More Subframe Mount Questions

[mbboy]

I've been reviewing some threads on replacing the subframe mounts on a 107, as I'm getting ready to replace the mounts on my 380sl. Based on what I've read, it seems to me that the easiest way to do this is the one RandyA reported in the following thread:

107 subframe mount replacement

According to his post, after supporting the car on jack stands, the subframe can be supported by a jack and lowered simply by loosening the 4 subframe mounting bolts without disconnecting anything else. Then, one bolt at a time can be removed and the corresponding mount replaced.

However, other threads state that the brake lines, calipers, sway bar, shocks, engine shocks, and/or motor mounts have to be disconnected or removed to lower the subframe enough to replace the subframe mounts.

For instance, the following thread, which has a fairly good description and pictures of the process, suggests that the brake lines, shocks, sway bar and tie rods have to be removed to replace the subframe mounts.

http://www.benzworld.org/forums/r-c107-sl-slc-class/1461717-front-subframe-bush-change-pics.html

Having thought about these different methods, it seems to me that it should be possible to drop the subframe enough to remove the mounts without disconnecting the calipers or brake lines, which would eliminate the need to bleed the brakes afterwards, and that the tie rod and shock absorber should just move with the control arm.

However, if I'm not mistaken, since the motor mounts are bolted to the subframe, and the engine is bolted to the motor mounts, wouldn't it be necessary to remove or at least loosen the motor mount bolts before the subframe can drop?

Also, in another post, someone stated that you can drop one side of the the subframe at a time simply by loosening the bolts on that side without loosening the bolts on the other side, and that neither the motor mounts, or engine shocks have to be disconnected.

It seems to me, however, that since the subframe is one piece, the bolts on one side would prevent the other side from dropping -- or that dropping one side at a time would have to abnormally compress the mounts on the other side?

In addition, I was wondering if dropping one side of the subframe at a time with or without disconnecting the motor mounts and or engine shocks could possibly cause the engine to tilt in a way that could bend or throw the drive shaft, linkage, or something else out of line, given how finicky these things are?

Since a number of people here have already replaced these mounts and or their subframes, I was wondering if one or more of you could clarify these things for me.

Thanks very much in advance.

[Gilly]

THE ENGINE HAS TO BE SUPPORTED!!!
(sorry for the caps and yes I am shouting!)

Gilly

[Deltacom]

I had replaced the subframe mounts, engine mounts, bushes etc as I had completely overhauled the front (and rear) subframes but removed the subframes completely from the car.

If you are only replacing the subframe mounts (though doing the engine mounts at the same time would be a good idea), it can be done by droping the subframe one side at the time (see Paratroop mounts replacement).

The engine mount bolts should be completely losened but not removed (it makes it easier to reasemble) after supporting the engine with a floor jack and a timber block, (or with straps as I did) but leaving you room to use a trolley jack to control the droping of the subframe.

Lossen the subframe 4 bolts just a couple of turns to allow the subframe to swing a bit and you can remove one side 2 bolts and drop subframe about 3", this will allow you to remove and install the new mounts. Dont forget to use de "c" brackets to hold the butterfly nuts that comes with the kit.

It helps if you remove the steering track rod end from the steering knuckle and the top nuts of the shock absorber.

[mbboy]

Thanks for the clarification. I think I'm getting the whole picture now. However, I don't have a trolley or hydraulic jack that I can use to lower the subframe only 3-4". So I'm wondering whether I can use a scissor jack to do that?

Also, I'm wondering if I can get away with lifting and supporting only one side of the car at a time, or if both sides have to be on jack stands to do it?

[Deltacom]

I would advise against those ideas for several reasons. Scissors jacks are not designed to lift the weight of the 107 particularly from the front to support the vehicle with robust axle stands. If you lift the car from one side the engine will not be level and you need to support it with a jack. On a tilted vehicle there is real danger of the engine slipping from the jack with substantial damage, it is risky and dangerous.

I would suggest that if you do not wish to invest on the required tools (namely a 3ton robust hydraulic jack) you would be better off having an indy to replace the mounts for you. Pls don’t take any risks with your safety. Think in the long term use of the tools rather than it will be expensive to acquire the tools just for this job!.

[mbboy]

Thanks for getting back to me Deltacom. However, I think you may have misunderstood what I was asking in the last message.

I was only going to use the scissor jack to hold and lower the subframe, since it gives me the ability to lower the subframe slowly in increments, which my little hydraulic jack doesn't. I can, however, use that jack or the MB jack to lift the car and place it on stands.

As for lifting only one side at a time, I asked because I suspected that this could cause a problem, which you confirmed.

I am debating whether to get a larger floor jack to do this job, and to keep around for other jobs. But that also means having to store it in an already cluttered garage.

OTOH, this still might be preferable to having an Indy do the job, given the hassle of having him find the time to do it, dropping the car off, picking it up, etc. Plus, as you and most other people who frequent this forum know, there's nothing like the satisfaction one gets from completing a job on these cars oneself. So I am still leaning towards doing it myself.

If I do, and assuming that everything goes well, I'll write it up and take pictures to add to those that people have already posted.


Thanks again for the help.

[RadioTek]

Keep an eye on your local Harbor Freight. They often have sales on things like jack stands, hydraulic jacks, creepers, etc... Get the heavy duty (6 ton) stands and a 4 ton floor jack (ratings). It may seem a bit of 'overkill', but the extra 20 or 30 bucks can mean a lot in terms of safety.

[mbboy]

I don't want to belabor this thread, but I found another technique that sounds much easier than the others written up here:

http://www.mbca.org/forum/107-front-subframe-bushings

"I drove the front end up on ramps, disconnected the tie rods, and unbolted the bottom of the shocks. I then unbolted the subframe bushings, one side at a time, and used a floor jack to raise the frame. I used a long piece of one-by-one wood between the top of the tire and inner fender to gently pry "that last little bit" as I replaced the bushings. Just leaning on the wooden pry bar (with my arm pit) while working was perfect. I didn't even need to remove the wheels. It was really a piece of cake."

Any reason why it can't be done this way?

[Gilly]

Oh, sorry, you just want to do the mounts? I keep having flashbacks to the several times I had to do the warranty subframe replacement.
YES, that way will work fine, just loosen all of the mounts, then you can replace each one individually. When you replace one, just don't tighten it, wait until all are replaced.
Gilly

[Philoprof]

If one did use this method, where would be the best place to place the jack to lift the frame?

Thanks