740 Driveline vibration from 35-60 mph

I flipped the driveshaft 180 and it might have improved things... The vibration doesn't start until 40mph instead of 35, and may be less violent. Just run it for a month and see if anything changes?

DET17 said:

OP, did you properly clock the drive shaft plate at the rear of your trans with the plate (and U joint) at the rear end flange? The green books show how this must be done. Basically they must be opposite......if the rear pin on the plate is horizontal, then the front must be vertical.

This clocking is separate to the center joint where you disassembled the halves..... I’ve seen some factory match marked, some not, and late versions are machined so they cannot be improperly assembled.

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I guess I'm not visualizing what you are describing. I've got the volvo greenbooks on CD, I'll try to find what you are describing.

oifish said:

I guess I'm not visualizing what you are describing. I've got the volvo greenbooks on CD, I'll try to find what you are describing.

Click to expand...

Each end of the assembled driveshaft has a U-joint cast/connected to a flat plate. If you assemble the 2 piece system on a work bench.... .just as you would bolt into the vehicle, the front plate "pin" must be a 3 and 9 o'clock, and the rear "pin" at 12 and 6 o'clock. Greenbook explains, as does the 700/900 Maint. pages fabulous data base.......

The driveshaft has 3 U-joints in it, it could be one of them has gone dry/worn out. Many many years ago I replaced mine. Actually come to think of it I might need to grease mine now.

This all started after replacing the U-joints. My 740 only has 2, the connection at the trans is with a guibo (which is only 2 years old and in good shape).

I've been fighting vibrations for a while, replacing U joints helped, I've tried lowering the center support, raising it, switching from the stock rubber to a generic DANA center support bearing (good idea, would recommend) If your car is lowered a lot then you might need to get adjustable sus parts.

I didn't see this up there, but when you have the rumble, is it when you're under load or when you're just cruising. This can help determine the origin. Also the type of rumble it is (first or second order) can help. I got my driveshaft balanced after the t5 swap and then my dumbass took the two halves apart and forgot the original alignment. Aligning the yolks is a good place to start instead of guessing.

I tried both raising and lowering the center bearing and neither helped. I got fed up and took it to a euro shop. They said the shaft is fine, and likely the problem is in the axle. They don't really want to mess with the axle. So I guess that changes the focus... Anything I should look at in the diff/rear axle that could cause this?

-Measure runout. Ok?

-Remove driveahaft, rotate 180 degrees and reinstall. Is it better?

-You can also see if you have any luck adding hoseclamps. The tail of the clamp is clipped off.