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This article was first published in 2009.
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A seat that is comfortable and supportive is
integral to enjoying driving. So what if your car has flat, hard seats that
allow you to flop around on every corner? The answer is to fit new seats –
either brand new, or from another car. In this story we’ll look at the latter –
sourcing secondhand seats and then installing them.
However, first a warning. Unless the seats are
from another version of your car, installing new seats is usually a lot more
work than it first appears: what looks like it might take a few hours often in
fact takes a few days. Also, when changing seats, there are safety, legal and
insurance implications. (And before beginning, also check out the breakout box
at the very end of this article!)
Picking New Seats
Selecting the right new seats is critical to
success – and there’s actually a lot to get right in the selection process.
What do seat-belts have to do with seat selection?
In some cases, a lot! In many cars, the seat-belt buckle is attached to the
seat. This means that as the seat is adjusted forwards or backwards, the buckle
moves with the seat – always placing it in the correct position.
However, it also means that seat-belt loads are
being borne by the seat. So in a crash, the seat-belt buckle is pulling on the
seat, rather than directly on the car’s bodywork. Both the seat and the seat‘s
fastening to the bodywork have to be strong enough to withstand these forces.
Other (rarer) seat-belt systems place both
lower anchorages on the seat – that is, the seat-belt attaches to the seat at
the buckle and also on the other side.
In any situation where the car’s original
seat-belts attach to a seat (either at the buckle or on both sides), the
replacement seat must use the same seat-belt design. Don’t ever be
tempted to consider installing non-seat-belt seats and then attaching the
seat-belts to them with custom lugs or bolts. If the seat didn’t originally
carry seat-belt loads, it won’t be strong enough to withstand the required crash
forces.
Another point to consider in relation to
seat-belts of any kind is that the new seat must position the occupant so that
the seat-belt still functions correctly. For example, if the upper seat-belt
anchorage is low (and not adjustable), a tall and wide seat may prevent the sash
part of the belt from sitting properly over the shoulder.
Finally, does the car use electronic seat-belt
sensors to detect when the seat-belts are done up? If the seat-belt buckle is
attached to the seat, the old buckle will need to be swapped to the new seat to
retain this function.
If the original factory seat contained air bags,
it’s very unlikely that you’ll be able to easily source a better quality seat
that is electronically and mechanically compatible with the car’s airbag system.
(The exception is if you take a better seat from a sports version of the same
car.)
If you want to improve the quality of an airbag
equipped seat, the best approach is to have the seat re-upholstered with better
padding and/or material. But again that can be problematic – the airbag must
still function as it should, for example deploying correctly through the new
seat material.
If the car uses only front airbags (or the side
airbags aren’t in the seats), do the factory seats have sensors to detect when a
person is sitting in them (or the weight of that person)? If so, these sensors
will need to be swapped into the new seats.
If the seat-belt buckle is attached to the seat,
and the buckle uses an active pre-tensioner (ie a device that tensions the
seat-belt in a crash), can these buckles be swapped across to the new seats? A
pre-tensioner may have an extensive assembly under the buckle itself – and there
may not be room for this in the new seat.
Seats vary a great deal in base width, backrest
height and width, height off the floor, and length of the base. So the starting
point in working out what will and won’t fit is to do some basic measurements of
the existing seats.
Will a wider seat fit? (And by ‘fit’, I mean not
just fit in the car, but also allow the occupant to still reach the seat
adjustment mechanisms with the door shut?) Will a longer seat base bite too much
into rear legroom? Will a higher head restraint block rear vision – or make rear
seat occupants feel claustrophobic? If the seat sits higher off the floor, will
you have headroom or visibility problems?
Does the seat need to flip forward (eg in a two
door car)? Do you want lumbar support? Height adjustment? Electric seat
controls? Leather or cloth? What colours will suit the rest of the car’s
interior? Do you want seats with rear pockets?
Visit a wrecking yard and there is a bewildering
array of options!
When selecting seats, the design of the runners
will make a major difference to how hard it is to put the seats in your car.
Look at the original seats and measure the
distance between the seat runners, and also the runner length. In addition, look
at how the runners are bolted to the floor – for example, do they use flat
brackets or are the brackets curved? Check carefully – are both runners the same
length, same height and attached to the floor in the same way?
The closer that the donor seat runner design
matches the original, the easier it will be to fit them.
Sourcing Seats
Seats can be bought wherever secondhand parts are
sold. However, there are some downsides to buying privately or sight unseen.
The major reason that you’re putting new seats in
your car is to improve comfort and support – so you need to sit in the seats
you’re thinking of buying! That ‘sit before you buy’ is best accomplished if the
seats are still in the donor car – that way you get a feel for how they are when
mounted with the original height and inclination.
If you have access to a large wrecker where you’re
free to wander around the yard, you can try out lots of seats, measure lots of
seats, and inspect the runner and seat-belt arrangement of lots of seats!
Interestingly, I also found that the wrecker
prices were cheaper than private secondhand prices – an unusual occurrence.
Legalities?
Changing
seats – especially if that requires altering seat belt mounts – requires legal
approval. That process will vary from location to location but in here in
Queensland, what is called a ‘blue plate’ needs to be affixed to show that
approval has been given for the modification. The inspection and provision of
the blue plate can be performed by an accredited workshop. The next step is to
inform your insurance company of the modification.
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Installation
The original seats in this Honda Insight are OK,
but on longer trips they lack support. There’s also no height or lumbar
adjustment. The seat-belts mount to the seats on both sides.
One of the new pair of seats. The seats are from a
Holden (Opel) Vectra. Of all the hundreds of seats I inspected in a wrecking
yard, only Astra and Vectra seats had two seat-belt mounting points. The seats
feature leather facings, height adjustment on the driver’s seat, lumbar support
and electric seat heaters. They cost $250 for the pair.
The Honda’s seats are held in with fine-thread 8mm
front bolts...
...and 10mm rear bolts. Because these bolts handle
seat-belt loads, they are very important. Note how the rear bolts are thicker –
in a frontal crash they undergo tension, whereas the front mounts are being
compressed.
The Honda and Vectra seats side by side. I am
using a level to ensure that the base of each seat is about the same distance
off the ground. A greater distance in the new seat would mean that headroom
would suffer (however, note that headroom also depends on how much the seat
compresses with body weight).
The underside of the two seats – the original
Honda seat is on the right. The green lines show that the Honda’s seat rails are
(1) each of the same length, and (2) are longer than either of the Vectra seat
rails (red). Also note how the Vectra’s seat rails are different lengths.
The Honda seat rails are further apart (green)
than the Vectra’s seat rails (red).
Finally, the front of the Honda seat rails (right)
have a riveted and welded lug for floor mounting, while the Vectra seat (left)
doesn’t appear to have any mount at all! (An advantage of having watched the
removal of the Vectra seats from the donor car is that I know the Vectra rails
slide into a cavity in the body of the Vectra – that’s why there appears to be
no mounting facility.)
The first step was to remove the seat belt buckles
from the Vectra seats. The donor car had been in a minor accident resulting in
damage to the front-left corner of the car. The seat-belt pretensioner on the
left-hand seat had operated, pulling on the seat-belt. You can see how this
assembly is now much shorter than the driver’s side unit, and how a tell-tale
flag has extended.
Here is one of the Vectra’s seat-belt mounts. Note
how dual rivets (arrowed) are used to hold the mount to the seat assembly.
The Honda’s seat-belt buckle mount needed only
this locating tag ground off before it could be bolted to the Vectra’s seat-belt
mount...
...using the original Honda bolt. Note the arrowed
shoulder on the bolt, that allows the buckle to swivel even when the bolt is
done up tightly.
The wiring for the Honda’s seat-belt sensor was
transferred and secured with cable ties.
Both the seat-belt and seat hold-down bolts in the
cars were Loctited into place. This practice should be followed when making the
swap!
The first mounting step was to drill holes in each of the
Vectra front seat rails. Mild steel angle (40 x 40 x 6mm) was then used with
high tensile bolts, nuts and hardened steel washers to join the two front rails,
providing a very strong mounting point. (High tensile hardware must be
used.)
The angle could then be rested on wooden packing
while...
...the seat was levelled and its height adjusted.
Lugs were then attached to the angle to provide
the front mounting points that bolt to the original Honda floor mounts. The lugs
were made from 40 x 8mm mild steel bar, with being nickel-bronze brazed to
the cross-member and also bolted in place (the top bolt also secures the seat).
Note how the greater width between the Vectra sat rails is catered for (green
arrows show seat mounting holes.)
The lugs were cold bent in a vice, using a big
hammer. A piece of bent wire was used as a guide.
A similar design approach was taken for the rear
seat mounts. With the seat installed, the outer seat-belt mount could be
Loctited and screwed into place. (The seat-belt buckle was installed before the
seat was placed in the car.) The fact that the Honda and Vectra used the same
seat-belt mount bolt diameters and threads made this part of the exercise very
easy.
The new seats in the car.
Conclusion
Unless the new seats use identical mountings,
swapping seats is no simple and quick task. However, if the new seats can be
picked up cheaply, it remains a very cost-effective improvement.
However....
After
fitting the new leather seats to my Honda, was I happy? No, I wasn’t – and the
reason I wasn’t is interesting.
In
short, the new seats transmitted too much vibration, a movement that made me
feel sick.
The
Vectra seats use firm foam rubber while the original Honda seats use a
combination of steel springs and foam. The Vectra seats – no doubt absolutely
fine in the softer riding, more refined Vectra - were not soft enough for the
3-cylinder, much more hard-riding Honda.
So,
despite the large amount of work involved in installing the seats, I removed
them.
Two
points come from this: (1) install the driver’s seat first and then do plenty of
driving to make sure that you’re happy with it, and (2) not all seat
padding/springing/suspension designs suit all cars.
However, based on our
previous experience of seat swaps, the problem I found in the Honda occurs only
rarely.
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