both coil spring conversions and leaf spring conversions.

My current 4WD van is a leaf spring conversions that drives great at 80+ MPH all day with NEVER any Death Wobble issues. Yes it rides rougher On-Road and particularly Off-Road than a any coil spring conversion.

Off-Road is 10% or less of my typical use of my van so I will take that less desirable ride aspect of a leaf spring 4WD conversion and NO Death Wobble issues any day over a coil spring conversion.

It will be interesting to see how much further in the future the 4WD van converters can take their coil spring conversions to make them BETTER than the leaf spring conversions concerning the total package of ride, handling, performance and No Death Wobble!

[SchultzBurrey]

I currently have a UJ converted B190 and I have had a quigley ambo as well as driven a Timberline van on the highway briefly. My current experience has been mostly paved road use with some off-road that both the Quigley and the Ujoint did require the use of four low as well.

The handling of the Ujoint has been phenomenal. It hauls ass at 85 on the interstate with one finger on the wheel( and that’s in Colorado debately some of the worst paved roads in the country!). The steering is tight, no wandering, the body roll is significantly less with Ujoint however it definitely is a little rougher than the quigley was on dirt roads and it is a 6” vs 4” on the Quigley which does make it harder for my short wife to jump in. The timberline was smooth on the brief ride however I did notice the van float more. The Quigley definitely had bump steer issues, horrible body roll and did not have great articulation.

All that being said I would go with the Ujoint everyday, I personally find the handling to be well designed. Hope this helps.