Cab & Seat Shake

try checkin your drive shaft yokes to see if they are out of round allowing u-joints to slop around.or the harmonic balancer ,good luck

 

Well, I was starting to get a shake just as you described a few months ago. I had it looked at and was told the same as you, not the driveshaft... well, it wasn't the driveshaft but a "hub" locking nut. The nut that hlds the drive hub onto the axle housing was broken and it was only hand tight. Replaced all 4 with a newer style (old style was discontinued) and no more shake.

 

SHC I have vibration from about 40 - 55 mph also, have had # 3 u joint come apart a couple of times. (Last time was bad, the driveshaft came loose on the go and started flying around under the truck. Ouch, never want that experience again! My 40 years experience mechanic is at a loss as to why. In the last year I've had all 5 u-joints replaced, the steady bearing, front diff + power divider, a couple of yokes, and the back section of the trans rebuilt including output shaft, nut, seal and bearing. I think I must have some obscure cause for this, perhaps as you describe above. By "hub nut" do you mean a wheel bearing retainer nut? Not a yoke nut on one of the diff's right? And, how the heck did they diagnose/and find that? You'd have to pull them all and check them, unless there was something indicating which one it was?

 

Get to the speed that the vibration happens. Put the transmission in neutral with the clutch out.
Still the same vibration? Tires, bent wheel, or bent driveshaft.
Vibration got worse? Rear gear (bearing issue allowed lash to go too far or lash set too far in the first place).
Vibration went away? U-joints, carrier bearing, clutch lost a weight, etc... OR....


If the vibration went away keep it in neutral then throttle up to 1300 rpm, if the vibration came back its the harmonic balancer.

If its got 600K or more you probably need a balancer anyway.

 

I am having the same problem with a 2010 that we have just purchased.The dealer has worked on it for a very long time.They have changed shocks,bushings,tires,motor mounts,cab mounts,front leaf springs,cab air bags,and the list goes on.They are telling me now that it is because of the wheelbase,242",and the frame is bouncing.The are going to put frame liners in it next.I have been told to "drive around it" and "other drivers don't mind it".I say"I shouldn't have to drive around it" and "those other drivers are not the ones paying for it". Lucky for me that they are footing the bill on this unit as it is a used truck.Hopefully the liners solve the problem.

 

MY god, there is no way a single frame is the problem. I have a 260" wheelbase with single frame, 40 rears no liners and do not have a bounce or vibration. I am sorry I am not close to you to try to help figure this out. There is something else going on and a frame liner is not the problem. In order for the frame to bounce, something has to make it bounce. Above all, good luck.

 

According to Western Star it is a problem with that particular wheelbase.They claim if it is 10" longer or shorter,that it is the frame.I really hope that they are right about the problem this time.I would have to say that there are not too many options left.It has been in and out of the shop for the last two month trying to correct the issue. I feel for the dealership that we bought it from,as they are paying for all of the work,but on the other hand, I don't want to bounce down the road when I have to do the speed limit.It should be going back for the liners in a week or two,so I will keep my fingers crossed.

 

My husband has 91 Peterbilt 379 ...he has been having vibration shake under cab when he is @ 75 mph speed what could be causing this

 

Your WST dealer should be able to get one of these and know how to use it and diagnose what type of vibration it is.