Peterbilt 389 Shakes So Bad It Will Take Your Virginity.

MD Alignment Services - Makers of MD Alignment QCT Alignment Systems

 

You can look as some of his videos like the Freightliner Lean. When the air bags lean you see it a lots but most people can't explain what is wrong. Most don't even know it wrong.
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I had a couple trucks just gave us fits, after one of them went through $9000 worth of trying to fix it, I sent it to a dealer about 300 miles away ... why? Because I felt like it.

The mechanic and driver got into the truck, they went for a ride of 50 miles and it was a mess. So he had the driver go back to the shop, he grabbed his laptop and plug it into the ECM and they went off for another 50 miles to record everything with the engine.

It was a fuel metering problem. When the ECM saw a specific speed, it ignored the load and tried to cut back the fuel then added more into it when the engine was struggling, making it shake badly ... it all happened in a split second.

replacing the ECM and wiring harness solved the problem for both trucks.

 

I had this same thing on an 05 KW dump that I did front diff work in. While the diff was being rebuilt, did shocks and figured the shaft could use some attention so sent them to a local guy who I've used multiple times. They sent all 4 shafts back and I reinstalled with the rebuilt diff. Test drove up to 50 (local roads) and the unit felt pretty good, the regular guy put a load on it and went to the job. He called me when he got there and said something may have come loose. I went to the job and drove it...shaking like no tomorrow. Rebalance...same thing. Sent for axle alignment...same. Pulled both left side axles, and started spinning up to 70 mph. Pulled prop shaft (between diffs) first, then rear piece of front, then center piece of front...same. Pulled front piece of front shaft and the vibration was gone. Turns out the guy I use has a balancer that won't fit a 3 piece shaft, so he spun the front piece yoke to yoke and never actually spun it on the carrier bearing. That was the missing link. One new carrier bearing later, and it's now silky smooth.

 

Good that you found the problem.
Thanks for posting update.

 

That sucks when you pay for a shop to replace parts as an experiment until they find fix the issue.