Low Buck NB-NA conversion shock mounts
I got in a jam and needed a set of NB shock tops for NA shocks in a hurry. The usual suspects that supply them either didn�t have them in stock with about a week wait, or they were across the country tuning a customer car and couldn�t ship until they got back.
So, I took some measurements, did a bit of experimentation, and made my own. This only works for Koni shocks. Most other shocks have a M10 threaded shaft. I don�t know what nut you could use for them.
What I started with.
I ordered a set of standard NA Koni adjustables. These are Koni part number 8041-1203 Sport for the front and 8401-1204 Sport for the rear. Race versions of these shocks are available for about $250 per corner. If I was autocrossing on �R� tires, I would have considered them. I�m in STS2 on street tires which I don�t believe need the stiffer valving. The shocks came in pairs. Each pair came with nuts, lock washers, one adjusting tool, poor instructions, a circlips (already on the shock body), spring perches, thin plastic washers and plastic boots to protect the threads during shipping. Best price I found on these was $117 each.
I also ordered a set of Ground Control springs and adjusters in the standard rates with adjusters for Koni shocks. The rates are 375 front, 250 rear. They came with four threaded adjuster tubes, four threaded spring perches, four aluminum washers for the top bushing, four vinyl (poly? rubber?) top spring perches, two front and two rear Eibach springs, an allen key to tighten the perches, and a wrench to adjust the perches. I was in a hurry and paid $400 for the set.
What I used to make Ground Controls and Konis work on my Miata with NB tops.
I ordered four NB tops from a Miata recycler for $20.
I ordered four Ground Control bumpstops. These are the 46mm �short shock� versions. They cost $12 each. Koni offers similar bumpstops, but I couldn�t get them in time.
I picked up these nuts at the local car parts chain store. They are shank nuts for mag wheels in a M12-1.25 size. That�s a 12mm thread with a 1.25 thread pitch. These nuts are Rally brand part number 4E. They came with some washers that I didn�t use. They cost $6 for the pack of four.
These are large, thick washers that exactly fit around the nuts, and cover the top of the bushing I intend to use. They are also from Rally and are part number 90702. A four pack cost $3 (there are four in one package).
These are shock absorber eye bushings. The center hole is exactly the right size for the shank nut to pass through. I ended up buying four of these at $4 each. They are HELP! Brand number 31010. If you were careful with your cuts you might be able to get by with just two.
I bought a poly cutting board from the dollar store. It was 1/2 inch thick. It was $1.
I paid through the nose for a section of heavy duty radiator hose. The Koni shocks have a 42mm body diameter. This was the closest hose I could find to fit outside the body, inside the adjustable perch, and keep them both tight. $11 for one foot of Gates Vulco 1-5/8 ID radiator hose.
I also had some thick cupped washers left over from a set of Energy Suspension sway bar bushings. If bought separately from the hardware store they would not have cost as much as $2. I also bought an aluminum rod from the local model shop for $4.
I used a drill with a 1/2 inch chuck, a four inch grinder, a round fine, a flat file, a hacksaw, a razor blade, a 21mm wrench, a sheet of 100 grit sandpaper, glycerin (you can use dish soap), a 1-3/4 hole saw, a 1/2 inch and 5/8 inch drill bit, cutting fluid (oil), a vice, and some poly glue (like Gorilla Glue).
Drill out the hole in the center of the smaller washers. I used a 1/2 inch drill bit. This allowed the washers to fit over the shock threads, but stopped at the shoulder.
Cut up the shock bushings. I ended up discarding the center part and used the grinder and sandpaper to clean up the thicker end parts. I ground them until they were 1/2 inch thick. You should end up with eight of these for four shocks.
The shank nut fits into the top hole for the shock top and allows about a seven degree angle. That�s more than a Miata shock will see, but to be on the safe side I opened up the hole with the round file so a 12 degree misalignment was possible.
Cut the tops off the shank nuts. I ground the hex portion down until it was about 1/4 inch tall.
The hex portion is not threaded and opens up a little. The threads end at the end of the shank.
Make the spacers. Spacers? Yes. Koni shocks bottom out with a significant amount of shaft still sticking out of the body. I measured .80 inches between the body and the lower washer seat on the rear, and .62 inches on the front. With the stock bumpstops you don�t need spacers, but with the shorter, softer bumpstops I am using, you need spacers. I sacrificed a little travel up front for the sake of speedy assembly. You can make the front spacer a little thinner.
I discarded the Koni plastic washers and made new spacers from the polyethylene cutting board. It just so happens that the inside diameter of a 1-3/4 inch hole saw is about the same size as the shock body. I cut out four spacers, drilled out the centers with the 5/8 inch bit, and slotted them to get them over the lower washer perch with the hacksaw. I cleaned them up a little with the flat file and sandpaper.
Glue the vinyl spring top perches into the NB shock hats. They fit perfectly. The lip goes down into the spring, not up into the mount. I used Elmers Ultimate, the same thing as Gorilla Glue.
Cut the hose into 2 inch sections. Slit down one side so it will fit over the slightly larger shock body.
Assemble all the components. I had to remove the Koni stickers from the rear shocks to get the Ground Control adjusters over the shock body. I inserted a piece of hose into the adjuster, lubed the inside of the hose with glycerin, and slid it down the body until it rested on the circlip. Then I placed the spring on the shock and then put all the small parts on in order.
1. Spacer spreads over the top shoulder and slides down to the body.
2. Bumpstop is installed with the tapered end towards the body.
3. The drilled out sway bar bushing is next. Mine are cupped and I installed them with the cup facing the body to allow maximum misalignment.
4. The lock washer that came with the Koni shocks is next.
5. A cut down shock bushing is next. These are slightly domed on one face. I put the domed portion towards the mount.
6. The NB mount with the opened up center hole is next.
7 Another shock bushing, again with the domed face towards the mount.
8. The oversized mag wheel washer is next.
9. The opened up shank nut is last. Use a 21mm wrench to tighten this until the lock washer is compressed. The threads of the shock shaft should just barely be visible when you look down into the top of the nut. Don�t hold the shaft with pliers or any tool. I grabbed it with a rubber glove to gain enough traction to tighten the nut.
The shock adjustment tool won�t work with the top of the shaft recessed in the nut. You have to make a new adjustment tool.
I pulled the business end of the adjustment tool out and made a new blade for the Koni knob.
I cut a two inch section of aluminum rod and sliced a slot in one end and ground a flat on the other end.
This was a semi secure fit in the knob, but I glued it in with the poly glue.
The final adjustment knob works just fine with the extended nuts.
A recap on the costs
4x $117 Shocks
4x $12 bumpstops
4x $4 bushings
$4 Alum Rod
Total for everything
NB Top parts, spacers, bumpstops, and adjuster tool