Driveline clunking while driving

[rattle_snake]

After 1st gear WOT pull (no hop) my cobra has developed a clunking noise that is dependent on vehicle speed, not engine speed.

Clutch in/out has no effect
Brakes have no effect
turning/swerve has no effect.
Same in any gear, including reverse

I put the car up on my lift and inspected everything. Definitely from the rear. No loose axle nuts, CVs seem tight and the same side to side. U joints tight. driveshaft not hitting anything. Brake look OK. Car has FTBR Delrin cradle bushing, solid diff bushings, diff brace. 63k miles. Stock diff/gears. Other than the new clunk sound, no other symptoms.

What to do next?

 

[01yellercobra]

Drop the diff and pull the cover. And hope no chunks fall out.

 

[Rambro]

Check the torque on the diff mounting bolts, rear sway bars, everything back there.

 

[03' White Snake]

Check tail pipes are hitting the diff too.

 

[railroad]

Is it a one piece driveshaft or have a hanger bearing. Hanger bearings can look good and be beat out.

 

[01yellercobra]

Is it a one piece driveshaft or have a hanger bearing. Hanger bearings can look good and be beat out.

These cars all have one piece drive shafts.

 

[Roush6018]

you should remove the driveshaft to check the U Joints, they should move smooth in all 4 directions, if one direction is looser than the other than replace the U JOINTS. if problem still continues i would remove the diff cover and inspect the gears for chipping and bearings for wear. also could be a broken bearing piece in the axle shaft CV joint.

you definitely have a problem with the driveshaft/gears and diff/axle shaft if the clunking changes with vehicle speed.

i only have a clunk when i am at a stop and put the car in first gear, my rear diff is pretty worn out but it still works.

 

[hotcobra03]

It's hard with basic description,

But being it makes noise both directions.

Hub bearing,tob shaft,rear spider gear

 

[rattle_snake]

When I can get some time I plan to put the rear on blocks and spin the drivetrain up to speed, shut engine off and listen. stethoscope. Go from there.
Thanks for feedback.

 

[rattle_snake]

Did above test, noise in rear end. Put on lift, disconnected driveshaft. noise in diff. Pulled the diff to inspect

Removed cover for visual, nothing obvious. Pulled carrier and disassembled, all good. All bearings are good. Pinion smooth, preloaded as expected.

Cleaned everything. Installed new clutches.

Installed carrier, verified backlash. Before pattern check, rotated carefully with ring preloaded. Found 3 teeth that didn't seem happy.

Close inspection now clean, many of the teeth are cracked at the root.

So pinion is done. Need new R&P.

 

[rattle_snake]

Cracks are deep. would have failed very soon.

3.73 going in instead of 3.55. This is only a 5% change. Trap speed of 120 should be around 5900 in 4th.

 

[Bullitt1448]

Good catch! Not everyone would have found those cracks. Those are a major failure waiting to happen

 

[hotcobra03]

I had 373 for awhile on stock setup,,

I went back to 355 on next repair,

It did make it snappy but as a daily driver at highway speeds it needed a 7th gear

2200-2250 rpm @70

 

[rattle_snake]

Good catch! Not everyone would have found those cracks. Those are a major failure waiting to happen

Thanks. I couldn't find them either until I cleaned everything. The oil film made it not possible to feel the few broken teeth in the car.
The pattern check should have found them.

I had 373 for awhile on stock setup,,

I went back to 355 on next repair,

It did make it snappy but as a daily driver at highway speeds it needed a 7th gear

2200-2250 rpm @70

I debated the ratio for awhile. Currently running Nitto DRs which don't grip as well as MTs. They hold 1st gear in the summer when pavement is hot and engine is down on power. They spin some in the winter. 3.73's 5% more torque will hurt 1st but help the rest. I don't drive very far at highway speeds.

 

[rattle_snake]

Ford has changed the manufacturing style of 8.8 gear sets since the 2000s. Used to be 5 cut and now 2 cut/face hobbed. So wear pattern is different.

 

[rattle_snake]

Finished out gear setup and install. Had to make and modify a few tools and parts to get it done.

Took a few pinion depth changes.

Ended up with a 0.027 pinion shim. 0.010 backlash, 21 in*lb pinion preload using crush sleeve eliminator. 28 total.

Sealed up and car back on the road. I didn't add any extra friction modifier over what was already in the 75/140. Needs break-in miles now.

 

[rattle_snake]

With some miles put on the new gears all is well. The 3.73 ratio at only 5% is noticeable. In cooler temps with not-so-sticky NT05Rs is will break the tires loose in 2nd. 1st is still manageable with throttle control. Reprogrammed axle ratio and result is quite accurate to GPS.

 

[Bullitt1448]

Great job! Good to see folks doing their own diagnostics and completing repairs successfully. Too many just drag it off to the local guy and let him have all the fun