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Old 11-10-2001, 12:18 PM
Posts: n/a
Question on changing 123 300D motor mounts

OK, folks. I'm probably gonna be done before I can get help, but here's the question. I'm changing motor mounts on a 1980 300D. The car has 230k miles, so need isn't the question. I'm following the manual to the letter, I removed the allen bolts on the bottom of the mount, removed the little nuts on the bottom of the two engine shocks, and I even disconnected the p/s return line that would be in the way.

The manual says I lift on the pan and the engine comes out of the mounts. The engine didn't read the manual and the whole front end is lifting with the engine. I don't want to overload the pan so I'm stopping and trying to regroup. I agitated the engine with the jack lifting the car about 1", but nothing happened. I figure either the mounts are stuck to the bottom of the bracket or the manual has something missing.

Any help is greatly apprecitated. I'll check back in a hour to see if anybody posted an answer.


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Old 11-10-2001, 12:55 PM
Join Date: Mar 2000
Location: Gainesville FL
Posts: 6,844
You didn't mention the larger bolt holding the engine arms to the mount. The mounts should have lifted from the body though. Don't forget that as you lift the engine the car will naturally rise since you are now supporting most of its load.

Place a 2x4 across the subpan to distribute the load. Place it across the front to take advantage of the stronger edges of the pan and lift away. Watch out for the fan interfering with the schroud.
Steve Brotherton
Continental Imports
Gainesville FL
Bosch Master, ASE Master, L1
33 years MB technician
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Old 11-10-2001, 01:30 PM
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Thanks, Steve. The big bolts holding the mount to the arm are the ones I mentioned coming out from the bottom. They're out. There are two smaller bolts threading down into the frame that complete the mounting arrangement. I've got the outboard ones out but the shields block the inboard ones.

I didn't think about the springs pushing back up with the load off. I'll try again and watch. So far, it looks like the pan is going to be holding the whole front end and that scares me. As I lift, I've watched the engine to shroud and there isn't any relative motion. This could be explained by the springs keeping up with the jack.

I'll give it a try. I hope I don't need a new pan when I'm done.

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Old 11-10-2001, 03:26 PM
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steve rules!

The suspension was flexing much more than I expected as I lifted with the pan. All done the mounts, much smoother, but still only has 77 hp. Oh well, it makes up in panache what it lacks in punch.

thanks again, steve.
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Old 11-13-2001, 02:20 AM
Posts: n/a

i was planning on changing out my motormounts soon and i was wondering, did you jack up the car on jackstands first then lift the engine or did you just do it with the wheels on the floor. if you did the latter how did you get the cleraence to move under there? also how did you get off the #2 , 6mm screw off without jacking up the engine first, as that one is actually under the strut itself and has caused many problems in the past.
thanks for the input.
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Old 11-13-2001, 09:05 AM
jcd jcd is offline
village idiot
Join Date: Jun 2001
Location: Northern New Jersey
Posts: 1,102
This thread may be helpful

The thread below is a review of my travails in changing motormounts on my 1977 300D. It may prove helpful.

Motor Mounts, yes again

To answer the question on jackstands,,,,,I ran my 300D up on ramps to gain access. Then jacked the motor with about 3 1.5 ft lengths of two by ten between the jack and the oil pan

I also found that I could access all of screws without lifting the engine. It took a little doing but I was able to get it done.

Send me your number via private message and I'll be glad to provide you with my 2 cents worth via phone.

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Old 11-13-2001, 11:39 AM
Join Date: Jul 2001
Location: Old Lyme, Connecticut
Posts: 3,596

Once you pick a side to work on, and you get the center 10 mm socket head capscrew out, I found it was much easier to lift the engine by jacking it up so the little drip shield made of galvanized sheet metal on the top could be rotated out of position. On my car the shield hindered access to the inboard socket head capscrew that holds the mount to the subframe structure.

I would recommend you not unscrew both sides at once as the reassembly can be more complicated if you are trying to align bolt holes for six bolts at the same time. I found by doing one side and then the other the bolt insertion was pretty straight forward. I also only loosened the fasteners on the "idle" side as I was a little concerned with how far I was lifting and tilting the engine that I might bend the center fastener.

In the end, only the center fastener on the passenger side (the second side for me) gave me any trouble. I had to loosen/remove the two smaller socket head capscrews on the sides and jack the engine into postion about three times to get the center fastener in without cross threading it. The motor mount strut with the tapped hole you are going into looks like aluminum to me, so you have to be careful to avoid cross threading. A bright, pencil beam flashlight to look into the alignment as you position the engine above the mount slightly was also a help. Don't forget the galvanized sheet metal shields when you put it back together. They have a little ">" mark to point forward to help get them in correctly. I just put them back in by positioning them so they made access to the capscrews that go in from the top as hard as possible, and noticed the arrow mark was pointing forward.

Good Luck, Jim
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

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 11-13-2001, 04:04 PM
Posts: n/a

Although others have already replied, I'll add my $.02 since you asked me. I didn't set the 300D on stands while I was changing the motor mounts. The springs are very stout on a heavy diesel motored car, and I was amazed at how much lift there was in the suspension before the engine lifted away. There is lots of room to work on a nonturbo 300D and I'm small enough (6'1" and 185 lbs) that I can usually crawl under the car and do what I want without a lift.

Access to the inboard hold down bolts is easy after you lift the motor an inch or so and slip the shields out of the way. The 123 diesels (nonturbo) are about the easiest motor mounts I've run into. I did a 760 Volvo turbo in March and the extra plumbing adds an amazing amount of pain to the job.

Good luck, HTH,

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Old 11-13-2001, 08:20 PM
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thanks guys but the main reason i put up this post is because i was wondering iif i should put the car up on jackstands and then lift the engine(with a jack) since i do not have ramps. i was afraid that this might affect the stability of the car. even though i am built like a blade of grass i still cannot fit under the front of the car even to change the oil , ie drain plug. but i think i shlould be ok since the weight of the chasis minus the the engine should be enough to keep the car on the stands. i only have one car so i have to have things perfectly planned and executed to stay out of trouble. believe me the key to anything is preparation, preparation and most importantly preparation. when i did my brakes for the first time i must have read you guy's post alleast ten times and when i finally did it i was done in about 30 mins including cleanup.
thanks for all the input, your experience is highly appreciated.
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Old 11-13-2001, 08:53 PM
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I would advise doing whatever you need to feel safe and have enough access. Jackstands under the frame to hold the car will work. No one ever complained of being too safe while working in their own garage. I often think about what I'm doing in terms of whether or not there is anybody around to help in case I do something stupid. I haven't yet, but the safety culture is ingrained into me after 24 years working in nuclear power.

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