How do polyurethane bushings work?

I've got a kit car with polyurethane bushings (came that way).  There is a bolt, a sleeve, the poly, and then the control arm hoop.  Which 2 parts make up the interface that allows rotation of the control arm?  I have a good idea how rubber bushings are supposed to work (the rubber shears to allow movement), but poly is new to me.  I have a suspicion that this setup is not working as intended.

Also, any downsides to switching to Delrin?

Is this a Factory Five Racing kit? Looks like their bushings and arms in the photos. 
 

Polyurethane bushings are supposed to be greased/lubricated with something like Energy Suspension lube. Very sticky tacky stuff. The point of rotation is between the steel sleeve and the ID of the bushings. The OD of the bushing remains fixed and rotates with the control arm. 
 

For example, the bolt clamps the steel sleeve tight between the chassis mounting tabs. Thus locking the pivot sleeve to the car. The bushings which are pressed into the control arms rotate about this now "fixed" sleeve. The ID of the bushing against the OD of the sleeve. Again, with liberal and specific poly grease, which should be checked and reapplied regularly, about once a year seems to work for most guys. 

Forgot to mention, but Delrin makes for great bushings. Haven't seen anyone put them in a FFR but no reason you couldn't. Self lubricating requires no grease or maintenance. Still requires a steel sleeve to be able to achieve clamp load torque though. 
 

Another option is spherical bearings. FFR sells them, direct replacement for the bushings. Press into the arms and bolt in the car. Benefit of totally free suspension motion, even when fully torqued. Does not add any artificial spring rate like all the others do. 

Poorly.  They work poorly. :)

Logan95 is correct about how they're supposed to work, but my experience is that they squeeze all the grease out in the space of a month or two and the only way to properly re-grease them is to disassemble the whole thing.  Zerk fittings help a bit, but the grease takes a single path out to the world so they don't get the whole joint.

And yes, the grease you're supposed to use is this nasty silicone stuff that gets everywhere, makes a huge mess, and nothing will clean it up properly.

Delrin will make for a harsher ride, but is supposed to be self-lubricating and thus avoids the grease issue.  One problem with it is that having zero deflection it can't accommodate joints that need small amounts of motion that isn't purely axial, such as when the inner joints on a lower control arm use eccentric/cam bolts for alignment purposes.

There are poly bushings that work like rubber - Polybush, I believe - but most of the time the normal ones are just seized up. Cheap to make and easy to install, though. 

When you install them and torque the bolts tight against the sleeve, you could darn near run the car without springs.  The friction is intense.

Delrin is great as long as you keep it lubed.  Otherwise the steel sleeve will eat the delrin quickly.  You will probably notice more NVH with Delrin, but it depends on the car.  I ran solid/spherical rod ends on a 66 Bonneville for a while while I was sorting things out.  I couldn't tell the difference, but when I went rubber to poly in the Impala SS, it was a notable difference.

I personally don't do poly anymore.  They wear quickly without proper lube, they squeak relentlessly, and don't seem to be a good trade off.  For the NVH they add, they don't seem to add as much stiffness/benefit.  Rubber or Delrin for me.

Thanks!

Car is a Beck GTS, used for street and DE.  So a lot like a FF, but with an order of magnitude price increase for anything related to the engine (aka Porsche tax)

I took things apart because of the squeaking - bushing flanges against the chassis made noise.  The working pivot was the bolt against the sleeve/spacer - didn't seem correct to me, but wanted to verify.  OTOH, neither the bolt nor the sleeve show any signs of wear.  The fit is quite close, so no slop either.

Taking the control arms out every 6,000 miles is going to get old really quick - I think I will try some Delrin.  I've got a lathe, should not be too difficult to turn a set. 

It's got a 2.1Hz ride frequency, every other suspension joint is a rod end, and it rides like an ox cart anyway.  I doubt the Delrin will make it appreciably more harsh.

In reply to burgermeister :

I have seen "high end" suspension parts where the bolt did not tighten against the sleeve.  The bushing just floated on the bolt, which required a Nyloc nut since there was nothing to tighten it against.

Utter trash.  But the company advertised in all the street rod mags so they had to be good! *snrk*

The Delrin may actually make it ride nicer by allowing the control arms to pivot freely allowing the springs & shocks to do their job better. If you can install a zerk fitting and grease channel they'd rotate smoothly for a very long time. Added bonus of not getting the poly squeeks.

In reply to NOT A TA :

Agreed.  Always do whatever induces the least amount of "phantom spring rate."

I did poly on a daily driver back in '01. I would very definitely squeak worse below freezing.  Every year I would disassemble everything and re-grease it all.  Eventually I got tired of re-greasing and just ignored it.  Drive the car 6 years before I sold it.  Told the new owner "it has polyurethane bushings, they squeak, just ignore it."

I did poly in the next daily, greased them and installed them and never touched them afterwards.  They, too, squeaked, but I ignored it and they were fine for the 7 years I drove it before I sold it.

I have poly in my current daily, greased them and installed them and never touched them since.  We're now 7 years in.

Poly DOES NOT like having to move in more than one direction.  Control arms bushings that share a common rotational axis - good.  Trailing arm bushings that need to deal with chassis roll - bad.

My recent vid on why poly bushings suck (on a panhard bar): https://www.youtube.com/watch?v=B5PWUnKYJdE

The issue with Delrin is that when everything is still tight and good, they seem perfect and after your first 3-5000 miles you're like "why didn't I do this sooner!?" But by then they're starting to get just a little bit a wear (since they don't deflect at all, something has to give), and once the bore starts to distort it's a rapid deterioration, so on the cars I've been around with Delrin, the 5-8000 miles is about it, and then the suspension is floppy due to wobbling in the bores. 

May not be as bad on Beck, though, what do they weight, 50 lb? :)

Well, whether I take it all apart because the Delrin bushings wore out, or because the poly squeaking is driving me insane, it's the same amount of work either way .  Maybe I'll learn something with the Delrin. 

The spacers were a decent press fit in the Poly.  No way those ever moved.  Also only 1/16" thick, and a bit mushroomed at the end - not really enough meat for a 1/2" grade 8 bolt.

My Beck comes in at 2000lb wet, sans driver.  Their 'official' 1750lb figure is likely based on a mag case motor & transmission, no roll cage, 16" wheels, seats without sliders, and dry.  Though, this is the front LCA, and my front axle is about 800#, so it is still light.

You can always mix and match poly and rubber, too. Any rotation that's not linear, rubber. 

Also, some poly companies groove the bushing to help trap the grease. 

I must be an outlier.  I have never had squeaky polyurethane bushings.

They also would not last very long before the material creeped and they got sloppy.

One interesting thing was that Energy Suspension rear bushings for RX-7s were three piece.  Two softer end pieces sandwiching a stiffer inner piece.  Still, though, even with having to replace them every year or so, they were cheaper than new links from Mazda.  Plus the handling was better if you didn't install the upper link bushings, so every set came with two go-rounds' worth.

I regret using an Energy Suspension full poly kit when I converted my junker Miata into an Exocet.  If I had to do it all over, I would have stayed with the stock bushings for both squeak abatement and freedom of a-arm movement without binding, particularly in the front.

Poly bushings work great, except in suspension parts.  I like poly for BMW rear subframe / diff carriers, and that's about it.

Pete. (l33t FS) said:

I must be an outlier.  I have never had squeaky polyurethane bushings.

They also would not last very long before the material creeped and they got sloppy.

 

One interesting thing was that Energy Suspension rear bushings for RX-7s were three piece.  Two softer end pieces sandwiching a stiffer inner piece.  Still, though, even with having to replace them every year or so, they were cheaper than new links from Mazda.  Plus the handling was better if you didn't install the upper link bushings, so every set came with two go-rounds' worth.

As a guy who just installed Energy bushings in the front of my RX-7 (lower control arm, sway bar and endlinks), how would you say they did up there?

In reply to 1988RedT2 :

First generation.  Had a front suspension like the bottom half of a 60s Ford: stamped steel TCAs, and tension rods on shock eye style bushings.

I did poly everywhere because I had a bad control arm bushing, only available as a $300 arm or somesuch.  Would not do the tension rod bushings again, those function purely in flexing.  Control arm bushings were okay, although with rear steer geometry (tie rods behind axle centerline) you REALLY feel it when those bushings go bad: you get the infamous wondersteer, side loads make toe change in a positive feedback loop.

In reply to Pete. (l33t FS) :

Thanks! 

I guess if there's a saving grace in this instance, it's that the car doesn't get driven a lot.  Although that could change...

In reply to 1988RedT2 :

First gen RX-7 had a much more crude and compromised suspension than the later ones:

Finished the Delrin bushings.  Turned out nice, I think.  Also made thicker (1/8" wall, vs 1/16" wall that came with the poly) spacers. 

Old, and new.

The RH side LCA ended up just as bound as it was with the poly... bolts really took convincing to go in also.  A closer inspection showed the LCA bushing hoops were not pointed at each other - they were about 1/4" and 5/16" off.  I thought this was a clever way to bend them into the correct orientation.  After this, the LCA was rotating freely.

Alignment check:

The pivots usually pull in when the control arms are welded.  I've "realigned them" with a floor jack.....

Any solid bush will eventually wear especially if you don't do the annual relube business.

The only way to get indefinite life out of bushes is to not have one part rotating against another. On the MGs I use MGB GT V8 bushes which are rubber bonded to  a central metal sleeve that is locked in by the nut tightened against the steel bush (one must only tighten once at ride height, or you will prestress the bush and lessen life).

That sort of bush will last until the rubber itself deteriorates, which in the case of the MG can be many decades.  Lots of other cars use similar bushes (e.g I used TR6 inner lower A arm Metalastic bushes to mount the differential in my TVR race car).

Anything rubber these days is fraught with risk - some of the all rubber Chinese A arm bushes last less than a year in use. The Metalastic bushes seem reliable long term, so far.