W124 Differential and Subframe interchangeability for M156 swap

[Brento]

Firstly, I will apologise if this subject has been covered in depth previously, my searching has not yielded any straight answer. I am undertaking a M156 and 6 speed manual swap in my 1988 300E. With the aid of the W124 Performance knowledgebase, particularly the differential information sheet I decided early on I would upgrade my 185mm differential to a 210mm unit for obvious reasons, and most likely I will fit a Wavetrac centre like I have in my W126.

I managed to secure a 210mm differential from a 1994 E280 it has the rear cover 1243513408 and I believe it to be 2.65:1 ratio. Now my question is will the 210mm bolt into my 185mm subframe and connect to the half-shafts? I am not concerned about the tail-shaft as I will use a custom one in any case to adapt to the manual gearbox. Is there any difference between the driveline componentry between the 185 and 210 such as the half shaft strength, hubs etc.?

I also have available to me a 300CE24V which I can remove the entire subframe and differential from and bolt into my 300E if needed. But it will require a complete rebuild due to condition whereas the subframe and half shafts in my 300E are already in really good condition and will only need minimum maintenance for the swap. I completely re-built the anti-squat rear in my W126 a few years ago and to be honest I am still a bit scarred from that experience and want to avoid it!

 

[gsxr]

Firstly, I will apologise if this subject has been covered in depth previously, my searching has not yielded any straight answer. I am undertaking a M156 and 6 speed manual swap in my 1988 300E. With the aid of the W124 Performance knowledgebase, particularly the differential information sheet I decided early on I would upgrade my 185mm differential to a 210mm unit for obvious reasons, and most likely I will fit a Wavetrac centre like I have in my W126.

Wow. The engine swap will be the main challenge. IIRC the steering box is in the way, possibly the oil pan too.

I managed to secure a 210mm differential from a 1994 E280 it has the rear cover 1243513408 and I believe it to be 2.65:1 ratio. Now my question is will the 210mm bolt into my 185mm subframe and connect to the half-shafts? I am not concerned about the tail-shaft as I will use a custom one in any case to adapt to the manual gearbox. Is there any difference between the driveline componentry between the 185 and 210 such as the half shaft strength, hubs etc.?

The 210mm diffs are wider and will use shorter half-shafts. I don't know the difference in dimensions. Either way, you will want the largest, strongest axle shafts which will be from the 034/036 with ASR.

Yes you can bolt a 210mm diff into your existing subframe with the appropriate rear cover, however I would NOT do this! With an M156 engine, you need the V8 (400E/500E) subframe and the "finned" diff cover that matches. The smaller subframe has tiny diff mount bushings that will disintegrate with 500hp on tap. Those bushings fall apart with only 150-200hp.

I also have available to me a 300CE24V which I can remove the entire subframe and differential from and bolt into my 300E if needed. But it will require a complete rebuild due to condition whereas the subframe and half shafts in my 300E are already in really good condition and will only need minimum maintenance for the swap. I completely re-built the anti-squat rear in my W126 a few years ago and to be honest I am still a bit scarred from that experience and want to avoid it!

That subframe won't help. You need a 400E/500E subframe. And, you should fully rebuild whatever subframe you install. Make sure to use all OE links if possible. Get the aluminum torque strut too (photos & part numbers are on W124performance). If budget doesn't allow OE, the only alternative I'd use is Lemforder (no longer made in Germany).

The 124 subframe is a totally different design vs the 126, and is much less scary. Get the "tall tab" front subframe bushings (this won't be easy, they are NLA and difficult to locate as NOS for good ones). There are cromulent aftermarket late-style rear Sportline bushing kits available. Search the forum for details on both. Main thing to worry about is NOT tightening any of the 5 links unless the suspension is in "ready to drive" position. All the bonded rubber bushings must be under zero tension at normal ride height.

 

[Brento]

Thanks for the wealth of information gsxr, it is much appreciated. I have a few solutions to the issues you have presented. With regards to the swap itself the main issue will be the starter motor on the same side as the steering box, i haven’t checked what side the start is on my ML63 donors yet but what I have seen of the M156 I should be able to mount the starter on the LHS with a bit of engineering worse case scenario. If I am still battling for clearance I will convert to rack and pinion like I did with my M113K swapped 550SEC. The ML63 has a deep front type oil pan and I think it won’t cause me and drama with the cross member.

I have basically zero chance of getting a M119 rear subframe. I am in Australia where these cars were not released and even so we all know how rare they are. I will have to look to strengthening the standard subframe where required. The bushes are no problem I can make my own poly bushes to handle to torque, once again this is a modification i did to the rear of my W126.

With regards to the finned cover has anyone tried using the one that kangaroosteam makes? They also supply some upgraded half shafts.

I will look into the upgraded torque tube cheers!

 

[gsxr]

I have basically zero chance of getting a M119 rear subframe. I am in Australia where these cars were not released and even so we all know how rare they are.

Oh no. How much is freight cost to have one shipped from USA? There should be plenty of 400E subframes here.

I will have to look to strengthening the standard subframe where required. The bushes are no problem I can make my own poly bushes to handle to torque, once again this is a modification i did to the rear of my W126.

The issue is that the 4/5/6-cyl bushings are small diameter. The V8 bushings are, relatively, HUGE. I don't know how long the small poly bushes will last, or if you might get unwanted NVH through them.

 

[Brento]

I don’t imagine it would be cost effective at all due to the size and also the weight. I’ve pretty much concluded it’s simply not feasible.

Have you got a comparison photo of the bushes?

 

[gsxr]

Have you got a comparison photo of the bushes?

I don't have a photo of both bushings side by side, but I do have loose bushings somewhere in the shop... need to find them and take a picture.

Here are some random Google photos. 4/5/6=cyl first:




V8:

 

[Brento]

Cheers gsxr

 

[gsxr]

Pics below.

6-cyl = 47mm OD
8-cyl = 66mm OD

Anecdotally... the V8 mounts almost NEVER need replacement. I've never seen them fail, and very few (if any) forum members here have reported failures. They are very robust.

OTOH, the 6-cyl mounts need replacement about every third oil change. OK, ok, that's an exaggeration, but only a little. The smaller mounts have a disturbingly short lifespan, even behind diesel engines making 125-150hp. They collapse as shown in the photo a couple of posts back.

 

[Brento]

The first job I did when I bought my 300E was replace those mounts, I didn't realise just how fragile they were though. Worst case scenario I think some poly mounts will solve the problem. On my 560SEC I used Superpro bushes for the subframe to chassis, then adapted an aftermarket pontiac poly mount for the diff to the crossmember at the rear and then fabricated my own poly mounts for the diff to the subframe.

 

[Brento]

Different concept I know, but you can see what's possible.