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Strong vibration during acceleration

14K views 34 replies 13 participants last post by  roncallo 
#1 ·
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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#2 ·
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.
 
#6 ·
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.
 
#9 ·
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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#22 ·
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.

https://www.youtube.com/watch?v=7N6AFSNzKvs&feature=youtu.be
Flex disks are definitely bad. I cant tell if its the angle or not but the center bearing does look to be sagging. Transmission mount I cant tell but the rubber may be compromised by the oil.
 
#12 ·
The problem was not noticeable when I purchased the car. I drove it from Dallas to Houston and did not notice it. It has gotten much worse during the last two drives. We only take it out on weekends. It was much much worse on the way home from our weekend trip than it was when we left for the trip.

The work done by Herndon was done in 2008-9. I do have the paperwork from the PO who bought the car from Barrett-Jackson. The engine was removed and rebuilt, suspension (front / rear) re-done. New factory color paint. They did not do the interior because its in good shape, and there is no mention of transmission work / removal and there is no reference to servicing flex discs, center shaft bearing, or transmission mount. I can assure you that the engine mounts were replaced during the rebuild in 2008-2009. I visually inspected them and had my wife stomp the brake while giving it gas in forward and reverse. The engine does not move at all. Very still. So the engine mounts are not the issue..before the rebuild they may have been bad and caused damage to the flex discs at that point, but now, the engine mounts are for sure not the issue.
 
#13 ·
Anyone have an opinion on the center bearing and transmission mount? Does the center bearing look normal? Is the play shown in the video normal? Does the transmission mount look ok? I would love the issue to only be the flex discs since I won't need to remove the shaft, but if the bearing needs to be replaced then I must do it. Let me know what you folks think.
 
#16 ·
They look ok, but as much as I've learned with these vehicles and the w123 I owned that appearances can be deceiving.

I had a rear end clunk that was driving me nuts. I ended up getting some new rear sway bar links and replaced them even though they looked good without any obvious play when grabbing at them. Sure enough, it took care of the problem.

Replacing these parts is very easy and straight forward. The only difficulty is getting the exhaust out of the way to work on them, something you don't have to do with the w123.

I'll be honest, if you're going to do this job I would go the full monty and get all new rubber down there. Having to drop the exhaust is a b!tch and something you don't want to do again. It just makes sense to do it all while you're in there.
 
#14 ·
I am no expert on the R107, but this drive arrangement is very similar to the W123. I don't see anything in your pictures and videos that looks bad enough to cause your problem. The center bearing runs through a flexible rubber donut, which looks in tact. I had seen flex disks that had reinforcement fiber coming loose that had no vibration.

Have you looked at the CV joints and axle shafts? That is another component that can cause vibration under load. Most of the time this is caused by lack of lubrication. The rubber bellows can deteriorate and loose the lubricant. In my W123 they used a gear oil type lubricant and when the rubber bellows goes, so does the oil.

Good luck - Hope you find the problem.
 
#15 ·
I had flex disks changed when I had front seal leak repaired on my 72, but they didn't provide break down of labor.

However, on my 85 300D which is similar, I had front flex disk changed - 1 hr charged. At a different shop, the hanger bearing and support - 2 hrs.

Don't now what you would pay down there, but having experienced shop do it might be worthwhile. I keep telling myself that, but still end up mostly DIY.

That mid shaft bearing got rid of vibration on the 300D.

The front flex disk was done after engine had been R&Red. Car was vibrating. Disk didn't show any cracking, but had likely been put back on in a different position. Somehow that threw things out of balance.

Good luck with it. It's a lousy place to work!
 
#17 ·
Hmm..now I am confused as ever. Most are saying that the photos do not show enough wear to cause the vibration! I was hoping that it would be definitive proof. So the only other possibility would be the axle shafts, cv joints, and engine mounts (i believe I ruled this out but I will check them again).

I looked at the cv / axle boots while I was under the car and they were intact and pliable..so I would assume those are lubricated. Must I remove the axles to really know?

Well, I guess I will just go ahead and replace the center bearing and flex discs (they are getting worn anyway). If the vibration continues then I will go from there. Do I need to completely remove the exhaust system from the car? Is it difficult?
 
#19 · (Edited)
Do I need to completely remove the exhaust system from the car? Is it difficult?
Your 73 is probably same as my 72, but I can't get at it right now to have a look.

Not sure if you could lower exhaust a bit. Or just remove the rear part that may be in the way? When I had work done on transmission leak, the shop took the complete exhaust off in one piece. Saw them re-install it and recall them having some difficulty - the bolts at the exhaust to manifold joint are hard to get at and likely hard to undo. If I remember correctly, car was on hoist and they had long extensions and an impact driver. Exhaust shop put in new seals later(some sort of soft metal) when I had them install a boss for my wideband O2 sensor. If those front joints can be avoided it may make job easier.
 
#30 ·
Post-repair update for those researching similar driveline vibration issues;

I ended up taking the car to a really good Indy who only works on older Merc's.

The main source of the vibration ended up being the transmission mount and the driveshaft Centering sleeve / bushing. The transmission mount was not only very soft (almost gooey), it was the wrong mount. The mount was for a different year model and the PO had used spacers to make it "work". The rubber in the driveshaft centering sleeves were nearly gone as well. Those were the two main culprits. The center bearing was ok and the flex discs only had very few small hairline cracks showing up.

In the end, I had the new transmission mount installed, new flex discs, new center support and bearing, differential mount (soft as well), and host of odds and ends replaced. The rear-end was whining so I had it replaced while everything was apart. New steering coupler, rebuilt steering box, and rebuilt the power steering pump and added new power steering hoses. Now she silently glides down the road like driving on glass. Its glorious....although my bank account is still smoldering.
 
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