Originally Posted by killboy
I've been dreaming about restoring one of these cars to my own specifications for many years, and as things stand now, I might be in a position to do so by year end, so I decided to do a bit of research first. I need to know before hand what I'll be getting myself into so I can plan ahead.
Once the project is complete, the car will have a lightly supercharged V8 (a low output 500SE unit), with power output at around 210kW. As I live at altitude, the idea with the supercharger is to prevent loss of power, not to actually increase power. The car will mainly be used for towing and long distance traveling.
I won't be in a position to do everything I want to at once though, so first off I need to find one. One that will suit. As the engine and transmission will be replaced later on anyway, I'm not too concerned about problems on that front. What I need to know is whether there are other problems (such as suspension maladies, electrical faults, braking and steering, chassis rust, that sort of thing) that these cars are prone to, what will need replacement regardless of condition, what will need to be looked at and so on. Besides the engine and transmission, I want to keep the car as original as possible, so all other components that are not directly related to those will be kept.
I know this is a great deal to ask, so I'll appreciate any help and suggestions.
The W108 Chassis is the same from the W111 through to the W109-018 ( 6.3 !!)
so installing a V8 like a M117 500 is no sweat.Just use the M116 3.5/4.5 V8 mounts on the stock crossmember.
The starter cable loom can be used but the alternator wiring must be replaced to suit the bigger out put.If you going to use the stock CIS you need to run two new fuel lines from the tank.Just Use a W126 Fuel pump and accumulator(+ filter) in the stock location by the tank.
A radiator from a W108 4.5 will be more than adequate for the M117 engine.
Biggest problem is the trans tunnel,you'll need a V8 trans tunnel to fit the 500 trans.
Steering pump on the M117 will work the W108 steering box,and the set up is neater.The Flex disc on the 500 trans is a lot bigger than the W108 stock item so you'll need the drive shaft too,try swapping over the front halves ,I'm not sure of the spline size but they may just be the same.
Because the alloy block engine is so much lighter ,the stock springs you have will be fine to use.
In a swap like this your best bet is to drop the front axle completely,you can remove the stock engine and trans in one hit by lifting the car up about 4 feet and lowering the engine,trans,and front axle out the bottom in one unit.
It comes out like this...
Once the front axle is out ,you can replace any worn parts and because there is nothing in the way ,you can cut the 6 cylinder tunnel out and fit a wider V8 tunnel.
there is no need to worry about cutting or fabricating anything as it's all a "bolt in ' job.
A friend in the UK is doing the same swap right now and included buying a worn out W126 to get all the little odds and ends to do the job.
You can use the stock diff,there being NO way a M117 could break it.although the final drive may be a bit low so keep an eye out for a 4.5 ( USA only) diff.
Brakes are more than big enough so theres no worries there either...