Installing BMW front seats + DIY speaker pod info

[BrennWagon]

I’d been wanting to reupholster my seats in leather and after a failed attempt with seat covers that had no hope of ever fitting started searching for a good set of leather seats. After a few months of searching, I picked up a pair of power heated seats from a 2002 BMW 325i from a BMW specialist for $100. The guy was kind enough to snip the wiring harnesses out of one of his donor cars, but that car didn’t have the wiring for the seat heaters, so I’ll have to assemble my own harnesses. The following is the process I took to adapt the seat bases, including my failures.

 

[BrennWagon]

After taking measurements, I got it in my head to make a swivel for the drivers side from 13 gage sheet steel and some 1/8” steel flat stock. Everything went great until I welded the bracing to the sheet, causing warping. I’m putting the swivel on the back burner for the moment, I’m fairly certain I can make it work with enough judicious use of a 4lb hammer and a bit of trimming

 

[BrennWagon]

I decided to move on to the passenger side, since this is my daily driver. I first attempted mounting the seat on the black steel base that attaches to the seat base using angle iron and some flat stock, however I forgot to take any pictures of this setup installed. This put the seat about 5” too high, so I scrapped that plan and went back to the drawing board. The Mrs is 5’2” and can hardly touch the floor when seated as is.
Pictured is the hopelessly tall setup after removal

 

[BrennWagon]

I made a frame from 1”x2” 13 gage steel squared tubing (old storm door display frame from work). This bolts down to the factory seat base, gets the seat to the proper height, and provides clearance over my auxiliary battery. To these 3” wide pieces of 1/8” steel are bolted with 5/16” grade 8 bolts and flanged jam nuts, then the seat is bolted to the plates in the same manner.

 

[BrennWagon]

Adapter base pictured. The base measures 19” long by 16”wide. The BMW mount needs Holes to be 18” center to center side to side and 14.5” back to front. I lined up the front edge of the seat tracks with the front of the adaptor plate. The seats are offset towards the outside, so simple centering isn’t the answer. I offset the outside bracket 2” and the inside at 1”, centering the seat pretty well. My notes on dimensions are attached as well, please forgive my handwriting, I have a neuromuscular disorder and penmanship has never been my strong suit.

 

[JonnyBoats]

WOW! You did an excellent job!

I'm curious how the comfort is compared to the original MB seats?

 

[BrennWagon]

After spraying a coat of flat black enamel on the brackets, I hit them with Rustoleum Leak Seal, a rubberizing spray paint. I’ve used this product with excellent results and it should soften the inevitable shin bangs. While the paint was drying, I pulled the armrest from my stock passenger seat and installed it in the new seat. I drilled into the steel frame in the side of the seat back and drove the stock bolts right on in. Remember to pull the spacers from your old seat and put them on the new one.
I’ll be pulling the passenger seat again this coming week to swap with the finished base and will be sure to document the process, then I’ll finish off the prototype and install that on the drivers side

 

[BrennWagon]

WOW! You did an excellent job!

I'm curious how the comfort is compared to the original MB seats?

Thanks. I’ve only sat in it to check fit and to make sure that the adjustments wouldn’t put the passenger too high or low (seat height is adjustable). That said, the seat is a bit more sculpted than the stock seat and felt pretty good. I’ll be able to give comfort opinions after I get the drivers seat squared away, hopefully this coming week

 

[Perce]

Good job ??

 

[full metal racket]

Did you make those 6x9 speaker door pods? I really want some but not sure how to tackle building them from scratch.

 

[BrennWagon]

Did you make those 6x9 speaker door pods? I really want some but not sure how to tackle building them from scratch.

I did. They’re made from a number of layers of particle board that I glued and screwed together, wrapped with vinyl, and screwed into the inner door panel. If I were to do it again, I’d do a better job matching the contours of the door panel to pull them forward a couple of inches. They’re Kenwood 4-ways and are a bit on the deep side at almost 4” but don’t significantly intrude on knee room. I have a matching pair in the side walls behind the doors and some Kenwood 2-ways the factory location with bass blockers wired in, all running through a small amp to balance the system. With the head unit I’m about $400 in on my sound system and I think it’s worth every penny, and as I tell the mrs, I always could’ve spent a whole lot more.

Here’s a quick primer:
Take a sheet of cardboard and lay out the shape you want as the base. This will be your template for the first layer. I went with a sort of egg shape.
Cut the first layer to your template, then lay out the next layer the same way, tapering your layers if you want. Continue in this manner until the desired thickness is reached, then cut out the centers of each layer to the template for the speaker cutout. Drill some pilot holes in each layer, use a quality waterproof woodglue (Titebond 3) and screw the panels together.
Once you have the layers firmly together, smooth the layers on a stationary belt sander or with a hand rasp if you don’t have a good reason to have one (I’m sure you can think of dozens of uses for a stationary sander if needing to justify a purchase).
After the outer surface is smooth, there are a number of ways to finish the pod. Wrapping with vinyl cloth is a quick and easy way to to it, primering and painting the particle board itself is another good way to go, a heat shrink vinyl wrap could be nice, be creative. To wrap with Vinyl cloth you’ll need a staple gun and 3M 90 spray adhesive. Play with the vinyl to figure out how you want it to lay and where your seam will be, then staple the edge down, spray the adhesive on the pod and the back of the vinyl, wait a few minutes and stretch the vinyl around the pod. Fold the loose edge under and staple it down. Trim the pod and pull and press the vinyl anywhere that it’s still loose, folding the edge over the mounting side. Then pull your door panels, mark where your pass through hole will be and cut it out. Mount the pods to the doors with plenty of pan head screws, run the wires, remount your inner door panel, attach wiring and mount the speakers in the pods and away you go

 

[BrennWagon]

I managed to mount the finished seat base and passenger seat permanently. I also shifted my Aux battery tray over a bit before starting. I’m also in the process of redoing my aux electrical system, so please forgive the mess of wires. I had already run the wiring for the seats through the ugly fuse box with 30A fuses but that’s going to change soon.
All nuts and bolts have a grade 8 rating.
I bolted the sides of the box to the factory base using 8mm 1.25 pitch cap bolts, three per side.
I then bolted the adapter plates to the top of the box using 5/16-18 flange bolts and flange jam nuts on the outboard side and cap head bolts with the same nuts on the onboard side, two per side. After everything was securely bolted down I attached the front and back of the box with No. 8 sheet metal screws through predrilled holes.

 

[BrennWagon]

The next step is to set the seat on the plates and plug it in. The seat needs to be moved fore and aft to access the bolt holes. 5/16-18 flange bolts and flanged jam nuts used again, two per side. I attached the seatbelt anchor with a 10mm hex bolt through a previously unused anchor point. I’m going to have to make up a bushing as the Mercedes seatbelt attachment has a larger hole.

 

[BrennWagon]

Attached are photos of the range of motion of the seat. Way more adjustable than the stationary stock seat One bonus is that I have excellent access to the under seat battery area with the seat in place and look, map pockets!! I will definitely have to make a cover and I’m still waiting for for the seat heater control switch to arrive but I’m pretty sure that I have the wiring figured out. I’ll probably wire up a temporary switch to test things before too long.
I trimmed, rounded, sanded, and painted the other base setup today and will be sure to give good dimensions before getting too excited and putting in the drivers seat

 

[BrennWagon]

I’m working on wiring all of my accessories through this box that I’m mounting to the back of the passengers seat base. I’ve drilled and tapped for 10-24 bolts for easy mounting. The box has brass threaded inserts for heavy ANL fuses that I’m using as lugs for connections and made a bus bar for the main power connections. It’s a neat little box.

Niome 18-way Blade Fuse Holder + 10-way Relay Socket Box Dust-proof for Car Automotive Marine https://www.amazon.com/dp/B07R2879FC/ref=cm_sw_r_cp_api_i_cuBWEbG6BX0HG

 

[BrennWagon]

I got an early start today and mounted my drivers seat on the mounting plates that I’d prepared. Disappointment occurred as soon as I plopped my butt down in the seat. I didn’t have it centered right and was offset inboard an unacceptable amount. So I got to work on the swivel base. A few judicious whacks with a mallet put things better, then I put a thin piece of nylon or HDPE (thin cutting board) between the plates as a bushing and trimmed down the top flange a bit. This allowed the plates to rotate as intended.

 

[BrennWagon]

The swivel base attaches to the box that I’d made. I drilled mounting holes into a piece of 3/4” x 1/8” steel that I attached to the underside of the top of the box with VHB as I’d made 1/2” clearance holes in the top of the box frame for the cup head bolts to attach to the base (visible in the naked base picture in the last post). I used flat head grade 8 5/16-18 bolts to attach the swivel base to the box with flanged jam nuts and the seat to the top swivel plate. The assembly is stabilized by 2 5/16 bolts screwed into lawn mower adjustment handles. The outboard one is into a nut welded to the underside of the base plate, the inboard one tapped into the crossbar. Stability when locked down is excellent. Rotating the seat requires a bit of a dance of moving the seat back and forth but it’s effective. I was thinking of mounting an outboard armrest, but I’m not sure that it would clear. Perhaps I’ll get that figured out perfectly if there’s a next iteration of the design.

 

[BrennWagon]

Attaching the armrests requires drilling into the side of the seat frame. Removal of the seat back is necessary at this point. The seat skin is held into the fiber board back plate by a gasket. Pull it out by using a flat bladed screwdriver to pry out the bottom, then gently pull it out of the groove. There are plastic push pins that hold the bottom of the back plate to the seat frame. Prying them out is the only way and they’ll look ugly.
To mount the armrests, use a 17/64” drill to make pilot holes into the seat frame, starting with the drill spinning backwards to pierce the leather and batting. Go back and forward with the bit to clear the batting, then once you’ve touched metal, drill through. The bolts are self tapping. I used a flat head screwdriver bit to drive them in for thread cutting, then pulled them out and used the Allen wrench for final mounting. Don’t forget to put the spacers in. Pictured is the location I chose for the rear bolt. It’s a little bit higher than the stock position, but I like it.
While I was in there, I put my lumbar support air bladder in. I slipped it between the wire frame and the foam of the seat back and ran the bulb out towards the seatbelt catch.

 

[BrennWagon]

Pictured is the finished (for the moment) product. The seats are definitely comfortable, although I think I’ll put some spacers under the front of the drivers seat mounts, as the bottom cushion rises up and down but doesn’t tilt.
I still need to give the seats and seat mechanisms a thorough cleaning. I wiped down the leather and exposed rails before starting but got em a bit greasy and dirty in the mounting process and once I put power on and opened the mechanisms I found an awful lot of ash and bits of cellophane.
Overall, I’m pretty satisfied with how this worked out but I’m sure that I’ll tinker with things as I go. Once I have the switch I’ll write up the wiring. Main power is the big red wire, big brown is ground on the seat plug, heater wires have been located but not tested yet.

 

[BrennWagon]

After a couple of weeks of use, I’ve made a couple of observations. The first is that these seats are significantly more comfortable than the stock seats. Pretty good lumbar support with my air cushion fully deflated, only need a couple of pumps to get the right support. The second observation is that having a passenger seat that can move forward significantly makes loading the kids in a lot easier (One on a booster seat, one in a car seat). I can get past with kids strapped in now without squeezing, and I’m pretty skinny. The third observation has made me a little irritated with myself for having already installed the arm rests though.
Due to the forward location of the seat switches, every time I lean over the seat to grab something from the cab, my leg hits a button. The solution is to swap the seats side to side, which I plan to do soon. I made up yet another set of brackets to attach to the inboard side of the box frame to get the seats properly centered on the steering wheel. I’ll have to bump out my Parking brake handle a bit, but that looks like a pretty simple spacer addition should do the trick. I’d like to have arm rests on both sides of the seats, but for now I suppose I’ll just have to pull them and install them on the opposite sides and just put some bolts in the holes I already made to make that look less crappy for now. I also made some bushings/spacers for the seatbelt bolts to properly adapt to the 10mm 1.25 pitch BMW bolt holes.
And I also added a powered 10” subwoofer to the drivers door and temporarily wrapped it with vinyl to make it less glaringly obvious
Seat heater switch has arrived and I’ve got it pretty well figured out, but I’m going to have to step up the voltage coming from the control switch by 2 volts to work with the BMW’s temperature control unit which operates at a range of 2-3.5V. I’m pretty sure a 2v step down transformer wired in series on each control circuit and powered by the relay should get me where I need to be