RV shakes from 55 mph- 65 mph

[CamperBerk]

I have a 1976 Yellowstone on a Ford chassis, at 30mph I have a very slight shimmy throughout the whole RV, this happens again and more aggressively at 55mph and continues to 65mph. At 65mph it then goes back to the slight shimmy that happens at 30mph. When I purchased this RV it had new tires put on but the previous owners hadn't had them balanced so I called a local tire shop and the manager told me to bring in the front 2 only, so the rear duals are not balanced. I was wondering if this may be the cause of the shake or if it is caused by a worn out steering coupler.
Thanks
Camper Berk

[Hitchhiker]

It's probably a tire out of balance or a broken belt in one.

Try moving a rear tire to the front one at a time and see if the symptom changes. Or, if you have a good spare, swap it for one of the fronts and then for the other front to observe for any symptom change.

[PlayItForwrd]

How many driveline's that thing got? I'm betting 2, and it's also a fair bet that being a '76, the hanger/support bracket bushing and bearing (where the drivelines connect) need changing. Check the U-joints too. Driveline shake can feel like many other types of shaking, and it's speed sensitive too...

[jhlady]

Camper Berk,

Is the vibration in the steering wheel or the seats? If it's the seats and other parts of the rig then most likely it is a rear tire/wheel or driveline like others have said. A good tire shop should be able to resolve for you if they are willing to spend some time eliminating variables and checking the driveline throughly.

Good luck!

John

[CamperBerk]

Thanks everyone for your input! Tomorrow I am going to change the rear wheel bearings and seals, U joints, and the steering coupler.. Also, I am going to have the rear wheels balanced.. I figure since it is a 1976 it can use an overhaul..
Edit: The vibration is in the seats and the steering wheel.

[Ridgerunner]

Had a vibration in my steering wheel that made it go side to side at 50 to 55 on my 79 brave, so i moved my front wheels to the inside back and put the outside back on front and now there's no more vibration at all man what a work out that was think i lost ten pounds...

[scenic route]

CamperBerk, The low speed shimmy (30mph) is a good indicator of a tire problem...excessive runout caused by a bad belt, high point (run out) of the tire matched to the high point of the rim or it could be a defect in the tire. I'd take it to a tire shop and have them do a runout check of the tires. Normally, an out of balance tire will not cause a shimmy/vibration at such a low rpm=mph.

As mentioned, rotating is a good trouble shooting technique and may quieten down the shimmy/vibration, but you'll still have an out of round tire on your RV. If your tires are still relatively new, have the manufacturer's dealer take a look see...may be covered under manufacturer's warranty and eligible for an adjustment. Good luck, Bob

[CamperBerk]

well i have replaced rear wheel bearings/seals, have the drive shafts out and the U-joints out also but the weather is not cooperating with me, looks like 2 more days of rain before i can even think about putting it all back together and then I will be taking it to the tire place that put the tires on to see about a bad belt or runout.. I will keep everyone posted as soon as I can return to tinkering on this machine...