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post #1 of 33 (permalink) Old 12-06-2018, 01:05 PM Thread Starter
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Strong vibration during acceleration

Hello!

I have just about all the gremlins worked out in the new (old) '73 450SL. I am sure this questions has been asked many times before but I can't seem to find a thread that answers my exact issue. The issue I am tackling now is a bad vibration during hard acceleration that seems to come directly from the middle of the car. It does not seem to be worse on the driver side vs passenger side, nor does it seem worse in the front vs rear of the car.

When I pull off from a stop light its smooth, but when I get into 2nd gear and start putting my foot down on the pedal, the car starts to vibrate badly; to the point that it makes the car rattle. The harder I push the pedal the harder the vibration. As soon as I let off the gas is disappears. Hit the gas pedal again and the vibration comes back. Its getting worse each time I drive it. Once I am up to 65-70 and just cruising, the car is smooth as silk. Hit the gas to pass someone even at 65 and it vibrates again.

This may be a separate issue, but when I come to a stop, I get a single clunk noise that seems to come from the rear of the car. It doesn't happen every time. And sometimes it happens when I take off from a complete stop. Not sure if this could be related. I know it can be several parts in the drivetrain causing the vibration, but what would be the most obvious parts to check first without pulling it apart? If you have had similar symptoms, what part failed? Any help is appreciated!
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post #2 of 33 (permalink) Old 12-06-2018, 01:51 PM
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Driveline vibrations are most likely caused by either bad flex discs and/or bad center carrier support.

From what you've said, you should stop driving the car and inspect the drive shaft flex discs and center carrier support. Don't keep driving until you've gotten this fixed as failure of those two items leads to destructive results.

Doing so will require you to drop the exhaust. Take the time to also do service on the transmission mount and parking brake systems since you will have access to them. A failed center carrier support will lead to the drive shaft splitting on itself. Not nearly as bad as a failed flex disc, but still a needless expense.

As for the clunking rear end, I would inspect the following: differential mount, CV axles, and rear sway links. Not nearly as urgent as the driveline vibration.
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post #3 of 33 (permalink) Old 12-06-2018, 02:36 PM Thread Starter
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Originally Posted by okyoureabeast View Post
Driveline vibrations are most likely caused by either bad flex discs and/or bad center carrier support.

From what you've said, you should stop driving the car and inspect the drive shaft flex discs and center carrier support. Don't keep driving until you've gotten this fixed as failure of those two items leads to destructive results.

Doing so will require you to drop the exhaust. Take the time to also do service on the transmission mount and parking brake systems since you will have access to them. A failed center carrier support will lead to the drive shaft splitting on itself. Not nearly as bad as a failed flex disc, but still a needless expense.

As for the clunking rear end, I would inspect the following: differential mount, CV axles, and rear sway links. Not nearly as urgent as the driveline vibration.
Thanks for the tips! I see how to inspect the flex discs, how hard is it to check the center bearing and what should I look for?

Thanks,
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post #4 of 33 (permalink) Old 12-06-2018, 10:54 PM
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Quote:
Originally Posted by okyoureabeast View Post
Driveline vibrations are most likely caused by either bad flex discs and/or bad center carrier support.

From what you've said, you should stop driving the car and inspect the drive shaft flex discs and center carrier support. Don't keep driving until you've gotten this fixed as failure of those two items leads to destructive results.

Doing so will require you to drop the exhaust. Take the time to also do service on the transmission mount and parking brake systems since you will have access to them. A failed center carrier support will lead to the drive shaft splitting on itself. Not nearly as bad as a failed flex disc, but still a needless expense.

As for the clunking rear end, I would inspect the following: differential mount, CV axles, and rear sway links. Not nearly as urgent as the driveline vibration.
Thanks for the tips! I see how to inspect the flex discs, how hard is it to check the center bearing and what should I look for?

Thanks,
If the exhaust is on, you'll need one of those cameras with the long fiber optic lense to snake down the drive shaft. Its the circular thing mid way down. It's held on by two bolts.

I would drop the exhaust and just replace them if you're looking for a project to do over the weekend. I did it for piece of mind, especially with an in km vehicle history.

Good luck!
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post #5 of 33 (permalink) Old 12-07-2018, 06:20 PM
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I second this, most likely you have worn flex disks. The only way to go with these is OEM parts.

Don't stomp on accelerator until you fix this or bad things may happen.
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post #6 of 33 (permalink) Old 12-09-2018, 06:15 AM
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Sounds like you have bad engine mounts. Open the hood put it in drive hold the brake firmly and give it a little gas while watching the left side of the engine. It should rock a little but it shouldn't rise. Repeat process in reverse to check right side engine mount.

Check flex disks because bad engine or trans mounts can damage these. Look for small cracks in rubber going from on hole to the next. Don't just change flex disk and assume that was the problem. Make sure you check your engine mounts and trans mount.

Center bearing will require removal of the drive shaft to inspect unless its real obvious. You can get a look at it with a mirror from just behind the trans. If it looks in tact, also look at it for sagging. The rubber settles downward over the years and it becomes an off center bearing.

Also check differential mounts, front and rear. The pinion will try to pitch up on acceleration and cause excessive miss alignment leading to vibration under load.

All these elastomeric parts , engine mounts, trans mount, flex disks, center bearing and diff mounts should only be sourced from Mercedes.

Good luck, and keep us posted.
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post #7 of 33 (permalink) Old 12-10-2018, 06:24 AM
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Carefully Mark the relationship of the front and rear driveshafts to each other. They are not marked from the factory. A vibration can result from a mismatch during reassembly

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post #8 of 33 (permalink) Old 12-10-2018, 07:50 AM
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Carefully Mark the relationship of the front and rear driveshafts to each other. They are not marked from the factory. A vibration can result from a mismatch during reassembly
X2!!!!

There are marks built onto the driveshaft, but do't let them fool you! They didn't start using them until the late 70s or early 80s. There's a warning in the FSM about this.
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post #9 of 33 (permalink) Old 12-10-2018, 08:19 PM Thread Starter
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Finally found time to get the car off the ground and get underneath it. Thank you for the replies, you folks helped me to the next step. I think I know the answer but check the photos and video below and let me know what you think.

First, I tested the engine mounts per roncallo. I had my wife put the car in drive / reverse with the brake down and gave it gas both directions. The engine had absolutely zero movement. You could not see it move no matter how much gas she gave it. Solid engine mounts. The motor was removed and rebuilt by Herndon Mercedes in Fresno in 2009..so I believe the engine mounts are fresh.

However, the flex disks are not so great, and I question the center bearing. The trans mount look intact but may as well replace it too. Check out the photos and really watch the video and let me know what you think. I really appreciate everyone's help on here, I had no idea where to start. I tried to put the photos in order. The first photos are of the front flex disk, then the center bearing and the last photo is of the rear flex disk. Oh, and I had 4 jack stands, wood blocks, and a 4 ton jack all supporting the car.....every few minutes I would imagine how it would be if the car crushed me..ha! No matter how much support, its still spooky laying underneath this heavy beast.

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post #10 of 33 (permalink) Old 12-10-2018, 09:47 PM
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Yeah, I totally understand the fear. Unfortunately, theae types of issues require you to lay on your back to do unless you're lucky like Roncallo with a home lift.

Don't be afraid, get to it!
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