Weird violent bouncing.

[Bamtech1]

I just set the slide in camper on my ‘96 2500 4x4 quad cab. (8800 GVWR).
I have previously hauled the same camper without issue on my other ‘96 2500. Essentially the same truck except 2wd. Both are manual trans.
Camper only weighs 1700#ish as it sits. Palomino Real Lite SS1608.

So that’s the equipment,here’s the issue: at around 40mph at part throttle I sometimes get a weird bounce started. It’s a fast maybe 3 cycles per second oscillating feel. It reminds me of like when you’re on a rough road and your foot bounces on and off the throttle, or say if you lugged the engine in too high a gear. Weird, and I can’t quite figure what’s happening. I can go real easy or hard on the throttle in that speed range and it doesn’t happen. I don’t know if it’s suspension bounce, or differential wrap, or what. The load just leveled the truck, not even on the overloads yet.
Been building this truck on a deadline to go on vacation Feb 22, had it well in hand but this is an unexpected wrinkle!
I’m considering adding airbags just to firm things up. For one leg of the trip I’ll be hauling a car/trailer maybe 5000#. Looked at StableLoads, but I think I prefer bags.

 

[Bamtech1]

One other detail- I did find some play in the driveline slip yoke, and plan to replace that before the trip, but I can’t see that causing this issue.

 

[TFucili]

No loose mounts or crossmembers? Axle U-Bolts tight, not rotted?

 

[Bamtech1]

No loose mounts or crossmembers? Axle U-Bolts tight, not rotted?

No sir. New trans mount, new South Bend clutch, new transfer case, new Bilstein shocks, southern truck, no rust at all. That driveline slop is the only thing I can see even remotely worn. It’s a strange one.

 

[Ozymandias]

Frame Flex?
Do you get that bounce always or just under certain circumstances?

 

[NIsaacs]

You are saying bounce, but your description sounds more like a vibration. Did you check your u-joints?

 

[Bamtech1]

Really more bucking than bouncing. Seems to be only 40ish mph at 17-1800rpm, and only since I put this moderate load on it.
U-joints and carrier bearing are new. The slip yoke was seized when I took it apart, had a hole in the boot. I had to dress up that blue permalube on the splines after I beat it apart. It didn’t last well like that, so it’s on my list this week to have a new one welded in.

 

[jhenderson]

Why all the new parts? Could it be undetected damage? Loose fasteners on one or more of those new parts or what has been molested to replace them?

 

[NIsaacs]

I know this might sound bad....but are you in 4x2?

 

[Cummins12V98]

Check your throttle return springs on the P pump. Weak/broken spring can cause this.

 

[Bamtech1]

All the new parts? Really just because I’m a nut. Bought this farm truck, cab-swapped it and have been building it to suit me. I’m an old tractor mechanic and purely hate what modern diesels have become. That’s why refurbished 12 valve. Every hose, belt, maintenance or wear item is replaced as I touch it. Way cheaper here at the house than in the everglades at 2am!
Has to be a product of spring position, driveline angle, torque... once it starts I have to just lift the throttle. I can baby it through the problem range. Hasn’t done it at any other speed as yet.

 

[Bamtech1]

Check your throttle return springs on the P pump. Weak/broken spring can cause this.

Will do, and it does feel a lot like throttle bounce, but not in a way.

 

[Bamtech1]

I know this might sound bad....but are you in 4x2?

2wd hi. I guess you’re asking if the front shaft is turning?

 

[Bamtech1]

Maybe a clue- I just looked it over again, on level ground the rearward end of the upper overload spring is touching the frame stop, but not the front. Wonder if it’s enough to nose the pinion angle up a little but let it oscillate at a certain speed/ load. Maybe it just wants more weight!

 

[BarryG]

I would guess axle wrap. I know on my 01 I had that problem at a couple different times if I was moderately accelerating from say 40ish to 50ish or low speed 15ish to 25 or so. One thing I did was lower the center carrier bearing about 3/4 of an inch by putting a spacer above the mount. That helped quite a bit. It didn't get rid of it completely but did very much shorten the interval and the severity.
Even the new trucks still have that problem to a certain degree Ram can set it up one way but one way does not fit all environments. Another reason they use torque management? If I recall that was one of the reasons the 3rd gens started using 1 piece driveshafts when possible. Getting rid of the center carrier bearing allowed the drive line angle to be better over a wider range of environments.

 

[NIsaacs]

All the new parts? Really just because I’m a nut. Bought this farm truck, cab-swapped it and have been building it to suit me. I’m an old tractor mechanic and purely hate what modern diesels have become. That’s why refurbished 12 valve. Every hose, belt, maintenance or wear item is replaced as I touch it. Way cheaper here at the house than in the everglades at 2am!
Has to be a product of spring position, driveline angle, torque... once it starts I have to just lift the throttle. I can baby it through the problem range. Hasn’t done it at any other speed as yet.

Sounds good, tractors are cool. I started my career with Allis-Chalmers in 1969. Yes, I was just wondering if maybe something is not shifting right with the new t-case and maybe it is engaged in 4x4.

 

[Bamtech1]

I would guess axle wrap. I know on my 01 I had that problem at a couple different times if I was moderately accelerating from say 40ish to 50ish or low speed 15ish to 25 or so. One thing I did was lower the center carrier bearing about 3/4 of an inch by putting a spacer above the mount. That helped quite a bit. It didn't get rid of it completely but did very much shorten the interval and the severity.
Even the new trucks still have that problem to a certain degree Ram can set it up one way but one way does not fit all environments. Another reason they use torque management? If I recall that was one of the reasons the 3rd gens started using 1 piece driveshafts when possible. Getting rid of the center carrier bearing allowed the drive line angle to be better over a wider range of environments.

That’s the way I’m leaning. I don’t know if a one-piece shaft is the answer, longbed long cab. What about traction/ladder bars? That axle is way on down there with those 4 1/2” spacers, lots of room to wobble. Maybe just accept it and drive accordingly?(not sure I’ve got that in me) Airbags would let me tune the height per load and therefore driveline angle, but wouldn’t address axle wrap.

BTW, NIsaacs, road tractors, not farm tractors. (Although we still call ‘em KornBinders and 13 letter sh!tspreaders!)

 

[Ozymandias]

You sure not need such band aid on your Truck, there are hundreds of thousands of them on the road with a camper on their back and they do not shudder.

Change first that slip yoke that was rusted solid and you have beaten with a hammer. That piece for sure is scrap metal now.

 

[BarryG]

I never put a single piece driveshaft on my 01 due to as like you long bed and long cab. Lowering the carrier bearing did quite a bit. I did try traction bars after the carrier bearing lowering chasing the last bit and they really solved the problem. However they have drawbacks and in the end after several years I took them off. The dang joints would freeze, come loose, make noise, reduce articulation etc. However after putting on the ones I did another company came out with a different style. I heard nothing but good things about them but have never used them. You may even find some old threads on here about them you certainly will about the bars in general and what people have used.
https://www.calvertracing.com/caltracs.html

I also agree with Ozzy change the yoke first and see what happens. Could also be your leaf springs are just getting tired and cant hold like they used too.

 

[AEdelheit]

Will do, and it does feel a lot like throttle bounce, but not in a way.

I have had a similar issue on a 97 and it was the throttle return spring, odd but replaced them and no more issues.

I believe there was a TSB or recall and the dealer will repair it for free, at least that was the case about 6 years ago.