High speed vibration after replacing transmission

[Gin+]

I have a vibration that generally goes unnoticed unless I'm cruising past 80mph+, which is pretty rare. I don't recall feeling any vibration before having the transmission replaced. It's the same with my snow tires and brand new summer tires mounted on separate wheels so I don't believe it's tire/wheel related. The car was just aligned and drives like new and feels tight. I've inspected the center bearing and it appears all intact. No clunks or anything like that.

A friend of mine suggested that the factory balances the driveshaft to the transmission and that I should try clocking it until the vibration diminishes. Does that sound reasonable to any of you guys? Anything else I should be looking at? My fear is that somehow the driveshaft got knocked out of balance during the transmission replacement...

[Audi body]

What kinda transmission are we talking about? Auto or manual?

[CyberPMG]

Many possible things can cause a vibration to happen.

Do you feel the vibration in the steering wheel or in the seat? If you rotate the tires, does the vibration location change? How many miles are on the car? Have the wheel bearing ever been replaced? How about the axles?

When the transmission was replaced, was a new transmission mount put in, or the original mount used? Was it installed properly (loose to allow self centering before tightening up)? If aftermarket mount, what was used and how many miles on it?

Also as said above, is this manual or auto?

[Gin+]

It's an automatic that I replaced with a used unit. I've tried different wheel combinations with slightly differing degrees of the same result. Original transmission mounts and axles. Vibrations do not feel steering wheel related and front end is tight. The snub mount might be on its out but I don't know if that would cause my symptoms.

[CyberPMG]

Was the used transmission rebuilt or simply pulled from some other car "as is"? You could have picked up a pre-existing issue with that other transmission. Check the snub mount and transmission mount. Check wheel bearings too.

[tHatOne guY]

I have a vibration that generally goes unnoticed unless I'm cruising past 80mph+, which is pretty rare. I don't recall feeling any vibration before having the transmission replaced. It's the same with my snow tires and brand new summer tires mounted on separate wheels so I don't believe it's tire/wheel related. The car was just aligned and drives like new and feels tight. I've inspected the center bearing and it appears all intact. No clunks or anything like that.

A friend of mine suggested that the factory balances the driveshaft to the transmission and that I should try clocking it until the vibration diminishes. Does that sound reasonable to any of you guys? Anything else I should be looking at? My fear is that somehow the driveshaft got knocked out of balance during the transmission replacement...

My B6 developed some vibes after my clutch install, I have tried re-clocking the driveshaft to xmssn output shaft 4 times by turning the driveshaft til the next set of bolt holes lined up but each try had no different or better result any of those attempts. My engine mounts were shot so I didn't really notice the drive train vibration until I put everything back together with fresh mounts all around and did some investigating.

The Bentley does have a procedure for clocking the final drive to the driveshaft but not the xmssn output to the driveshaft. Out of balance is not likely unless you changed some of the driveshaft components or took it apart and reassembled it differently, it could possibly be out of phase with the final drive, that is if you unbolted it from the final drive.

Did you allow the driveshaft to hang downward w/o support at any point during your trans install? That could possibly cause the U-joint to bind and cause your hi-way vibration.

[Gin+]

Did you allow the driveshaft to hang downward w/o support at any point during your trans install? That could possibly cause the U-joint to bind and cause your hi-way vibration.

I'm certain this did happen although I don't believe any weight or stress other than weight of itself was applied. My guess is I tweaked the driveshaft just right, combined it with a used transmission, all on top of a 140k car, and now I'm living with the results.

[diagnosticator]

Replace the front axle shafts. That is the most likely cause of the imbalance at higher road speeds. Specifically, the inner tripod CV joints are worn out. I recommend Raxles replacement axle shafts.

The propeller shaft driving the rear differential is not critically balanced according to the installed angular position of the propeller shaft relative to the internal TorSen center differential angular position.

[tHatOne guY]

Does your rear or front axle flanges have a lot of play? The rear flanges have about 1-2mm of play at the flanges on my B6, in a radial direction.

[Gin+]

Thanks for the replies gents. I would think if it were the front axle's I would feel it more in the steering wheel and under my feet. This feels mostly under the seat. I need to get the thing up on a lift and start looking a little more closely.

[MacFady]

What happens to the vibration when you put the car in Neutral vs. Drive vs Reverse.

[diagnosticator]

With the mileage on your A4, the axle shafts especially the inner tripod CV joints, are the most likely source of vibration considering the frequency/road speed it is happening at. Determine the RPM/Hz of the wheels/axles at 80mph, and compare. With the car on a hoist, grip the axle shafts near the inner CV joints, and try to move the axle shafts sideways in a radial direction. If there is any radial play in the inner CV joints, the joints are beyond the useful service life and need to be replaced. Using a roll-on hoist is best for this.

[diagnosticator]

Wheel rev/1 min X (1 min/60 seconds) = wheel rev/60 seconds = wheel rev/(1 seconds) = Wheel rotation rate, Hz = wheel revolutions 1/minute = wheel revolutions/60 seconds = wheel/axle shaft rev/second = wheel/axle shaft rev 60 sec = wheel/axle shaft rotational speed Rev/1 minute/ 60 seconds = wheel-axle shaft rations /1 second = wheel rotation speed, Hz. = ~840 rev 1/min =840 rev / 60 seconds = rev 1/60 miniute, = axle shaft rotation rate Hz = 840 rev / 1/min / 1min/60 seconds = wheel rotation, Hz = (840 1/min)/60 sec = wheel rotation speed 1/min = wheel speed, Hz @ 60 mph = wheel rotaton speed, 840 wheel rev/60 seconds 1 mile = 840 1/min = 840 rev/1 min/1/60 min/1hr = 840 wheel rev/1 min = 840 rev /mile = wheel /axle shaft speed 840 wheel/axle rev/ min = 840 revolutions/60 seconds = Wheel /axle shaft rev/60 secons/1 min min = Wheel/axle shaft frequency, @ 60 mile/1 hour = wheel -axle shaft speed, Rev/1 min = Rev/ 60sec /1/seconds Hz. @ 80 mph. = ~14 Hz @ 80 mph.

[tHatOne guY]

Is there a reputable source for the inner joints only? I saw the OEM inners on ECS, big bucks though.

Shaftec?