Installing BMW E46 M3 Seats in K5 Blazer

Anyone with the original front seats in their Chevrolet K5 Full-Size Blazer knows that they’re not the best seats. This blog post was going to be the first blog post I made on this site, however, I held off hoping to fix an issue with the drivers side so that I’d have accurate information. The problem is that the original seats in my 1988 K5 are not mounted the same distance from the center, or from the doors (depending on how you want to look at it). I had wanted to fix that before making this post, but I have not been able to spend the time to do so. It’s possible that I’ll have a follow-up part 2 to this post.

These seats are awesome and worth all this effort!

I got this idea from the very knowledgeable and entertaining James Merrick of Merricks Garage YouTube Channel, from this video where he talks about putting BMW seats in his K5 (starting around the 4:50ish mark). He also put a rear seat from a Escalade in his K5! Subscribe to his channel, I’ve learned a lot from him.

What Seats to Look For:
You want BMW E46 M3 Seats from a 2001-2006 M3. Note that M3s are coupes, meaning 2 door. M3s also have manual seats as the M3 is a performance car.

I started the project by searching on Craigslist for the seats. I searched for various phrases like “parting out BMW M3”, etc. Not knowing much about BMWs, I made a big mistake. I found a local guy parting out a wrecked BMW sedan with a M3 “package”. This is not the same thing. It’s a sedan which is 4 door. The seats did not fold forward!

The seats we want are from a 2 door coupe and will fold forward. What’s more, they even lift up like the original passenger side seat on the K5 Blazer (but not quite as much). The original driver’s side seat on the K5 did not lift up, so this seat upgrade fixes that: both sides will fold forward and lift up to make accessing the back seat from either side easier.

So I had to sell the sedan seats I bought (I hate making stupid mistakes). While I was doing that, I found the correct seats, even in gray to match my interior. The seats I found were in excellent mechanical shape, but the leather on the driver’s side was worn and torn, but not bad enough to bother me. I paid $150 for the pair.

I assume that you could work out the wiring details and install electric seats, but I really like the way the manual seats work.

Brackets:
The hard part is fabricating the brackets. I made lots of measurements and sketches. I was finally confident enough in my measurements to get a local machine shop to make the brackets. I used 3″ channel that has an approximate 1.3″ flange. They boxed in the ends of the brackets with 1/4″ steel. I also had them cut up shims out of 1/4″ steel and 1/8″ steel. These shims are 2″ long x the same width as the channel flange. I used 3/8″ grade 5 bolts, so I had to drill 7/16″ holes in all this steel! Not easy. I had some more shims made up and they “cut” the holes this time – the machine shop I used cut out the shims from 1/4″ sheet steel with their laser and also cut the holes the same way.

The BMW seat’s mounting rails are not positioned the same as the K5 original seats. The outside rail of the BMW is out farther, where the K5’s seats have the rails the same. This makes it a little confusing. Adding to this, the inside mounting rail on the BMW seats is longer by about an inch.

The 3″ channel I used is overkill and I’m sure you could use a lighter stock the same size, but that’s what the machine shop had.

Asymmetrical:
You know where assumptions will lead you! I assumed that if I made all my measurements and plans based on the passenger side seat, then I’d just need to reverse them for the driver’s side. Wrong! At least on my K5, the driver’s side seat is closer to the door by about an inch than the passenger side seat. Even more confusing, the spacing (distance) between the holes between the two sides is slightly different. So if you follow my plans, please double and triple check the measurements to make sure they make sense for your vehicle.

I had planned on using the original mounting holes to mount the inside brackets to the floor, and drill new holes for the outside brackets. This is what I was referring to in the opening paragraphs. When I started working on mounting the brackets on the driver’s side I realized my mistake. So far I’ve lived with it, but I really want to go back and move the driver’s side seat in towards the center between 1″ and 1.5″.

The problem with this is that the floor of the K5 is not really flat (hence the large number of shims used). It has stamped channels and ridges, etc. I think from what I’ve eyeballed that when I move the brackets in, I will have the mounting hole at the rear of the outside bracket over a non-flat area. So I’ll either need to move the rear mounting hole forward or backwards to get to a flat spot, or, build a short (4″ or 5″) “bridge” out of the same 1/4″ steel that the shims are made from. If/when I do this I’ll make a second post with all the info.

The other possible issue moving the driver’s side seat in could be the inside bracket. I’m using the original mounting holes and would need to drill new holes closer to the center. I’d need to verify that there’s not a problem there as well with non flat parts of the floor, or some other interference.

The only issue caused by this is the right seat bolster digs into my right leg a little more than I’d like.

Safety:
Drilling 7/16″ holes in 1/4″ steel is best accomplished with a drill press with the part being drilled in a clamp, vice, etc. You will want to get new cobalt drill bits! However if you don’t have a drill press, you can use a hand drill as I did. In either case, it’s best to drill a 1/8″ pilot hole first for accuracy and to make it easier. Luckily I have 2 drills, a regular hand drill, and a larger one with a side handle. I used the larger one for the 7/16″ bit and it’s side handle helped control it when it would grab. This could potentially break a finger or wrist if you didn’t have the side handle!

Parts List:

Brackets
- 3″x 1.x” channel 17 3/8″ long, quantity: 2
- 3″x 1.x” channel 18 3/8″ long, quantity: 2
- Note: the above lengths INCLUDE both ends of channel being boxed in. You can box in or not, but make sure the final length is as shown, or all other measurements will be off.
Shims
- 2″ x 1.x” x 1/4″, quantity: 22
- 2″ x 1.x” x 1/8″, quantity: 6
- These quantities are exactly what I ended up using, but I’d make extra so you can adjust as needed.
- Obviously you could use 1/2″ or even 1″ thick shims and reduce the large number of 1/4″ shims used, but drilling that would definitely require a drill press.
Bolts, Grade 5 or 8
- Bottom of Bracket (mounting to floor)
  - 3/8″ 1.5″ long, 16 thread pitch, qty: 4 (these are for use in the original holes)
  - 3/8″ 2.5″ long, 24 thread pitch, qty: 4 (outside)
- Top of Bracket (mounting to seat)
  - 3/8″ 1″ long, 24 thread pitch, qty: 8
- + Flat washers, Blue Loctite (I used Loctite vs. lock washers)

Basic Procedure:
If you notice from the drawings, I tried to drill the holes in the bottom of the inside bracket offset to move the seats out a little (this was before I realize the issue with the driver’s side). I don’t know that this is really necessary. I was concerned that they’d be too close to the console. In reality, because of the curve of the metal on the inside of the channel brackets, I could only gain 1/2″ at most.

I made 2 “jigs” from scrap wood (see photos) with holes the same distance apart as the left and right mounting holes from the bottom of the BMW seats. These I used to verify the distance between my brackets when marking holes for the outside brackets, and to help with leveling.

My work area (carport) is pretty level, so I could use a level and adjust the combination of 1/8″ and 1/4″ shims and get the brackets level and square (required patience!).

I cut the carpet and padding out from under the positions of the outside brackets so that I’d have good solid contact with the floor. The inside, since I used the original mounting position was squashed flat and hard from being compressed under the original brackets since 1988. I also think the padding was pre-cutout from under the original mounting brackets.

I Drilled the holes in my brackets and shims (verify the spacing of original holes for bottom of inside brackets)
Cleaned and painted all the steel
I marked the center of the original seats on duct tape on the floor
Removed the original seats
Temporarily mounted the inside bracket on passenger side
Used “jigs” and square to position outside bracket and mark hole positions
Verify hole markings look square
Drill outside holes
Cut out carpet under shims on outside
Play around with shims to get brackets level, etc.
- Final shim configuration
- Outside Front: 5 x 1/4″
- Outside Rear: 4 x 1/4″ + 1 x 1/8″
- Inside Front and Rear: 2 x 1/4″
- Under body Outside Bolts: 2 x 1/8″
Mount brackets
Mount seat
Move to driver’s side and basically repeat.

The nice thing about this setup is that if you want the seats to closer or farther away from the steering wheel or dash, you can drill another set of mounting holes on the bottom of the brackets.

Drawings with measurements: BMW-E46-M3-Seats-in-1988-Chevy-K5-Blazer.pdf

Click image for larger size…

BMW E46 M3 Seats from a BMW M3 2001-2006. MUST BE 2 DOOR COUPE, or else seats will not fold forward. They lift up almost like the original K5 passenger seat, although not quite as much, however now both drive and passenger sides will fold forward! The M3's have manual seats, however other coupes have an "M3" package and will have either manual or electric seats. I advise sticking with manual!

Marking center of original seats with tape on carpet.

Passenger seat out!

These are the 4 brackets.

If you don't have a drill press, then use 2 hand drills to make it faster. Or, get the machine shop to drill the holes for you.

Drilling holes in the shims... drill a small 1/8" "guide" hole first to make drilling the 7/16" hole easier and more accurate.

Use a drill press, or, a larger hand drill with a side handle so that if/when the drill bit catches it does not break your hand/wrist/etc.

Some of the drilled shims

Two of the drilled brackets for one of the seats

I primed and then painted the brackets and shims to match my interior.

I used the original inside mounting holes, and made some "jigs" (2 scrap pieces of wood with the correctly spaced holes marked directly from bottom of BMW seats) to make sure I marked the outside holes in the correct places.

Holes marked on tape

After I drilled the outside holes, I cut the carpet out under where the shims will go.

Brackets mounted to floor on passenger side.

View of outside bracket bolts/nuts/washers/shims from under the truck. I used 1/8" steel the same size as the shims for reinforcement.

Remove all seat belt and extra hardware from BMW seats.

This part contains an explosive cartridge similar to a shotgun shell... don't apply voltage to the leads! It is used to tighten the seat belt when the BMW sensors sense an impact.