Opel GT Forum banner

1 - 13 of 13 Posts

·
Opel Key Master
Joined
·
5,071 Posts
Discussion Starter #1
Installing Mazda Miata Seats into an Opel GT
By: Keith Lundholm

With our factory seat facing 50 years of age, many Opel GT owners understand the frustration of having them sun baked and broken down. Aftermarket racing seats tend to be too wide and too tall to fit proportionally inside the GT cockpit. I have found that the 1990-2005 Mazda Miata seats are a great choice for the interior and have many features if you know what to look for. First off, they are plentiful. Mazda built a billion of these cars, and seats can be purchased for cheap in most cases. Many times these seats come out of a wrecked Miata that was babied its whole life. I like the 1990-97 style seats best, as they featured speakers in the headrests. If you search carefully, there are seats with a special option called the "Mazda Sensory Option". This option included not only the head rest speakers, but a back rest seat bass speaker. This allows the driver to feel the music, and it works amazingly!
429407

This tutorial is going to make it simple to perform the conversion, as I have documented all of the measurements and tools needed. First we need a set of seats, so recently I purchased a set of black leather ones off eBay. The leather was really nice on these seats, but the purchase price was $600 shipping included. There are aftermarket seat covers available in all varieties and options, so you do not have to find a perfect set, if you are going to recover them. I've purchased seats from a wrecking yard for $200 a set. You will not need the seat tracks from the Miata, but will need the bolts. If the seats come to you all together, you will want to separate the backs from the bottoms.
429408

429409

We need some flatbar steel to build our supports for the Opel GT seat tracks to mount onto the Miata bases. 1-1/2 x 3/16 flatbar can be picked up in most cases at your local hardware store's project section. I bought two sections of four foot pieces. The end result will be four pieces at 15" each.
429410
429411

I make short work of cutting these up on an iron worker. I have set these measurements to be as accurate as possible, so the hole pattern was drawn out on a layout table. My results are right on, so if your measuring is replicated, the results should end without any hole enlargement to make fit. I use Dykem layout dye on the ends of the pieces and also the center. I begin by scribing a line .375 from the base on each end. I then scribe a line at .875 above the base of the layout table on each end. This will be the spacing of the holes for all 4 pieces. Then starting about a half of an inch from the end of the bar, I scribe another line to form a cross on the .375 marked line. These will be my outer holes to line up with the Miata.From that intersecting line, I raise the caliper up .8 of an inch, and scribe the line at the .875 measurement. From the point of the first intersection, we need to raise the caliper 12.937 to mark the other end. My caliper only goes 12" high, so I scribe a center line, flip the piece, and set my scribe to the center line. I then subtract the difference from where I am at, in relation to the 12.937. I then add .8 of an inch to scribe my 4th hole. I then center punch all the holes.
429412

429413

429414

429415

Important note: The driver side and passenger side have a different distance to seat bolts. So only two supports will be made at these measurements. The passenger plates are at 13.687 between centers, and the inner hole spacing is 1.175 from each hole. Refer to the drawing for all of this info.
The intersections will need to be center punched and then drilled. I used an iron worker to punch the outer holes, but a 3/8 drill will be used on the outer holes. The inner holes will be tapped to 8mmx1.25 thread, and a 17/64 drill bit will be close enough for you to start the tap.
429416
 

·
Opel Key Master
Joined
·
5,071 Posts
Discussion Starter #2
429421

Now that you have four pieces, you can test fit onto the front seat bolt holes to determine if your work is accurate. The Miata seat base comes down too far to allow the rear seat support to be bolted on. Draw a line around this hump to remove it with a cutoff wheel. If your material on the seat is nice, you will want to wrap it up for protection. The seat foam does not need to be cut out. Be sure to allow the rear hog rings to go back into their location. We can massage that metal down so it clamps with the rear support.
429417
Bolt on the supports, and then with a punch, mark the seat track holes onto the seat frame. We want to provide clearance for these bolts. The supports work for either front or back, with the Opel threaded holes positioned outward. Once marked, remove the supports and drill out these with a 3/8 drill to provide clearance.
429418

Use the original Opel hardware from the old seats to mount the tracks onto the supports, making sure everything lines up. You can also remove the supports, bolt the Opel tracks onto them, and test fit in the car.
429419

429420

At this point, once you have both seats fitted, you can paint the supports and install your seats. Spend a little time on your original tracks to clean and lube them, and then you have modern day seats in your vintage ride!
429422
 

·
Just Some Dude in Jersey
Joined
·
14,498 Posts
I did something similar to this mod, but did not want to cut the support for the foam off of the bottom of the seat. Yes, if you don't cut some of the bottom metal, the seat belly will hit one of the seat mount crossbars. My solution was to screw the oem rails directly to the Miata seats and add 3/4" of shimming to the chosen adapter concept to lift the seat to avoid hitting the crossbar. When I did mine I was out of strip metal, so I used 3/4" red oak for the crossbars. When I do this again on my new car I will use strip metal and then about 1/2" of washers or stand offs.

Keith's design concept of cutting out the bottom of the seat will keep the relative height of the seat roughly similar to the height of the oem seats. My method elevates the seat 3/4" and keeps the seat belly intact. Folks taller than 6' should probably go with Keith's design.
 

·
Opeler
Joined
·
381 Posts
Installing Mazda Miata Seats into an Opel GT
By: Keith Lundholm

With our factory seat facing 50 years of age, many Opel GT owners understand the frustration of having them sun baked and broken down. Aftermarket racing seats tend to be too wide and too tall to fit proportionally inside the GT cockpit. I have found that the 1990-2005 Mazda Miata seats are a great choice for the interior and have many features if you know what to look for. First off, they are plentiful. Mazda built a billion of these cars, and seats can be purchased for cheap in most cases.
How thick is the bottom of the Miata seats vs. the thickness of the original seats? It seems to me that the original seats have almost nothing between you and the floor at the back part of the seat bottom. The biggest problem I've had with trying to fit updated seats is that there is nothing out there as thin on the bottom as a GT seat. I had Acura Integra seats in my GT for a while and they looked nice and provided a lot better support than the GT seats, but even with removing foam from the seat I could not get them low enough. I either had to drive with the seat forward and back reclined gangster style, or I had to hunch over while driving. I finally yanked them out and put the old GT seats back in. They may not be in good shape or be very supportive, but at least I can sit up straight again while driving.
 

·
Opel Key Master
Joined
·
5,071 Posts
Discussion Starter #5
I don’t know, but I guess I look at it like this, I have full range of recline, and full range of sliding forward and back, the top of the seat is narrower than stock, so if you have three point seat belts, you can pull it around you with the door closed, where if I have factory seats, I have to open the door back, and pull the seat belt over, then close the door
 

·
Just Some Dude in Jersey
Joined
·
14,498 Posts
You basically have 3 choices of seats that are super low and commonly available: Miata/Mx5's, racing seats, and oem GT ones. In the past I have used Pontiac Fiero ones, they sit a little higher than Mazda's, but they are hard to get. Some of those had speakers in the headrests. Personally, I didn't like the quality or the concept of the speakers in the headrests in those. The sound was muffled. I'll have to take Keith's comment on faith that the speakers and the added bass woofer in some of the Miatas are pretty good. I've heard that very early Firebird/Camaro seats fit. I'm sure there are others. Unless you are taller than 6', the seat height isn't an issue and people shorter than 6' can use any seat they want with no issues. I'm 6' and I found that angling the rear view mirror to see out the back becomes an issue if I use a seat any taller than Miata ones. The Fiero ones I used had my rear view right at the edge of acceptability.

I haven't autopsied a Miata seat, but I have had 2 sets of those and they appear to be solid foam with no wire or some other type of support within them for the foam. It appears to me that the foam is entirely supported by the sheet metal at the bottom of the seat. The sheet metal will hit the floor or the seat mounting cross rail at the front unless you boost the seat up 3/4" or do as Keith has done and cut the bottom of the seat out. I don't want to dispute his idea to do that, he does Opels for a living and fixes up many cars, so he must have experienced success with no complications. But to my eye, it looks like cutting out the bottom of the seats would leave the foam unsupported and it would eventually sag and hit the floor, unless there is some other wire reinforcement embedded within the foam to stop that from happening. With sheet metal under the foam to support it, I can't see any reason why they would have additional supporting wires within the foam.

Oem GT seats have wavy wire springs to support the foam.

Racing seats use the same concept as the Miatas and use plastic or sheet metal to support what little foam they have in them.

One of the great things about the Miata seats is that they are narrow at the top. This vastly increases the perceived room inside the car. You can easily reach behind the seats to get at stuff. The car feels much more roomy and less cramped. Racing seats often have "wings" at the top to hold crash-worthy seat belts. I tried fitting the racing style seats from my Pontiac Solstice in my GT and door closing issues and ceiling clearance became issues right off the bat and rear area access sucked. Solstices/Skys/New GT's have the same height roofs(48") as GT's and the floor is a little higher, so both cars have the same need for very low seats. The Solstice/Sky seats kinda suck in those cars because there is structure behind the seats that won't let you recline them. That said, I drove my Solstice from Jersey to Vegas and it was a wonderful drive with no back stiffness. I gave the seats to Karl Senula(I installed nicer looking seats from a Saturn Sky).

Okay, so the "height" of a seat, for our GT purposes, is defined by where the lowest part of the seat of your pants is when you are sitting on the seat. Some folks only weigh 150lbs, whereas others weigh 250lbs, obviously heavy dudes are going to compress their seats more. So, a seat that works for a 6' 250lb guy might not work well for a 6' 150lb guy because the lighter dude will sit higher. I'm kinda light at 6' 180lbs and the Miata seats, with belly metal intact and 3/4" shims, works out just right for me.

I've taken many pictures over the past 10 years, so I'll start dumping them in this thread.

The black cloth

These are the black/charcoal cloth seats currently in my GTX car.

429519


This pic shows the Miata slider rails on and removed from the seat.

429518


With the GT slider rails installed

429520


In this pic you can see how little room there is to work with. The GT rails are tight against the bottom of the seat and the sheet metal belly of the Miata seats protrudes down about 1" below the rail near the back of the seat. This is why they hit the seat mount crossbar.

429521


This pic shows the situation in a GT(Disregard the arrow). The front seat mount crossbar is 1" above the floor and the rear mounting points are only about 1/2" above the floor

429522


These are measurements I took of the rare beige leather 25th anniversary edition Miata seats I had in my previous Red Baron GT. In this pic, the seat is sitting on a table with 3/4" wood blocks, like I use on my seat installs, to boost the belly of the seat off the table. This is where my concept positions the seat from the mounting points in the car. Keith's concept cuts out the seat belly, so the seat sits about 5/8" lower. I would think that the foam MUST hit or rub against the floor using his concept. But how much do you really move your seat back and forth? Once your seat is in position, who cares if the foam belly touches the floor or crossbar? If the foam is actually touching the floor, well, then it's supported, so my previous comment about the foam sagging if the belly metal is cut away is moot.

429523


This picture shows a measurement of the seat of your pants lowest part of the Miata seat with no weight on it that you can reference with the above pic to guesstimate how high the lowest part of the seat is from the floor. The table is basically where the seat bolts to the GT mounting points:

429524


This picture shows the height of the seat back measured to the floor:

429525
 

·
Just Some Dude in Jersey
Joined
·
14,498 Posts
These are the Pontiac Solstice seats I tried to fit in the car. They are basically the same shape and height as the racing seats you can buy, but they are a bit more sophisticated than most and can be reclined, elevated, slid back and forth, etc. They don't look that much different than the Miata ones, right? They were freakin' HUGE inside the GT. The charcoal Miata seat is on the passenger side for comparison.

429526

429527
429528
429529


This is a pic of my beige leather seats in the 2000se Mazda MX5 they came out of:

429530


In my GT:

429531
429532
429533
 

·
Registered
Joined
·
600 Posts
One addendum of trivia...

A popular mod for Miata seats for taller drivers is a "foam delete". You scoop out some of the foam so you sit lower.

You could keep the foam support and the ride height by doing both a partial foam delete and a shim.

Just food for thought.

... I love the idea of Miata seats having the speakers in them. Two birds with one stone. I like how they're slimmer too.
 

·
Just Some Dude in Jersey
Joined
·
14,498 Posts
Good info! There's about 3" of foam at the "seat of the pants" location and it looks like removal of the foam pad and some foam reduction would be fairly easy, if tall drivers felt the need.
 

·
Registered
Joined
·
124 Posts
I wonder if Ibuy a pair of seats and the drivers side is worn, is new foam available ? I sure would hate to have a set recovered and have lumps (bun marks) in the upholstery/
 

·
Just Some Dude in Jersey
Joined
·
14,498 Posts
I decided to do the calculations of how far from the seat mounting points the lowest part of the Miata seats' are. This is what I have been calling the "seat of the pants" point.

I looked at this pic and figured that ZERO on the tape measure is approximately at the bottom of the seat handle:

429538


.....and then this pic showing that, with 3/4" shims, the lowest part of the seat would be 4" away from where the seats mount to the floor:

429539


So, without shims, the lowest part of a Miata seat is 3 1/4" from the rails that the seat mounts to. And the sheet metal belly of the seat hangs down about 1" below that point.

So, now we have a metric to compare to. Someone else will have to measure and oem seat and calculate where the lowest part of an oem GT seat sits in relation to where the seat mount frame rails on the floor are.
 

·
Just Some Dude in Jersey
Joined
·
14,498 Posts
They seem to be made of very high quality foam that resists staying compressed. Neither of the 2 pairs of used seats I have show much if any evidence of "bun marks".
 

·
Registered
Joined
·
611 Posts
My Miata seat mounts are 1/2" thick and I have full travel of the seat without any modification of the seat pan.
 
  • Like
Reactions: The Scifi Guy
1 - 13 of 13 Posts
Top