[anthonymey]

Hey,
I was wondering if it is possible to swap over a full F80 M3 rear subframe into a 340i xdrive. Any help is appreciated.

[cfm56d7b]

What's the primary reason for the swap?

[Logicoeur]

But why?

[Pussiwillow]

I was curious about if the subframe mounts in the same pattern. I know there's been successful e diff from an f80 in an f30 which was also an s55/dct swap, Cant find much info on the build tho. Would be cool if it lines up; as you can score them fairly inexpensive in relative sense; but it would add up quick if you aren't resourceful or versatile.

[Polo08816]

This sounds like it would be too much work.

[mike082802]

on the e82/90 this was common to swap the whole subframe and lsd. dont know if mounting points are the same on the f80 and f30. i would think if it was possible a shop would have done it by now. the f80 has been around for over 6 years now.

[Pussiwillow]

Originally Posted by mike082802

on the e82/90 this was common to swap the whole subframe and lsd. dont know if mounting points are the same on the f80 and f30. i would think if it was possible a shop would have done it by now. the f80 has been around for over 6 years now.

There's an f30 overseas with an s55/dct/e diff in it, I can't find a lot of info on it, however, that e diff is likely attached to the f80 subframe to

[WDE82]

The subframe itself probably fits but who knows about all the suspension links that connect to it. If you use M3/4 suspension components the wheels will be out too wide so you'd need to cut your fenders out. It may also change the driveshaft length.

It's really a silly question. If you want an LSD, you buy an LSD that fits your car.

[Pussiwillow]

Originally Posted by WDE82

The subframe itself probably fits but who knows about all the suspension links that connect to it. If you use M3/4 suspension components the wheels will be out too wide so you'd need to cut your fenders out. It may also change the driveshaft length.

It's really a silly question. If you want an LSD, you buy an LSD that fits your car.

I'm fully aware of the wider track width of the front and rear on the f80, that being said; I'm fairly confident that if the subframe bolts up, you could still fit f30 oe wheels under stock fenders, if you look at f80, on stock, more aggressive wheels, people still run spacers to fit; I have approx 20mm of clearance on a 255 tire in the back with the current set up, I'm doing the f80 front suspension soon, which per my measurements should put my tires very aggressively flush in the front; considering I've had access to a full rear subframe drop out from an f80 for under 1200$, if it bolts up, you get a lot of upgrade for the money if you can get someone to code the diff etc, it could be a worth while set up.

I'm more interested in a wider track width vs wheel spacers, along with a cheap diff alternative, I'm fully aware that a true lsd diff is far superior, it's better than the current one. On top of that the subframe is a solid mount set up, so when you factor in the time to access and install as well as the cost of solid bushings, if you're a diy person, this project isn't as outlandish as it sounds, I may contact some people to find out the bolt pattern measurements of an f80 subframe and compare to f30.

[WDE82]

Originally Posted by Pussiwillow

I'm fully aware of the wider track width of the front and rear on the f80, that being said; I'm fairly confident that if the subframe bolts up, you could still fit f30 oe wheels under stock fenders, if you look at f80, on stock, more aggressive wheels, people still run spacers to fit; I have approx 20mm of clearance on a 255 tire in the back with the current set up, I'm doing the f80 front suspension soon, which per my measurements should put my tires very aggressively flush in the front; considering I've had access to a full rear subframe drop out from an f80 for under 1200$, if it bolts up, you get a lot of upgrade for the money if you can get someone to code the diff etc, it could be a worth while set up.

I'm more interested in a wider track width vs wheel spacers, along with a cheap diff alternative, I'm fully aware that a true lsd diff is far superior, it's better than the current one. On top of that the subframe is a solid mount set up, so when you factor in the time to access and install as well as the cost of solid bushings, if you're a diy person, this project isn't as outlandish as it sounds, I may contact some people to find out the bolt pattern measurements of an f80 subframe and compare to f30.

Not a worthwhile upgrade. If you're looking for flush you can just get spacers or wheels of a different offset.

And if your car is automatic there is almost certainly no driveshaft length that fits if the diff flange is in a slightly different position forward to back.

Swapping a subframe is a lot more work than just upgrading some bushings and the diff on your current frame.

EDIT: did some searching for you. The base F80 M3 has a 1603 mm track width with +23mm offset wheels so the hub faces are 1649 mm apart. The F30 base has a 1572 mm rear track width and +37mm offset wheels for a hub face width of 1646 mm. That's pretty damn close actually. WAY closer than I would've expected. So it's not really gaining you anything for wheel fit but you aren't losing anything either.

Still, personally I would do some poly subframe bushings and upgrade to some ball joints and an LSD on the stock subframe. You still have to make sure the spring perches line up as do the shock mounts. Also the M3/4 may have significant reinforcement in the body for the solid frame mounts. Remember, E46 M3s used to tear out their rear body mounts pretty regularly. With bushingless mounts the peak forces at the mounting points will be increased by a lot.

[Pussiwillow]

Originally Posted by WDE82

Not a worthwhile upgrade. If you're looking for flush you can just get spacers or wheels of a different offset.

And if your car is automatic there is almost certainly no driveshaft length that fits if the diff flange is in a slightly different position forward to back.

Swapping a subframe is a lot more work than just upgrading some bushings and the diff on your current frame.

EDIT: did some searching for you. The base F80 M3 has a 1603 mm track width with +23mm offset wheels so the hub faces are 1649 mm apart. The F30 base has a 1572 mm rear track width and +37mm offset wheels for a hub face width of 1646 mm. That's pretty damn close actually. WAY closer than I would've expected. So it's not really gaining you anything for wheel fit but you aren't losing anything either.

Still, personally I would do some poly subframe bushings and upgrade to some ball joints and an LSD on the stock subframe. You still have to make sure the spring perches line up as do the shock mounts. Also the M3/4 may have significant reinforcement in the body for the solid frame mounts. Remember, E46 M3s used to tear out their rear body mounts pretty regularly. With bushingless mounts the peak forces at the mounting points will be increased by a lot.

I appreciate the research info you provided, it appears it'll be close to 15mm added track width per side based on that over f30, which would yield a near perfect fitment, the suspension geometry may be very similar to the point adjustable links may yield something similar, I came from the e36 world and built a full track set up in my 1 car garage as well as 2 engine builds and swaps, I love wrenching on these things, I just haven't spent much time on this chassis yet.

It seems people with f chassis are not the type to do much beyond basic basic stuff. I had this idea a few months ago when I saw a dct swapped f30 and thought hmmm, if they can make that work now I wonder about the rear diff, a full drop out with diff is less than half of an lsd, and you get a solid subframe and more track width out of the deal once you work out the kinks. I'll revisit this idea when I have access to more info, the drive shaft side of things may work with stock shaft if people have done a dct swap with stock f30 rear end without having to modify it, I'm just curious about it at this point, but I'm not about to buy a drop out and be left with a paper weight.
I have akg 75d poly subframe bushings and diff bushings sitting around, waiting for cool
Weather, I figured if this is achievable I gotta pull the subframe down anyway… I dunno, I'll see soon

[WDE82]

Originally Posted by Pussiwillow

I appreciate the research info you provided, it appears it'll be close to 15mm added track width per side based on that over f30, which would yield a near perfect fitment, the suspension geometry may be very similar to the point adjustable links may yield something similar, I came from the e36 world and built a full track set up in my 1 car garage as well as 2 engine builds and swaps, I love wrenching on these things, I just haven't spent much time on this chassis yet.

It seems people with f chassis are not the type to do much beyond basic basic stuff. I had this idea a few months ago when I saw a dct swapped f30 and thought hmmm, if they can make that work now I wonder about the rear diff, a full drop out with diff is less than half of an lsd, and you get a solid subframe and more track width out of the deal once you work out the kinks. I'll revisit this idea when I have access to more info, the drive shaft side of things may work with stock shaft if people have done a dct swap with stock f30 rear end without having to modify it, I'm just curious about it at this point, but I'm not about to buy a drop out and be left with a paper weight.
I have akg 75d poly subframe bushings and diff bushings sitting around, waiting for cool
Weather, I figured if this is achievable I gotta pull the subframe down anyway… I dunno, I'll see soon

You know I made the assumption that you weren't that experienced because of exactly what you said about the forum. The newer a model is the more nonDIY non-modding the forum seems to be. If you're experienced then you know all the potential pitfalls so you don't need me suggesting not to do it as if you don't know what you're getting into.

Lots of newbs seem to come around with bright ideas that are pretty silly when analyzed but if you know what you're getting into absolutely have at it. Could be a fun project. And that's a perfectly valid reason to attempt anything at all.

[Pussiwillow]

I figured as such, when I see posts like mine, even, I assume the same as well, I've had the car a year, done a lot of work to it for maintenance etc, and I've asked things that seem simple enough but cannot be answered along the way, so I got the vibe people don't work on their cars anymore lol.

[damack]

I've seen a few F31-F80 swaps. Might be some info in those threads

https://www.bimmerpost.com/forums/sh...php?p=27392459

[Pussiwillow]

Originally Posted by damack

I've seen a few F31-F80 swaps. Might be some info in those threads

https://www.bimmerpost.com/forums/sh...php?p=27392459

Yooo you're awesome I just messaged OP

[mike082802]

also on the e82/90/92 when swapping in the whole rear subframe the driveshaft had to be shortened so you would probably have to consider that as well. it was and still is a cheap upgrade when you consider if you buy the whole subframe usually comes with the hub/brakes/axels and lsd usually for around 1500.

[Pussiwillow]

Originally Posted by mike082802

also on the e82/90/92 when swapping in the whole rear subframe the driveshaft had to be shortened so you would probably have to consider that as well. it was and still is a cheap upgrade when you consider if you buy the whole subframe usually comes with the hub/brakes/axels and lsd usually for around 1500.

The other side of this spectrum is, car has 75k on it
I'm doing a full front suspension overhaul f80 arms etc, the rear I had plans to do the bushings and all ball joints and adjustable camber and toe arms, so I think this would be ideal

Also rk tunes made their f80 drift car and was able to lock the diff in full lock, so if I have a wiring situation, or something I can't immediately get resolved, I can probably do something like that

[Pussiwillow]

Confirmed, subframe bolts right up

[casualDIYer]

Along with the complication of the rear wheels being a different offset (which was previously mentioned doesn’t seem too great) isn’t there a complication of matching the f80 subframe to the f30 hard points?

[megaocher]

Has anyone actually attempted this? I'm looking at getting a subframe to attempt this on my car, as far as I can tell everything should work aside from the driveshaft, the diff ratio, and the headlight leveling arm, none of which seem insurmountable. My car is RWD so it seems as though the spline for the driveshaft is a similar size. With a standalone controller becoming available soon, the diff seems like a much better value than the MP LSD. Sorry for resurrecting an old thread but it seemed like a good place to start.

[mike082802]

someone did it on the facebook B58 page, i say if you have the time and means go for it.