I need some help diagnosing a problem. At a very low crawl speed either coasting or at low power creeping, I have what feels like a bubble in my left rear side tires. I know it's not actually a problem with the tires, but at higher speeds it feels like I'm riding on those big half round lane dividers. The only thing is though that it has a rythm to it. It will pulsate and then lessen, then pulsate and lessen, never really going away. I have over 185,000 on the truck and am wondering about axle bearings. I am wondering because of just recently having the truck in for a VP44 (1st one of the truck's life might I add!!) and an ABS light that turned out to be a RWAL sensor out. Do I have a vibration from a flat spot in a bearing? Do I have a bent axle shaft( highly doubt this one) do I have a bent rim? I've checked the air in the tires, balancing, rotated, check the brakes and recently (within 5000 miles) replace the universal joints that were still decent, but original. I also have a new set of shocks with about 7000 miles on them. Any advice would help out. Let me know if I forgot to include any pertinent info on the truck.

 

I'd say that that is a tough one.
Considering that you say you had the wheels balanced as well as rotated them, they are probably not the problem. Although you could have an issue with the tires that would not show itself on the tire balancer (even a square tire can be balanced).
Axle bearings would be my guess on this one, but don't rule out a problem with your rubber. If the tires are getting close to needing replacement, I would go that route first and see what happens.

Good luck!

 

Thanks for the help mikelr. The rubbers are only about 10,000 mile old Uniroyal load range E's. They have been a good tire so far, I will still take a look at them again just to make sure. I actually had changed all the fluids on the truck about the same time as the tires and inspected all the teeth on the ring gear when I had the cover off, and everything looks good, so I don't think I have any interal workings going out, but I'm just stumped on this one. Could I be looking at a brake drum that has lost it's balance, it would not explain the low speed lope, but I know it could give a vibration at higher speeds.

 

A warped or imbalanced drum would probably give you some peddle feedback under braking.
I would jack up the rear, remove the tires and drums. If the wheel bearings are gone they are not doing as good of a job locating the axle shaft in the housing as they should, which may cause a leak at your axle seals. Look for leakage at the seals, if you find leakage wheel bearings may be your problem.
And lat's face it, with over 185,000 miles I think you may be due!