rear end bounce at lower speeds

[Marauder4]

So, I am somewhat at a loss. My 1984 M1008 will suddenly start a MASSIVE rear-end bounce at speeds below 40mph. I have to pull off and slow down to around 5mph and it settles out, then I'm back on the road again. It usually starts due to a small bump or something and once it starts, it doesn't get worse if I keep going.

The rear of the truck feels like it's bouncing from tire to tire until I get slowed down. I have replaced the rear diff oil, and everything LOOKED like it was doing what it was supposed to be doing, and I have replaced the rear brakes from the baking plate out, all the drive-line bits and bobs are right and tight from the tranny to the axle.

Suggestions?

 

[WWRD99]

So, I am somewhat at a loss. My 1984 M1008 will suddenly start a MASSIVE rear-end bounce at speeds below 40mph. I have to pull off and slow down to around 5mph and it settles out, then I'm back on the road again. It usually starts due to a small bump or something and once it starts, it doesn't get worse if I keep going.

The rear of the truck feels like it's bouncing from tire to tire until I get slowed down. I have replaced the rear diff oil, and everything LOOKED like it was doing what it was supposed to be doing, and I have replaced the rear brakes from the baking plate out, all the drive-line bits and bobs are right and tight from the tranny to the axle.

Suggestions?

I'd be curious if your spring bushings are worn out. A locked up shock can make things go nuts too....even if it's new it can be bad...or bent.

 

[porkysplace]

You could have a broken belt or severely out of balance tires or as already stated shocks , spring bushings.
Since your in Alaska are talking on paved roads or washboarded gravel roads , if it is washboard gravel roads try adding about a 100 pounds
and see if it still does it , there is no give in these suspensions when empty .

 

[Marauder4]

This is on all pavement driving as of now. Tires came off a newer Chevy and were fine on that truck. I added about #400 to the bed already. Haven't checked the shocks!

 

[87cr250r]

Are you sure it's the rear? The Dana 60 front axle is notorious for causing death wobble.

 

[Finnegan1008]

I would also ask if it could be coming from the front aka death wobble.

What about your drive shaft? Is it bent? Or maybe the U joints are majorly worn out?

 

[porkysplace]

This is on all pavement driving as of now. Tires came off a newer Chevy and were fine on that truck. I added about #400 to the bed already. Haven't checked the shocks!

All it takes is one good pothole to screw up the tires .

 

[Marauder4]

I would also ask if it could be coming from the front aka death wobble.

What about your drive shaft? Is it bent? Or maybe the U joints are majorly worn out?

I thought that too, but it is purely in the rear. Front tracks fine, but the bed is vigorously trying to dance off the truck.

Drive shaft is tight, U-joints look and feel okay. When the rear wheels are up in the air, there seems to be a LOT of play in the drive line. Like, around 45 degrees of turn before it engages.

 

[Finnegan1008]

I thought that too, but it is purely in the rear. Front tracks fine, but the bed is vigorously trying to dance off the truck.

Drive shaft is tight, U-joints look and feel okay. When the rear wheels are up in the air, there seems to be a LOT of play in the drive line. Like, around 45 degrees of turn before it engages.

That doesn’t sound right, is the truck lifted? I’m wondering if your driveline angles are off and it’s causing everything to wear out prematurely. I bet if you go through all of those joints and replace with qualify hardware you would make a big improvement

 

[porkysplace]

I thought that too, but it is purely in the rear. Front tracks fine, but the bed is vigorously trying to dance off the truck.

Drive shaft is tight, U-joints look and feel okay. When the rear wheels are up in the air, there seems to be a LOT of play in the drive line. Like, around 45 degrees of turn before it engages.

Maybe post some pictures .

 

[Jbulach]

I’d start by rotating the tires to see if anything changes.

 

[Marauder4]

**UPDATE**
So, a friend of mine happened to watch me bouncing down the road like a rubber ball the other day and tonight casually said 'That was a hell of a death wobble you had there'. I told him it was all in the ass-end and he goes 'Nope. I watched the front tires go crazy.'

After slapping myself in the back of the head several times, I stopped the video of a rear-axle rebuild on YouTube and I am ordering new ball joints, new tie-rod ends, and I already have a new steering gearbox to go in.

Thank you everyone for helping me along the wrong path I set us on and I will endeavor to persevere on the CORRECT path of a front-end rebuild.

 

[ehuppert]

Dana 60 front end in a M1008 does NOT have ball joints....

 

[Finnegan1008]

Glad you found it! You’ll love the way she drives with all new hardware in the front suspension.

Also check your king pins

 

[porkysplace]

**UPDATE**
So, a friend of mine happened to watch me bouncing down the road like a rubber ball the other day and tonight casually said 'That was a hell of a death wobble you had there'. I told him it was all in the ass-end and he goes 'Nope. I watched the front tires go crazy.'

After slapping myself in the back of the head several times, I stopped the video of a rear-axle rebuild on YouTube and I am ordering new ball joints, new tie-rod ends, and I already have a new steering gearbox to go in.

Thank you everyone for helping me along the wrong path I set us on and I will endeavor to persevere on the CORRECT path of a front-end rebuild.

Your going to need these : https://www.steelsoldiers.com/threads/tms-for-the-cucv.77609/

 

[Marauder4]

Your going to need these : https://www.steelsoldiers.com/threads/tms-for-the-cucv.77609/

Already downloaded and studying them!

 

[Marauder4]

Dana 60 front end in a M1008 does NOT have ball joints....

King Pins, but I misused the name for the ball joints on the ends of the tie-rods and drag link.

 

[Marauder4]

As of now, replacing the steering gearbox took MOST of the slop out of the steering. The tie-rod ends are next.
After learning that the upper kingpin needs 550 ft/lbs of torque, I'm praying that it's just the bushings that are shot. The truck is almost 40 years old, but only has 35k on her.

 

[cucvrus]

My experience of working on these heavy GM K series trucks has been that the front end needs several things corrected to go down the road smoothly. On the K30 all I ever done was replace the tie rod ends and drag link joints. Also replace the steering stabilizer. That corrected 99% of the trucks I had and drove. A few had brake calipers that were seized in the mounts and I cleaned and lubed the slides on the caliper and the brake mount at the outer hubs. I had 1 or 2 that had bad seized outer front axle U joints that would not allow the steering to return to neutral straight-ahead position. Tires seldom played a part as I always ran good tires and never cheaped out and ran used tires. Lift kits. bad sway bar bushings and lack of grease can also contribute to poor steering and unbalance. Check out the front end closely like your life depends on it. It may. Be Safe and Have a Great Day.