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Old 04-17-2019, 09:59 PM   #1
oifish
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Default Driveline vibration from 35-60 mph

Car is the 740 in my sig. I recently replaced the u-joints in my driveshaft with Moog components. After reinstalling it, there was a bad vibration above ~20-30 mph. Being fed up I took the driveshaft to a specialty shop to have them make sure I did the u-joints correctly and balance it.

They replaced the central bearing and supposedly balanced the driveshaft. I installed it today and thought everything was OK. Nope, starting at 35 mph a vibration starts and gets really rough in the low 50's. Once above 60 it somewhat smooths out. The vibration persists with the car in neutral coasting at those same speeds.

I never separated the 2 halves while installing it, and I mads sure (at least I think so) that central bearing was aligned correctly on its mounting plate.

The only thing I didn't double check was that it attached to the diff in the same orientation it was in before originally removing it. My next step is to flip that attachment 180* and see if any thing changes. Besides that I'm at a loss on where to look next.
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Old 04-18-2019, 12:04 AM   #2
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Try using a Noise Vibration and Harshness (NVH) kit on a Pico Oscilloscope.
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Old 04-18-2019, 01:37 AM   #3
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Did the center bearing support rubber get replaced too?
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Old 04-18-2019, 05:16 AM   #4
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Did the center bearing support rubber get replaced too?
This would be good to check!
Had the same thing with my buddy's car:
http://forums.turbobricks.com/showthread.php?t=346078
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Old 04-18-2019, 08:36 AM   #5
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Did the center bearing support rubber get replaced too?
It sure looks like it. The old one was oily and this rubber looked fresh.
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Old 04-18-2019, 09:01 AM   #6
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Did you do anything else at the same time, because this sounds like a tire vibration.
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Old 04-18-2019, 09:22 AM   #7
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Did you make sure they put the 2 pieces of driveshaft back together in the correct orientation? Just because someone else did it, doesn't mean they did it right.
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Old 04-18-2019, 09:44 AM   #8
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Did you do anything else at the same time, because this sounds like a tire vibration.
I did put on my summer tires, but they've been balanced and I've never had problems with them before. I'll take the rear wheels off with the car jacked up and run it up to 45.

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Did you make sure they put the 2 pieces of driveshaft back together in the correct orientation? Just because someone else did it, doesn't mean they did it right.
The markings line up on the driveshaft. I guess I could flip it 180 and see if anything changes.
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Old 04-20-2019, 11:23 PM   #9
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Without the wheels on the vibration is the same. I double checked the alignment of the driveshaft and all the markings are lined up. The rubber for the central bearing is new. This is weird...
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Old 04-21-2019, 12:11 AM   #10
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Nope, starting at 35 mph a vibration starts and gets really rough in the low 50's. Once above 60 it somewhat smooths out.
That's because 740s are only meant to be driven by grandpas, under 35 mph. Its like the rumble strips to tell you where the ditch starts.
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Old 04-21-2019, 10:50 AM   #11
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Without the wheels on the vibration is the same. I double checked the alignment of the driveshaft and all the markings are lined up. The rubber for the central bearing is new. This is weird...
I’ll admit, this part is gonna be unsafe, but did you watch the driveshaft as it was turning?
If it’s bouncing around, it needs rebalancing.
Another idea: unbolt the driveshaft from the transmission flange, and give the flange a wiggle. If the flange moves, you need to replace the tail shaft housing bushing.
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Old 04-21-2019, 11:12 AM   #12
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How are the rear end bushings? Worn suspension bushings, and also lowering the car in the rear can cause pinion angle to change. If it isnt right you will get vibration. Adjustable torque arms are used to correct the pinion angle on a lowered car.

Bad driveshaft vibration can take out both the pinion and tailshaft bushings/bearings. Take the shaft off, and check for play in these. While you have it off, turn the yoke on the tranny and the rear end lightly and feel for the backlash. The yoke should not turn far before you feel the gears engage in either direction.

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I’ll admit, this part is gonna be unsafe, but did you watch the driveshaft as it was turning?
If it’s bouncing around, it needs rebalancing.
The safe way to do this is to put a magnetic base dial indicator under there measuring the runout of the shaft and flanges. Point a gopro at the dial indicator face. Mag base indicators can be bought here for under 35 bux:
https://www.shars.com/products/measu...ndicator-001-3
https://www.shars.com/products/measu...ine-adjustment
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Old 04-21-2019, 06:20 PM   #13
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THere is a factory fix for this; I've done it. You Raise the center bearing closer to the body/tunnel, with spacers on the mount plate. The plate stays the same, the center bearing gets closer to the tunnel. This counterintuitively increases the angle of the two pieces. Maximum is 12 mm, I did 11 mm and it worked.
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Old 04-22-2019, 03:16 PM   #14
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The bushings aren't in the greatest shape, but they are not completely blown out. I'm starting to think one half of u-joint was installed 180* in relation to the other. If that happened the 2 halves of the driveshaft would be 180 out of balance even in the marks line up, right? So I'm going to rotate the halves 180 then report back.

It just doesn't add up that the pinon or tailshaft bearing/bushings would go out when the car has been on jackstands. I will test the play in both with the shaft out.
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Old 04-22-2019, 05:01 PM   #15
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Quote:
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Without the wheels on the vibration is the same. I double checked the alignment of the driveshaft and all the markings are lined up. The rubber for the central bearing is new. This is weird...
Yes, new central bearing bushing... There's your problem. I just used a sharp scalpel and cut away some material from the bushing. The damn driveshaft was held too tightly in that rubber. If you look in that bushing from the back you can see how it sits against itself if its moved just a bit...

Car was droning/vibrating horribly, when i tried before on jackstands. Tried lifting the support bearing aswell, it just shifted the ranges a bit. Cut some rubber away, became silent and nice...
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Old 04-24-2019, 02:29 PM   #16
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I have heard that new support bushings can be too stiff and transfer vibrations, they typically wear in and calmn things down.
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Old 04-26-2019, 11:06 AM   #17
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Good to know about the new central bearing wearing in. I rotated the drive shaft 180*, but haven't tested it yet. If it's worse, I'll flip it back and just run it for a while to see if things need to calm down.
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Old 04-26-2019, 11:44 AM   #18
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I had a rumble/deep bass tone in my wagon from 40mph to 55mph, I tried shimming up the center bearing, different tires, different driveshaft, different transmission and nothing worked. I ended up selling it so the mystery was never solved. I am guessing worn rear bushings may have been my problem.
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Old 04-26-2019, 12:39 PM   #19
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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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Old 04-26-2019, 05:06 PM   #20
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Yes, new central bearing bushing... There's your problem. I just used a sharp scalpel and cut away some material from the bushing. The damn driveshaft was held too tightly in that rubber. If you look in that bushing from the back you can see how it sits against itself if its moved just a bit...
Hey, sorry to bother and interrupt the thread but could you explain a bit more about what/where you cut away at the bushing?
Are you talking about where the center bearing metal "dust shield" meets the rubber carrier bushing? Something else?

I ask as I noticed that the dust shield for the bearing is pressed onto the driveshaft and also essentially gets pressed into the rubber carrier. But maybe your taking about something else entirely.

Sorry again and thank you
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Old 04-27-2019, 11:18 AM   #21
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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?

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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.
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.
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Old 04-28-2019, 07:54 AM   #22
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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.
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.......
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Old 04-30-2019, 12:42 AM   #23
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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.
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Old 04-30-2019, 02:58 PM   #24
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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).
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Old 05-01-2019, 07:02 PM   #25
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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.
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