Bouncing/teeter tottering suspension bounce depending on the road

I don't think there is much of a solution here, but wanted to discuss.

I drove my truck several hundred miles a couple weeks ago. At one point of the trip, the road was a concrete highway, with a lot of repair work that ran perpendicular to the travel lanes. Sort of like expansion joint repairs. The spacing was close on these. It was like a ripple, wash board highway. Cars were traveling 70 mph no problem.

The road conditions caused my truck to buck violently, enough so that I had to slow down to a crawl. I was literally bouncing in the seat to the roof, and it felt like the back end and front end was coming off the ground. It was bad enough that I stopped, and checked the truck for flat/low tires or any other indication to the cause of it. I could only travel at 20 or 25 mph on the highway or the oscillation was dangerous. The truck was see-sawing, if you will.

The road eventually leveled out, and the truck was fine again. The problem was associated with the striations in the road. Beyond weight in the bed, would there be any solution to preventing this from happening? The shocks on the front of my truck are ok, but can you put shocks on the rear tandem? I assume not, due to the articulation.

BTW, I run 395's at around 30 psi.

Yeah have been through that a few times check your front shocks, but pretty sure that you can add rear shocks, I think I remember someone here that has done it.

I have experienced something similar on some road trips, it occurred on concrete highways with expansion joints, but not as severe as you describe, the truck gets into a "rocking" mode...
A spring leaf-pack provides damping without addition of shocks and should therefore never be lubricated.

I have been thinking of how to add shocks to the rear for a while now. The best thing I can think of is some kind of quick disconnect for when going off road and to swing them out of the way. I haven't thought about it in a while, maybe I'll look more into it this year.

There's a section of road in Shreveport that causes my truck to seesaw and buck side to side. It gets interesting fast. I don't really have a good solution to offer. I just feel your pain.

Is your deuce duel or single in the rear? Singling it out will help if you are interested.

cranetruck said:

A spring leaf-pack provides damping without addition of shocks and should therefore never be lubricated.

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Not to argue but I have seen you post this before and I don't see lots of guys running out to put grease on there leaf springs but what do you base this on? The older manuals actually did say grease them and the newer trucks actually have plastic sliders on them to keep them from sticking.

gimpyrobb said:

I have been thinking of how to add shocks to the rear for a while now. The best thing I can think of is some kind of quick disconnect for when going off road and to swing them out of the way. I haven't thought about it in a while, maybe I'll look more into it this year.

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I would think that you could get a long travel shock that would not have to be disconnected.

Csm Davis said:

Not to argue but I have seen you post this before and I don't see lots of guys running out to put grease on there leaf springs but what do you base this on? The older manuals actually did say grease them and the newer trucks actually have plastic sliders on them to keep them from sticking.

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When doing research for one of my MVM articles some years ago I ran across this and it has to do with friction between the individual leaves producing a damping effect. I'll look for the reference, but anyone can probably find it now with a little help from Google.

Note the need for shocks when there are fewer leaves as in the Ford M656 design (vs the M35).

The probable cause was how the road was laid. Expansion joints may have been close to the wheelbase of your truck. That coupled with a vehicle equipped with stiff springs for carrying a load.
Two solutions-dint drive that route or if you do, put some weight in the back.
Pete

cranetruck said:

I have experienced something similar on some road trips, it occurred on concrete highways with expansion joints, but not as severe as you describe, the truck gets into a "rocking" mode...
A spring leaf-pack provides damping without addition of shocks and should therefore never be lubricated.

Click to expand...

Dried out or rusty spring leaves put the strain on the ends near the shackles; a greased spring will allow all the leaves to move and share changing loads. 'Frozen' springs ride like a pea in a drum.

You can add shocks to the rear without ever having to disconnect them. Start with a mount that affixes to the sling load point on top of the tandem pivot using the 1" pin to hold it in place. You need this bracket to fit snug in that pocket and protrude from the top about 1/4". Take a piece of 1/4" wall 2"x2 square tube and weld to the top of that parallel with the leaf spring pack and cut it about 4" short of the leaves on each end. Weld on a tab mount for the top of the shock on each end of the tube at a slight upward angle so the shock can be mounted at an angle, then build another simple bolt on tab mount from plate that you can bolt to the leaf end pocket on each axle. You will need to use short shocks, but this way the whole thing pivots with the axles and won't put a bind on the shocks. The springs don't flex so much so I can't see pulling one apart either. This is just preliminary thinking on my part. I haven't actually entered the design and measuring phase yet. It should help dampen things a bit anyway.

Jeepsinker said:

You can add shocks to the rear without ever having to disconnect them. Start with a mount that affixes to the sling load point on top of the tandem pivot using the 1" pin to hold it in place. You need this bracket to fit snug in that pocket and protrude from the top about 1/4". Take a piece of 1/4" wall 2"x2 square tube and weld to the top of that parallel with the leaf spring pack and cut it about 4" short of the leaves on each end. Weld on a tab mount for the top of the shock on each end of the tube at a slight upward angle so the shock can be mounted at an angle, then build another simple bolt on tab mount from plate that you can bolt to the leaf end pocket on each axle. You will need to use short shocks, but this way the whole thing pivots with the axles and won't put a bind on the shocks. The springs don't flex so much so I can't see pulling one apart either. This is just preliminary thinking on my part. I haven't actually entered the design and measuring phase yet. It should help dampen things a bit anyway.

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I would have thought it would have needed to be a dual shock approach on both sides like what cranetruck posted further up. No?

I'd think that'd depend on the amount of damping force your were trying to exert and what the shocks could handle.

On some stretches of asphalt road around here, going only 40 mph on regular tire pressure, can make the rear end "jump" sideways so much that I have to be quick on the steering wheel to catch the truck that is now pointing towards the ditch or into oncoming traffic.

My truck is singled out on 11.00R20 Goodyear radials. When running empty (most of the time), I need to lower the air pressure in the rear tires to a ridiculous (for radials) 50-55 psi in order to avoid the worst bucking and side-shifting on some bad roads, much similar to what the original poster describes. The front stays aired up to 90. I was concerned about sidewall bulge and heat at first, but the bulge is not larger than in front (what little weight there is in the back is distributed between 4 tires) and they do not get hot, either.

One shock at each wheel end is all you need. You can experiment with different shocks at your discretion, but some light pickup truck shocks should work fine. I am going to try some rear shocks from a Jeep Cherokee XJ first. I really just need to buy some steel and get started, but good steel is so expensive anymore. And in case you were wondering, you could probably be just fine using 3/16" wall square tubing instead of 1/4" wall. If and when I ever get my design built I'll do my best to post some pictures here.

Jeepsinker said:

One shock at each wheel end is all you need. You can experiment with different shocks at your discretion, but some light pickup truck shocks should work fine. I am going to try some rear shocks from a Jeep Cherokee XJ first. I really just need to buy some steel and get started, but good steel is so expensive anymore. And in case you were wondering, you could probably be just fine using 3/16" wall square tubing instead of 1/4" wall. If and when I ever get my design built I'll do my best to post some pictures here.

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Great, thanks. Post up when you get around to it, as it will probably be before I get to address it myself.

cranetruck said:

When doing research for one of my MVM articles some years ago I ran across this and it has to do with friction between the individual leaves producing a damping effect.

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Absolutely correct. Here's a power point that explains it.

http://www.google.com/url?sa=t&rct=...=VJ5csOBI79-9fO3fiWSWPA&bvm=bv.84607526,d.cWc

Its a good power point ... but the first 10 pages explain what you want to know.

Quote: When assembling multi-leaf spring packs, never paint or lubricate the contact surfaces of the individual leaves. The result would limit the self-dampening characteristics of the spring.


ALSO ... In the 40 or so years I've been repairing cars, I have seen countless shock absorbers that "looked good" ... some even looked almost factory fresh. But, when I disconnected one end and compressed the shock ... there was NO pressure, the shock was dead.

One more thing. When I bought my Deuce home, it pretty much did the same as your truck over similar surfaces. I replaced the front shocks and everything was fixed.

I have since bobbed my truck, and to my rear-end, the ride quality decreased a bit. A set of shocks for the rear is on my list of stuff to do, but its not real bad so its not real high on the list.

Odd thing, I seem to recall a PM task for my '43 Humber Armoured car that calls for precisely doing so. There are shocks though so perhaps the damping effect is undesired in this instance.