If you don’t like words then the TLDR summary is ”Yes, this kit is certainly worth consideration IF it fits your requirements”.
And if you like videos, enjoy this supplementary content:
Otherwise please read on!
What’s a SadFab?
For those of you who are not aware, SadFab are a two or three man operation from the USA that produce a collection of small run performance components for the MX-5. One of their products is the delrin suspension bush kit for the NA/NB cars that I’ve recently installed into my car. The kit is costly compared to the more common rubber or poly kits available, but the cost may be justified by the additional benefits to the performance and function of your suspension. With that cost alone in mind, right up front I would suggest that this is the sort of kit suited primarily to those with serious performance in mind, or with some money/time to burn (or maybe both) – it’s really NOT a logical choice for a street car.
Why I chose this kit?
In my car, the existing bushes had spent their entire life over the last 6yrs (or more) in 2 separate track cars, I deemed my car ‘due’ for a complete bush replacement/upgrade. And I was suffering from a failed bush in a front upper control arm that left the wheel flailing about like one of the wacky inflatable dudes at a car dealer – so that one NEEDED to be fixed.
There’s always a balance between cost and performance, but this particular car tends to get more ‘financial attention’ than my average street MX-5. Suspension performance is pretty important to me, so I didn’t want to replace like for like with poly bushes again. I also haven’t seen any good and reliable off the shelf aftermarket arms with heim-joints that are within the average-joe pay grade. So I was happy to justify the slight premium cost of a set of the SadFab delrin bushes (with poly+bronze sleeves in certain locations to ensure suspension doesn’t bind) – these seemed the logical balance between cost (the delrin kit being expensive, but still a lot less than custom arms) and performance (these will allow free suspension movement and avoid the binding issues of poly).
What’s included?
The kit is comprehensive in so far as it comes with every bush and sleeve plus zerk fittings, but that’s about it. I had to print my own installation instructions which are located on the SadFab website, and I needed to source my own grease/lubricant for bush installation.
You will need some “special” tools, specific drill bit sizes, thread taps, and a press/vice etc to be able to make the install a success too which can add to the pain slightly – depends how complete your home workshop is… but hey If I can do this in my driveway then anyone car.
Removing suspension arms
The first part of the process here is to obviously remove your old bushes, this requires removal of all the suspension arms from the car.
For me, I chose to work corner by corner, rather than to completely undress the car of all its arms. This kept things a little neater, but meant I perhaps didn’t quite get into a nice production line like rhythm.
I am lucky in that I’ve had the suspension apart before, and I live in an area where corrosion isn’t a huge concern, so all of my cars undercarriage comes apart quite nicely. Naturally, every car is different, so if your car has never been touched in its 20+years, you may be met with some very stubborn nuts and bolts.
Similarly, I could push many of the old Energy Suspension poly bushes out with a forceful hand, or a mild tap with a hammer, or a quick wind of the vice… none required superhuman strength to remove. OEM rubber bushes, if I still had them, would be much trickier to remove.
With the suspension arms bare, I gave them a quick de-grease and clean to remove the existing sticky grease in the bores that came from the existing poly bushes along with any dirt and dust.
Bushing installation
The bush installation process is documented by SadFab quite well with images included where needed. It is a slightly more convoluted process than a rubber or poly bush install. Fundamentally it’s a matter of pressing in the delrin, reaming out the bore to suit the sleeve, drilling and tapping a thread for the zerk, then installing the sleeve. The delrin bush needs to be reamed after install into the arm as it may deform slightly after installation, and this reaming ensures that the supplied sleeve fits perfectly with just the right amount of freedom of movement. Because the MX-5 has cam adjustment bolts for the lower suspension arms, this means that the bushes may not always be perfectly square, as such there are certain locations that require a poly bush (rather than 100% delrin). To alleviate the negatives of poly, the kit includes a kind of “double sleeve” (a sleeve with a bronze insert) for the poly bushes to maintain the free movement and avoid the dreaded binding issues. Installation of the poly is much the same, but without the reaming.
Then the arms are ready to go back on the car, and it is simply a case of “reinstall is the reverse of removal”. With the arms reinstalled and their mounting bolts torqued up at the sub-frame, you’ll be impressed to see the delrin can freely rotate around its sleeve – perfect, this is just what we wanted!
Testing on track
At this point, I gave the car a string alignment in my driveway (marking the cam position before removal is a good idea to get you in the ballpark on re-installation).
Logically, this kit does not alter your suspension geometrically, nor does it change the adjustment range of your suspension. It just permits the suspension arms to move freely and do their job. In theory you won’t be able to “get more camber” with this kit and it isn’t going to change things like roll centre or ride height. (Although an incorrectly installed rubber-bushed arm will act as an additional spring and influence ride height.) That said, for the sake of science I should add that I run around 3.8deg camber at the front, and around 3deg at the rear with no power steering and running on A050 Yokohama tyres on 15x9 rims – on a dedicated track only car.
More detail on the car in question here: https://www.beavismotorsport.com/cars/NB/
This car has always been quite sharp and raw. It handled fairly well before, on the poly setup. It’s far from a comfortable Sunday driver and already has a solidly mounted driveline.
Since installation, I’ve had the car out at a track event where it performed fantastically.
The change to the SadFab Delrin bushes resulted in:
- No perceivable change to the ride quality (it was already pretty serious), but certainly no increase in vibration or harshness.
- A mildy sharper and more distinct feel to the suspension – not a night and day change that I can detect.
- Confidence for me as a driver that the arms now have free movement.
- A contributor to a ~3.5sec improvement in lap time at Winton. (the only other changes being upgraded front brakes going Wilwood to AP racing, and more practice for the driver)
Final comments
Lastly, I suggest anyone who hasn’t seen it yet, to take a read of the Bushing Mega thread on the MiataTurbo forum, here: https://www.miataturbo.net/
It has lots of good information, details and certainly some internet opinions.
I do want to add that I purchased the kit on my own accord for about $950 (AUD) delivered, I have no involvement in SadFab and in no way is this me spruiking their product for any benefit to me.
And as a sort of disclaimer: I am not a professional driver, I am not a mechanic, and I am not an engineer. So please don’t take this as gospel. Make your own decision on what is right for your car. I don’t necessarily have the finesse or experience to really tell the intricate differences or detect the before/after changes of a suspension bush change. I also don’t have the technical knowledge to tell you what is mechanically or scientifically good or bad about this setup. I simply base my judgement on the experiences and opinions of others, along with the data in the above forum link, and form my own opinion based on “research” (AKA googling).
Thanks for reading!
Beavis
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