135 bounces per minute on the highway

[K10-Kansas]

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?

[Shark_13]

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

[kwmech]

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

[Dead Parrot]

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....

[LONGHAIR]

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.

[K10-Kansas]

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.

[K10-Kansas]

Do MT 35’s bounce like that just because?

[LONGHAIR]

Originally Posted by K10-Kansas

Do MT 35’s bounce like that just because?

"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.

[K10-Kansas]

Originally Posted by LONGHAIR

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.

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

[MS66]

Originally Posted by K10-Kansas

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

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?

[geezer#99]

Correct tire pressure!
What is the pressure?

[K10-Kansas]

Originally Posted by geezer#99

Correct tire pressure!
What is the pressure?

I've got them at 35 PSI cold.

[geezer#99]

Originally Posted by K10-Kansas

I've got them at 35 PSI cold.

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

[K10-Kansas]

Originally Posted by geezer#99

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

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.

[geezer#99]

Originally Posted by K10-Kansas

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.

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

[v30crewcab]

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

[Shark_13]

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.

[K10-Kansas]

Originally Posted by Shark_13

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.

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

[c30]

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

[K10-Kansas]

Originally Posted by c30

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

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.

[c30]

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.

[v30crewcab]

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.

[K10-Kansas]

Originally Posted by v30crewcab

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.

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.

[K10-Kansas]

I didn't measure them but I watched them quite a bit before deciding to true them. I imagine they were off by 3/16 of an inch. You can see that in the video here. https://youtube.com/shorts/0dyl9bDy7...YU5gthL7S9MhIP