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Discussion Starter · #1 ·
For some reason at 60km/hr or at about 1100rpm the truck starts to hope or have like a vibration to it. It's not the death wobble as I can let go of the steering wheel and the steering will is not vibrating at all either. U-joint where all changed so it can't be that either. Tires are almost new and balanced. Not sure what is going on.....

Here is a link to the video I made of the truck acting up
98 Dodge Cummins 12 Valve Vibration - YouTube
 

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A few questions.

(Primary) Are you in 5th gear lugging the engine? If the truck does not vibrate at the same speed in the next lower gear you are simply abusing the truck. Every vehicle with a stick will shake and vibrate if the engine is running to slow for the gear and load. Basically you are going so slow you can feel each time a piston changes direction.

I have seen several vehicles shake because the engine rpm was to low for the speed it was being driven. It is not a vehicle problem. It is a driver problem. Lugging is hard on the transmission. That makes it more likely to have 5th gear fall off. It is not good for the engine either. 1100 rpm is probably to little at that speed.

What is your rear axle ration 3.54 or 4.10?

(If the above is off base)
1 Does it keep vibrating getting worse as you go faster or does it only happen at a specific speed then smooth out? (If it gets worse as you go faster I suspect a bent driveshaft)

2 How were the u-joints changed? (Just beating might have bent the driveshaft)

Are you sure you put the driveshaft snout back in the same position it was in before disassembly? ( Incorrect reassembly could throw the driveshaft balance off)

3 Did it have the vibration before changing the u-joints?

4 How long had it been acting up or did you buy it that way?

5 How many miles on the truck?

6 Has it been in an accident or offroading where it could have hit some rocks?

7 Is there a dent in the driveshaft? (obvious)

8 When you grab the ends of the driveshaft (both ends) do you feel any movement at all? (could be sloppy bearings in the axle or transfer case)
 

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Its an auto so....


Right when it started your rpm's started jumping up and down, was that you or the truck doing it itself?
 

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Discussion Starter · #5 · (Edited)
Yea to the first reply. AUTO trans. Also stated the drive line as in the drive shafts and so on where gone threw when I purchased the vehicle. There is 320,000 KMS on the truck. It is an AUTO. It has a powrlok dana 70 3:55 rear diff. The rear diff does howl a bit and does need to be re bearing. No accident. No off roading. Drive shaft was marked and put back on the same. It did vibrate like this before changing u-joints. Pinion bearing does need to be changed but its not that bad.
 

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Discussion Starter · #6 ·
nor easter yes it does start itself you just have to keep it at that speed or rpm
 
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