The new Penske shocks are now shipping to Spec Miata competitors across the country. That means drivers will have to retrofit their old Bilstein setups. This feature will detail how the shocks go together. This is a new build, not a retrofit, but the steps are largely the same.
It’s probably a good idea to have a lot of space on your work bench for putting them together, the cleaner the better. The new handmade Penskes are such a remarkable step up from mass-produced Bilsteins that you won’t want to get them dirty before you put them on the car.
A couple of words of warning. The upper shock mounts need to be drilled out to 15/16 inch accommodate the new hardware. The mounts are made of thick steel, which is hard on drill bits and the user. We took ours to a machine shop and had them done on a milling machine. You can see a short video of that process here. It made it much easier and more precise, and was well worth the money we spent to have it done.
Machining Spec Miata Top Hats on a Milling Machine
If you’re building a new car, note that neither the new shocks nor the springs come with the rubber isolators pictured in the assembly instructions. You can get them separately from 5XRacing.com. Before you begin assembling the shocks and mounts, glue the isolators in place and allow them to dry.
The assembly process is pretty straightforward. The quality of the new shocks actually make it fun. Here’s a quick rundown of how they go together.
The lower shock mounting sleeves take an O ring to help hold them in place. They can still fall out so be aware of that.We used a little white lithium grease on the O rings on the shock bodies to allow the sleeves to slide over them easily. If you don’t grease them, the sleeves won’t slide on well, and they can even roll the O rings out of their grooves on the shock body.The sleeves arrive with the spring perches already in place, so you just need to slide them into place. Slowly, evenly and gently is the best method.The springs drop right into place. If you’re doing a new build, be sure you pair the 700-pound springs for use on the front shocks and the 325-pound springs for the rears. They’re marked from Eibach, and the 700-pound springs are thicker, but because they’re similar in length, people have mixed them up and put the rear springs on the front shocks and vice versa. The car does not work at all with that setup.Before you begin assembling the shocks, glue the rubber isolators to the bottom of the shock mounts. On retrofits, you can pull them off your existing mounts. They were part of the FatCat kits that were necessary on the Bilsteins. For new builds, they’re available separately from 5XRacing.com. We used 3M Stage 2 weatherstrip adhesive because it’s strong and remains flexible when dry.Lay a solid bead of the adhesive all the way around the bottom side of the upper shock mount, put the isolator in place and allow to dry.Push the threaded collar through the bottom of the shock mount and drop on the flat washer.Three Belleville washers come with the hardware. Drop them over the threaded collar with the angled surface facing the flat washer and the upper shock mount.Take the top nut, which encapsulates the pivot ball and thread it onto the sleeve and torque it to 50 foot-pounds. That’s not a lot, so we used a dab of blue Loctite to help things stay put.Slide the bump stops over the shock shaft, orange one first, then the black and place the upper mount over the shaft. These bump stops are much, much stiffer than the FatCat bump stops on the Bilstein setup.Remember to place the small washer over the shaft before you install the Nylock nut.The Nylock nut threads on after the washer.The Nylock will spin the shock shaft when you go to tighten it. The best trick I’ve come up with to grab the shaft without harming it is to use a rubber glove around the shaft and several layers of a shop towel clamped with a Vise Grip. It’s not terribly sophisticated, but it works and the shafts were fine after torqueing the nuts.The procedure for the rear is largely the same, but there is only one orange bump stop and a flat washer that goes on top of it.
