Drive line noise mystery? Solved

[alborz]

Here is the story
I called peterbilt dealership to make an appointment for a three axle alignment. They said they don’t do it at their shop and send their customers to another shop nearby. Ok took the address and drove there. They said your bushings are bad and need to be replaced before aligning axles. “Ok do it” I said. After few days They informed that my truck is ready. Ok I picked the truck and on way home I heard a strange noise from under the cab. I pulled over checked everything and backed to the shop. He looked and said we’ve done our job and that noise is not from our job.
I did some research and did the following.
Replaced air ride level valve. And
Checked/ rechecked height level over ond over and over
Rebuilt transmission because I thought that might be from bad tranny
Cut and balanced new drive shaft
Changed u- joints and carrier bearing
Dropped and Checked both differentials and their components
Put new driver tires

And still the noise is there. At 55 mph when bobtail or from 60 plus mph when hooked to trailer and truck simply coast or downhill. If I push the clutch or put the gear in neutral or when accelerating [/b]the noise goes away. Other than that it is on my nerve.

[Waterloo]

Assuming you have a Pete, which one? Motor, transmission? Year?

[alborz]

2010 Pete 387
880xxx miles
Cummins ISX 15 liter
Trans. 13 speed eaton

[Chamberpains]

It looks like you did some pretty extensive work. Just throwing it out there, did you check all the linkages in the clutch connections? Sometimes they just Rattle and need rubber washers put behind the actual washers to shut them up. Does the rattling go away when you just rest your foot on the pedal or do you have to fully disengage the clutch?

[redtick]

While you had the transmission down did they pull the clutch out for inspection?

Things I've found in the past.
Motor mounts worn or loose mounting bolts
Flywheel mounting bolts loose or sheared off.
Cracked flywheel housing.
Clutch housing loose.
Cracked center plate in the clutch
Rivets loose on the hub of the clutch disk.
Center plate dowels on the flywheel worn/notched, allowing the center plate to chatter or notched to the point of binding the disk.
Someone replaced the flywheel housing and failed to dial it to center. Which causes side pressure on the input shaft of the transmission.

Years ago I worked as a line mechanic for a company. One of the guys in the shop rebuilt a 10 speed.
He left a spacer out, which let the mainshaft move forward, almost an 8th of an inch. The truck made one 350 mile round trip, the driver told us of a noise in the transmission. Transmission was pulled and corrected. But the wear pattern had changed on the gears and the transmission had whine from that day forward.

[Chamberpains]

Just thought of one other dumb idea that crossed my mind. I know the engine torques to the passenger side but do you have any exhaust parts that may be resting on the frame rail or cab? I recently had to rearrange my exhaust from where a flex pipe settled one of the solid pipes on to the frame rail which caused a grinding type noise while accelerating. I know my suggestions are a bit on the stupid Common Sense side, but I usually find it's the stupid stuff I've overlooked.

[redbeard]

If you grab the gearshift knob when making the the noise does it change?

Had a 10 speed that would make a noise like that, drove me crazy. Ended up tieing a rag around the gearshift and noise stopped. It was like that for a couple of years.

[alborz]

Thank you all for your comments
When I rebuilt the trans, I put a new clutch. And pilot bearing
Linkage is good.
Checked the motor mounts, nothing unusual
Nothing is touching the drive shaft
I have to disengage the clutch to make noise go away
Touching the gear nob when driving does not effect the noise
The oly thing that I haven’t changed are shocks.

[Chamberpains]

THE FOLLOWING IDEA IS VERY DANGEROUS AND CAN CAUSE HORRIBLE DAMAGE IF DONE IMPROPER!!

Here's an idea to expose any problems in the Driveline. Chain your drive axles tight to the frame rail with the air suspension fully engaged. You want it fully engaged to keep proper Driveline angles. If the air is out or they are just hanging you will get driveline angles that will cause grinding noises in the Driveline.Then pick the whole back end up to get the wheels off the ground. Put it on jack stands and frame stands the more support the better and safer. And make damn sure it can't fall off of them. Then you can essentially Drive the truck through the gears without moving. This is real good at exposing noisy rear ends, out of balance or bent drive lines, noisey transmissions and clutches, out of round or poorly mounted drive wheels. You can hear and visually check all components at speed. I never had to take one above 30 mph to expose noisey parts and far less mph to see unbalanced or bent parts. You will not need to use the accelerator pedel. You can just put it in the gear with the speed you want to turn the drive line at. The engine at an idle has more than enough torque to turn any gear from a dead stop. You do not want to do anything fast such as accelerating or braking because it will snap driveline components or break gears. Remember there is no weight on the wheels to absorb the output of the engine or for the brakes to not over react. You want to be very easy on taking off and slowing down. Also make sure the wheels are completely stopped before trying a different gear or speed.

USE AT YOUR OWN RISK. THIS METHOD IS VERY DANGEROUS!!

I've had great success using this method to find those hard to find noises or shimy and shakes at certain speeds drivers complain of.