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Discussion Starter #1
I have completed the following in order to try and diagnose the vibration/rumbling/thrumming that occurs at a road speed of approximately 58 – 62 MPH (the vibration is torque sensitive in that changing from acceleration to deceleration affects it. Sometimes it is possible to "feather" the throttle so as to make the vibration disappear).

I replaced the homekinetic shaft with a new genuine MB shaft per the WIS and the W463 service and repair manual. The vibration remained after replacement. Note: the new MB shaft did not have the "green marking dots" per the WIS, so I oriented the shaft clamps in the same orientation as the original shaft.

I found CV joint grease in the right front axle joint housing and subsequently dismantled it and replaced the CV boot which was broken. The CV joint and the axle were is good condition so I replaced the boot. I also replaced the axle seal and the axle bushing. Again, no change in the vibration issue.

I have also replaced the drag links/ball joints for the steering as these were worn or the boots had been damaged (old age, not impact). The front end has been re-aligned and the tires have been road force balanced. No change in the vibration issue

All fluids in the TC and differentials have been changed with the approved fluids. The drives hafts have been greased as well.

I also replace the TC front drive shaft flange seal on the TC (per the WIS) since it appeared to be leaking slightly.

I did the following "diagnostic" tests:

I drove the truck at 28 – 32 MPH with the transfer case in Low. This results in the same homekinetic shaft speed as 58 – 62 MPH in High. There is no discernible vibration under these conditions.

I marked and then removed the front drive shaft and drove the truck (TC diff locked) at 58 – 62 MPH in High – vibration still present. I replaced the front drive shaft in its original orientation shaft and drove the truck at 58 – 62 MPH in High – vibration still present.

I marked and then removed the rear drive shaft and drove the truck (TC diff locked) at 58 – 62 MPH in High – vibration still present. I replaced the rear drive shaft in its original orientation shaft and drove the truck at 58 – 62 MPH in High – vibration still present.

The bearing free play is essentially unmeasurable on both the left and right side; there is no bearing free play if you try and rock the wheels either.

So I am stumped as to the source of the vibration. My local Indy shop doesn't have a clue either. I don't want to get into the mode of just throwing time and money at it, so any suggestions would be greatly appreciated.

Thanks!

- FD
 

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Discussion Starter #3
The steering shock was recently replaced (at the dealer) by the previous owner. The vibration is not in the steering wheel - you can mostly hear it and faintly feel it in the floor. The magnitude of the vibration is such that I basically consider the truck un-driveable for any highway distance more than a few miles.
 

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Have you checked the tires for balance or defects? What about the wheel, are they bent or damaged anywhere? its very hard to track down vibrations on nay car let alone a G...perhaps some of the more experienced owners can chime in and help. What about front suspension bushings? I had death wobble in my F250 until I changed out the worn suspension bushings.
 

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I drove the truck at 28 – 32 MPH with the transfer case in Low. This results in the same homekinetic shaft speed as 58 – 62 MPH in High. There is no discernible vibration under these conditions.

I marked and then removed the front drive shaft and drove the truck (TC diff locked) at 58 – 62 MPH in High – vibration still present. I replaced the front drive shaft in its original orientation shaft and drove the truck at 58 – 62 MPH in High – vibration still present.

I marked and then removed the rear drive shaft and drove the truck (TC diff locked) at 58 – 62 MPH in High – vibration still present. I replaced the rear drive shaft in its original orientation shaft and drove the truck at 58 – 62 MPH in High – vibration still present.
Wow.. that is a LOT of work chasing a vibe...

With that, you've eliminated from the end of the transmission all the way to the axles.. Does the vibration rear its head when you leave it in any particular gear and get the engine up to a similar RPM (e.g. torque converter causing the issue, though your TC Low test would probably have been similar engine-wise, and ruled out the converter and engine mounts)?

What about when turning and traveling at those speeds (e.g. freeway on-ramp), does the vibe show up when the left/right sides are spinning at different rates and force on the front end bushings (trailing arms) are other-than-straight?

Have you rotated tires to see if the characteristics of the under floor vibes move to another point in the chassis?

Another, albeit slightly dangerous, test would be to get it on jack stands and run it up to that speed and see if the vibe exists. Or better yet, find a chassis dyno where you could get it up to speed under load to see if it can be pinpointed.

The suspension design on these things is ancient and can be prone to harmonic vibration.. There's only the panhard bushes, shock absorbers, drag/steering links, and trailing arms holding the axle under the truck. Any one of the rubber pieces dampening where it meets the frame could be a culprit as well. (I sincerely feel your pain. I chased a low-speed steering clunk with my wallet a couple years ago. After steering shock, rod ends, steering link, shocks, and king pin bearings I finally got around to changing the panhard bar -- problem solved..)
 

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Discussion Starter #6
Have you checked the tires for balance or defects? What about the wheel, are they bent or damaged anywhere? its very hard to track down vibrations on nay car let alone a G...perhaps some of the more experienced owners can chime in and help. What about front suspension bushings? I had death wobble in my F250 until I changed out the worn suspension bushings.
Yes, the tires have been balanced twice as well as rotated front to back and cross rotated left front to right rear, etc. No change in vibration. I have had the truck up on a two post lift, locked all differentials and let the truck "idle" along. This allows for direct, precise inspection for bent wheels and out of round tires. I was shocked at how true and precise all of these were given the vibration issues.

I will check out the bushings to see if there issues there.
 

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Balancing is great but have they checked the road force measurement of the tires? This happened to me with most of your symptoms and it solved the problem. Whatever garage is doing the check must have road force specific equipment. Good luck in finding your solution!
Kayrunner
 

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From bad to ugly . . ?

I took the G to another Indy who was recommended by my first guy. He checked it out and has found play in both the front and rear drive shaft flanges on the transfer case. He invited me to come over and check in out while it was on the lift and the play is quite substantial - the flange/shaft will "tilt" (e.g., move off-axis) a good millimeter or two. This tells me that at the very least the drive shaft flange shaft ball bearings (one on each shaft) are bad and that the tapered bearings on the differential carrier may be bad as well. If you look at the design of that section of the transfer case, the drive shaft flange shaft is supported on one end by said ball bearing (part no. 0059811525 on the front and 0039818725 on the rear) and by the inside splined differential carrier which is in turn supported by the tapered bearings (0099815905 front, 0079812105 rear).

This type of "play" is exactly what I what I would think would cause the type of noise and vibration I have been experiencing. So a couple of questions if I might

- Is play in the drive shaft flange shaft "normal" (I would think not)
- Can such play re resolved by just replacing shaft the ball bearings (in each end cap) or is one looking at all four bearings?
- Can the shaft bearings be replaced with the transfer case in position by simply removing the end caps or does the TC need to be removed from the truck?
- Why would both bearings be bad at the same time?

I would appreciate any thoughts/help people have.

Thanks!

- FD
 

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Discussion Starter #10
Anyone . . . ? :)
 

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I have read on the forum on a DIY that if you pump too much grease on the splines of the driveshafts you can cause damage to the TC bearings because the grease dosn't let the driveshaft compress under suspension travel. I guess some damage could be expected to the diff pinion bearings as well. Maybe the driveshafts were overgreased by the previous owner. I want to know how you are going to take care of this and how much is going to cost so please update us.
 

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Update . . .

I took the G over to a friend who has a lift that can support the G (mine does not have the necessary weight rating) and we carefully examined the transfer case flanges and determined that the "play" that was observed by the Indy was axial only. Pushing up on the drive shaft was causing the overall length of the flange-U-joint-shaft junction to increase which was pulling the flange in and out of the TC housing. This gave the illusion that the flange was moving radially, but in fact it was moving axially. If one looks at the design of the transfer case, some in/out play would be expected because the shafts that drive the output flanges are splined at one end and held by a ball bearing/circlip on the other, thus allowing some end movement. We could find no measurable radial movement of these flanges.

BTW, I tested the TC further as the source of the vibration by using wooden wedges to firmly anchor the TC to the chassis, effectively bypassing the TC bushings. The theory here is that if the TC is the source, the vibration should get worse when firmly anchored. Well, it made no difference, so I really don't think that the TC is where the vibration is coming from.

While we had the truck up on the lift, we took off the wheels, locked the differentials (to avoid spider gear damage) and ran it up to ~60 MPH and I could feel the vibration. But unfortunately, we could not localize the source of the vibration. Testing in this mode was very difficult because the electronic throttle system for the M113 engine can easily become unstable when the engine is run at speed with no load (the feedback transfer equation assumes a phase shift based on a loaded engine; when unloaded, the phase shift can approach or exceed 180 degrees which results in system instability). Running this way also makes the truck prone to throwing "transmission output speed sensor" codes as well.

So we let the drive train just idle along while we observed each component very carefully. What we noted was the both the front and rear drive shafts appeared to "wobble" - each in different places on the shaft and each with different amounts. The "wobble" was easily observable with the naked eye and was probably on the order of 1 - 2 mm. I took some crappy iPhone video, but have no way to "post" it. So the question if, how much "run out" or "wobble" is allowable on these drive shafts? What are the odds that both drive shafts are "bent"

What ever the source of the problem is, it is getting worse. The truck is now only really drivable under ~50 MPH. The affected speed range has increased to ~ 52 - 70 MPH. In a way, I sort of think of this as good news because I keep hoping that something will just break outright so I can fix it!

Does anyone have any further thoughts?

Thanks!

- FD
 

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I suspect I may have a similar problem. My Indy is a porsche guy and working on trucks seems to be slightly beyond his grasp, but I have a fair amount of wobble in the +50mph range. He thought it was due to my 35"s and tried to tell me all lifted trucks experience this. However this is not my first rodeo with a truck on large mud tires(though I suspect it may be his). He suggested researching steering stabilizers or just living with it, which is easy because I rarely get above 50mph anyways. I'm going to make a run to the stealership to code out the damn outdated SOS system anyways so I may have them take a look at it if they aren't too busy.


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I have read on the forum on a DIY that if you pump too much grease on the splines of the driveshafts you can cause damage to the TC bearings because the grease dosn't let the driveshaft compress under suspension travel. I guess some damage could be expected to the diff pinion bearings as well. Maybe the driveshafts were overgreased by the previous owner. I want to know how you are going to take care of this and how much is going to cost so please update us.
Can you update us, were you able to pin point the problem?
 

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You said it does it in low range at half the speed of high. The issue is between the transfer case and motor.
But seeing as the motor only has issues at x speed is not the motor.
Driveline between trans and transmission also is not an issue as it would repeat with every rpm range it sees.
This leaves transmission, transfer case.
I suspect what ever gear your in in h and l range is the same when it happens.
My vote is transmission but I'm no automatic specialist.
 
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