BMW M5 Forum and M6 Forums banner

1 - 15 of 15 Posts

·
Registered
Joined
·
231 Posts
Discussion Starter #1
Even though I regularly track this car, I sometimes use it as a DD too and have wanted rear folding seats for some time. I searched on line but couldn't find much information about converting my non folding rear seats to folding seats. And so the project began.

From this:
940343


and this:
940344


to this:
940346


and eventually this:
940347


and this:
940348


The project took more effort than I expected. In fact, at one point early on I decided it wasn't going to work so I threw the fold down seats in my dumpster at work on a Thursday. Over the weekend I reconsidered and climbed in my dumpster on Monday morning to retrieve them.

I'm SO glad I did.

No rattles, the car isn't any louder inside than before and now I can take my neighbor who uses a walker to the store when he needs to go. Before we had to take my truck because there wasn't enough room in the trunk even though his walker folds up (somewhat). Other than the added weight (and it's a lot!), there is no downside for me and I couldn't be happier with the outcome.
 

·
Registered
Joined
·
318 Posts
I think you just need a donor car, so you can cut out the required sheet metal and take the interior trim. Then it is just a matter of seeing how it is put together in the donor car and reproducing it in your car.
 

·
Registered
Joined
·
238 Posts
I think you just need a donor car, so you can cut out the required sheet metal and take the interior trim. Then it is just a matter of seeing how it is put together in the donor car and reproducing it in your car.
Sounds really simple, have you done it yourself?


Sent from my iPad using Tapatalk
 

·
Registered
Joined
·
231 Posts
Discussion Starter #8
Wow. Do you have anymore pictures while in process?
I do.

Thanks to my good friend Gabe for generously donating his M5 so I could cut out the body panels I would need.

940382


When I started this project, I wanted to see if it could be done by a DIYer with minimal tools. Meaning no plasma cutter, no TIG welder and even no MIG welder if possible. I thought maybe I could use 3M Panelbond instead of welding, a DeWalt cordless cutoff tool, a jig saw, a cheap spot weld cutter and hand tools. Well, that didn't last long.

First thing to go was the ebay spot weld cutter, replaced with a Blair Premium Spot Weld Cutter kit. Best $36 you can spend, even if you only use it on this one project.

940389


I started by cutting out both side panels as seen above. The parts I needed from this panel is the seat pivot point bracket at the bottom of the panel and the bracket that locates the top of the outer most seat. I thought about just cutting off these brackets but by removing the entire panel, I could locate the brackets exactly where they need to go. Also, by attaching the entire panels over the existing ones in the car, I effectively doubled their thickness. More on this later.

This bracket had to be removed from my car on both sides:

940390


Seen here removed:

940391


Then I was able to test fit the panels before cutting out the rear bulkhead of my car:

940392


Not only is the rear bulkhead different on a Fold Down car, the floor pan is different too. The factory installs a four bolt bracket in a trough beneath the floor for a Fold Down car. Of course my car didn't have this bracket. The purpose of the bracket is to locate the center pivot for both folding seats. Here is a picture of the trough cut open revealing the four bolt bracket:

940394


It was at this point that I had to decide if I was going to proceed with the project or abandon it. I wasn't ready to cut out the floor of my car just to have folding rear seats, so this is when I threw the seats in my dumpster. Thankfully, trash pick up wasn't for four more days which gave me enough time to reconsider my decision.

Coming up: The discovery that lead me to forge ahead, more pictures and a mistake I made.

Thanks to everyone for the kind comments. I appreciate you.

Doug
 

·
Registered
Joined
·
231 Posts
Discussion Starter #10
I apologize that some of the following photos will not be in the sequence that the work was done. I failed to take some pictures as I went along so we will have to jump around a bit. Sorry about this. Starting with the first picture below.

As mentioned previously, a fixed rear seat car doesn't have the four threaded mounting holes in the floor that secure the center pivot bracket for the seatbacks. But wait! In the picture below you can see two threaded holes. I wondered if these holes were in the right place for the center pivot bracket?

941206


Before the above picture was taken, I test fit the seat and the brackets to make sure that this was going to work. You can see in the picture below, I hadn't even cut the rear bulkhead yet because I was still unsure. I did cut out a piece of the bulkhead where the seat latch mounts and discovered that behind the bulkhead, the inverted U shaped cutouts for the bracket are already there! Also there is the pocket that the bracket mounts beneath and the pocket is slotted which allows adjustment of the latch. In this picture, the top of the bracket for the latch is sticking up through the pocket. It isn't painted and I haven't welded it in place yet.

941208


The next step was to cut out the bulkhead. I drilled a hole through it to see where I was in the trunk. I decided to cut the bulkhead about 3/4" higher than the trunk floor for two reasons - I wondered if I might need to fold the 3/4" lip over into the trunk to fill any gap thus creating a smooth transition to the trunk and secondly, if I didn't need this lip it would be easier to cut it out later rather than to weld it back in. Keep in mind that at this point, I didn't have any of the interior panels so this was a lucky decision rather than a smart one. Later, when I bought and installed the carpeted trunk panels, the trunk floor panel raised the height 3/4" which was exactly the height of the lip and everything lined up perfectly. Beginners luck!

Also in the picture below you can see the two center pivot mounting holes (with the bolts threaded into them) and the pivot bracket laying on the floor. And you can see the factory inverted U shaped cutouts. I only had to drill out one spot weld and cut through one layer of the bulkhead to get to them. Sweet!

I used a cheap jigsaw to cut out about 1/3rd of the bulkhead still thinking this project may fail so this way, I would only have 1/3 of the bulkhead to weld back in.

941212


The next step may have been the worst of the entire project. BMW used seal sealer EVERYWHERE. Scraping the seam sealer off is no fun! It took me hours to get to the bare metal you see in the above photo. I probably broke 25 razor blades trying to scrape it away. I heated the seam sealer with a heat gun and a torch. I froze it with CO2. Nothing helped. To get the metal clean for good adhesion, I tried various 3M Roloc discs, sanding discs and even a grinder. Adding to the problem was the time I wasted repeatedly vacuuming the car clean. I should have waiting until everything was done but my OCD would have nothing of it.

How to attach the side brackets? At this point I am still trying to see if this work could be done with a minimum of special tools. My plan was to use 3M Panelbond adhesive instead of welding as anyone can apply it. But how do you "tack" a panel with adhesive? I hadn't thought about that! What if I needed to cut a tack welded panel loose and move it?

There are two holes on each side of the factory bulkhead that I have no idea what they are for. They are located just below the bracket that I'd cut off earlier. You can clearly see them in the above photo - I've ground all of the paint off around them. I positioned the new panel where I thought it needed to go and amazingly, one of the holes lines up perfectly with a hole in the new panel. I used this hole as reference point and it worked great.

I clamped the first panel in place and at this time I decided welding was the best way to go. Maybe adhesive would have worked but I wasn't going to take the chance. Sorry about that!

Since I was going to MIG weld everything, I was very nervous about welding splatter so I used welding blankets to protect the back window and the door.

941213


No turning back now! With the passenger side panel welded in place, I finished cutting out the bulkhead. I usually work with cutoff wheels but I was very impressed with the jigsaw. It worked great! And it made a lot less mess than a cutoff wheel would have.

941214


After attacking more of the toughest seam sealer known to man and sanding to bare metal, I welded the driver side panel in place and ground down the welds where needed. With cutting, grinding and making more mess over with, it was time to begin assembly. Finally - the fun stuff.

The next and final installment will be a couple of pictures, the lessons I learned, how much weight was added, impressions after driving the car on two tracks for numerous days and revealing the mistake I made so that you won't.

Thank you to the forums members who PM'd me asking questions. I appreciate your patience and your interest in my little project.

Doug
 

·
Registered
Joined
·
231 Posts
Discussion Starter #13
I apologize for taking so long to finish this writeup. COVID-19 has us busier than ever at work and somehow I managed to get in 10 or so track days with the car this summer.

The folding rear seat back adds more weight than I would have guessed. The fixed rear seat back weighs 19.75 pounds. The folding seat back is in four pieces. Here are their weights:

lateral trim panel, left - 2.36 lbs.
folding seat, left - 15.32 lbs.
folding seat, right - 29.63 lbs.
lateral trim panel, right - 2.34 lbs.

That's a total of 49.65 pounds versus 19.75 pounds. And yes some of that weight is higher than the center of mass. How does this affect the handling of the car? I can tell you that I can't feel any difference at all. This car has Bilstein B16 coilovers and I run R888R or Proxes RR tires on track. The rear bulkhead that I cut out weighed 5.9 lbs. and the insulating trunk carpet that was removed weighed 1.85 lbs. but those weights were offset by the panels and brackets I welded in along with the new plastic trim pieces. I thought I would lay the folding seats down to get their weight lower in the car when on track but as you can see below, with the Schroth four point harness I use that wasn't possible:


945730



Speaking of welding, I tried to be careful with the heat because I didn't want to compromise the undercoating on the back side. I had removed the inner fender liners just to make sure the coast was clear but I don't think this was necessary. As you can see below, I only affected the undercoating in two small areas. I've since sanded these areas, primed and then painted them. And reinstalled the inner fender liners of course.


945729



My excitement as I neared finishing this project lead to my biggest mistake.

After diligently vacuuming every nook and cranny and wiping down every surface in the back of the car, I bolted the seat belt receptacles to the floor and installed the rear seat bottom. Wahoo! Finished! I flopped the rear seat backs down and drove around that way for several days happy that I now had rear fold down seats! It is a little bit louder in the car with the seats folded down but I think the Dinan exhaust exacerbates the sound. When I finally lifted the fold down seats, I discovered the seat bottom for the fold down seats is thinner to allow the seat backs to lay flat. Why does this matter? See below:


945731



I had reused the seat belt receptacles from the non folding seats and because the are too tall, they left huge imprints in my beautiful seat backs! 😢 I had been so careful throughout this entire project only to make a glaring mistake in the end for everyone to see!

Thankfully Gabe had left the correct seat belt receptacles in his car. They had turned pink but I was able to clean them up on my buffing station:


945732



The correct seat belt receptacles installed below:


945734



The above picture was taken four months ago when I finished this project. I am happy and relieved to tell you that the imprints are now gone. Whew! The seats do not rattle at all, the car is as quiet with the fold down seats in the upright position as it ever was and I can fit two EZ-Up canopies in the back with the seats folded down. Unlike some other projects I've dreamt up, this one worked out great and I am very glad I did it.
 
  • Like
Reactions: neilb62

·
Registered
Joined
·
937 Posts
Very impressive work - kudos to you!
I was always wondering if this was possible, but was told it was "impossible".
So I bought a E63 station wagon for those days when I need speed and space!

:D

Your solution is better, nicer, much more innovative, and frankly, much cooler.
 
  • Like
Reactions: dougsic
1 - 15 of 15 Posts
Top