How to change front subframe mounts on a 380SL?
 

In my continued effort to sort out our "new" SL, I am now looking to change the front subframe mounts. The fron end of this car sits low, which I read somewhere is typical for a car with bad subframe mounts. So, how does one change these out?

There's a lot of information on this site about this (that's how I figured out how to do it, essentially), but I would add that this is a very good time to change the motor mounts also.

If I were you, I'd check with your dealer or MBUSA to see if your car has had the front frame recall done. That invloves checking for cracks and beefing it up if it hasn't been done. That job calls for removing the front subframe mounts, so if MB is going to be paying for the labor for that job, you buy the new mounts and let them put new ones in when they put it all back together. All you pay for is the parts. Now if your car has already had that recall done, it will cost you a few bucks ot have someone do it. :)

Len

I thought that recall was for the 450's. I guess I would just need to call the dealer, give them the VIN# and they can check that way?

I looked up the subframe kit on Fastlane and it shows 4 rubber mounts. Now I am a little confused because I am also looking at a diagram of the front suspension in my Performance Products catalog. It shows only 2 mounts. I have looked under the car and the mounts that I see that are rotted away are not up by the coil spring, but just forward and behind it. I guess it would help if Fastlane had diagrams like PP, becuase I see what's shot, I am just not sure what they are called. The whole subframe assy. appears to be bolt to the body in 6 places, 3 on each side. The big mount in the middle near the coil spring and one smaller mount forward and aft of that. It is the smaller ones that are completely gone on my car. The PP catalog doesn't even show these as being available. So when I looked up the "kit" on Fastlane is shows me 4 mounts, bolts, plates, etc. So I am throughly confused. Could anyone clear this up for me? The kit by PP is for the big mount near the coil spring and cost $42, whereas FL is $74, but it has twice the parts. I am getting a headache.

There are two rubber mounts on each side of the R107 subframe (same as on the W114/115 which shares the part, I believe).

The subframe mounts are oval, about 1.5" wide and 2.5" long, one in front and one behind the spring. The other "mount" on there has the engine sitting on it....

If the mount bolts stick out from under the subframe, the mounts are flat for sure. Should be an inch or so of mount visible above the frame, too. Likely, unless replaced yours are quite flat.

Replacement is similar to the W115, which I have done:

Jack up and support FRAME (not subframe) on jackstands. You can do just the front or front and rear, whichever is easier for you.

Remove engine shocks (front of engine on the accessories brackets, I think)

Put a floor jack under the engine pan, padded so that it won't damage the pan, or you can use an engine hoist attached to the top if you prefer.

Lift engine and remove the subframe bolts on one side. Watch for the nut plate breaking (at least on the W114/115 chassis, not sure what they bolt to on the R107).

Pull bolts out, then lower engine/subframe assembly until you can remove the mounts upward from the subframe. Spray new ones with silicone lub or spread some undiluted dishwashing detergent on them, and put them in place, then raise subframe and install bolts. You may have to press some to get the mounts into their pockets. Leave the bolts loose, but screwed most of the way up, until you have both sets in.

If the subframes does not drop far enough, you must pry between the top spring cup and the frame to force it down. Usually necesary only on the second side.

Repeat for the other side. You will almost certainly have to pry this side down -- you need a bar or pip about 3 ft long, maybe more. Have a care to keep fingers out of pinch points.

Tighten bolts and replace engine shocks.

Note that if the subframe mounts were bad, the engine mounts are too, and the fan will now probably rattle on the fan shroud or other signs of flat mounts will appear as you lower the engine in the body. My 220D started banging the AC compressor on the fender when I replace the subframe mounts, quite a surprise. I'd get the engine mounts and do the whole thing at once.

If you have the appropriate tools, you can suspend the engine and drop the subframe down separate (if you are doing the engine mounts this will work better anyway). Watch for strain on the brake lines if you do this.

Peter

Best to have a helper on this job -- watch for engine clearance as you drop the subframe, this isn't a problem on the W115 but the W107 with the V8 is more complicated.

The 107 is a little different than described above; I would check that forum specifically.

It is an extremely good idea to loosen the fan shroud before doing this (and, of course, reinstall it properly before starting the engine!). Note that dimensions of clearance between the fan and shroud will have to be rechecked after the mounts are done (proper dimensions from the shop manual, on a 560sl:top of shroud to fan: 20mm, bottom of shroud:15mm). Mine noticeably changed after doing this work and I had to move the shroud a few notches under the clips. Breaking the shroud: fairly expensive. Breaking a fan blade: really expensive. Damaging the fan clutch: really, really expensive. Overheating: don't even want to discuss it.

Lowering the frame was much easier with the motor mount loosened.

I guess the confusion is due to PP's catalog. I just noticed that for the 107 series, they don't show/list "engine mounts". For the 123 series they do. But their catalog clearly shows/list the center mount, by the coil spring as a "subframe mount kit" and cost $46.