vibration at speed !

sledhead · October 12, 2013, 02:23:52 PM

Hi all I have had a slight vibration at 72 mph ? Now it's not that bad . But over the years I have replaced 8 tires , all balanced and put on the balance master rings . I do have an air bag leveling system . When I installed it I measured the height of the coach when it was stock and adjust the air to match while driving. So I don't think it has anything to do with the vibration but who knows ? My tires all show no unusual wear . Any ideas ?

thanks dave

Dave5Cs · October 12, 2013, 02:37:09 PM

Cracked hub, bad bearing or race, bent something on your control arms, cracked U-joint or loose bolts on your drive shaft? That's all I got!...

Dave5Cs

sledhead · October 12, 2013, 02:52:27 PM

All new air bags ( 8 )
new shocks (

new brake shoes , seals

I grease all the nipples drive shaft , brakes , all the other ones (100rds , 100rds of them )

It has had the vibration for years .

on the control arms how do I check them ?

wg4t50 · October 12, 2013, 03:58:56 PM

Found an issue with too low air psi in the tag axle bags, caused the tag to hop. Had the MC7
If you knew the frequency of the vibration, it would be very simple to locate.

Dave5Cs · October 12, 2013, 04:06:35 PM

Rarely happens but if they are bent you will see it especially if you ran over something or it was hit etc. I was just throwing some things out there that it might be...You said you greased the U-Joints but did you check the bolts and nuts.

Dave5Cs

edroelle · October 12, 2013, 04:22:22 PM

Usually, a vibration is caused by a rotating element. Bearings can cause it BUT, they are a small diameter and relatively light unless there is significant wear and loosness. I would first check tire balance and universal joint wear. A tire with a loose belt can cause a problem. What brand are you tires?

A resonance in the body can also cause a problem. You want a sturdy, tight, body. Are there rivets loose or indications the side walls are bending?

Ed Roelle
Flint, MI

sledhead · October 12, 2013, 04:53:08 PM

Tires fs400 firestone new and all balanced dave

skihor · October 12, 2013, 06:52:05 PM

I once ignored a vibration and I found the issue was loose and eventually sheared driveshaft flange bolts. Out of time u joints, worn splines on a 2 piece driveline, worn u joints are all suspect. Also, with my 6V92/5 spd allision conversion, it has a very short driveline. It is VERY critical on ride height. Worn shocks can allow harmonic vibrations to happen. Many suspension components could lead to harmonics.
Don

Dave5Cs · October 12, 2013, 08:33:08 PM

Does it happen all the time, when up at running temp only at 72MPH. Where do you feel it? In the rear, front, all over, Is there a noise with it and where? Is it felt from drivers seat or when foot is on the brake or fuel peddle etc.? Check air pressure in all tires against a weigh stations reading and then a tire chart with the weigh chart to see if you might be running to high or low pressure.

Dave5Cs

wg4t50 · October 12, 2013, 11:44:57 PM

Another question, vibration occur when coasting, accelerating, or just cruising ?
Have also had the U Joint issue, vibrate when adding power, smooth when coasting, yup, loose bolts on beating caps.
Why I have enjoyed the bus sperience, never a day of no education

sledhead · October 13, 2013, 07:14:10 AM

Over the years I have tried lot's of things. It is only at 72- 77 mph after that I can't feel it. I thought it had to be a tire problem . But I think it,s time to remove the drive shaft . Would it be wise to put in a new u joint and have it balanced ? if so who, would balance it ? machine shop ? transmission shop ?

let off on the gas no change
once I put in neutral and coasted down to a stop no change

about the only time I have not felt it is when you first start out when its cold out side . But after driving for say 1/2 hour if I drive at 72-74 mph I can feel it.

now this spring was the first time ever that my son was driving the coach and I went for a walk in side ( wow was that weird ) I could feel a small bouncing up and down when I was sitting on the toilet ( just sitting ) which is just in front of the drive tires on the driver side .

again this is a very small vibration .

thanks again dave

luvrbus · October 13, 2013, 07:20:52 AM

Probably just a out of balance or out of round brake drum high speed vibrations can be a PITA to chase down I had one it took me for ever to figure out the the 3 longer studs on 1 wheel was causing the problem.

If you can find a truck shop that spin balances on the rig they can find it if a tire or wheel problem

Len Silva · October 13, 2013, 10:18:12 AM

What is the frequency of the vibration. At that speed the wheels are turning at 425-450 rpm and the drive train at 16-1800. It sounds like something rotating at wheel speed, so if not the tires, it is likely a brake drum.
Did you have them spin balanced on the bus?
Can you get it to a chassis dyno? That might help.
Can you jack up one rear wheel at a time and spin it at that speed? That would tell you front or rear.

ol713 · October 13, 2013, 03:56:07 PM

Hi;
When you greased the u-joints, did you happen to grab the
drive shaft and see if it moves up or down??
Merle.

Quote from: sledhead on October 12, 2013, 02:52:27 PM
All new air bags ( 8 )
new shocks (
new brake shoes , seals

I grease all the nipples drive shaft , brakes , all the other ones (100rds , 100rds of them )

It has had the vibration for years .

on the control arms how do I check them ?

pvcces · October 13, 2013, 10:42:43 PM

We had a pretty good vibration at the same speed as you have. Ted Campbell pulled the parking brake drum and rear axle. Then, he had me spin the drive shaft at the same speed. Most of the vibration was gone. I was shocked at how much that small drum threw the line out of balance.

It might be something to look into, if you still have the drum.

Tom