Bushing Materials

So I'm looking into finally replacing bushings on my Miata. What are the relative advantages and disadvantages of different bushing materials?

I had been planning just to get some Energy Suspension poly bushings. A mechanic I respect though said he wouldn't use poly because it doesn't hold up, and recommended the mazdacomp rubber bushings, that the Spec Miata guys use.

This was news to me. I figured rubber gets used as OE because it's cushier, and is used by Spec Racers because they have to.

Also, should I replace ball joints and such when I do bushings? Aren't the uppers part of the A-arms?

i have heard this about poly bushings as well, a lot of honda guys are out there claiming that using them in trailing arms and such equal certain failure. mine have been in for a year and look brand new. no cracks, no rot. i know i havent had mine too long but i figured i would throw it out there.

I think poly leaf spring bushing last longer than rubber ones by a good margin so by extension, I would say poly bushings will last longer for the Miata application too. Really thought, this is just a semi-informed guess.

I just bought a full kit of poly bushings for the Celica. Only to find out that when i started tearing things apart, it already had poly bushings in great shape on it. They look almost new. And that's with 35k miles of abuse, including but not limited to two trips to Deal's Gap, back road shenanigans, and terrible city roads.

I didn't realize how much of a difference it made until i drove a Celica w/ toyota bushings.

Go with the poly. Or have custom Delrins made.

Yes, on the Miata the upper ball joints are part of the upper arm and are changed out together.

Poly is a good, inexpensive choice for suspension bushings. Pros: They are fairly cheap, the bushings will rotate fairly freely (unlike rubber or other bonded bushings), it will resist deflection, it will last a long time with maintainence. Cons: it requires a force fit that will squeeze out all the lube, it requires lube frequently and usually has to be disassembled to be lubed.

You might also think about Delrin. Pros: does not "require" lube, is not a force fit, resists deflection more than rubber or poly. Cons: pre-made kits are more expensive than the cheap poly, requires custom fitting/reaming, dirt and dirty water can scratch and wear the bushing but using lube can seal it to prevent water from intruding.

For a daily driver though, I'd recommend Mazda Motorsports rubber bushings.

If the suspension has twist in it, and uses the rubber bushings elasticity, a urethane bushing creates all kinds of problems. Either the suspension effectively locks up, or other things that weren't supposed to flex are now flexing. Not good.

Urethane bushings require lubrication. Some more than others (there's a lot of variability in the quality). I've yet to find a good lube that stayed there. So then the suspension squeeks and binds. If you take it back apart and relube it, you're fine. Be realistic about your likelyhood of actually doing so.

There can be more vibration and such through a urethane bushing. Again, this depends greatly on the bushing maker.

Delrin is a much harder more slippery bushing material. Harder to find, generall race specific applications. Good bit more expensive. Great on a-arms and such, terrible if flex is needed to prevent bind.

Bronze bushings can be neat. Surprisingly available through unconventional sources (motor shops, etc). Same comments as Delrin above.

This is not a DD. It's a track toy. I'm looking at the Energy Suspension kit, like what Flyin' Miata sells. And planning to get offset bushings for the front control arms to gain some negative camber.

What is typically involved in lubricating urethane or delrin bushings? And how frequently does it need to be done?

Poly bushings suck, IMHO. I put a couple of prothane kits on various MR2s and regretted it. They are better than rotten OEM bushings, but have far more slop than new rubber bushings.

They have a big dead zone around their 'neutral' position and made both of the MR2s I put them on twitchier on turn in, until the bushing was loaded. Both cars wandered in a straight line after poly bushings.

With the car jacked up, you can see ~1/16" of slop in the rear control arm bushing on an MR2.

I'm going OEM or upgraded rubber from now on.

Delrin is rigid and thus can can 'pound out' (deform under shock loads). BTDT witht the Delrin bushings I made for the Abomination.

For a street car, I'd go urethane with a heap of the special snot Energy Suspension supplies and also some silicone dielectric grease. Regular grease is water based and thus will wash out, causing squeaks and squawks. Silicone grease is not prone to that. The J-H has urethane bushings which I installed almost 8 years ago that still do not squeak. One funny characteristic of urethane: when the car sits for a while, the bushing will 'stick' to the sleeve even with grease. It takes a couple oscillations of the suspension for everything to free up.

The problem with rubber bushings in a competition or performance application: the rubber does not slide, it twists. This means it acts a lot like a torsion bar, it stiffens the spring rate as it twists. Not to mention the deflection which means the suspension geometry changes.

Is longevity really an issue on a track toy?

Even if you run it every weekend, it's still likely that you'll put less than 500 miles per year on it.

They'll dry rot before you wear them out.

So put in new ones at the beginning of the season, and have a ball.

As a product designer I often get to say this catchphrase:

"There are no bad materials, just bad applications"

Urethane is an exceptional bushing material provided it's used in the right places. In the case of my e36 M3 I used Powerflex urethane bushings for the points where the front lower control arms pivot relative to their rear mounts and for the points where the rear subframe is retained to the unibody. The outer rear CA pivots are ball joints as are the middle and outer lower front CA pivots. The rear LTAs have new stock rubber with Delrin limiters in the front, lower rear CA inner are rubber with UHMW limiters, and uppers are new stock rubber. The upper strut and shock mounts are spherical, Vorshlag and AST respectively.

The car is firm but has no harshness over irregularities and I expect all of these parts to offer excellent service.

For a track car I recommend good quality urethane where you want to control but not eliminate compliance, spherical mounts at the tops of the shocks and struts, and rubber where you need extra compliance.

To give a more specific answer to your question, I just installed the exact ES kit you are looking at, a few months ago, and used a ton of the supplied grease and some synthitic super lube as well. And the Miata is a changed car, much tighter feeling and my car only has 54k miles on it. My OEM bushings were fine except for the ones in the stock Bilsteins, which had deformed. Since my car is a garage queen, I didn't even consider getting the Zerk fittings, as I anticipate not having many binding problems. It's too soon to give a long term review, but I had a Z car back about 20 years ago that had all ES bushings in it and it never had squeaks or binding, and that car was a DD and was using regular grease.

There has been a lot of discussion about the ES kit for the Miata lately, but I think a lot of the nay sayers are full of crap because the kit only came out last fall, so no one has had any real time to use the kit in question to give an accurate long term evaluation on it, and some that are poo pooing on the poly stuff for Miatas were using custom kits. Also if you are worried about them drying out just get a set of Zerk fittings and occationally lube them, how hard is that? Personally I really like them and would do this again in a heartbeat.

Chris Rummel

motomoron wrote: For a track car I recommend good quality urethane where you want to control but not eliminate compliance, spherical mounts at the tops of the shocks and struts, and rubber where you need extra compliance.

Woah... okay, that was awesomely technical. I think I understood what you're saying, but want to be sure that I did.

The main location for these will be control arms, which only pivot one direction. It sounds like you're saying that Urethane will be a good material for that application.

Rumnhammer wrote: Also if you are worried about them drying out just get a set of Zerk fittings and occationally lube them, how hard is that? Personally I really like them and would do this again in a heartbeat.

Just right on the outside, drill it into the mounting tube? Easy enough. I'm going to have to do that with the eccentric bushings to hold them in place anyway.

In reply to Salanis:

Yeap, that easy, the ES bushings are two piece ones that are cake easy to press in by hand and to add a zerk fitting just find the middle of the mounting tube where there is a small gap natrually between the bushings and put your fitting there. Honestly as easy to do as it is, I'm really supprised that so many people are turning their noses up at the ES stuff just because they need to have lube in there.

Chris Rummel

That's about what I was thinking. Sounds like a great idea to me. I'm liking this plan!

Any particular type of grease that is supposed to be used? Just lube them a couple times a year?

And I recommend Amsoil synthetic grease in the 1# tubs. I keep one in the garage and one in the shop and use it for virtually everything. Before I get pig-piled for lack of lubrication specificity, I keep aluminum and nickle based anti seize in stock as well as moly disulfide and a tin of stinky atmy surplus long-fiber wheel bearing grease.

But for PU bushings the stuff that Powerflex (or Energy) includes or Amsoil Synthetic works great. The M-sled has spent much time in the rain this season to and from and on track at VIR and Summit and the bushings are silent and still have visual evidence of grease.

Use the right grease and don't open 'em up unless they ever make a noise that really bothers you.

Salanis wrote: This is not a DD. It's a track toy. I'm looking at the Energy Suspension kit, like what Flyin' Miata sells. And planning to get offset bushings for the front control arms to gain some negative camber. What is typically involved in lubricating urethane or delrin bushings? And how frequently does it need to be done?

Urethane is a very vague term, having all the descriptive accuracy of the word rubber. Urethanes can be extremely soft, extremely hard, short lived, long lasting, etc. Same with rubber.

For example, buy a Rancho shock with the urethane bushings and watch how fast it breaks down. Not uncommon for them to be beaten into pieces (literally) in just a few weeks. Now go buy a Koni shock with rubber bushings. Notice how hard the rubber is. Notice how good it still looks years later.

I've used energy suspension urethane bushings before (I think). They were middle of the road when it comes to firmness and longevity. Firmer than oem rubber, but certainly not what I would call hard. I did rip up a set used as sway-bar end link bushings.

In applications that require no deflection, like A-arm suspension arm bushings, I'd be much more inclined to go very solid. Bronze, delrin, etc. A-arm bushings simply rotate and should not do anything else, so a very solid bushing is usefull here.

But, something like the radius rod on an a-arm suspension, or a semi-trailing link rear suspension, where deflection is absolutely necessary, I would not go with a solid bushing. For doing so would require the mounts to flex instead of the bushings, and this leads to metal fatigue and failure. Not something I actively seek.

As for lubrication, that varies every bit as much as hardness. Some makers of urethane (and nylon) impregnate the plastic with graphite. These bushings supposedly require no lubrication at all. Others use a sticky plastic that seems to require relubrication with every oil change it seems. IMO, it would be quite wise to modify any mount with a grease nipple to facilitate lubrication.

Then there can be the further discussion of the type of lubrication. Again, my opinion, but I would think food grade lubricants, dedicated rubber lubricants and brake lubricants (for the rubber seals, not the metal slides) would be fine.

OK, a track toy wants solid bushings typically.

If its a track toy then by all means consider delrin. Go here for Miata specific bushings:

http://www.iscracing.net/Miata_Page.htm

I don't like Delrin bushings. Even on a track car. You want some give.

EvoRoadster wrote: If its a track toy then by all means consider delrin. Go here for Miata specific bushings: http://www.iscracing.net/Miata_Page.htm

I'm looking there for the offset bushings for front camber. I don't see what they sell in terms of all the other bushings control arm bushings I'd need.

http://www.iscracing.net/Miata_suspension.htm

ISC doesn't appear to have a full set of bushings though... I don't see: front lower, rear upper hub, or rear lower inner bushings.

Onle area where i know poly bushings are a poor choice is on the front a-arms on cars that use the flew of the rubber to let the suspension move. I put poly bushings on my old shelby charger and it caused noticable binding in the front suspension, and it was greatly improved by putting fresh rubber ones in (the actuall problems i noticed were skipping sideways when i would hit a bump in the middle of a corner, and wheelspin accelerating out). I have put poly bushings in my milano though and they are fine, although I am going to replace the caster rob bushings with ball joints (the design allows for the use on a normal car type ball joint, so I see no reason not to do it).

Try here.

http://iscracing.net/Miata_suspension.htm

As an engineer, I hate the word "tolerance." It implies slack, space, or play. I want A + B to equal C - not, C plus or minus the amount of slack that is required to add reliability and/or driver comfort.

However, in the case of suspensions, there is no greater place where these compromises must be made.

First of all, the best suspension is one in which the components offer the least amount of resistance to movement as possible. You want the resistance to be in the shocks and springs. On a street car, low durometer rubber is a great choice. It isolates the most NVH while providing modest resistance to movement. In the purview of the amount of control arm movement on a street car, rubber is great.

Poly has advantages in some situations. In center-bore bushing applications, I find them to suck more than Jenna Jameson. Their typical durometer is so stiff that they provide huge resistance to suspension travel. Most of the NVH added with poly is typically due to the torsional rigidity of the bushing, not the lateral transference of impact forces. Put poly bushings on your lower arms, then stand on the ball joint. I'll bet your arms don't deflect more than 1-2". That's just frightening to me. Using poly bushings (IMO) to get improved handling is like using those screw-on spring compressors to lower a car; they are a stab in the dark - an unpredictable po-boy way to add rigidity to a suspension. Add in the fact that they are maintenance-intensive, and the durometer means that under hard use they tend to tear, and its a no brainer for me. Going up from rubber to poly (urethane) adds 20% benefit and subtracts 80% desirability from an engineering standpoint. I've used Poly extensively on a few cars with horrific results. Not for me, man.

Delrin is a nice idea. Its basically removes a HUGE restriction to movement in the suspension, and does a very small amount to reduce NVH. In my engineering opinion (haven't personally done a lot with them on the track) they seem to provide a great benefit; they can be installed with little or no tolerance, provide mostly free motion, and aren't as maintenance-intensive. They do wear out eventually, but on the track the benefits outweigh the wear.

Spherical rod-ends (heim joints) provide absolutely free motion with very little friction, but they accomplish that by using that dreaded word: "tolerance." That drastically increases NVH, but positively locates the components with very little resistance to movement.

Here is my usual recipe for a performance handler: Any single-axis component (like front control arms) have a real need for free movement since their primary purpose is to swing in their arc. They also need to stay in the same place so you don't have unexpected camber/caster changes as lateral forces are applied. Many of my all-out builds incorporate solid bushings on upper control arms and Delrin on the bottom. Spherical (heim) joints are fine, but unnecessary since we are only dealing with rotation on a single axis. The added play in spherical rod ends is a downside, and the multi-axis articulation adds no benefit.

Four-link rears on solid axles (as in drag racing) follow this same basic principle, however as the vehicle twists under its own torque relative to the axle, that adds a second axis of rotation. In that case, the control arms either twist (resistance to movement) or the bushings need to be made of something that will allow it. Poly is abysmally bad in this application. It prevents motion on all axes, meaning most of the torsional load falls to the trailing arms. In these cases I use spherical joints on the car end and rubber or spherical joints on the axle end depending on application and trailing arm angle.

If this is a straight up track car, go solid. Who cares about NVH? Solids offer a bit of tolerance, but its minimal. They are reliable, strong, offer very little resistance to movement, and easy to deal with. I put a set of dirt-track race, solid bushing, upper control arms on a 66 bonneville just to get it on the road. It actually did so well for me, they're still on the car, even though this was a luxury/cruising build project.

Single-axis movement; concentrate on freedom of motion while providing the least slop.

Multi-axis movement, concentrate on freedom of motion on all axes.