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Recently I had the opportunity to bid on eBay for a set of
Mazda MX5 seats and subsequently won the bid at a very
reasonable price.
My interest in the seats had been as a result of an article
some time ago in the Chicago Chapter of the MGCC online
site, detailing one member’s adventures in fitting a set
of Mazda Miata seats to his MGB roadster. My own
roadster, a ’68ish Australian built MK II with Overdrive
and dubious pedigree, was fitted with an equally dubious
pair of seats looking similar to those I remember in my
73 model GT way back in the late seventies. A number of
holes had been drilled in the floor pan to accommodate
these seats, the original mounting points being of
incorrect dimensions and location to cope with the
mounting hole pattern of the seat rails. I managed to
source a set of very average MGB MK II seats but they
were going to cost far in excess of what I was prepared
to pay to refurbish.
Enquiries through local (Queensland) second hand dealers
failed to bring to light a set of seats; apparently they
are very popular items and are snapped up quite quickly.
An importer in Adelaide advertises sets for $400 plus
freight, however, last enquiries; the price was around
$600 and climbing…
The article on the Chicago site has since disappeared; I
guess the legal side of following advice of such a
nature may have certain ramifications so I offer my
experiences as just that. If you intend to follow a
similar path as I did then find a mechanical engineer to
endorse the modification to your vehicle. I cannot
stress the importance of using high tensile bolts to
mount anything you are strapping your butt to. The
mounting holes for the seats in my MGB are tapped ¼ UNF,
any decent hardware or parts supplier will carry a range
of high tensile UNF and UNC hardware. Use nyloc nuts –
100’s of aircraft manufacturers cannot be wrong. Using
those original mount holes, to me, is critical -
someone, somewhere, sometime, designed that part of the
car to safely mount the seats to, using any other points
is compromising the structure of the vehicle and,
ultimately, putting your safety and the safety of your
passenger at risk.
The MX5 seats fit easily providing some reasonably accurate
engineering is carried out, they are very comfortable
seats, the comfort level in the MGB, particularly in
hard cornering, increased dramatically. I had read
reports that the MX5 seats were much preferable over the
standard seats for touring; having done the conversion I
can well believe that.
The original article made it sound so easy – just mount the
seats straight into your MGB, you need to grind off a
locating spigot or two, make up a small adaptor plate
for one of the mounting holes and voila! Well, not
quite. I achieved the following conversion in about 4
hours, including removing the old seats, fabricating the
adaptor plates and fitting the new seats. Oh, and 3
visits to the hardware store for bits I forgot I
needed…I also had the assistance of my 12 year old son
Cameron, who was rewarded for his efforts with a
subsequent 1½ hour drive in the lovely countryside
northeast of Oakey as a test for the seats.
The MX5 seats are mounted quite differently to an MGB – any
similarity ends with the word ‘seat’. However, the size
of the seats and the pitch of the seat rails make the
conversion easy. My conversion involves the manufacture
of adapter plates that mount onto the Mazda seat rails,
the adaptor plates are then bolted directly to the seat
pan, using the original bolt holes. The Mazda seats
aren’t modified in any way, the MGB remains stock and
original seats can be refitted at any time. I used a
small bench mounted pedestal drill, a step drill bit
(for hole sizes over ½”), plus a vice and rubber mallet
for bending. You do not need a fully equipped
engineering workshop. Total cost for the steel and
hardware to do the job was under $30.
The MX5 seat mounts appear to take 12 - 13mm studs or bolts -
doesn’t really matter here but they are angled or
pitched down, not flat like the MGB seats. Also, the
right hand rail front mount point is offset from the
rear mount point and locating spigot. The seat mounts
are not handed, i.e. left or right, or mirrored,
however, for some reason, the right hand seat fits
better in the left hand side of the MGB, and vice versa
for the left seat. One of my seats has a map pocket,
this ended up being the drivers seat so is relatively
inaccessible whilst driving solo. Some MX5 seats
apparently have speakers mounted in the headrest – your
choice if you want to take advantage of this
opportunity. I much prefer listening to the Lukeys up on
pipe!
The adapter plates are made from 3mm bright mild steel;
extend from the rear MX5 seat mount to 25 mm in front of
the forward seat mount. The plate is profiled to match
the angles of the seat mounts, drilled to take a 3/8 X
1” UNF high tensile mounting bolt and hardware, with the
bolt inserted from the bottom.
Even using nyloc nuts it is worth being able to check to see
they haven’t come loose. |
A
hole is drilled aft of the front mount to clear the
locating spigot. I used 3 X 50cm lengths 50mm wide and 1
X 50 cm length 25mm wide. I also used pieces of hardwood
as spacers, to the width of the relevant adapter plate
and 5/8” or about 16mm thick. These act in compression so are simply pinned to each
adapter plate using 2 self tapping screws.
Even with all this extra packing you end up sitting an extra
inch lower because of the lower profile of the MX5
seats. Your MGB may have hardwood spacers fitted under
the original seat rails. This conversion does away with
the need for these spacers. Keep them as souvenirs or
for retro fitting original seats later. You don’t throw
anything away, right? If you have any doubt as to the
structural integrity of 3mm steel, just look at what was
originally mounted to the seat pan…
I first manufactured identical adapter plate sets for both
seats then found minor differences meant I needed to
approach each seat installation separately. I found the
RH MX5 seat fitted better into the LH side of the MG.
This means the recliner lever is towards the centre of
the vehicle, however, it does not interfere with the
seatbelt operation and is still readily accessible and
useable. The seat rack adjuster lever ends up on the
outer near the door sill but is hidden under the seat,
is readily and easily operated and does not interfere
with entry or egress from the vehicle. For this seat I
used one adapter plate 25mm wide for the mount and
spigots that are in line, plus one adapter plate 50mm
wide for the offset mounts. Mount the adapter plates to
the seats then transfer the pattern of the MGB seat
mounting holes, starting with the forward holes. These
are drilled in the forward extension of the adapter
plate. Measure back for the rear mount holes, these end
up in the area of the adapter plate supported by the
timber packing piece, so you will need a longer ¼ UNF
high tensile bolt to cater for the extra thickness.
Check, measure, check, measure, drill.
I fitted the adapter plate assemblies to the seat pan, using
¼” UNF high tensile bolts with spring washers under the
heads. I have this thing about ensuring attaching
hardware has some form of mechanical locking – I have
spent over 20 years maintaining and flying in Army
helicopters as an Airframe/Engine Engineer and have a
healthy regard for ensuring all parts remain securely in
their allotted location. Make sure the 3/8” bolts for
attaching the seats are in place, the head of the bolts
are easily accessible with a spanner after installation
but very difficult to install if left out. Drop the seat
over the mounting bolts (a variation on this would be to
have studs welded to the adapter plates), fit washers
and nyloc nuts and the seat is fitted. Lovely.
Buoyed by my success with the now LH seat, fitted nicely and
neatly into the passengers seat well, I manufactured
identical adapter plates for the drivers side. Well, the
seat fitted, but wouldn’t easily slide rearwards,
fouling with the curved intercostals at the rear
outboard of the driver’s seat well. Being 6’2” and often
wearing Army boots I need as much rearward seat travel
as I can possibly get. A good think, strong coffee, a
bit of head scratching and measuring and I found I had
room to move the seat inwards laterally 25mm. This was
achieved by replacing the 25mm wide adapter plate with a
new 50 mm wide plate, shifting the mounting holes 25mm
laterally, giving the clearance required to allow the
seat to travel fully forward and rearward and still have
adequate clearance on the handbrake lever. After all
this I found I had to have the seat a couple of clicks
forward to comfortably reach the pedals! The rear squib
of the MX5 seats seems to be thinner; however, the
lumbar support cushion on mine can be adjusted with
packing for us in mid life crisis sporting ongoing back
problems! The problems with the RH seat may be a quirk
of my vehicle; my advice is to check your own carefully
before drilling any holes…
The original article made comment about the tonneau not
needing any modification. Certainly, the head rests are
in the same location but are physically larger and
significantly taller. My tonneau was modified by a local
canvas place for $25. Champions!
Finishing consisted of priming and painting matt black all
metal components. The timber spacer I painted with clear
epoxy. Araldite works okay if you are quick, but a
modelling epoxy like Great Planes 20 minute epoxy will
be absorbed by the timber a bit better. So, I also build
model planes…and helicopters!
This seat conversion is quite achievable – provides a
relatively low cost, comfortable and stylish alternative
to genuine MGB seats and does not alter the structural
qualities of the vehicle. So far I have seen the seats
in tan leather and black cloth – seat covers are readily
available for the MX5 in a range of colours and finishes
which should be enough to complement any colour scheme.
I have deliberately not included any plans, drawings or
photographs of the conversion process with this article.
However, if you are contemplating fitting MX5 seats into
an MGB, having a bit of a head scratch and want to see
how I did it, drop me a line at
marty@uavaus.com and I will be happy to
oblige. |
