... but I is a fool. Poly bushings on the Miata. I've put them on several cars, always enjoyed the extra crispness they bring.
I've read they bind, school me, por favor - how often, how bad, under what conditions (please don't say autocross...), etc?
I installed poly bushings in my Miata. Haven't had an issue yet in the 2 years since, although when cold they can be a little squeaky. They suck to install though. I just take them apart every winter and lube them up with a ton of silicone grease
Basically, for any bushing, you want to look at its function. The ideal bushing material is different for different bushings, as they move in different directions. The goal is to use a material that lets the bushing move as freely in the directions it needs to as the suspension travels, but is as stiff as possible in every other direction. Flex joints or spherical bearings can often provide that in situations where poly would bind.
The thing that irritates me is that there are so few aftermarket bushing manufacturers that offer traditional rubber bushings.
It's all poly, poly, poly because bright colours and "race car parts."
For awhile you could buy a full "Group N" bushing set from Subaru that was a harder-durometer rubber equivalent of every single bushing on the chassis. If I were President I would write that into law.
ssswitch wrote: The thing that irritates me is that there are so few aftermarket bushing manufacturers that offer traditional rubber bushings. It's all poly, poly, poly because bright colours and "race car parts." For awhile you could buy a full "Group N" bushing set from Subaru that was a harder-durometer rubber equivalent of every single bushing on the chassis. If I were President I would write that into law.
Poly is also cheap. In the Jeep world, most of the times where rubber and poly are both options for bushings in an aftermarket part, the poly is significantly cheaper.
I put poly bushings on the front of my Corolla, only drove it for a matter of minutes since, but I can hardly feel the difference from rubber so far...it's almost disappointing.
For arms that strictly rotate along one axis there's no problem with bind, it's when a bushing needs to not only rotate but twist or deform (like any joint in a triangulated 4-link setup, or the trailing arm in just about any suspension) where you'll have a problem with bind when using poly bushings. For those your options are to:
Stick to rubber
Use poly only on the suspension side. This is a compromise, it will give you some flex and keep any noise away from the frame. This may accelerate wear on the remaining rubber bushing though and there will probably be some increase in bind over stock.
Change to a non-bushing alternative like a superflex joint or spherical bearing.
The price is always what killed it for me. $200 or less for poly, $450ish for stiff rubber. So I did neither!
The price of bushings has come down considerably over the years. 15 years ago, it was $650 or so for a set of Miata poly bushings and close to a grand for high durometer rubber. Now we have poly for $284 and rubber for $419. Given how long they last, there's not much difference in the cost.
There's a fundamental difference in how they work. Rubber bushings have the steel sleeve bonded to the rubber, so any movement of the suspension requires the rubber to deflect. There's no relative movement between any individual parts. This also gives the bushings a bit of a spring rate, and why they have to be torqued down with the suspension in the resting position.
Poly bushings - every one I've come across with the exception of Polybush - have a separate sleeve and poly shell. When the suspension moves around the primary axis, the sleeve rotates inside the poly. That's why they're so sensitive to lubrication. But it's also why they feel the way they do - they're more like a bearing, free to move in one axis while resisting others. When they're fresh, they feel good.
If you're lucky, a set of polys with bad lubrication will squeak. If you're not, they'll basically seize up. We've had cars here that had control arms that were essentially locked in position. This is not conducive to a functional suspension. To make matters worse, some of the budget brands (I'm looking at you, Energy) tend to get the width a bit off of the various bits. If the poly is wider than the steel insert, then you have the bushing crushed down when it's installed and this adds a lot of resistance. If the steel insert is longer, then you have fore-aft movement of the suspension. I've had to tweak a lot of different bushings to get this right.
In my experience, I've had a set bind up on me in almost no time. I probably had 1500 miles on them and one rainstorm. I still have those bushings installed in a set of control arms, someday I'll put them up for sale.
Note that I'm talking about bushings that are only expected to move in one primary axis. Once you get all sorts of weird twist going on like 3-link suspensions, you're deforming the poly the way you do rubber. It may very last longer in this form. They're sure a lot easier to change.
Just get the rubber competition bushings - stiffer but no squeaks
Any way to add zerks to a poly?
Appleseed wrote: Any way to add zerks to a poly?
The kit I got, Energy Suspension, suggested drilling a small hole where the two bushing halves meet and threading in a zerk fitting to pump grease in.
Installing zerks is not hard
http://949racing.com/installingzerkfittings.aspx
Poly bushings suck because they get play in them. Rubber won't.
They're usually a lot cheaper and sometimes the only option for failed rubber bushings, so there is that.
I'm not hung up on material, just want the harder durometer for that nice feel.
Nick D, how was the install with the ES? Like Keith, I've had an issue with the sizing from them, but not terrible.
If the bushing set Keith mentions is only a $100 and change more, that's probably worth the hassle of squeaking and such even presuming no issues with poly bind.
I'm still trying to get my head around them binding so much it stops suspension movement, that's wild.
I considered this and then Brandon from Keith and Brandon told me not to and I chickened out and went with their experience over my gut feeling. I still have not got them installed but as soon as I have time a build thread will start.
Physically putting the Poly bushings in the arms is really easy. Pressing out the old ones is a bit of a pain, I used a length of allthread and some fender washers with a piece of pipe to press them into last time. This time I had a shop press - either way is not bad. You may have to do some adjustment of the sleeve or bushing so the scenario Keith described above doesn't happen, but the set I bought (Energy suspension in black) was pretty good in that respect. They're also available for $211 shipped on Amazon.
Appleseed wrote: Any way to add zerks to a poly?
I'm also a big fan of high density rubber suspension bushings....
You can add zerks to a poly bushing, but in my experience it only sort-of works because the grease will take the single least-resistance path to the open air rather than spreading out through the entire bushing-to-sleeve surface. An arm with freshly-installed, properly-sized, well-lubed poly bushings will drop to point straight down under its own weight (assuming the outer end isn't connected), but you can really only get that for a month at best after a complete suspension disassembly.
The other bushing solution out there is delrin. Delrin doesn't have the lubrication issue, but because it's got essentially no deflection you can only use it in pivot points that are happy with a single plane of motion. In particular, for a Miata, this means you can't use it on the lower arm inside pivots (basically where the alignment adjustors are). There's an interesting thread on miataturbo.net about using poly bushings with bronze bearings for those joints and delrin for the rest that has the potential to give you the bearing-style motion of well-lubed poly bushings without the maintenance headaches.
I've installed poly bushings on the control arms of two cars that saw DD duty in rain and sunshine and cold canadian winters. My Maxima was like that for the last three years / 40k miles that I had it. No squeak or play. For my Saabaru, it was 1 year and about 10K....no problemo.
I believe most problems are caused by bad installation. Improper lubrification at the install or bolts torqued while the suspension isn't in its operating position. YMMV of course.
Have you ever checked to see how easily your control arms move after your tests?
Using the proper grease apparently helps:
http://polybushings.com/pages/bushinglube.html
If you're going to add a zerk fitting, make sure there is a path for the grease to reach the areas required.
I changed all the original bushings for the FM stiffer ones in my Miata. It was all done with hand tools and a homemade sleeve. No press needed. The bushings are noticeably stiffer ,but the handling doesn't change all that much. It did make the car feel "newer".
Stefan (Not Bruce) wrote: Using the proper grease apparently helps: http://polybushings.com/pages/bushinglube.html If you're going to add a zerk fitting, make sure there is a path for the grease to reach the areas required.
I've not been impressed with the sticky green marine bearing grease. I've been using Sylglide, a silcone brake lube of late. Seems to work pretty well. SuperPros ship with what looks like white lithium, and it actually lasted longer than expected.
I've used a E36 M3 load of lithium grease on my installs.
Sylglide is all I use on poly bushings. Works fine so far.
I have poly bushings in the lower links of the RX-7 (3 link suspension). The rear axle articulates just fine. The bushings go loose over time and need to be replaced. Fortunately, every RX-7 bushing kit comes with twice as many bushings as you need, since even with the stock 4 link you should never put poly bushings in the uppers. So you automatically get spares.
Because I'm kind of a dumbass, when I yank out the Mazda bits and install the Ford rear, I'll be going with a combination of Summit "Black Magic" rod ends and UMI rod end joints. The rod-ended upper link doesn't rattle enough, I guess.
UMI rod ends are greasable and adjustable. Probably rebuildable too, but in my experience any time a part is rebuildable, it is cheaper to replace it than to buy the parts to rebuild it.
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