vIbRaTiOn at 35 and 70mph with New Flex Discs, Center Bearing, and Carrier. Ideas?

[Build]

I just finished putting my new flex discs, center bearing and carrier in the 380sl and I still have a vibration; but now at 35 and 70mph.

I had a vibration at 32 and 64mph before and noticed the carrier rubber was completely separated and torn from the bearing.

Now after the hard work of installing them, it still vibrates the same, but at a slightly higher speed. It doesn't matter which gear/engine rpm, the vibration is only at those speeds.

I know the tires and wheels are balanced because I've tried two different sets of wheels and tires and had them balanced twice; no difference in vibration.

I read about adjusting the carrier for better alignment, but I see no real adjustment possible. Any ideas as to what could be causing this?

[nobby]

Originally Posted by Build

I just finished putting my new flex discs, center bearing and carrier in the 380sl and I still have a vibration; but now at 35 and 70mph.

I had a vibration at 32 and 64mph before and noticed the carrier rubber was completely separated and torn from the bearing.

Now after the hard work of installing them, it still vibrates the same, but at a slightly higher speed. It doesn't matter which gear/engine rpm, the vibration is only at those speeds.

I know the tires and wheels are balanced because I've tried two different sets of wheels and tires and had them balanced twice; no difference in vibration.

I read about adjusting the carrier for better alignment, but I see no real adjustment possible. Any ideas as to what could be causing this?

A couple of things come to mind.
Maybe you should have the prop shaft balanced............someone in the past might have had it removed and not put back together properly. When the propshaft is split it needs to go back together exactly the way it came out. It is balanced as an assembly. I scribed everything before dis-assembly.
Also.engine mounts and trani mount should be inspected / replaced.
You could see the trani mount when replacing the flex disc in the front. A good way to check engine mounts is by having someone in the driver's seat with a foot on the brake and car in drive. Apply a little gas pedal and see if the left side of the engine comes up on rotation. Putting it in reverse will check the right side.

[Build]

Thanks for the ideas Nobby. The transmission mount physically looked ok and seemed somewhat solid, but I'm not sure how much flex it should have?

I marked the driveshaft before I removed the halves and I doubt it had ever been apart since the flex discs, center carrier and bearing were original to the car. The driveshaft could still be out of balance though I guess?

I'll check the engine mounts; how much movement is acceptable?

[nobby]

Originally Posted by Build

I'll check the engine mounts; how much movement is acceptable?

I don't know what the specs are, but you'll know when you see it. It'll come up a couple of inches or more.
Usually the cause of the radiator neck cracking as well.

[Build]

Thanks Nobby,

It seems the engine mounts are good; they dont move anywhere close to 2 inches. I am going to replace the transmission mount as it seems it might have the most effect on the driveshaft moving around.

I did a few tests and if I have the car under a heavy load up a steep hill, it doesn't vibrate as much at those speeds than if I'm coasting or de-accelerating; the load holds the mounts from moving. Seems if it were the driveshaft out of balance it would vibrate the same regardless of load.

Good call on the mounts Nobby and thanks!

[Roncallo]

See the drive shaft alignment marks in post #10. These alignment marks are on all the later driveshafts all 560 series have them. Not sure about 380 series. If it has these marks they better be lined up.

If you can get the car on the lift with the wheels turning you might gain some insight.

560sl flex plates and diff mount. NEED HELP

[Build]

I've replaced the transmission mount and engine mounts. The vibration is much better, but I can still feel it around 35 and 70mph. It's not as exact speed specific now, more general. Both flex discs, center bearing, center carrier have been replaced. The u-joint feels tight.

Ideas? Thanks

[Graham]

Originally Posted by Build

I've replaced the transmission mount and engine mounts. The vibration is much better, but I can still feel it around 35 and 70mph. It's not as exact speed specific now, more general. Both flex discs, center bearing, center carrier have been replaced. The u-joint feels tight.

Ideas? Thanks

Seems like you have covered most of bases.

If the prop shaft marks line up, maybe it could be wheel bearings? And then, there is still the diff mount - maybe at least have a look at it.

Have you tried coasting say on a long downhill and see if the vibration changes when you move from D to N?

I had a bad vibration on my E320. Even with rebalanced wheels, it vibrated. But it was the tires. The edges were scalloped. I got rid of 90% of the vibration by increasing the tire pressure so car ran more on middle of tire instead of edges.

Wish I had your energy - that's a lot of work you have done!

[Build]

Hi Graham,

The wheel bearings are smooth and quiet. The vibration does change somewhat when shifting into neutral at speed, but it's still there, just different slightly, and difficult to explain. The tires have a few thousand on them and have been rotated and mounted on two different sets of wheels.

The differential mounts looks fine, but I'll jack it up and see if I can stress them for movement. Perhaps the driveshaft has lost a weight? The car vibrated when I got it so I guess it's possible? I really hate to pull it again if it's something else.

I guess I do have some energy left in me, don't know how long it will last though. The heat and sunshine does help.

[Build]

I've noticed that the vibration is much less early in the morning when it's (relatively) cool. If I take the car out in the 100+F heat of the day it vibrates more and over a slightly wider speed range.

Maybe one of the tires is bad afterall even though they're newish and only have a few thousand miles on them. How to tell? They've been balanced twice at two different places and check out good. I've watched and measured them spinning and they check very true in all ways physical.

What about a CV joint? The right has a little more play in it than the left, but actually seems much tighter than other cars I have.

[compress ignite]

"Roll the Chassis back and forth 15 to 20 feet on it's wheels ,by hand before
tightening the Propeller Shaft Nut."

(I always assumed it was so the propshaft would "Settle In")

[GGR]

The trans output flange and diff input flange have to rotate in parallel plans. I think there is a tolerence for 1 or 2% which is not much. The relative position of the intermediary bearing is less important as angles on both sides cancel each other. The rotating axis of the flanges may not necessarily be precisely aligned but they should obviously also be parallel.

One way of checking it is to lift the car on a lift where the car sits on its wheels. Then you disassemble the prop shaft at both ends and fix two straight metal rods to the flanges, vertically (You can use flat iron rods drilled to one end to match two of the flanges holes). You then measure the distance between the rods at the flange level and then one meter down. You repeat the measurements by pushing the rods as much as you can on the left side and on the right side (45°?). This will tell you if and how your flanges are mispositioned and you can then add shims under the trans, engine or diff mounts to correct the position.

While you are there with the prop shaft disconnected you could have it checked for proper balancing as a whole unit.

[Build]

I've tried many different things and have checked every moving part on the car (I think). I jacked it up and took off both rear wheels. The car doesn't have the 35mph vibration at all, but it starts slightly vibrating at around 55 and by 65 it has a major thump thump thump. It's a very different vibration than while driving. Taking it on up to 80 and more, the thump gets stronger and really starts shaking.

Any ideas? Thanks!