Shaking 1991 W250 Cummins
Many of the readers of this forum and others have complained about their 1st Generation Cummins Rams shaking at some point well into their trucks' life spans. I, myself, experienced such a phenomenon, and scoured the various pages looking for some advice. Although I discovered many people who experienced the same symptoms, no one seemed to really eliminate the problem altogether.
But armed with a lengthy span of time in which to diagnose the effects, a GoPro, my truck's antenna, and my son, I was able to correctly deduce the origin. The story goes like this:
In May of 2018, I took my 1991.5 W250 5 speed to Driveline and Gear Service in Sparks, Nevada to have a number of things inspected and repaired. I had noticed some oil leaking from the pinion seal on the Spicer 70, had a bad axle seal, and had some braking issues. I had them inspect the Powr-Lok differential, and go through the entire Dana 60 up front as well (wheel bearings, king pin bearings, etc.).
The Powr-Lok had reached the end of its life, so the tech found one that was in fairly new condition that had been removed from its housing to be replaced by some sort of locker. The axle seals were replaced on both sides, the drive shaft was inspected for balance, and new u-joint cups were installed. New brake pads were installed up front, the rotors were turned, and new brake drums were installed, as the old ones had reached their end. The linings were replaced, but not the cylinders, I later discovered.
After about a month, I picked up the truck, and could immediately notice a tighter feel in the grip of the rear axle, and the brakes worked fantastically. When I got on the freeway, however, I experienced the issue that would mystify me for the next 11 months. Starting at about 55 m.p.h., the truck would start to shake, violently enough that my teeth would chatter, and my mirrors became unusable. Any cargo in the bed would skip around, and it felt as though I was in the nascent stages of a death wobble development (which I experienced 18 years prior in the same truck).
I gave it a few weeks to develop an extended profile under different driving conditions, speeds, and road surfaces. After about 6 or 7 weeks, I called Driveline and Gear, and explained the problems. I had also noticed that the brakes started pulling hard to one side, and I thought that I had forgotten how to drive a manual transmission, as I kept getting rear wheel chatter no matter how I feathered the clutch when accelerating from a stop. Perry, the foreman that supervised the other technicians, suggested that I needed to first get my wheels and tires balanced, as I had a lot of weights on the wheels, and the new, perfectly-balanced drive train could be sensitive to erratic rotation. I had this done, but nothing changed. We played phone tag for a couple of weeks, and eventually Perry met me after closing as he was certain that my wheels were the culprit. They are 10 D-window Daytona-style steelies. Perry has a '92 W250 with a Cummins, so we removed his forged aluminum wheels with BFG 285/75 R16's (which I have on the steelies), put them on my truck, and went for a drive. There was almost no change.
Perry was stumped, but told me he'd call me in a couple of weeks after finding a spot on the schedule, and they'd go over everything again. A couple of months later, I contacted him, and was able to get the truck back in the shop. Perry's son, Cody, who had performed some of the work, told me that they had discovered at least one spindle nut was not seated all the way, which would suggest the vibration I experienced. They checked everything, and noticed no other problems. After I picked up the pickup, Cody called me to check, saying that the truck should ride better. But it did not.
I had been mulling the symptoms over, and realized I needed to determine from exactly where the vibrations emanated. I borrowed my son's GoPro, and mounted it under my front bumper to montior any lateral or vertical movement of the wheels. Nothing, I then mounted it on the starboard chassis rail and filmed the drive shaft. Nothing. I then mounted it to the back bumper and, like I had with the other recordings, filmed the back wheels at various speeds. Something...
The wheels started jumping at over 55 m.p.h., and was more noticeable on the driver's side than the passenger's side. Oddly, I noticed a "wobble" in the light coming through the d-windows at low speed. When I got home, I decided to experiment with the wheels to see if they rotated in a plane or wobbled. The wheels seemed to rotate properly when turned by hand. I had noticed for months that the vibration would change intensity and duration, as if the amplitude was changing during the vibration's wave. I suspected my exhaust line, since its welds were broken and it was falling apart. So I replaced that with a Diamond Eye system, and the vibration continued. I removed my 14-year-old rear shocks, to see how the truck drove without them, and it was the same. I checked the shocks, and they were suprisingly even with compression and rebound, so I re-installed them.
Eventually, it occurred to me to take one wheel off of the back axle, set up my antenna as a feeler on a chair to keep it still. with it oriented parallel to the axle, and just barely touching the circular surface of the brake drum, and had my son turn the remaining wheel. To my surprise, my theory that the brake drums were out of round turned out to be correct. Both the driver's and passenger's side were out of round. And the vibration would change as they would get out of phase and then back into phase as I rounded bends and turned corners.
I talked to Tom, the owner of Driveline and Gear, and he insisted that out of round drums could not be a problem, even if out of round a full 1/2", as in my case. He then said, "What do you expect me to do about it?" At this point, I had learned from a co-worker about Folbeck 4-Wheel-Drive, just down the street from Driveline and Gear. I explained the saga to R.J., and Folbeck went through the whole thing. They were surprised that anyone would suggest that drums so out of round could not cause massive harmonic vibration when a weight as small as a nickel, welded to driveshaft, can make all the difference in the world. The guys at Folbeck installed new drums that were machined inside and out, installed new cylinders, and refilled my diff. oil and added the necessary friction modifier I can only assume was overlooked a the other shop. Now, miraculously, I have had no shaking and no rear end chatter since.
If this epic account helps just one person, it will be worth it.