Installing 4 Point Racing Seatbelts Into A Mk1 MR2.

Copyright (C) 1996, All Rights Reserved.
David Kucharczyk (ssr@netcom.com)

WARNING: Use of non-factory seatbelts, modifications to, or removal of the factory seatbelts may cause injury or death. Any information presented here is used at the readers own risk.

Introduction

I have used 4 or 5 point racing seatbelts since my first car. If properly installed, they may give better protection than the factory units and also serve to keep you put under hard cornering. On the down side, they can be a real pain or downright dangerous when other people drive the car since the belts must be adjusted when the seat is moved or a different shaped person drives the car. Also, simple things like reaching into the glove box can be impossible while you have the seatbelt on.

Some states or localities may have laws that prohibit the use of non-factory seatbelts or the removal or modification of the factory belts. I have been pulled over for not wearing my seatbelt because the observer could not see a shoulder belt in use. I have never been cited for no-seat-belt-use when wearing a racing belt.

The seatbelt and all of it's hardware. Most seatbelts come with an eye hook, washer and nut for each end of the seatbelt. As we will be using the stock mounting points for the lap belt, only the eye hooks are shown.

Racing belts come in a number of varieties and shapes. Two common buckle types are the cam lock (such as the Sabelts pictured) and ones that have a buckle which requires inserting a part of the lap belt buckle through the shoulder belt ends before closing the buckle (as is common on many small planes). The cam locks are more expensive, but much easier to put on and you can get out of them with a simple twist on the buckle. Shoulder belts can come in a Y configuration or as two separate straps. A Y will not fit properly since the seat is so close to the mount point. Since the fire wall was not designed to have a belt mounted into it, spreading the load over two points is probably also safer.

Mounting the lap belt

The mounting points for the seatbelt are the most important part. The lap belt can usually be mounted into the stock mounting points using the existing hardware or hardware that came with the belt. It appears that there is some standardization on bolt size and thread, as the Sabelt eye hooks screwed right into both of my MkI MR2s as well as my Ford Mustang. Make sure the bolt is all the way in and not cross threaded as this can weaken the available holding force. I re-used the lock washers from the old seatbelt hardware.

The Sabelt eye bolts are the same thread and diameter as the stock Toyota bolts, thus they bolt into the original lap belt mounting holes. This is the drivers right hand side lap belt mount. Note the white wire, a leftover from the seatbelt warning system. If you want to return the car to stock, make sure you leave enough wire on both sides to re-connect the original latch.

If you cannot use the stock mounting locations, you will need to drill holes through the floor and use the mounting hardware supplied with your seatbelt. Running the hardware through reinforced parts of the floor pan such as the rails is best. Make sure that the seat will not interfere with the hardware of the seatbelts when it is moved before you drill the holes. Also, be sure to use thread locking compound, stake or safety wire the mounting hardware.

If your belt is a 5 or 6 point and has an anti-submarine belt you will have to drill holes into the floor pan and possibly cut a hole in the seat cushion to run the strap(s). This part of the belt is designed to prevent you from sliding under the lap belt and to keep the shoulder straps from lifting the lap belt up as it is loaded in a crash. This feature is oriented more for a real race car where the driver lies back at a much steeper angle. Since you sit in a more upright position in most production cars I have opted to not install this part of the belt.

Mounting the shoulder belt

Shoulder belt placement is usually the hardest to do. If you have a roll bar, then it will provide the best mount points. Since most cars don't, you will have to drill holes through the fire wall into the engine bay. Try and keep the two strap mount points reasonably close together. If they are spaced too far apart you may slip out of them in an accident. I try and keep the belts as close together as the seat headrest will allow. The factory seat headrest is a bit wide for my taste and may cause problems with shoulder belt spacing if you are tall and have narrow shoulders. If in doubt, replace the seat, headrest or use the factory belts. Eating steering wheels is not good for you...

The two shoulder harness mount points are about 3.5" down from the trim edge. The higher the points the better, as this prevents the belts from pressing downwards on the shoulders when they are loaded. An extra coat hook is visible at the very top center. It has been attached to the hidden bolt to match the factory hook on the passengers side. The hooks should not be used as seatbelt mounting points !

Locating and drilling the shoulder harness mounting holes is the most difficult part. The drivers side is the hardest. One point goes just under the drivers side rear deck hinge. Removing the battery makes this easier. The other point will go under the cruise control servo (if you have one). If you have cruise control, you will need to remove the servo to place the bolt. You can drill from either side. I prefer to drill from the passenger cabin out to the engine compartment as this gives the most room to work.

First, remove the storage compartment that lives between the two seats. Next, remove the metal trim that is just under the rear window. Undo the four plastic plugs that hold the engine firewall carpeting near the floor. Then unhook the top of the carpet from the retainers on the firewall. This can be a pain in the ass to do and is next to impossible if you don't remove the plastic plugs that hold the bottom part of the carpet. Use an upholstery tool to remove the plugs if possible or they may not be re-usable after extraction.

This should enable you to pull the carpet back enough to drill your holes. Make sure the drill points don't interfere with anything in the engine compartment and place rags under the drill sites to catch any metal that exits the holes while drilling. I used a sharp punch to make dents in the firewall and then checked the location from the engine side. Once you are sure the locations are acceptable, use a small bit to drill a pilot hole. Re-check that the location is ok, and if it is drill the appropriate sized hole for the mounting hardware that came with your belt. If the pilot hole is not located where you want it, drill another one. If it was close, you may get lucky when you drill the actual mount hole and it will eclipse the extra pilot hole(s). If not, use some silicone sealer on both sides to cover the hole and prevent rust form starting.

Once the holes are all drilled replace the carpet and use a sharp, fine point knife to cut away the carpet and sound insulation where the holes are. If you expect to remove the belts in the future, cutting an X instead of a hole will work and keep holes from showing in the carpet after the bolts are removed. Install the hardware, make sure it is tight and that the nuts are locked down with thread-locker compound or some other method.

Mount the belts to the hardware and double check everything, as your life may depend on it. The factory seatbelt can be left in place if desired and bolted down with the aftermarket eye hooks, but it can get in the way. I usually remove all of the stock belts unless I expect other people to drive the car regularly.

The drivers side shoulder belt mounts as seen from the engine bay. The right hand mount is hidden by the cruise control servo (black and gold cylinder on the upper right). The left hand mount is visible above and to the left of the battery. Note that the left side washer has been cut down to fit between the engine cover hinge. Making the washer smaller was a strength trade off for allowing the bolt to be further inside the re-enforced part of the hinge. Always use a thread locking compound on these bolts.

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