I did the 4x100 conversion this weekend and wanted to share my thoughts and process. I'm happy with the results but mis-stepped a couple of times so, hopefully, this will help the next 4x100 FiST conversion go a little more smoothly.
There are a number of different ways to convert, depending upon the tools that you have, your budget, and your core strength.
1) Drill the hubs and rotors while they're on the car. This, in theory, is the easiest. Buy a template off of eBay for $120, grab a bad-ass 1/2" drill motor, and go to town. The reality is that you should start doing planks right now, because it's a bitch. You'll have to lean into the drill with about 100# of force to make progress against the cast iron rotors and steel hubs for about 5-10 minutes per 1/4" pilot hole and 1-3 minutes per 1/2" final hole. Times 16. I do planks, a lot, and I gave up after the first wheel. Other's on this forum have said that drilling all of the hubs while on the car took them all day. I have much respect for them.
Tools required: 4x108 -> 4x100 Template, extra high-quality 1/4" and 1/2" bits, 1/2" drill motor, open end lug nuts (I think that the stock ones will bottom out, 949 Racing nuts worked perfectly for me), ibuprofen.
2) Pull the knuckles and drill the hubs on a drill press. This is what I ended up doing. It's still a day's work of work, but without the beat up hands and back. Pulling the front knuckle is a big 1 1/4 nut for the half shaft, two strut bolts, tie rod end, caliper, brake line mount, anti-lock sensor, and popping the knuckle off of the ball joint. Pulling the rear knuckles requires freeing both shocks to drop the sway arm, pulling out the springs, caliper, brake line mount, anti-lock sensor, and 4 knuckle bolts. Drilling the hubs is the same process except with a glorious tool called a drill press - sooooo much easier. Assembly is reverse of disassembly.
Tools required: 4x108 -> 4x100 Template, drill press, extra bits, metric socket set, 1 1/4" socket with 1/2" breaker bar and torque wrench (adjustable to 170 '#), tie-rod end tool, ball joint tool, jack and stands, open-ended nuts.
3) Buy a 4x100 conversion kit and install. These kits come with rotors and hubs drilled to 4x100. I don't really understand this option. You'll have to pull all of the knuckles in order to push out the old hubs and press in the new ones and, in the process, have to replace all of the wheel bearing, which are $40 a piece for decent ones. And, unless you have a hydraulic press, you'll have to have a shop do this for, say, $40 a corner. If you do have a hydraulic press, then you probably have a drill press, too, and you can use option 2 and save yourself the cost of 4 hubs, 4 rotors, 4 bearings, and whatever the machine shop charged you to drill the hubs and rotors.
Tools required: Same as Option 2, minus the drill press, add 4 wheel bearings, and a hydraulic press or a local shop.
My advice is, if you're patient, option 1, if you're not, option 2.
As far as studs go, I suppose that you could reuse the original stubs (I banged my out with a BFH and they looked no worse for wear). I used the ARP 100-7708 studs and they fit perfectly with the 949 lug nuts - just 1/2 of a turn showing past the end of the nut on the front and flush on the rear. There is no problem with installation on the front as there is a spot on the knuckle where you can slide the stud into the hub. The rears were much tighter because of the longer stud and larger head than the original. I had to convince them just a tad with a solid tap from my BFH but I could push the head past the knuckle with just a little bruising of the finish on the stud. I sat them by tightening them down with a couple of washers and a 12mm x 1.5 nut.
Slide on your center bore adaptor, mount your wheel (I chose the lovely 6UL in 17x8), repeat 3 times, and you're done. Do NOT sell your adaptor!! Why? Because you're going to need it every time you change your rotors, that's why. You're also going to have to find a 4x108 hub to use as a fixture for your 4x100 template, too, unless you used option 3, which means that you have 4 already..., which is good, because you've spent $600 more than anyone else doing the conversion. For those of you that don't have 4 extra 4x108 hubs, check eBay or a local junk yard - new from Ford is $34.
I did the conversion just to get access to the 6UL wheels. Having said that, there are a LOT more options in 4x100 than in 4x108, especially when you get past 7" in width. Anything that will fit a 4-lug Miata will now, likely, work with your FiST and there are lots of well maintained used Miata A/C wheel sets available.
It's a day of work with tools that most gear-head garages already have. I'd do it again in a heartbeat.
There are a number of different ways to convert, depending upon the tools that you have, your budget, and your core strength.
1) Drill the hubs and rotors while they're on the car. This, in theory, is the easiest. Buy a template off of eBay for $120, grab a bad-ass 1/2" drill motor, and go to town. The reality is that you should start doing planks right now, because it's a bitch. You'll have to lean into the drill with about 100# of force to make progress against the cast iron rotors and steel hubs for about 5-10 minutes per 1/4" pilot hole and 1-3 minutes per 1/2" final hole. Times 16. I do planks, a lot, and I gave up after the first wheel. Other's on this forum have said that drilling all of the hubs while on the car took them all day. I have much respect for them.
Tools required: 4x108 -> 4x100 Template, extra high-quality 1/4" and 1/2" bits, 1/2" drill motor, open end lug nuts (I think that the stock ones will bottom out, 949 Racing nuts worked perfectly for me), ibuprofen.
2) Pull the knuckles and drill the hubs on a drill press. This is what I ended up doing. It's still a day's work of work, but without the beat up hands and back. Pulling the front knuckle is a big 1 1/4 nut for the half shaft, two strut bolts, tie rod end, caliper, brake line mount, anti-lock sensor, and popping the knuckle off of the ball joint. Pulling the rear knuckles requires freeing both shocks to drop the sway arm, pulling out the springs, caliper, brake line mount, anti-lock sensor, and 4 knuckle bolts. Drilling the hubs is the same process except with a glorious tool called a drill press - sooooo much easier. Assembly is reverse of disassembly.
Tools required: 4x108 -> 4x100 Template, drill press, extra bits, metric socket set, 1 1/4" socket with 1/2" breaker bar and torque wrench (adjustable to 170 '#), tie-rod end tool, ball joint tool, jack and stands, open-ended nuts.
3) Buy a 4x100 conversion kit and install. These kits come with rotors and hubs drilled to 4x100. I don't really understand this option. You'll have to pull all of the knuckles in order to push out the old hubs and press in the new ones and, in the process, have to replace all of the wheel bearing, which are $40 a piece for decent ones. And, unless you have a hydraulic press, you'll have to have a shop do this for, say, $40 a corner. If you do have a hydraulic press, then you probably have a drill press, too, and you can use option 2 and save yourself the cost of 4 hubs, 4 rotors, 4 bearings, and whatever the machine shop charged you to drill the hubs and rotors.
Tools required: Same as Option 2, minus the drill press, add 4 wheel bearings, and a hydraulic press or a local shop.
My advice is, if you're patient, option 1, if you're not, option 2.
As far as studs go, I suppose that you could reuse the original stubs (I banged my out with a BFH and they looked no worse for wear). I used the ARP 100-7708 studs and they fit perfectly with the 949 lug nuts - just 1/2 of a turn showing past the end of the nut on the front and flush on the rear. There is no problem with installation on the front as there is a spot on the knuckle where you can slide the stud into the hub. The rears were much tighter because of the longer stud and larger head than the original. I had to convince them just a tad with a solid tap from my BFH but I could push the head past the knuckle with just a little bruising of the finish on the stud. I sat them by tightening them down with a couple of washers and a 12mm x 1.5 nut.
Slide on your center bore adaptor, mount your wheel (I chose the lovely 6UL in 17x8), repeat 3 times, and you're done. Do NOT sell your adaptor!! Why? Because you're going to need it every time you change your rotors, that's why. You're also going to have to find a 4x108 hub to use as a fixture for your 4x100 template, too, unless you used option 3, which means that you have 4 already..., which is good, because you've spent $600 more than anyone else doing the conversion. For those of you that don't have 4 extra 4x108 hubs, check eBay or a local junk yard - new from Ford is $34.
I did the conversion just to get access to the 6UL wheels. Having said that, there are a LOT more options in 4x100 than in 4x108, especially when you get past 7" in width. Anything that will fit a 4-lug Miata will now, likely, work with your FiST and there are lots of well maintained used Miata A/C wheel sets available.
It's a day of work with tools that most gear-head garages already have. I'd do it again in a heartbeat.
