135 bounces per minute on the highway
 

Hey all. My truck has a 1976 4x4 chassis. While driving down the highway my truck bounces up an inch and down an inch and up an inch and down an inch. I think that’s about the duration of the bounce. It does this a little over two times per second on most highways around Kansas City. Does that sound like bad shocks?

Re: 135 bounces per minute on the highway
 

How old are the shocks?
Tires at correct pressure?
Does it bounce on all types of roads or concrete with joints only?

Re: 135 bounces per minute on the highway
 

What about bad winter roads? How old are the tires, shocks and suspension. Also, being from Kansas, do you have the steel frame or the oxidized version

Re: 135 bounces per minute on the highway
 

If it bounces on smooth roads, seems more like bad/out of balance tires. Shocks dampen vibration. They don't prevent it.

Or take the tire chains off....:lol:

Re: 135 bounces per minute on the highway
 

A bounced like that is normally a tire issue, either very out of balance or a big ol knot, from a broken belt.
Balance problems start showing up around 45mph, but it depends on the diameter.

Re: 135 bounces per minute on the highway
 

The tires are new. The shocks look to be pretty old. The tire pressure is correct. It bounces when driving faster than 55 mph. Kansas highway are fairly decent. It seems to do it on any road if I’m going 55 or faster. I have no idea if the tires were properly balanced.

Re: 135 bounces per minute on the highway
 

Do MT 35’s bounce like that just because?

Re: 135 bounces per minute on the highway
 

Correct tire pressure!
What is the pressure?

Re: 135 bounces per minute on the highway
 

I've got them at 35 PSI cold.

Re: 135 bounces per minute on the highway
 

jack it up and see how out of round they are. I've had a bunch that don't run true.

Re: 135 bounces per minute on the highway
 

Try different pressures.
Bump them up to 40 to start with.

Re: 135 bounces per minute on the highway
 

I was thinking the same thing. The max is 65 for heavy loads. 20 to 30 for off road. And 30-40 for daily driving.

Re: 135 bounces per minute on the highway
 

It might like higher. But it might like lower pressure.

Shocks sounds like the next thing.

I have lost a weight on a wheel and things get bad quickly.

Re: 135 bounces per minute on the highway
 

Oh good tip. I need to check and see if I lost a weight.

Re: 135 bounces per minute on the highway
 

Last bfg all terrines I had were rated 75 max.
I ran them at 50 psi.

Re: 135 bounces per minute on the highway
 

71 body on a 76 chassis? Check your body mounts.

Re: 135 bounces per minute on the highway
 

"Just because" ....No.
Even though they haven't been legal here for decades, I have personally run 40" mud tires for thousands of miles. They do not have to be abusive.
Back then, especially with those big bias-ply tires, actual roundness was the biggest factor. Some were so bad that balancing was very difficult. Truing was the solution.
Radials are generally better, in that aspect, but it's not absolute.
Even if they don't shake the truck, truing them can make a big difference.
It is hurtful to see how much rubber can sometimes need to be removed, during the truing process, but it really does extend their life.
Smoother rolling tires reduce the load on the suspension/shocks, which are trying to control them.
The springs are doing the lion's share of the work. Shocks are really only dampening the action.
I would take them to a place that can dynamically balance them. It can tell you a lot. If they are out of round, they can tell that too.
Finding a place to do the truing, might be a challenge though.

Re: 135 bounces per minute on the highway
 

Hey, just saw this post. Glad to see you're still out there. Tried to PM but it was full.

Re: 135 bounces per minute on the highway
 

Thanks for the info. I am replacing the leaf bushings, "freshening up the springs" then the cab mounts next week and then the shocks the week after. I was already planning on doing all that anyway. If that doesn't work, checking the tires sounds like a good idea.

Re: 135 bounces per minute on the highway
 

I had a bounce in my 06 crewcab. couldn't balance it out, even with road force. ended up shaving the tires(I have my own machine to do it), and they are smooth as glass now.

Re: 135 bounces per minute on the highway
 

I guess that will be my last resort. It’s good to know that that’s an issue that can exist and that there’s a way to fix it. But man holy cow before joining this forum. I would’ve never have guessed that that could be a thing. :)

Re: 135 bounces per minute on the highway
 

Thanks, yeah definitely. I did the core support mounts two months ago and bought the cab mounts a few weeks ago. I’ve been saving them to put in over Christmas break. I just hope I can get them in there. A 71 cab sitting on a 76 chassis the way they did it didn’t leave much room for mounts unless the mounts are squashed flat for 20 years. After I do the cab mount in two weeks, I might have to put washers under that bed to keep everything straight. :)

Re: 135 bounces per minute on the highway
 

You will need the shortest rear cab mount, like 1 1/2" to clear the frame.
With about 3" body lift blocks under the core support and bed to make it all straight.
Let us know what you end up with.

Re: 135 bounces per minute on the highway
 

That ended up being the exact problem. I jacked up the truck, spun the tires and sure enough they weren't round.

So I took a bed frame, cut it up and welded it together with 2 sets of drawer slides and strapped a grinder to it. I put the truck on stands and ran it in 4 low lock and trued the tires. Worked perfect. I drove on the highway today and the bounce is gone! :)

Here is a video of it running https://youtu.be/m-gSHW6Vx88

Re: 135 bounces per minute on the highway
 

I came in here to say this. I bought brand new Cooper tires a couple years ago with huge anticipation of a silky smooth ride in my '68 only to have basketballs dribbling down the road. Had me stumped for a minute. Got home, jacked the truck up and spun the tires, they weren't round. I ended up putting different tires on it.
Years ago retread tires were super popular. When pop bought retreads, they had a tire truing machine that cut the "egg" out of them after they were mounted on the wheel. I remember the mountains of rubber laying in there from cutting tires all day long.

Did you happen to measure how much run out they had before you began cutting on them?