Replacing front frame mounts

[twistedtree]

I just finished replacing the front frame mounts on my car.  Wow, what a pain in the ass.  I needed a 5' pry bar to spread the chassis and front frame apart enough to get the old mount out and the new one in.  Not an easy job.

But one of the mounts had completely separated into two pieces, and the other was inches away from separating as well, so it was a much needed repair.  I replaced the engine mounts at the same time, and now everything is nice and tight with no undue sags when the car goes up on the lift.

[Charles 230SL]

My 64 230SL is over at Bud's Benz undergoing restoration and they recently replaced the sub-frame mounts.
Brad (at Bud's) showed me where, rather than replace the rubber frame mounts, the previous owner had fabricated and installed an aluminum plate on each side. Bolt patterns were drilled through each plate to match the mounting surfaces..The plates were approx 1/2 inch thick.  Why on earth would someone go through the trouble to fabricate aluminum plates? 

[twistedtree]

Interesting.  I actually wonder why those mounts exist at all.  Other cars just have the frame rigidly bolted together.

[wwheeler]

The reason I think is because the cars that have the rigid mount to the frame, have rubber bushings at the suspension pivot points. Our cars have solid metal pivots and rubber bushings at the frame mount. So you need to have some cush somewhere otherwise you have a race car. The problem with rubber bushings at the pivots, is that the suspension/steering geometry changes as the rubber bushings give. Urethane is better than rubber for this, but can ride rough. Mercedes maintains perfect geometry with the solid pivots yet a fantastic ride.

[twistedtree]

I think you've nailed it.