Shock selection for city driving 3

[knowlittle]

I have a pickup (Ford F150) that is retired from farming and used only for city driving. Front is shock/coil spring and rear is shock/leaf spring. The pickup has new shocks. Still it rides rough compared to sedans. I know a pickup is a pickup, but is there a room for ride improvement by careful selection of shocks?

 

[MikeHalloran]

Fill the bed with shocks. ... or bags of sand, or bottles of water, or whatever you can get your hands on that's heavy. For the common 1/2 ton pickup, you want about 1000 lb. of stuff, or whatever the owner's manual says its rated load is, maybe a little less to allow for potholes.

OR, convert it to air suspension, which I think is cheaper than it used to be. You still need shocks as travel limiters.


Mike Halloran
Pembroke Pines, FL, USA

 

[GregLocock]

It is possible to vastly improve the ride of light trucks, but I don't know of a way of doing so using off the shelf components. One serious issue is that leaf springs are very non linear, that's why they are used in that application, as they can provide a ride frequency that varies less with load compared with a coil spring. The downside is that the shocks have to be designed to cope with wide variations in load, and also in the case of leaf springs, rate.

Another fix might be decent tires.

It does rather depend what you mean by 'ride'.

Cheers

Greg Locock


New here? Try reading these, they might help FAQ731-376

http://eng-tips.com/market.cfm?

 

[BrianPetersen]

Also ... are we talking about a 1966 F150, or a 2016 F150, or somewhere in between and if so, where? There's a rather large difference in suspension designs between them. Also ... 2 wheel drive, or 4 wheel drive? And what wheel sizes and tires are on it?

 

[knowlittle]

Thank you for your notes. What is the principle of air suspension? I mean where does it go in principle? Between wheels and chassis? Parallel to shock? In some vehicles, I saw air springs between rear axle (rear wheel drive) and chassis. In another (F150), between leaf spring and frame. I fail to see what is common among them.
Vehicle is 1997 F150 rear wheel drive regular cab long bed 16" wheel 235-70-16 (OEM wheel/tire size). Thank you again.

 

[MikeHalloran]

The typical old school installation of air suspension in a truck is in parallel with the rear springs, so as to add load capacity when you want to carry something heavy, by adding air to a Schrader valve somewhere.

The most extreme installation is what hot rodders do nowadays, replacing every suspension spring with an air bag, with air pressure (or perhaps ride level) manually controlled from the driver seat, individually, so the driver can jack up or drop any corner on a whim, as lowriders do to negotiate railroad tracks.

My 2013 Navigator is sort of in between; regular coil springs up front, and air bags (only) in the rear, with an automatic leveling valve on each air bag, and an electric compressor hidden somewhere. So when the load changes, the vehicle will adjust itself to a fixed ride height within a couple of minutes.

The Navigator also uses a lot of rubbery/squishy bits to make the ride quiet and limousine-ish, most of which should interchange with a similar year F150. That's a hint. Some comparative anatomy in a junkyard might improve your situation.


Mike Halloran
Pembroke Pines, FL, USA

 

[BrianPetersen]

If I remember right, the Navigator may be loosely based on an F150 vehicle platform but the rear suspension is an independent design, and if my memory is also right, at least some models of the Expedition use a similar IRS but with coil springs instead of the Navigator's air bags. Since the vehicle is platform-related, there might be some interchangeability, but I would expect that the frame for the IRS uses different attachment points welded to it, which makes swapping to the Expedition/Navigator IRS a big job. I've been in a long trip in a 2003-ish Expedition (same vehicle generation as the F150 we are talking about here) and I thought it rode pretty well.

The front suspension of the '97 F150 is an upper and lower A-arm design, not the old "twin I beam". The Expedition/Navigator of the same platform generation should have interchangeable parts with the F150, which SHOULD make front-end parts swapping as easy as it gets. The next step is for you to go into parts diagrams and find out what's different between an F150 and an Expedition/Navigator up front. I would expect different springs and shocks and antiroll bar, but wouldn't be surprised at different control arms and different bushings (which might not be separately available from the control arms).

The rear is another matter. The leaf springs are designed for load capacity without excessive compression of the rear suspension at max load ... i.e. high spring rate. The shocks are calibrated to maintain ride control at max load capacity. The leaf springs likely have minimal bushings between the front pivot and the frame (i.e. NVH goes straight through to the frame). The good thing about leaf springs is that you can usually pretty easily add or remove leaves to customize the spring rate. The bad thing is that reducing the spring rate by taking out leaves introduces potential bad side effects - excessive sag under load (i.e. it will reduce your load capacity - which may or may not be an issue), axle wrap-up under acceleration (because the live axle drive torque twists up the leaf springs), excessive body roll when cornering, etc. Taking out a leaf won't fix the way the front leaf spring pivot goes into the frame.

A trip to a Chrysler dealer for a test-drive in a current-model Ram pickup with coil-spring rear suspension may be instructive. They do sag a lot under load.

 

[knowlittle]

Thank you. There is much information to digest.

Expedition and F150 use the same upper & lower control arm, same spindle, etc. (I haven't checked Expedition vs. Navigator yet.) So I suppose rear is where the suspension is different and ride difference comes from. Removing a leaf (from a 3-leaf spring) and adding an air bag seems to be the way to go. As Greg indicated above, it may not be an easy job. Thank you again.