A dummies guide to a 560/500 M117 W108 conversion

[Haris]

Hi All,

I hope you and your families are keeping well in this unprecedented time.

My car is an M130 280SE LHD originally from the US and I'm in the UK.

I have a 6.3 rear axle that I'd like to get prepared to go on to the car for a 560 or 500 engine swap, unfortunately, with being on lockdown I am not near the car and cannot compare the rear axle I have on the car so thought I'd ask here. My search has been inconclusive so far, I know the 6.3 has anti-dive mountings which would need to be adapted if I am keeping that system, as well as no centre compensating spring or hydropneumatic compensator and different spring mounts (bag mounts instead with the 6.3 having air). I also don't know if mine has an anti roll bar?

1. Before I start stripping down unnecessary bits I've read that I can simply swap over the axle tubes and that would be sufficient to get it mounted to a W108 and would do away with the air bag mounts and anti-dive system obviously. Would I also be able to mount the compensating spring using the bracket I already have?

2. The plan is to do the engine conversion in few years time, is there any point having the lower ratio mated up to the M130? (A few years because I plan to upgrade to do aftermarket air suspension and make sure the brakes are sufficient, not only that I have 190E project I need to finish before I tear into this one). I know someone here in the UK did this for better cruising ability, dropping the revs at higher speeds, the only reason I ask is because it would mean one less thing to do once the engine was ready to be dropped in.

3. I also want to slowly start getting any other parts I need for this together, my shopping list so far includes:
- R107 560 Exhaust Manifolds or can I get away with 3.5/4.5 M116 manifolds?
- Electronic to manual speedo signal converter
- M117 engine & gearbox complete, either a late 560 or 500. With fuel pumps, ancillaries and any wiring with the ECU
- M116 3.5 engine mounts
- Custom exhaust from manifolds back

- Smaller brake booster?
- Not sure what happens propshaft wise?
- Different radiator?

Am I missing anything from the above list?

Pictures of the axle in question below









Your help would be appreciated!

[CraigB]

I don't have a lot of experience with the w109 rear ends. Mercmad who is sometimes on here is the person I know with most experience with these. He also did a conversion to put a W126 rear end with trailing arms into a W108 - then you can get much taller ratios (but not sure ratio of 6.3 though). I guess it would be good to have antidive with the extra grunt of the conversion, and having a swing axle still that changes camber. But I am guessing you don't still have access to the brackets from the car it came out of.

The spring platforms look easy and I am sure they just bolt to the arms or looks like you could swap arms.

Just relying on memory, but I think the main issue to bolt in is that the backing plates rotate. Looking for easy, is there a way to lock those? The only problem I can see from changing axle tubes from a 6 cyl car, is that there are differences to the sprung 3.5 diff casing. The people who swapped tubes, did they swap from a 6 or from a V8 with springs? And of course you would need to set up backlash etc I think, which is a bit of messing about - but then also, how good do you think the diff is.

And to answer the ratio on the 6, I know lots of people have done it because they want lower cruising revs, but if like me you live in hills, I am sure this would kill the performance. To me the characteristics of the 'designed to be' a high revving engine and the ratio, means that the power characteristics match those higher revs. I can pull it back a gear and it picks up and goes, but if you try and slog away or your kick down is not adjusted, the cars feel like absolute slugs and need to rev. I also have a manual trans W113 with M130 and without the auto, instinctively you do tend to rev it and it is a sweet motor and even at high speeds I think of the revs as 'singing' . Each to their own but I have never been tempted to change the ratio - my only temptations have been to put shorter ratios in a W126 with 2.24, because I think it takes that 'excitement' away, that is in a shorter ratio 380 I have - smaller engine but just feels more spritely in normal driving, just a bit higher revs on highways. But then depends on what driving you plan. You have lots of motorways over there, but I always preferred the B roads!

[Haris]

Thanks Craig.

No I don't have access to the original brackets from the car that this came from.

If there isn't too much fabrication involved I would prefer to keep the anti-dive too but I have no idea how it is meant to mount to the car usually.

I will try search a bit more on swapping axle tubes or just wait for this lockdown to be over so I can compare what I have on the car.

[sebada]

Thanks Craig.

No I don't have access to the original brackets from the car that this came from.

If there isn't too much fabrication involved I would prefer to keep the anti-dive too but I have no idea how it is meant to mount to the car usually.

I will try search a bit more on swapping axle tubes or just wait for this lockdown to be over so I can compare what I have on the car.

How are you?

Did you find out how the anti-dive mounts to the car?

Regards