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Old 12-27-2005, 03:00 AM
glenmore's Avatar
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Join Date: Sep 2002
Location: Los Angeles
Posts: 963
Oh boy! new engine mounts w124 1991 300CE

Here are some notes on changing the engine mounts on a W124, 1991 300CE.

The symptoms were (now that they are gone) a slight rattle on acceleration, seemingly heat shield related, clearance from the mount skirt to the frame far less than the 13mm suggested and a "sloppy" starting of the car. When starting, the car would have a shudder and you could sorta feel the engine torquing. The ride itself was still pretty smooth but now smoother still and the start is nice and solid now.

Front wheels on ramps. I like ramps. I have solid jack stands but they still give me the willies. Unhook the fan shroud and let it hang on the fan blades. Remove air filter, housing and breather hose. You might cover the intake with a clean rag. Caution here as there is a little 1/8" vaccum? line that goes into the bottom of the breather hose. I always forget to gently disconnect this first. It is brittle and if you just whip off the breather hose, the end of the vaccum line will break off in the hose. Hopefully you'll have extra slack.

Remove belly pan. Remove 8mm allen bottom mount bolts. I decided to do the more difficult driver's side first, figuring a new mount here would lever the engine onto the easier passenger side rather than vice versa. Top bolt is easy on passengers side. I used a 17mm flex socket. (This was from my bonus set of new tools made affordable by doing the repair myself, a set of craftsman metric flex sockets!) The driver's side was a real pain until I figured out the right way. First I tried going in from above, slipping extensions thru gaps in the intake manifold. I couldn't get close enough to the bolt head even with the flex socket. You have to be careful here as there are all sorts of fragile springs and linkage stuff. Wasted 15 minutes here. Then tried from below. You can get a socket on the nut with a small 3/8" breaker bar but very limited room. No leverage to break this nut, unless you have forearms like Popeye. Wasted a half hour here. I then figured that the only way to break this bolt had to be from above. I tried different gaps and finally found the right hole to pass the extensions thru. Then put the flex socket on the bolt head from underneath and connected it to the extension. An assistant would have been handy here, one person fishing from above and another person grabbing from below. Got a pretty straight shot at the nut now, and with an adapter and 1/2" breaker bar finally got it loose. Again, be careful here. Lots of fragile stuff around here. You can't slip. Just make sure you are solidly on the bolt with your socket.

Piece of wood on your jack and gently lift under the oil pan. I would lift, check, lift , check, until I could wiggle the mount free to the rear. Raise it a little more to get the new mount in. Thread in the upper bolt, less than finger tight as you'll need to wiggle the mount to get the lower bolt started. Same for the easier passenger side, except for the added heat shield. Lower the engine until the mounts almost touch the frame. Get the lower bolts started and finger tight and pick up the slack in the upper bolts. Lower the engine the rest of the way and torque the lower bolts to 25Nm (1Nm = .74 ft lbs = 8.9 inch lbs). 25nm is not that much. Upper bolts to 55Nm. I don't have a mid range torque wrench and am not sure if you have to make allowances for the flex joints so I just made the upper blots snug.

Put everything back together and you're done! Took me about 3 hours, but shouldn't take you more than two. A 17mm flex socket plus lots of extensions and the right hole thru the manifold is all you need.

I've also need to do the mounts on my Lexus LS400. After reading about the procedure, there is much caution on removing tie downs, else you break brittle hoses. If there are the same precautions that I SHOULD have done with my procedure, please add to this post. Hopefully the next few days will show no unfavorable consequences from my DIY.

1991 300CE
1990 LS400
2000 C280

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Old 12-27-2005, 04:17 AM
haasman's Avatar
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Join Date: Jun 2001
Location: San Francisco, CA
Posts: 3,097

Nice write-up. It is amazing how many different benefits come from repalcing worn out engine mounts. Thanks for sharing this with us.

Another one I like the results from that is even easier are the two top shock mounts. If there is any apparent cracking, they should be replaced. Afterwards the steering and front end just seem more solid.


'03 E320 Wagon-Sold
'95 E320 Wagon-Went to Ex
'93 190E 2.6-Wrecked
'91 300E-Went to Ex
'65 911 Coupe (#302580)
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