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Discussion Starter #1
I'm about 95% certain that I've narrowed down a vibration source down to the rear axle pinion flange/shaft. Pretty much everything else has been determined to be "known good" by swapping out components with another Bronco I have. With the vehicle up on blocks and driving slowly, you can see the flange is "warped"just by looking at it and holding an object against it confirms it even further (you can feel oscillation).

When this axle assembly was on my other Bronco, it also had a cracked rear u-joint mount requiring the drive shaft to be rebuilt. I theorizing that this thing took some hard hits in that area that likely caused the pinion flange damage.

So, as I recall, there is a flange adapter that bolts to the pinion shaft, is that correct? I guess I'm hoping that, somehow, it will just be replacing the flange that connects to the drive shaft but I'm bracing myself that the whole pinion assembly needs to be replaced. Which scenario (or another one) would be likely?

Thanks,
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Discussion Starter #3
Is the vibration constant or does it start a any certain speed?
Well, in theory it's there all the time but you can't really feel it until about 50 mph or so and it doesn't go away (only gets worse). I think you could feel it a little sooner on the jackstands.

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yo,
E6 DRIVESHAFT RUNOUT (ONE-PIECE DRIVESHAFT)
With vehicle on hoist and wheels off, measure runout at front, center and rear of driveshaft with indicator, while rotating driveshaft by turning the axle.
Does runout exceed 0.89mm (0.035 inch)?
Yes If runout exceeded specs at front and center, REPLACE driveshaft. If runout exceeded specs at rear only, MARK driveshaft at rear runout high point, then GO to E8.

No REFER to driveshaft runout and balancing procedure in Section 05-00.

E7 DRIVESHAFT RUNOUT (TWO-PIECE DRIVESHAFT)
With vehicle on hoist and wheels off, measure runout at front, center and rear of driveshaft with indicator, while rotating driveshaft by turning the axle.
Does runout exceed 0.89mm (0.035 inch)?
Yes MARK driveshaft at rear runout high point, then GO to E8.
No REFER to driveshaft runout and balancing procedure in Section 05-00.

E8 INDEXING DRIVESHAFT AT AXLE
NOTE: With driveshaft disconnected from vehicle, manipulate universal joints in each direction of rotation. If universal joint feels stiff, lumpy or gritty in any direction, replace universal joint.

NOTE: Circular rear axle universal joint flange can be reindexed in 90-degree increments to fine tune the runout condition.


Note or mark indexing of driveshaft to rear axle universal joint flange. Disconnect driveshaft at axle, turn 180 degrees, and reconnect.
Recheck runout.
Does runout exceed 0.89mm (0.035 inch)?
Yes GO to E10.
No PERFORM Road Test. If vibration is present, GO to E9.

E9 INDEXING DRIVESHAFT AT TRANSMISSION
NOTE: WIth driveshaft removed from vehicle, manipulate universal joints in each direction of rotation. If universal joint feels stiff, lumpy or gritty in any direction, replace universal joint.

Note or mark indexing of driveshaft at axle and transmission. Remove driveshaft, and turn 180 degrees at transmission only. Reinstall driveshaft.
Is vibration still present?
Yes
REFER to driveshaft runout and balancing procedure in Section 05-00.
No Vehicle OK.

E10 CHECKING REAR AXLE UNIVERSAL JOINT FLANGE FOR EXCESSIVE RUNOUT
Compare two high points of runout marked in Steps E6 or E7 with Step E8.
Are marks within 25mm (1 inch) of each other?
Yes REPLACE driveshaft. PERFORM Road Test. If vibration is present, REFER to driveshaft runout and balancing procedure in Section 05-00.

No If marks are on opposite sides, REPLACE rear axle universal joint flange. PERFORM Road Test. If vibration is present, REFER to driveshaft runout and balancing procedure in Section 05-00.

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Universal Joint Flange Runout Check, Rear Axle, Circular
SPECIAL SERVICE TOOL(S) REQUIRED Description Tool Number
Companion Flange Runout Gauge T92L-4851-B
Clamp Plate T92L-4851-C

CAUTION: This operation disturbs the pinion bearing preload. Pinion bearing preload must be reset if the pinion nut has been loosened or removed for rear axle universal joint flange reindexing or replacement.

Raise the vehicle on a hoist that supports the rear axle (twin-post hoist). Refer to Section 00-02.

Remove the driveshaft assembly. Refer to Section 05-01.

Check the rear axle universal joint flange for damage.

Position Companion Flange Runout Gauge T92L-4851-B on rear axle universal joint flange.
see diagram marked e8356b
1 � Pilot (Part of 4851)
2 354845 Pinion Nut
3 T92L-4851-B Companion Flange Runout Gauge
4 � Bolts (2 Req'd)
(Part of T92L-4851-C)
5 T92L-4851-C Clamp Plate
6 4851 Rear Axle Universal Joint Flange


Install Clamp Plate T92L-4851-C on Runout Gauge.
see diagram e8357a
Align holes in clamp plate with holes in rear axle universal joint flange and install bolts. Snug bolts evenly.

see e8358a


Using Dial Indicator/Magnetic Base D78P-4201-B or equivalent, turn companion flange runout gauge as shown to locate and mark high spot on rear axle universal joint flange. If flange runout exceeds 0.254mm (0.010 inch), remove rear axle universal joint flange, reindex 180 degrees on pinion and reinstall. Check runout again. If necessary, rotate rear axle universal joint flange until an acceptable runout is obtained. If flange runout is still more than 0.254mm (0.010 inch), replace rear axle universal joint flange.
see diagram marked e8359b below
If excessive runout is still evident after replacement of the rear axle universal joint flange, replace the differential ring gear and pinion. Repeat the above checks until runout is within specification. Install the driveshaft assembly.

and for posterity;
8.8 Noise, Vibration and Harshness Inspection, Verification & Pinpoint Tests
Typical Low-Speed Vibrations (Less Than 72 km/h [45 mph])

exhaust vibration
engine harshness
driveline vibration due to improper driveline angles
power steering pump disturbances
air conditioner compressor or drive belt (8620) vibrations
take-off shudder (driveline problems)
brake roughness or harshness
driveline roughness
driveline slip-yoke or rear axle universal joint flange (4851), automatic or manual transmission clutch slippage
Typical High-Speed Vibrations (Above 72 km/h [45 mph])

rear axle universal joint flange runout or imbalance
driveshaft (4602) imbalance
excessive tire-wheel and drum assembly imbalance
tire roughness due to high non-uniformity (force variation) or out-of-balance condition
rear axle pinion gear pitch line runout
excessive tire and wheel runout
worn suspension components
front end accessory vibrations
exhaust vibration (greatly reduced in exhaust systems de-coupled by a flexible coupling and mounted with blade and block hangers)


Harshness is the term commonly used to describe the ride quality concern of the vehicle. A hard ride or harshness is usually caused by the tires or suspension system, namely:

overinflated, wrong size or wrong type tire installed on the vehicle
suspension not sufficiently lubricated
worn suspension components
suspension components installed with preload on pivot point, bearings and bushings
vehicles equipped with tires not specified by the manufacturer (different brand tires often give different ride qualities to the vehicle)
bent or bound-up shock absorbers
heavy-duty components installed on vehicle
Other harshness conditions that affect ride quality may be summarized as follows:

Vehicle bounce � the vertical motion of a vehicle on its suspension system, front and rear in phase, a low frequency "float" or an intermediate frequency "kick."
Vehicle pitch � the out-of-phase vertical motion of the front and rear of the vehicle. A flat ride would be considered the opposite of a pitch ride.
Vehicle roll � the side-to-side rotation of the vehicle body about the front and rear axles.
 

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Discussion Starter #6
Thanks guys (you too M5!), I have definitely narrowed this down to the companion flange. The DS was rebuilt two years ago and was running fine until I swapped this axle back into my 96 (long sob story, don't make me tell it). This axle was also vibrating when it was in my 95 but, for some reason, it's a bit worse in my 96. I can't sell it this way which is the plan. To the naked eye, it appears that just the flange is bent and, since there' no detectable noise, I'm hoping it's just the flange. There WAS some damage to the drive shaft, hence why it was rebuilt, there was a clear crack due to a hit. Both that driveshaft and this axle originally came from the 96. I know this may all be a bit confusing but it's definitely the flange. Now it's just a matter of determining if the pinion is bent as well, looks like I need to do the dial indicator thing.

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Maybe the top pinion bearing is bad and your getting runout or some slop in it. A bent pinion is highly unlikely as they are extermely hard. It would break before it would bend and the force necessary to break a pinion would undoubtedly destroy the carrier casting and more than likely destroy the whole gear set up.
 

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Discussion Starter #8
Maybe the top pinion bearing is bad and your getting runout or some slop in it. A bent pinion is highly unlikely as they are extermely hard. It would break before it would bend and the force necessary to break a pinion would undoubtedly destroy the carrier casting and more than likely destroy the whole gear set up.
Please note that I didn't conclude the pinion is bent. The flange for sure, and I am told they can bend. They look "stout" but, if they took a "head on" hit they look like they could deform. When you watch it from the side, the wobble is primarily "front to back", not up & down. However, I think it would be prudent to check the pinion runout before attempting any repairs.

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Please note that I didn't conclude the pinion is bent. The flange for sure, and I am told they can bend. They look "stout" but, if they took a "head on" hit they look like they could deform. When you watch it from the side, the wobble is primarily "front to back", not up & down. However, I think it would be prudent to check the pinion runout before attempting any repairs.

BB
Well I've seen strange things but that flange is made of cast iron and cast iron doesn't bend or deform very well if at all...it breaks, cracks, shatters. It's strong but brittle... it has no ductility. Steel on the other hand will bend. I don't doubt that it runs out laterally but I have to doubt that the flange is bent. Must be some other reason. But it's your vehicle so you would know.
 
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