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  #1  
Old 01-01-2004, 09:46 PM
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New Motor mounts, What a difference!!!

A few weeks ago I broke down and bought two new motor mounts and a tranny mount for my '82 240D. I've had the car since March, and the very rough idle has been a continual gripe. Last weel I got the right side mount and the tranny mount changed, and it made quite a difference. This morning I finished the left side mount and the difference was amazing! The hood no longer visibly shakes at stoplights. It looks just like any other car when I stop! viva la difference! outstanding!

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Old 01-02-2004, 12:33 AM
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Actually when I first swapped in my new motor mounts I'd say the shaking was 10X worse since it wasn't free to move anymore. I ended up getting a new upgraded rack damper pin and adjusting it out, there is still a little side to side motion but nothing real horrible.
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Old 01-02-2004, 05:56 AM
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I forgot to mention that in a side-by-side comparison of new-to-old mounts, there is about a 1 inch difference in height. The old mounts have compressed to where the center is almost level with the perimeter. I will post pic if I get the chance.
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Old 01-02-2004, 09:57 PM
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MS Fowler,

When I changed the mounts on our 1982 240D (which I do not believe has a rack dampner pin) the difference was also dramatic. The driver's side mount was sheared in half and allowed the engine to flop around way too much during start ups and any other time the engine felt like it. This added motion wasted the starter torque by allowing the engine to be lifted instead of turned over, which contributed to the demise of the starter and the exhaust manifold to head gasket/fasteners.

The major role of the mounts is to absorb vibration energy from the engine. Their design is tailored to absorb that energy in a specific frequency spectrum, along with the design of the support structure. This process, given that it is a passive system, has specific physical limitations. One of those limitations is the mount system resonant frequency. When new that frequency is intended to be as low as possible, and definitely below the source frequencies with any power of note.

As the rubber elements age and harden, their natural frequency is raised. As this process continues the system resonant response frequency creeps upward where it begins to be close enough to the source frequencies to cause resonant excitations of the mounting system. We, the machine operators pick this up as shaking. In a 240D you can put this off for a while by using the idle speed controller to tweak the engine speed so the mounting system resonances are not excited. In a 300D TurboDiesel this is not an option.

So, it sounds like you got to the mounts before there was a lot of collateral damage. Once I got a new starter and new mounts in there, the machine responded not only by becoming a smoother operator, it also responded by starting in nearly any weather without being plugged in, and it now has 312,800 miles. It even quieted down when I replaced the exhaust manifold to head gasket and the EGR tube (which had also shattered). Good luck with that fine automobile, Jim
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Own:
1986 Euro 190E 2.3-16 (291,000 miles),
1998 E300D TurboDiesel, 231,000 miles -purchased with 45,000,
1988 300E 5-speed 252,000 miles,
1983 240D 4-speed, purchased w/136,000, now with 222,000 miles.
2009 ML320CDI Bluetec, 89,000 miles

Owned:
1971 220D (250,000 miles plus, sold to father-in-law),
1975 240D (245,000 miles - died of body rot),
1991 350SD (176,560 miles, weakest Benz I have owned),
1999 C230 Sport (45,400 miles),
1982 240D (321,000 miles, put to sleep)
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Old 01-02-2004, 10:10 PM
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Actually since you brought that up Jim my lack of proper motor mounts cost me a new header pipe. Perhaps it caused the failure or maybe it just accelerated the process but a couple months after getting the new motor mounts it failed in the flex section of the pipe. The mounts pretty much let go before which allowed the motor to sway freely from side to side at idle.
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Mercedes W123 DIY pages are now located here.
1983 / 1984 300D Sold
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2005 Avalanche 4x4 ~66k
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  #6  
Old 01-02-2004, 11:21 PM
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The difference between old motor mounts and new is like night and day. Once I replaced them on my car, I couldn't even feel the engine move when starting the car.

I too have a little side to side movement at stop lights etc....from reading several posts here, I believe this is due to the two little engine shocks being bad. I am betting that the two on my engine are the original ones and it is about time to replace them. I believe my dad said he did his awhile back and it got rid of the previously mentioned movement.

Mike
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Old 01-03-2004, 01:41 AM
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new mounts for everybody!

I think I'm in serious need of all new mounts. When I first start the car cold, the vibration in the passenger seat makes my teeth chatter! At stop lights, I put the car in neutral to still the vibration. It runs fine and once warmed up the vibration settles down. I wonder if I have any mount left at all under the transmission. I would imagine that after 25 years I don't!
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  #8  
Old 01-03-2004, 07:26 AM
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Jim Smith
I agree exactly with your analysis of the design and deterioration of rubber mounts. I fact, I used that line of reasoning precisely when a friend questioned me as to why they would make such a big difference--and mine were not broken....yet.
As for collateral damage--I believe I have sustained none so maybe my timing was good (for a change).
(Maybe I should get a commission from Phil at fastlane for the run of motor mounts he is about to sustain....)

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