96 Bronco Vibration. ****

So I just replaced leaf spring hangers, leaf packs, shackles, shock mounts and radiator core support on a customers 96 bronco. Went to test drive yesterday after finishing up and there's is bad fast paced vibration at 25-35. After that it lightens up but still feels present. You can feel the vibration slightly begin as soon as you start moving. At 25-35 it does it whether I'm on the gas or not however it seems a bit worse when on the gas. Checked the diff fluid and he was scary low!! Maybe 3/4 of a quart... yikes. What I'm thinking is a pinion bearing went out. If put on jackstands and set cruise control at 40mph there is a loud roaring noise from the rear which seems to be intermittent. I think I lucked out and the bearing finally went out on my watch. Mistankingly Didn't test drive before hand however the customer said it didn't vibrate before. He is very understanding and said to do whatever needs to be done. However do not want to throw parts at it and cost him more money. What's your guys opinions on the pinion bearing? Took the carrier out and the carrier bearings look good, not discolored and spin freely.

Thanks

Greg

Yo Greg,
From 96 Bronco-F-Series Workshop Manual (PARTIAL) by FORD via http://www.diesel-dave.com/vehic/manual/stj/stjleft.htm
...
Section 00-04: Noise, Vibration and Harshness
DIAGNOSIS AND TESTING
Symptom Charts
ROAD TEST DIAGNOSIS
AXLE DIAGNOSIS REAR
Condition Possible Source Action
Vibration and Boom Ring gear and pinion.
REFER to Axle Pitch Line Runout and/or Boom under Component Tests in this section.

Section 00-04: Noise, Vibration and Harshness
DIAGNOSIS AND TESTING
Components Tests
Noise or Vibration, 4-Wheel Drive Vehicles:
"Pinion bearings are frequently replaced unnecessarily when correcting gear noise. They should not be replaced unless they are actually scored or damaged, or there is a specific pinion bearing noise. Examine the large end of the rollers for wear. If the original blend radius has worn to a sharp edge, the bearing assembly should be replaced."
...

Road Test Quick Checks
http://www.diesel-dave.com/vehic/manual/stj/stj04005.htm#ppt0402
24-80 km/h (15-50 mph): With light acceleration, a moaning noise is heard, and possibly a vibration is felt in the floorpan. It is usually worse at a particular engine speed and at a particular throttle setting during acceleration at that speed. It may also produce a moaning sound, depending on what component is causing it.
Refer to Pinpoint Test B. miesk5 note, this is just for TIP-IN MOAN;

(Check engine air cleaner, ENGINE MOUNTS, EXHAUST SYSTEM)
Scroll down to PINPOINT TEST G: AXLE NOISE
G1 CHECK DIFFERENTIAL LUBRICANT
Check for low lubricant level.
Check for wrong or poor grade axle lubricant.
Is lubricant level low or not to specification?
Yes ADD or REPLACE lubricant. REFER to appropriate section in Group 05.
No GO to G2.
...
G8 INSPECT PINION GEAR/BEARINGS
Remove pinion from axle.
Inspect pinion and bearings for wear.
Are pinion bearings OK?
Yes Axle OK. REFER to Symptom Charts in the Diagnosis and Testing portion of this section.
*** NO REPLACE faulty bearings.*** REFER to appropriate section in Group 05.

Section 00-04: Noise, Vibration and Harshness
DIAGNOSIS AND TESTING
Symptom Charts
ROAD TEST DIAGNOSIS
Condition: Possible Source: Action:
Noise or Vibration — 4-WD Vehicle/Wheels/tires.
PERFORM Pinpoint Test A.  miesk5 note, I didn't go further than to list these.
Wheel bearings.
PERFORM Pinpoint Test H.
Driveshafts/U-joints.
PERFORM Pinpoint Test E and/or Pinpoint Test J.
Hubs, automatic or manual locking.
PERFORM Pinpoint Test H.
Engine/transmission mounts.
PERFORM Pinpoint Test C.
Transfer case.
PERFORM Pinpoint Test H.
Engine/transmission.
PERFORM Pinpoint Test A.