Mission Purple Part 2: Powerflex Poly Bushings Miata Installation

Project Purple Part 2 - Powerflex Polyurethane Bushings Installation Project

The RallyWays Miata is getting a full suspension bushing job. We’re looking to improve the Miata’s handling and tightness using polyurethane bushings from Powerflex USA.

This is part 2 of the installation process. There is also an intro article that explains our goals, and of course, part 1. For reference, below are links to the two previous stories:

Intro: Mission: Purple Polyurethane Bushings to Improve Car Handling

Part 1 (disassembly): Mission Purple Part 1: Powerflex Bushings Miata Polyurethane Bushings Installation

In part one we left off having dismantled the front end and having removed the stock rubber bushings from the control arms. We disconnected the outer tie rods, lower and upper ball joints from the hub carrier and removed all the parts. We also removed the stock sway bar mounts to replace them with AWR sway bar mount brackets.

So where does this leave us? Well, let’s see…

I have a bunch of parts laying around from the front suspension as well old bushings, cracked and rotten ball joint boots and ugly control arms. The radiator is out and the cooling system is empty and I had to disconnect and reroute the return power steering lines. Those last two things I had to do in order to install the AWR sway bar brackets.

But let’s focus on the task at hand which is the poly bushings.

Sanding and restoring Miata control arms

Miata suspension control arms restored

Before installing the new Powerflex poly bushings I washed the old upper and lower front control arms with degreaser and a Brillo pad. I then sanded them down and sprayed them with satin black Krylon Rust Tough rattle can paint.

While I trust Powerflex’s instructions that say that if lubed correctly, the poly bushings will not squeak, Powerflex does recommend they be re-lubed at intervals – once a year if I’m not mistaken. In order to lube bushings one must take apart the suspension again. I’m sure as heck not going to do that again. Screw that. So I decided to fit every pivot point in the suspension with a Zerk fitting (grease nipple) so that I could pump grease into every bushing assembly should they begin to squeak after a period of time.

Kingfisher 6mm x 1.00 Zerk fitting from Grainger
Kingfisher 6mm x 1.00 Zerk fitting from Grainger

I ordered 6mm Zerk fittings from Grainger. See the end of the article for a link to the actual fittings I bought. Grainger has a number of different Zerk fittings, but I decided this size was good. They had a few different 6mm brands. These were made in UK so I opted for them over the ones made, umm, somewhere else. They were only a bit more expensive. Not much.

I would need one for each pivot point. I also wanted a couple of spares so I decided to buy 3 bags of 10. I only damaged one during installation.

Making space for the Zerk fitting

The stock suspension arms have these holes near the weld points that were likely created to hold the parts during manufacturing. What I did was I used a large drill bit to open up the holes near the control arms weld joints to allow me to tuck the grease fittings in those little pockets. I then used a smaller drill bit to drill through the wall where the bushings are held. Finally I de-burred the holes I made with my Dremel tool and a grinding bit, as seen in the photo above.

I originally intended to tap the holes before installing the fittings. However, the crappy tap and die set I bought from Harbor Freight didn’t work. I tapped 1 hole and the tap was dead. Harbor Freight is usually awesome, but every once in a while you do get what you pay for.

Because it was late at night and I didn’t want to have to come back to the job later, I decided to try and self-tap the holes using the fittings themselves. That worked brilliantly. I also found that spraying the hole with a little bit of penetrating oil helped the fitting cut easier into the metal. I installed all the Zerk fittings like this and only damaged one. After double-checking I realized the description of the grease fittings I bought read, “thread-forming.” I gather that’s the reason I was able to self-tap them in. So I highly recommend you buying these same ones. There’s a link at the end of the article to the actual ones I bought.

Cutting a channel for grease into the bushing

Channel for grease is done

Taking it all a step further, in order to help channel the grease pumped via the Zerk fittings I used my Dremel tool to cut a tiny channel into each of the Powerflex poly bushings. The way the Powerflex polyurethane bushings are installed, one half goes into one side of the bushing holder and the other goes in the other end and they meet at the center. I install the grease fittings in the center where both bushings meet. By adding a little channel it should help the grease take the path of least resistance and flow through that channel until it reaches the metal sleeve that fits through both bushings.

One piece Miata front upper wishbone Powerflex bushing

NOTE: Not all the bushings are in two parts. The front upper wishbones for example use a full long bushing at each pivot point. For those I simply drilled straight through the bushing at the point where the grease fitting would be. See photo above.

This was not an original idea. On many car forums I found a number of people had done something similar and had good results. At least this would help me avoid having to take apart the suspension just to re-grease it.

My intention was not to use the Zerk fittings right away. Those are for later on when the bushings need lube. The rest of the installation went as per Powerflex’s instructions.

This one's for Adam @RevLimiter

This one’s for Adam @RevLimiter – If you read his blog, you know what this is about.

There is one thing I do highly recommend though. Powerflex ships their bushings with little sachets of lube to be used during installation. The lube is not grease but rather a type of copper anti-seize. This is the type of stuff used to put on bolt threads to keep them from seizing over time. They are probably enough if you are very careful and frugal in the application of it. But let’s face it… Who is? I sure am not. I immediately found out the little sachets of lube weren’t going to be enough so I bought a big bottle of copper anti-seize – see the list at the end for a link to it. Plus, I got to use it on many of the bolts during reassembly.

Inserting the Powerflex poly bushings into their respective places on the control arms was a piece of cake. You really don’t even need an arbor press for that like you do to take the stock ones off. Just pressing them in by hand is fine. You will have to work a little harder to insert the metal sleeve that belongs in the center of the pivot point. But if you lube it well with the copper anti-seize or with Super Lube, it’ll go in fine. If you’re having trouble, you can use a simple big C-clamp to press those in.

Miata Powerflex poly bushing prep

If you did what I did and installed grease Zerk fittings to re-grease the bushings, I recommend you line up the slits on the bushings with your Zerk fittings to better channel grease in the future. While the little channels I added with my Dremel tool are not necessary, if you do make them, I recommend you keep them in line with the slits on the sides of the bushings. That will help spread grease more easily and evenly.

Miata Powerflex Poly Bushing Installed  - Front Upper Wishbone.

I got a little messy with the copper anti-seize. Having bought a big bottle, I was generous at applying it. When I pressed the new poly bushings in I would get excess pushed out the sides. I then cleaned that up with a shop rag. However, by the end of the project I was working in a hurry. This project had already ran right past my original deadline. For this reason I didn’t do that great of a job cleaning out the excess as you can see in some of the pics. Eventually I got around to wiping a lot of that copper mess off.

For Pete’s sake… Start at the back!

While I was working on the front of the car and waiting for parts to arrive – namely the coolant, rubber ball joint boots, etc – I decided to tear into the back.

The Miata is a rear-wheel drive car. For this reason, I figured the rear would be more complex to work on. That’s why I decided to start the project at the front. Holy crap was I wrong! If I ever do this again with a different Miata, I’m starting at the back – SO MUCH EASIER.

I kid you not, I took apart the left rear suspension in less than 40 minutes. The right side I did in 30 minutes. The best part was having no ball joints to deal with. Using an extra pair of jack stands I supported the loose hubs so I didn’t even have to disconnect the half shafts!

Basically, I removed the upper wish bones and the bottom wish bones after removing the brakes and I left the hubs floating there supported by jack stands. Easy as pie.

Plus, the control arms at the back as well as all the hardware was much cleaner than those at the front. That meant less corrosion. Everything came out easily. Note, just like I did at the front, I marked the position of the eccentric cam bolts so that I could put the suspension back together without losing my alignment too much. Yes, I would have a pro-alignment done anyways, but at least I could test the car for a good number of miles before re-aligning knowing that at least it would be close to where it was.

I did encounter one small problem at the back of the car. There is one set of bushings that you have to make sure to order 3 packets of. It’s the PFR36-112 Rear Upper Wishbone Inner & Outer. It’s this set right here.

Powerflex USA does have a diagram on the car’s page, for example with the Miata here, where they show what bushes it is that you need and for what location. What I wish they were a little more clear about is how many of each packet you need to buy. The packaging itself says it, but the site is not very clear about it.

When I looked at the packaging for that specific bush, it says, “6 per car – 2 in this pack”. I had 2 packages which meant I had 4 bushings. I was 2 bushings short. Because each bush is divided in 2 pieces, it becomes even more confusing realizing what you actually have in your hands.

Miata Rear Hub Carrier Stock Rubber Bushing.

At that point in time I discovered the bushes I was missing were the ones that go directly into the top of the hub carrier at the back for the joint where the upper rear wishbone connects to the hub carrier. There’s one on each side – so, two.

I decided not to bother with that one then. I didn’t have the bushes and I would’ve needed to devise a way to push the stock rubber ones out without removing the hub carrier. Not to mention, by then the RallyWays Miata had been on jack stands for 2 months and I needed it out of the garage to make space for an upcoming project. The stock rubber bushes in the hub carrier looked fine, so I decided to keep those.

Good thing, Powerflex USA is great with this sort of thing so I’m going to run it by them with feedback on how to make the bushing quantities needed a bit more clear. Having said that, as it is, it’s not too bad. This was the only mistake I made choosing the parts I needed.

The rear wishbones were in much nicer shape than the front units, so I decided to just clean them and not paint them. I also added Zerk fittings in much the same way as I did in the front. However, in the back you have to be more careful as to where you install those fittings because they can actually interfere with the control arm movements during suspension travel. This is specially true for the inside upper pivot points. Be very careful with those. I’m pretty happy with where I installed mine, but I could’ve done better. They are very close to touching, but they clear OK – barely.

Miata Rear Suspension Redone

I took the time to clean out the rear fender wells and also painted them with Rust-Oleum undercoating like I did at the front. By the way, if you decide to use Rust-Oleum spray undercoating be sure to buy the $10 professional formula can. Don’t go cheap and buy the $5 one. I hear that one sucks. You’ll need 1 can for the front and another for the back. Also, try and coat the fender wells in one go. Basically, one thick coat. The instructions on the Rust-Oleum can call for spraying a second coat. But what I discovered at the front of the car is that the second coat didn’t want to cure as well as the first coat did. It stayed sticky and I don’t know why. At the back, where I sprayed just one thick coat, the undercoating dried and cured nicely. By the way, that’s also the reason I recommend the more expensive professional formula. What I’ve read about the cheaper version is that it doesn’t dry well and it stays sticky.


Miata Front Suspension Fully Assembled

I’ll admit, putting everything back together was much easier than I expected. I’m not going to go much in depth on how to assemble everything back together in the Miata because it’s really beyond the scope of the Powerflex poly bushings project. However, I will point out a few things…

  1. If you are going to tackle this project – GET THE SERVICE MANUAL FOR YOUR CAR. This is IMPORTANT. You will forget where a bolt goes and how to reattach a part. The manual is invaluable for both taking apart the suspension as well as putting it back together. Also, the book will have the torque specs for every nut and bolt you need to reattach.
  2. Have a quality torque wrench. In fact, get two. Have a big 1/2” drive clicker type and a 3/8” beam style torque wrench. That way you have all bases covered. I’ll list the ones I used at the end of the article.
Use a torque wrench to finish the job.
Don’t half-ass the project! Use a torque wrench!

When you assemble suspensions with standard rubber bushings it is recommended you only tighten pivot points softly and then lower the car onto ramps or cradles so the suspension is in compressed mode before you go and torque everything down.

The reason for this is because rubber bushings stay in the position you toque them down at. Rubber bushings are designed to twist, like springs, and they are actually part of the car’s spring rates. If you torque them down with the suspension at full droop, as is the case when the car is on jack stands, you will end up with too high a ride height.

With polyurethane bushings, I didn’t find this to be an issue. Poly suspension bushings are designed to spin on their axis. They work with friction instead of spring and twist. For this reason, I found that it doesn’t matter where the suspension is in its travel when you torque them down because the suspension will settle correctly regardless.

There is another very important point that I haven’t seen anybody mention in any write-up I’ve read about installing polyurethane bushings. Because of the twisting nature of rubber suspension bushings, they are actually part of the car’s total suspension spring rate. When you replace the stock bushings with poly units, the entire responsibility of the weight of the car now rests on the springs. Essentially, this means your overall spring rate is reduced. At least this was my experience. Maybe some will disagree.

I found that after I lowered the car back on its tires, it sat lower than it did before. Like I said, the overall spring rate of the car is reduced.

This may matter to you or it may not. It really depends on the ride height you’re aiming for and the current spring rates you are running. I’m running Koni coil-overs and the spring rates, while higher than factory, are somewhat low. I’m pretty sure they are 180F / 108R. That’s higher than stock, but not by much. For me, I found it to be a bit of a problem because for one, the car ended up lower than I wanted and I also experienced rubbing when the suspension bottomed out, which also happened sooner.

Miata Adjustable Koni Coil Overs

Luckily, these Koni coilovers are height adjustable so I was able to dial in the ride height I wanted. I’m still hitting the bumpstops sooner than I want, but overall it’s acceptable. It’s no big deal as I intend to replace these shocks with upgraded units or maybe just upgraded springs in the near future.

To wrap up this installment…

Let’s look through a final gallery with more shots from the install:

The project of installing Poweflex polyurethane bushings in the RallyWays Miata took a little longer than originally expected. That said, it wasn’t just because of the bushing job, but also because I did a bunch of other things on the car while I had it apart. I even took the time to correct the CAS o-ring oil leak I had, flush the cooling system and add new Miata coolant while the radiator was out. I even replaced the stock power steering fluid with Redline ATF since I had to re-route those lines when I installed the AWR sway bar brackets.

1993 Miata LE Tie Rods

While I was researching parts, I discovered the recommendation of replacing the standard steering Miata outer tie rods with 1994 LE Miata tie rods. I credit RevLimiter for that one on his write-up here. Apparently, replacing the standard ones with the ’93 LE (Limited Edition) units helps reduce bumpsteer in lowered Miatas. The original ’93 LE Miata came a little lower from factory. Mazda used different tie rods for these cars for better suspension geometry.

Those were the only ball joints I ended up replacing. For the upper and lower ball joints, I simply bought new factory rubber dust boots, repacked them with grease and carefully installed them. Big thanks to my friends at Crowley Car Company and their Mazda dealership, Mazda of El Cajon for the genuine Mazda parts.

In the next installment, we’ll take the RallyWays Miata for a drive to see how she performs after the upgrade.

Below is a list of some of the supplies, parts and tools that I used during the project and where to buy them. If there is a link to the part or tool in the actual story above, I’m not listing it here.

Craftsman 3/8” Beam Style Torque Wrench

Harbor Freight 1/2” Drive Clicker Style Torque Wrench

Copper Anti-Seize

Super Lube (For regreasing via the zerk fittings – as recommended by 949 Miata Racing.)

Grainger 6mm (M6 – 1.00) thread-forming Zerk Fittings (grease fittings).

The undercarriage coating I used:

Krylon Rust Tough Semi-Flat Black Enamel (What I used to paint the control arms I restored).

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