Fitted some boot hold-down springs to the MX5 today - thought that it might be worth doing a 'how to' on these because a surprising number of people screw it up...
I like these on motorsport cars because they are simple, reliable and they avoid a repeat of the incident where the 244 rally car's keys were locked in its boot thanks to a service crew member trying to help. I have had a number of cars' boot latches get full of dust and either refuse to latch, or become very difficult to open.
Obviously these springs are not a good option for road cars that require any sort of security. And don't be tempted to fit both, 'cause that's the worst of both worlds.
These are chinabay copies of the Sparco ones. They do the job are well as the real ones, but they will get surface rust on the stainless springs over time, and the 6 year old Chinese kid who assembles them screws the brackets too far into the springs causing them to sit badly on the bodywork.
The one on the left is how they come out of the packet, the one on the right has been 'fixed'. This is a way harder job than it would appear, because unscrewing the bracket tightens the spring onto the bracket and locks it all solid.
Proper ones don't have this problem, but its $45 vs $15 too...
Work out where you are going to mount them! This one is about the easiest I have ever done - plenty of meat on the bootlid, and plenty in the top part of the rear bumper.
This photo is meant to show how much cavity space there is between the boot skin and the inner frame. Makes life very easy.
Remove the original boot latch components - having to manually unlock/release the boot every time you need to open it, will wear thin quickly.
Locating the brackets evenly/equally is important for avoiding the job looking like crap.
I forgot to take a photo of sitting the assembled spring up against the car to make sure it was all going to work, but you should do this!
Again, the MX5 was super easy with a nice edge to measure off.
I don't use the pop rivets that come with these. They're waaaay too long and simply don't work. This is one task where my hatred of self-tappers is forgotten. If there's any chance of dragging clothing or body part across the end of the self tapper (inside the boot), then either don't use self tappers, or cover the pointy end of screw with a short length or rubber hose.
Two important things in these two photos.
First is that I've hooked the spring onto the lower/looser of the two options. This means if the spring is stretched/fatigued, you can do to the tighter/higher hook position.
Second is that I've marked only the top mounting hole on the bootlid.
And drilling the pilot hole.
And then that hole is used for the BOTTOM mounting point. Doing this gives a good amount of spring preload for a mostly horizontal bootlid.
The more vertical the bootlid is (like a wagon tailgate), the more preload you need but this method has served me well on numerous cars now. There comes a point where these springs simply won't be capable of holding something like a 245 tailgate shut.
And done. I like to use a straight edge across the mounting points to locate the second set of mounting holes.
Some people prefer to mount these 'upside down', so the spring is mounted to the body and the clip moves with the bootlid. Their reasoning is that these hooked finger holds could catch a person's eye or nostril.
I don't do this for two main reasons:
A) Most cars move the bootlid up and forward, away from soft human parts, so the risk of this actually happening is very low - I've never seen or heard of it actually being a thing. Even on the MX5 (which is low to the ground and has a short bootlid), the resting position is comfortably above my head height.
B) Closing and opening the bootlid is far easier - you simply grab the hooks and pull down. You can do both hooks at one, or if you only have one hand free, you can do one side and then the other. The 'upside down method' requires one hand to close the boot, and then the other to hook the spring - not so good if you are in a hurry and/or have something in one hand.
As I said, the MX5 was ridiculously easy. Many cars are more difficult. The BMW hatchback needs them mounted on an angle.
I haven't worked out a nice way of mounting them on a 940/960. Current thinking is to drill a hole through the bumper bar, and mount them upside down with the springs bolted to the body behind the bumper. Still needs more thought before I commit to anything.
Occasionally you'll see a Swedish or Norwegian 940 rally car with the springs mounted above the tail-light, and on a very shallow angle - and these cars usually seem to have the bootlid bouncing partially open through the stages, so I'm not doing that!