mx5cartalk.com

Please be prepared, this is a long post.
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

Great work BB!

I support your conclusions - not for street use, big difference in 'seat-of-pants' feel with resulting increase in confidence in car control, leading to faster times. This stems from the virtually friction-free movement of the suspension, and the precision with which the suspension is located, even under extreme duress. I too recommend a good read of that thread on MT.net, not just for prospective purchasers, but for anyone interested in performance suspension modz.

Like Brendan, I am 'only' a DIYer, and the fitting was a breeze. Just follow the instructions, I used a standard vise to press in the bushes. In my case I already had the SADfab spherical conversion in the RUCA-O location (the knuckle on the rear upright), but with hindsight that was probably a slight overkill.

While this is a racer-oriented solution, SADfab also offer a solution more suited for the road car, or dual-duty car. This is the 'poly/bronze' bushing - a poly bush (softer than delrin, so a little more compliance) with a bronze sleeve within which the clamped pin rotates. For a (glowing) review of this setup see my build thread for the 'Red Greenmachine'.

Note that the MT.net thread linked by Brendan contains all dimensions necessary for producing your own delrin bushes from bar stock, but the poly/bronze bushes are only available from SADfab, and require the separate purchase of VERY specific commercial polys - not Whiteline or Superpro. I should add that our own Mad Jack has made his own version of the poly/bronze kit, that is written up on MT.net as well.

So, for the racers - delrin rocks! For the dual-duty cars, and maybe some road cars, poly/bronze FTW!



On Preview: I find that I have not said a lot about my poly/bronzes in my build thread. Bearing in mind that this is a dual-duty car, and the springs and shocks are custom set up by Heasemans for the old racecar, I can only say that it rides and handles like heaven on a stick! Compliant, quiet, ultra precise, as a touring car on full soft it is simply superb - precise without harshness, road feel without noise, soaks up bumps, potholes and undulations like what I think a high end GT should do. On track it with the shocks hardened up, it is controllable with bags of 'feel' for the car's grip and attitude.

The poly/bronze are obviously only part of the equation that produces this result, but a significant part as they allow the springs and shocks to work uncompromised by friction or suspension movement under loadings.

Hi Brendan,
Thanks for the write up!
I put myself on the wait list back in August, and I’m going to hang in for as long as it takes.

The White Mouse has OEM rubber bushes installed. My primary reason for looking at Delrin is wheel hop. I know some also install beefier lower rear arms and see an improvement through reduced flex in the arm.

The events I do all involve a launch, up to 20 times each event, which has taken a toll on my driveline, in large part because of wheel hop. Mostly, I’ve found that I can reduce hop by launching with higher RPM, and then ‘pedalling it’ off the line so that the wheel spin does not slow enough for the grip-spin-grip cycle to begin.

This is still not ideal, and I’d prefer to be able to launch ‘softer’ at lower rpm, and I think this would probably be quicker (and extend the life of my tyres too).

If you get a chance to practice racing starts, it’s the review of your rear delrin bushing performance that I’m most interested in, and if you note a reduction in tendency to hop.

I have read up on this before, but am not liking our dollar.
Looks like a great off the shelf kit. My rubber ones are not that old in the current car, plus other more important stuff has to be done first.


However I have actually run Delrin in the past. 2014.
I give the material a thumbs up for track purposes.


ISC racing used to supply Delrin for various NA/NB suspension locations, mainly in offset bushings for camber increase/decrease.
I had the front upper control arm bushings, that were offset.
At the time in 2014 extended lower ball joints were not a thing and it was well known that the Superpro Poly offset bushings were crap because they rotated over time. Plus they did not give that much extra negative camber. Half a degree from memory.
ISC Delrin kit was the answer as you could lock them in place with a grub screw or grease fitting and they gave an extra 1.5 degrees of camber.
On my previous SE I could get up to -3.75 degrees of camber with my Teins at whatever height they came out of the Box. I used to run 3.25 degrees.

There is one thing ISC did not specify or recommend which gave me noise issues in the long run.
ISC said nothing about the requirement for grease!!!
This only came up, because in their install instructions it had grease fittings which I asked what type of grease would be required before purchasing.
This is there exact quote to me in 2014.

We dont grease them in racing we use wd40

To top it off, I received the bushings without the grease fittings, so did not fit any as they were not needed.... I put grub screws instead to lock the bushings in place.
There is also false information around that Delrin is self lubricating. No it is not!!!
Guess what, mine eventually squeaked terribly about 6 months later. 99% of the squeaking was coming from between the faces rubbing on the big washer on the rear bush. I could loosen the nut a bit and smear some grease in every 6 months or so.
When I pulled the bushes out of the car at the end of last year(4.5 years of service) to return it to stock before sale I found that the metal centre sleeves had corroded inside the delrin. They were hard to push out. That is where grease should have been and had never been.
Surprisingly the Delrin still looks like new. If I get some new sleeves made up( I am sure it just 3/4inch O/D with 2mm wall), I could reuse them so it is tough stuff unlike Poly which I destroyed a few of in that car.


So you definitely need grease fittings and you definitely need to re-grease every now and then.
Hats off to Sean/Sadfab for making it so clear in the instructions.


Internet infos.
One huge advantage to POM(Delrin, Acetal etc) is its high lubricity. POM is often mistakenly said to have self-lubricating properties. However, it simply has a high abrasion resistance and a very low coefficient of friction, making it appear to be self lubricating. POM can benefit from correctly chosen lubricant. Properly lubricating a load bearing POM part will lengthen its service life. A dry lubricant like Moly or Graphite will work. Also a Teflon based grease such as Super Lube is a good choice.


I was lubricating mine with Penrite Molygrease in the end as it seems to wash out the slowest.
It is black grease though which looks crap on the white Delrin.
https://www.penriteoil.com.au/products/molygrease-ep-3
Just wish I had grease fittings in my previous setup so I could pump it to the bore where is was needed.

Great review as usual Beavis.

I'm still torn between the Poly Bronze kit and the full Delrin kit for my car. GM, did you already have the poly bushes and just bought the retrofit kit from SadFab, or did they supply the poly bushes with their kit?

I have the poly/bronze in my car, if we ever get around to that catchup you're welcome to go for a spin, SKYHI. It's definitely a step up the NVH ladder, but it's not horrible. Probably perfect for you doing street/track setup. I think if I did it again I would just go to I.L. Motorsports rubber bushes, firmer than stock, but still rubber.

There really is no binding, even after more than a year's use. I recently pulled my shocks and while they were out I could easily move the assembly by one hand, all I felt was the weight of the control arms.

Sean doesn't sell/supply the poly bushes, but I emailed him and arranged it so I got the poly kit sent to him from Supermiata.com, he lathed out the necessary bushings (front upper, I think) and sent the full package on to me.

You could get the bushings lathed yourself if you had someone to do it, but I don't so this was easiest for me.

Thanks for the info Lachy. I think I'm leaning towards the Poly Bronze kit over the full Delrin kit for my purposes..

Maybe you just sell me your arms with the kit already fitted, and my standard arms as part payment. Then you can get your IL Motorsport bushes fitted

Found this review of the Poly Bronze kit from TheCarPassionChannel if anyone else is considering the alternative option from SadFab.

SKYHI wrote:Found this review of the Poly Bronze kit from TheCarPassionChannel if anyone else is considering the alternative option from SadFab.

That is the SADFab kit ;) He's just installing it.

I did consider a swap, but it's a PIA job. But maybe. Let me get my bucket of bolts rolling again first, I've forgotten what it's like!

Yeah I know, I meant the alternative option from their full Delrin kit

Keep me in mind if you do decide to swap. I need to do something with mine soonish.

SKYHI wrote:Great review as usual Beavis.

I'm still torn between the Poly Bronze kit and the full Delrin kit for my car. GM, did you already have the poly bushes and just bought the retrofit kit from SadFab, or did they supply the poly bushes with their kit?

No, I ordered the bronze elements from Sean, and bought the polys from someone in the States, arrived direct from memory. I paid extra for him to supply the four(?) machined polys, because machining poly is not a simple exercise - be warned! Means I have some surplus polys, but it was cheaper to buy the kit than cheap out and try and package up the kit less a few selected bushes, not only was that more expensive, it introduced the potential for errors, delays, and additional shipping.

I've been corrected by SadFab, they are actually a one man operation. (I mentioned 2 or 3 man in the original post).

Also, in case anyone was wondering... there is a delrin kit from one other US seller, but it is 100% delrin only and they don't include the provision for a poly+bronze to account for the cam alignment adjusters in the suspension arm, so there is a potential for binding. I haven't seen the kit in person though.

And glad to see I've sparked some discussion :-)

The American wrote:If you get a chance to practice racing starts, it’s the review of your rear delrin bushing performance that I’m most interested in, and if you note a reduction in tendency to hop.

I am sorry but I don't think I'll get a chance to comment on such a case, that is just not really in my cars curriculum.

SKYHI wrote:Found this review of the Poly Bronze kit from TheCarPassionChannel

Indeed, for anyone that wasn't 100% sure, that video does NOT specifically cover the Delrin kit, just the bronze with poly solution that SadFab also offers.

The bronze bearings are the magic sauce! Whether you run delrin or poly (probably still want some poly with your delrin, as the SADFab kit does), you need those bearings for the arms to rotate properly.

I don't understand why it's not a more widely used solution (I've seen it in some other cases, I think there's a Porsche kit, but it's not common). Yes, it adds to the overall cost, but even for the ease of maintenance it's worth it. And if you're a racer it will hardly be the most expensive mod to your car, and will last a long time to boot. And it would still be cheaper than a full set of sphericals.