I'm looking for a way to upgrade the rear-end in my car and I just thought about this. 240sx rear-ends are very common and cheap around here, and also the whole subframe can be removed from the car. If it were possible to fit the whole subframe into a thirdgen, does anyone think that it might work?

Here are some pictures of the 240 rear subframe, differential, and axle assembly:



I have seen some threads about swapping in a C4 IRS setup, but it looks more complicated because mounts have to be made for each of the control arms, instead of swapping over the whole subframe. Rear diffs from 240s have been known to hold up to 500hp and although that's in a lighter car, that would still seem to be stronger than a 10 bolt or 9 bolt in stock form. The width of the 240 rear seems to be about 3.5-4" shorter from the specs I have found. If the rear diff is a R230, it will also have a ~9" ring gear and 31 spline axles, which is a significant upgrade, even though the R200 would still be a minor upgrade IMHO.

Personally I think that if the gas tank were out of the way, it would be possible to use the subframe and the only thing that might not work is the location of the shock/coil-over mounts, along with brakes of course.

If you don't think it's a good idea because a 240 rear doesn't 'belong' in a thirdgen, just don't reply.

So what does everybody think? COULD it actually work and be less complicated/cheaper than a C4 corvette IRS swap?

 

can it be done? with enough time sure, less expensive? hell no. probable the same in the long run, and the c4 parts will be lighter, have the right bolt pattern for the wheels, IDK about strength.

I would be curious to see this fitted in a car though. would be different.

FWIW, the new camaro/g8 rear subframe is a similar setup.

 

Just curious but why don't you think it would be less expensive than a C4 setup? Right now there's a 240 subframe, differential, and axle with big brake setup for sale locally for $450. There are no corvette rear ends for sale locally and in Vancouver (across the water), there is one '92 complete rear end for sale at $1495. Corvettes are also much less common here in junkyards. A brief search of car-part.com reveals nothing locally, closest being Alberta at $1500.
I am thinking of buying the $450 setup, so if I do, I will probably mock it up a bit later in the fall. If I decide it's too much work/wouldn't work at all then I can probably resell it without too much loss.
I do realize that it might also be cheaper to do a Ford 8.8 or 9" swap but if this option turns out to be no more than twice as much, I think it would make for an interesting project at the very least. And it should definitely be cheaper than a full-on aftermarket rear setup.

 

Well, its the nature of cheapest & easiest to maintain here in the US. A Dana 44 IRS can be found just about anywhere in the US and the local car parts store will be able to supply most any part you need should something break. The only real custom work involved is making the sheet metal fit the IRS & mounting it in a structurally sound manner.

The C4 IRS swap was born out of seeing one bolt straight up to a Gen I Camaro, no kidding. A 1980's Corvette IRS had the exact same suspension mounting bolt pattern as the solid axle 1960's Camaro did. With easy access to the IRS, someone tried it on a 3rd gen after GM built one, maybe two, 3rd gens with the IRS in there. Its the cheapest solution we have down here, and at that its a figure it out along the way conversion. I've read several of the threads and no two have been done exactly the same.

You'll be treading new water with the Canadian version of the IRS swap.

 

If you have the tools and know how I say go for it, but you will have to attach it to the rear frame rails, or at least the LCA mount brackets, though I would reinforce them with some steel plate if you go that route. And if it doesn't line up with either, you will have to fabricate something up, also I would say SFCs are a must if you put that on, ESP if that's IRS, but hard to tell for sure.

 

So here's some pro's and cons I see to attempting this:
Pros:
Stronger (most likely anyways) rear end and axles
IRS - more adjustability, better handling
More desirable rear end gear ratio than what I currently have (around here 240sx's most commonly have a 4.083:1 rear ratio)
Cheaper than a bolt-in aftermarket rear-end
Torque arm is no longer part of the suspension, taking stress off the transmission and opening up room for exhaust.
240sx's are very common around here and replacement parts are plentiful and cheap.
Cons:
New rear subframe has to be mounted somehow
Either rear wheels will need a different bolt pattern or I will need conversion hubs (5-lug hubs are available)
Driveshaft should be the same length if the axle is mounted in the right place, but conversion u-joint would be necessary
Rear end width would be skinnier, so axles may need to be lengthened (esp. because I use vette wheels with 2" spacers already).
A Ford solid rear axle swap would be cheaper and may or may not be stronger.

The way I see it, it's definitely doable. My thoughts as far as fitment goes is that it might actually be better to fabricate a custom subframe for the setup, and widen it in the process. In that case, if I wanted to run my current wheels, I could make a wider subframe and have the axles lengthened. The other option I see for making it wider would be less desirable; making longer custom lower and upper control arms AND lengthening the axles. Making a custom subframe would also allow for more flexibility with where it would mount.

In any case I won't be able to get a really good idea of whether or not it would work until I pull the rear end and exhaust from my car, which probably won't happen until I park it for the winter. Any thoughts would be welcome. I plan on taking a look at the subframe/diff setup tomorrow to get some measurements. The seller sent me some pics today and the setup actually looks to be in very good condition.

 

I don't think theres going to be anything "cheap" about this. Sure, you're not paying for your labor, but this is going to take quite a lot of labor to do. And yes, you aren't out a pocket a ton for the large items, but there's several indirect costs to think about. Bushings, hardware, sheet steel, welding gas & wire, electricity, gases for cutting torches, needed to make the swap work custom parts, small parts that you don't think about until you need them, case of beer for a helping hand for those two person tasks, and several more miscellaneous out of pocket expenses. See where I'm going. Your direct costs of the swap are really low, but all the indirect costs incurred are just as expensive or more so all told than a decked out bolt in Dana S60 swap.

The more I look at it, the simplest thing to do in my mind is back-half the car and then mount the subframe/IRS assembly to the frame tubes. That way, you have monster space for wheels & tires without having to widen the IRS, but I get a feeling you'd have very poor kinematics with your drive wheels being 4" inboard of your turning wheels. If you back-half the car, you won't be able to have anyone as a passenger or be able to carry cargo. It would allow you to run a fuel cell that you could relocate in the frame out of the way.

 

the 240sx's have a r180 ~7" ring gear which isn't going to hold any amount of power in a heavy car. 300zx's have r200 ~7.9" ring gear and seems to have a pretty good reputation from the z-car swapped cars. They also have a 5x114 bolt pattern and would probably be closer to the right width. Wilwood makes hubs for our cars that can use 5x114 wheels.

Structurally though, all the sheetmetal frames on a thirdgen are on the outside, a dual a-arm rear end would need some major structure built in to support it.

If you want cheap, thunderbird 8.8" stuff is dirt cheap and if you manage to break it you can just start upgrading to cobra stuff.

 

Yeah I looked for thunderbird 8.8 stuff and there isn't much around here. In the end I probably will stick with a solid rear axle, but just a few more notes; Inifiniti Q45s it turns out use the same sub-frame mounts as a 240 and they are wider cars with V8s in them, so a diff and axles from one of those cars would be stronger and more suitable for my application. And the 240 subframe would still be a cheaper place to start. Once the summer's over here and I have the rear-end out of my car I might borrow a 240 subframe from a friend who has a parts car just to see how it would fit. Structurally, yes I would imagine it would require quite a bit of bracing, but it's just an idea I wanted feedback on.

Thanks to everyone for the replies.