vibration

i have a 2001 378 daycab around 55 plus you feel vibration in seat an floor had cen tramatics on all axles took off rears no change at times it's worse than others it varies during the day once in a while it stops found parts in rear diff changed it not fixed changed rear u joints not fixed jacked up an blocked ran 55 nothing seemed out of whack can a bad tire change it doesn't have a pattern weather or temp not a factor drivn me crazy trailer no trailer doesn't change it any ideas

 

Are you talking a driveline vibration or wheel-hop?

Wheel hop can come from anywhere...bad tire, bad rim, bad king pins, out of balance brake drum...

 

forgot to mention all newbrakes and drums also doesn't change with diff lock in or out can be coasting in nuetral and vibration doesn't change have checked driveline from front to back and can't find anything tires seem to be wearing good at about 60 to 70% tread how can i tell if it's drive line or tires

 

Driveline would be a vibration... an out of balance drive shaft, bad carrier bearing, bad slip joint(s), something in your clutch assembly.

The wheel hop would be a hop relative to how fast your tires are turning. I'm trying to sort out a wheel hop situation too and it's gotta be the most annoying thing to deal with all day.

 

55 mph is classic tire shake. If you feel it in the seat, then it is at the back. Check for any mud build up on the inside of the rims. Other than that I would say you still have a bad tire back there somewhere.

 

had a similar problem in a 2001 sterling single axle day cab (we service a fleet of them)went through everything you did ,plus more.motor mounts,steering shaft u joints,spring bushings.ended up being the pilot bearing in the flywheel.

 

you didn't say what type of suspension you have, some are more picky than others when it comes to ride height as it changes pinion angles also

 

if it was a tire wouldn't it be consistent ? throwout bearing i would think engaging clutch and coasting would stop it this isdrivingme crazy have spent over 3500 $ an nothing has changed i think maybe tires but they wouldn't come an go would they ? thanks for everyone's thoughts an opinions

 

It's almost impossible to say without looking it over. Vibrations can come from anywhere and always go throughout the drivetrain so it's hard to pinpoint. I can give you the chassis vibration diagnosis flowchart that the mechanic is more than likely using so you can try to isolate it. Or I can list 500 things that it might be but that probably won't help lol.