Grinding sound at highway speeds

[Ironforger]

02 3500 2WD 6speed dually  214,000 miles

This is kinda hard to describe but I'll try

Over the last few months, started to notice while driving down the road at highway speeds - most notably above 60 mph, whenever I hit a slight (or any sort of) bump in the road - as the suspension bounces down - I hear a whining gear-ish grinding sound. It only happens on the downward bounce.

Points to ponder -

- Truck has a service body installed. it's not super heavy but the helper springs are just touching.  I also have firestone air springs installed - but I don't use them to "hold" weight or lift it up etc. I usually keep the pressure low for added stability - 10 to 20 psi.

- One of my rear shocks is blown. I mean totally blown - oil leaked out etc. I mention this because with a blown shock it's more bouncy in the back, for every bump the truck bounces 2 or 3 times etc and yea, at the bottom of each of those bounces I hear the whining gear-ish grinding sound.  (BTW I just got new rear bilsteins from Geno's shocktober fest.  Puttin them on today - will report after test drive)

- Axle - Original limited slip dana 80. A Couple years ago I did the clutch plate re-stack & new 85w90 gl5 & 1 bottle friction modifier. At the same time put in all new timken inner and outer wheel bearings.   The axle was tight after doing the -re-stack and I had some chattering around tight corners.  Changed the diff fluid 2 weeks ago - this time I put in synthetic 75w140 and 2 bottles of friction mod.  (it took 5 quarts of 75w140. I filled it right up to the bottom of the fill hole).  -  No more chattering around tight corners. Didn't seem to make a difference for the sound issue described above.

- Drive shaft, U-joints and center bearing are all factory original

- The sound issue described above happens both while engaged or coasting in neutral.

- Not sure if it matters but I do have a minor leak which just started at the drive shaft yoke on the back of the trans.

- While towing I NEVER use 6th.  Prefer the 5th gear 1:1 straight through.

 

Anyway your opinions or thoughts would be greatly appreciated. I'm thinking maybe U-joints? Making noise only when they are flexed a little beyond normal ?- as in full suspension travel on the down stroke?

 

Thanks

 

 

Edited November 1, 2015 by Ironforger

[JOHNFAK]

Sounds like something binding on downward travel ...... might need a gopro to check. Or look for damage. 

Just check u joints and carrier for play. Truck parked and transfer in neutral .... wheels off ground rotate drive shaft and push watching for flex in joints.

New shocks probably be fine ..... else gopro it ;)

 

 

[Ironforger]

Well after installing the new rear shocks, the issue is not as pronounced but it's still there.  - I'm guessing it's not as bad now since the suspension is properly dampened it's not traveling down as much on bumps.

1 hour ago, JOHNFAK said:

Sounds like something binding on downward travel ...... might need a gopro to check. Or look for damage. 

Just check u joints and carrier for play. Truck parked and transfer in neutral .... wheels off ground rotate drive shaft and push watching for flex in joints.

New shocks probably be fine ..... else gopro it ;)

You mentioned check carrier for play. Are you referring to the differential/ring gear carrier assy? or the drive shaft center bearing?

1 hour ago, JOHNFAK said:

 

 

 

[JOHNFAK]

Drive shaft center bearing. 

It's usually that or more commonly ujoints.