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Hi all,

Probably been asked somewhere before, but I couldn't find it so please humour me.

Really simple question. Is it feasible to change non folding rear seats for folding ones? It's obviously possible, 'cos anything is possible but is it practical?

Ta.
 

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Honestly, you're better off with fixed rears. Much better styling and comfort.

Practical to use, but a PITA to retrofit.

Good news is with so many E39s being scrapped you can get the mounting points for the cost of a plasma cutter /TIG welder and a lot of mock installing time.
 

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Thanks fr the beautifully direct answer.

Glad I've got a towbar fitted then - I can use a trailer for anything too long to go in the boot.
 

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Non folding seats are so much better in the M5. The e39 is like all BMWs of that generation, the folding rear seat cars are missing a steel bulkhead that runs behind the seat. You have to cut this out, it’s a big job, and you are removing a large structural support from the car.

The non folding seat BMWs of that era have much higher torsional rigidity than the folding ones. For instance the E46s without folding seats will twist one degree at 18,000 nM, folding seat models twist at 13,000 nM. Thats close to 2 tons of torque difference. Same for any model where one has a bulkhead vs not. E60s got a support beam so the seats are interchangeable.

If you need extra trunk room rent a pickup for a day, and then go enjoy your M5 with much less chassis twist. Also the folding seats are heavier and squeak.
 

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I am about to undertake this project. I can tell you it's a lot of work. It took me several evenings cutting spot welds and removing the floor where the bulkhead meets the area under the rear seat.
This is not a project of just welding some tabs onto the area above the wheel arches. I was surprised to learn how different a fixed rear seat and a folding rear seat car is.
My car sees regular track use. It will be interesting to see if I can feel the difference after the rear bulkhead is cut (it doesn't get removed entirely).
 

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Dougsic I’d be curious to know as well. On my e30 M3 the previous owner had cut out part of the bulkhead behind the seats for a subwoofer box. I had that replaced/repaired and it was definitely noticeable on the track (then I caged it and boy does that make a difference). The cutting however was obviously not done with any care (seriously, I think a sawzall was used), sounds you are doing it right, and it’s a totally different car.

It may only make a difference on paper; but I always feel like the folding models have a little rear seat creak when twisting, like when turning into a steep driveway. May not mean anything practical though.
 

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mattparsons Being on the east coast, I've already had 3 track events canceled due to the COVID-19 circumstances so who knows when I will get out on track again.

Yikes! I hope I don't experience what you did with your e30! My e30 convertible is laughable. I only drive it a few times a year but it makes me chuckle every time. Talk about cowl shake.

I feel like the e39 is a pretty stout platform so maybe cutting a section out of the bulkhead won't be too compromising? The car is an S2 so it has the rear strut brace. Don't know if that matters but I doubt it hurts anything. I have no experience driving an e39 with folding rear seats so this will be new to me. I figure worse case I'll weld everything back the way it was if I don't like it. I haven't tossed out the old rear seat yet just for that reason.

I will be sure to post my findings after the first event. I guess if I don't post that I can feel a huge difference, then I'm just a terrible driver, don't push the car hard enough and don't belong on any track. : )
 

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I'm of the impression that as the suspension is rubber bushed connected to a rubbed bushed subframe body torsional numbers were not that high up on the priority list for the engineers, I'm thinking comfort and road noise were much more inportant to them. I wouldn't trade mine for one with out through loading.
 

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I have never tracked my M5, so I can't really comment on the loss of stiffness due to removing the bulkhead. I can say, however, that having through-loading immensely expands the utility of the car. My M5 is my only car here in Florida, so I have used it to haul furniture, shrubs, lumber, carpeting, etc., most of which would not have fit were it not for through-loading. I can also say I have never heard any creaks or rattles from that area of the car. So you can count me as fan of through-loading.
 

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It’s a personal choice for everyone! Awesome we can all have the car the way we want that makes us happy. I like my non folding ones, even if the benefit is all in my head :D

Dougsic I know lots of people who track folding seat models and they never complain about flex, and the rear strut brace will actually be functional in your car. So long as you’re having fun who cares, right? Maybe I’ll see you at NHIS or Lime Rock if this thing ever ends (our Maine BMWCCA is tiny, so we run with NH and Boston).

I have the luxury of our x7, which is the family hauler. If I didn’t I would probably curse my non folding seats repeatedly while trying to shoehorn some large box in the trunk of the M5, they certainly are practical if you need them.
 

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mattparsons You were very correct about the added weight! The folding rear seats sections have a combined weight of over 48 pounds. Guess I'll have to fold the back section down to lower the center of gravity when on track! And if I was a REALLY good driver, I could tell if the rear seat was upright or lowered by the way the car handled, right? Haha.

I have other vehicles to haul stuff but sometimes I happen to be in the e39 when I find myself needing to transport something that just won't fit in that little trunk. So I end up moving the passenger seat all the way forward, then laying it back as far as it will go just to get something home. Thankfully my wife is a good sport and will sit behind me in the back seat. Though I have to hear, "I told you I should have driven." all the way home. (She has an SUV). I like Boomster's view that through loading will expand the utility of the car (well said by the way!)

I've never driven Lime Lock but have always wanted to. You will know it's me - I'm the guy with one hand on the steering wheel and the other out the window giving point-by's to everyone.
 
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