Resonant Oscillation on certain roads

71GMC_3/4T · May 29, 2005

I have an '03 2500HD Crew Cab, towing package, 6.0, 4L80E, bone stock except Michelen LTX 1 size over (285?) tires.

There is a spot on I-25 in Colorado between Mead and Loveland exits where I almost can't stand to be in the truck. It develops a shake that's about 3 to 5 times per second, front to back, or up/down in back that makes it kind of hairy to just change lanes at times. It does this at 65 to 75 mph, maybe more but I ain't got the balz up yet. The pavement in that area is concrete, and is bumpy in other vehicles, but nowhere near what I experience in mine. I've found other spots that are bad, but none like this, yet. I plan on taking a road trip but I'd really like to dampen the shake before I find a road worse than I-25 (I'm sure they exist!).

Does anyone else experience these types of shakes/shudders at highway speeds? Have you found a solution?

I tried to buy a set of Lord isolators, but found they no longer make or stock them. Can anyone tell me of another maker?

I'm running 45 PSI front and rear. They were all at 60 when I bought her, but it really rode like crap then. Should I go back up to 60 and try I-25 again?

Has anyone found better shocks that help the ride?

It's kind of embarrasing to have someone else riding and have them complain about the ride. I'm kind of afraid to take my wife on a long road trip as she still likes the truck right now...

Thanks for any help or suggestions you can provide!

-71GMC

Wingnut · May 29, 2005

The "pogo" is what I like to call it.

There are two or three areas of town that I have to slow down to 60 to keep my butt touching the seat.

It got really bad after I cranked my torsion bars, until I bought longer shocks.

The Velvet Ride Shackles (Lord Corp) are supposed to help a bit, but I doubt that they would get rid of it.

mmmikkke · May 29, 2005

I've got an '05 2500HD extended cab, and I have also noticed these disappointing frame oscillations. There's a road near my place of work which was once concrete, but has been repaved with asphalt once or twice. The road has nicely-tapered grooves across the road at most of the pavement joints. Kind of like negative speed bumps. At each pavement joint, there's just one groove, but when I drive over the joint with my truck it feels like there are 2 or 3 grooves, the frame is set into some kind of oscillation by the rear wheels as they cross this groove, and then the truck shudders until the oscillations damp out.

Positive groove pavement joints, where the road comes *up* at the pavement joint, don't cause the same problem. You feel the bump, but it doesn't set up an oscillation.

It's annoying, but since this is the only place where it happens, and it's a 35mph road, it's not a safety issue for me. I've learned to just ignore it. And I've ridden in the cars of coworkers through the same sections, and even their cars do annoying things on these bumps. Different, but still annoying. So I chalk it up to poor road construction.

The severity of the oscillations changes from day to day, almost as if the temperature of the shocks changes the situation.

I've wondered if the staggered rear shocks, where one attaches to the frame rail forward of the rear axle, and the other attaches to the frame rail behind the rear axle...I've wondered if the jounce of the bump and the resulting force vectors at the shock mounts is twisting the frame beneath the bed, in a way that no structural resistance exists, so the oscillation occurrs.

So my focus is on the shocks. I wonder also if gas-charged shocks, or lighter-duty shocks, would make any difference.

Shawn T · May 31, 2005

When I lived in Southern Colorado, there was one stretch of road on Pueblo Blvd that would get my truck's frame to it's "resonant frequency". It had to be a certain speed. I asked a professor at school (Mech Engineer, Phd) and this was his explanation: "Your truck frame is just like every structured piece of ore, it has a resonant frequency and when the bumps in the road are taping both ends of the frame, at a certain frequency, via the springs this causes the energy waves to bounce off of eachother rather than be absorbed". Like a giant tuning fork. I don't know if this was BS, but it made sense. If this is true, all makes and models, will do this. I guess it depends on the spacing and size of the bumps, the length of the frame, suspension, blah, blah, blah, and a little bit of dumb luck. Other than that little stretch of concrete, my truck has never done it again.

asilverblazer · May 31, 2005

I gotta few concrete blocks in the bed of my truck, the very back. Seems to help the excessive bounciness. The extended cab short bed trucks seem to be cursed by the concrete expansion joint gods.

c5hd · May 31, 2005

I gotta few concrete blocks in the bed of my truck, the very back. Seems to help the excessive bounciness. The extended cab short bed trucks seem to be cursed by the concrete expansion joint gods.

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SF Bay area here and I get this too on some parts of some roads. Definelty worse with the cranked t-bars and big H2 wheel/tires. I origanaly switched to Adjustable ranchos hoping that would help, but no improvemnt (stock length up front were too short). Put longer Bilstines up front and it is much better. You can definitly feel the improved ride of the bilsteins. I kept the ranchoes in back so that I could adjust them for load and towing, but I like the bilsteins up front so much, I may just swap them out too. I also found that with about 150# - 200# in the bed, it eliminated the occelation, however the ride is still rough.

I just deal with it and slow down in the sections that are bad. It would be nice to find a perminant solution though.

Scyry · June 1, 2005

I drive that stretch ~5 times a year and my truck does the same thing. The dealership in Loveland asked me if it did that, on I-25 the first time I took it in for servicing after I bought it. So I am guessing it is a common thing. I noticed it is lessened at 85+ mph. If I have a load in the truck it seems to get worse also.

71GMC_3/4T · June 1, 2005

Hmmm... Glad to hear someone else is experiencing this same problem. It's kind of strange that asilverblazer and C5HD say a load helps, while Scyry says it gets worse though.

I wonder if it might also be the cab mounts. Maybe they're too soft and allow a resonant standing wave to build up?

How stiff are the shocks on a 2500HD? Would a set of shocks for a lighter pickup help, or are the stiff springs the culprit?

I guess I'll have to try driving it at 85 mph or more! Heck, most people go faster than that on that stretch anyway. I almost felt like running on the shoulder since I was *only* going 75!

Thanks all for the replies so far!

-71GMC

Scyry · June 1, 2005

The "pogo effect" on I-25 seems different to me than the roads here in Denver and headed South of Denver on I-25. You don't get the same effect in similar trucks (1994 1-ton extcab Ford or a 2003 Single Cab Long Bed 3/4 ton Dodge) on the stretch of road near Loveland, friends' trucks I have rode through there. To me that stretch of road feels like you have 4 really out of balance tires, not like the pogo you get on regular freeways. It is more like the tires are going in and out of grip rapidly, and you are see sawing front to back at the same time.

I am wondering if the highway wasn't built with random distances between expansion joints. If there is a pattern to the expansion joints you can get resonance in a vehicles suspension at certain speeds, similar to an out of balance tire. I think that is what is going on here, thus why it happens 65-75 mainly.

I know what you mean by the "getting ran off the road" up there, d**n semis are doing 80+.

silverado3500 · June 1, 2005

Theres a stretch of I-75 in Macon from I-16 south to I-475 where my 02 would do this, but only in the far left lane. The 2 right lanes were fine, and it was only in my extended cab. None of my other trucks ever did it. It must be hitting the frame just right.

042500HD · June 1, 2005

Like I keep saying the imports don't have these kinda problems. 30k to 50k for a truck and still have little problems like this, something tells me to say the word....JUNK....

Shawn T · June 1, 2005

Like I keep saying the imports don't have these kinda problems. 30k to 50k for a truck and still have little problems like this, something tells me to say the word....JUNK....

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Do you want to make a bet? My buddy has an 04 Tundra and he gets the same vibrations on the same stretch of road, only worse.

71GMC_3/4T · June 7, 2005

Like I keep saying the imports don't have these kinda problems. 30k to 50k for a truck and still have little problems like this, something tells me to say the word....JUNK....

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Yep, them new Nissan trucks ain't got any problems at all!

My buddy bought one and has regretted it since. I think it's been to the dealer 15 times. 2 sets of brakes in 15,000 miles, and countless other problems.

MS3DALE · June 7, 2005

Like I keep saying the imports don't have these kinda problems. 30k to 50k for a truck and still have little problems like this, something tells me to say the word....JUNK....

Yep, them new Nissan trucks ain't got any problems at all!

My buddy bought one and has regretted it since. I think it's been to the dealer 15 times. 2 sets of brakes in 15,000 miles, and countless other problems.

Scyry · June 7, 2005

Like I keep saying the imports don't have these kinda problems. 30k to 50k for a truck and still have little problems like this, something tells me to say the word....JUNK....

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Like people keep saying, every brand has Lemons, deal with it.