Bushings?

I'm a little confused on bushings, more specifically on control arm bushings.

It almost appears they work differently depending upon the material.

I am replacing some Delrin bushings with some Poly to be a little more NVH friendly.

The Delrin bushes easily rotate around the metal sleeve so it appears that the sleeve stays stationary and the bushing rotates on it.

The Poly bushes fit so tightly they appear to stay stationary & any rotation is around the outside of the bushing.

Factory bushes seem to be bonded to the metal sleeve and the bushing seems to deform/twist to do it's job.

Poly rotating around the outside of the bush would explain the squeaking you get from them and why if you put a zerk and add grease periodically (which basically goes on the outside of the bush) you can quiet them down.

Am I completely wrong on all 3 counts?

Also is Grade 5 hardware adequate for control arms?  It seems Grade 8 would be too brittle.

You're basically right on your bushing observations. I personally don't like the theory behind OEM rubber bushings having to twist because it ultimately makes your suspension less supple and limits free movement. It literally is like having another progressive spring, getting stiffer and stiffer the further the suspension travels. However, these bushings are a very good design for the OEMs and most consumers because they are maintenance free, long lasting, and no chance of producing their own noise.

You have to be really careful on many modern cars now if you're looking into replacing rubber with delrin or even ployurethane. There are quite a few cars with suspension designs that will bind / lock up with bushings that only have one degree of freedom (twisting). And suspension bind is the enemy of keeping your tires happy and hooked to the pavement.

Well since mine is a homebuilt I don't need to worry much about locking up.

I'd never really thought about how the bushings worked even tho I've burned out more than my fair share of factory bushings and replaced them with poly.  It was only when I decided that Delrin was just too harsh and noisy that it was illustrated so graphically how different the Delrin was than the Poly.

Actually the Delrin was so smooth operating that it made think that Delrin might be considered a consumable as it would introduce slop as it wore.

Any bushing that isn't bonded to the inner and outer sleeves will rotate.

Poly bushings tend to be sized to be a real tight fit.  The poly will eventually wear and/or creep and then it will rattle around loose.

Grade 8 for all suspension IMO, if you can't use 8.8 or 10.9 hardware.  It's 12.9 that is too brittle for suspension, IIRC.

Thanx.  Isn't 8.8 & 10.9 AN?

You've figured out the basic concept, but the Delrin and poly bushings work the same way. Ideally, it's the steel crush sleeve moving inside the bushing but depending on how the dimensions work out, the bushing could rotate in the control arm. It's this need for relative movement that requires low friction. Delrin is a very low friction material so it's not very likely to squeak, polyurethane does not have this feature.

Rubber bushings do act as a little spring, but they can also absorb a lot of small amplitude high frequency noise so your NVH is lower. Add in their lifespan and the fact that they don't require any maintenance, and it's pretty obvious why they're the material of choice in just about every street vehicle.

carguy123 said:

Thanx.  Isn't 8.8 & 10.9 AN?

Those numbers are the bolts strength rating. 8.8 could be said to be like SAE grade 5 and 12.9 is more like grade 8.

10.9 is somewhere in between.

AN are bolts rated for use in aircraft, etc. They are stronger then grade 5 and 8.8 but not as strong as grade 8 or 12.9 bolts.  They are however less likely to snap under load, but to  bend rather then break.

There are whole books written on nuts and bolts etc. Carroll Smith wrote 3 books on race car engineering and the proper use of and the proper fastener to use is covered in them.

Poly bushings work like delrin bushings when they're properly lubricated.  IME, that means for about a month after you install them, after which they squeeze all of the lube out.  Maybe two months if you use the proper nasty silicone sticky stuff.  After that, they start to bind, which is where the squeaking comes in.  Worse than that, though, is that they're adding "stiction" to your suspension, which is like a higher spring rate that goes away once the pivot starts moving.   You can get them to partially working again if you drilled and fitted zerk fittings, but they'll never be as smooth as when first installed until you take them all apart and relube everything on the inside.

Alas, you can't use Delrin everywhere because there isn't enough "give" in it to accomodate slightly-misaligned pivot points, as are commonly used for alignment cams.

The key with AN/aircraft bolts isn't the strength rating, it's the quality control and the guaranteed consistency of them.  The nominal strength of "grade 8" bolts is just fine, the problem is that they vary too much, and some are quite a bit lower than the spec.  Since that can result in an airplane falling out of the sky, AN/aircraft bolts are tested and tracked much more closely, with paper trails, etc.

Control arms pickup points are pretty important, if they fail it can easily result in fatalities especially on the race track.  Personally I wouldn't use hardware store bolts there -- OEM or (if they aren't available) something with the kind of quality control that aircraft bolts get.

You know what doesn't have any stiction at all?  Rubber bushings.  No sliding components means no stiction.

I know, that isn't as fun.

I'm not a fan of drop-in poly bushings where a rubber bushing was specified. Think about how hard it is to remove OEM bushings vs installing the new Poly bushings.    I think poly bushings introduce a lot of slop unloaded and then transfer weight abruptly when the slack is taken up.  They're inexpensive, easy to install, and feel a lot better than a busted OEM bushing, but that's about the end of their virtues.

They work good for bushings that don't need to rotate or deflect in more than one plane.

I'll stick with rubber bushings or upgrade to a spherical joints after 2 disappointing bouts with Poly bushing upgrades.

The only experience of using of Poly by me was on my Fox Mustang track car. There the use of poly must be tempered as in the rear suspension you have bushings that travel in curved arks and not linear so poly just adds bind. You can use them at one end of each of the 4 links but not at both. Knowing this I drilled the shell and installed a zerk in the center of the shell. I also sanded one of the bushings so that the grease from the zerk would travel to the center of the bushing and into grooves I cut into the steel center sleeve. This provided a path for grease to travel all round the sleeve and adding a lubricant between the ID of the poly bushing and the "fixed" steel sleeve. The rotation of the bushing then was much smoother and I could grease the bushing as required.

Tyler H said:

I

I'll stick with rubber bushings or upgrade to a spherical joints after 2 disappointing bouts with Poly bushing upgrades.

And I've never had luck with spherical joints.  NOISE, NOISE, NOISE plus they wear out faster than I can replace them.  I think there are 26 joints on this car.  I am going to leave the spherical joints for the pushrods & inboard shocks but I am replacing them everywhere else.

I've never had much trouble with squeaking with Poly.  I've lubed them well initially and added grease fittings then I had to lube them every month or so for about 3 months and then things quieted down so that I only had to lube them about once a year

I too have never had squeaking issues with poly.  Probably because I always bought Energy Suspension and their bushings are too soft/gooey to squeak.  They do, however, wear out and then they get sloppy, so they need periodic replacement.

10-4 on the rod ends.  Teh RX-7 has two rod ends in the rear suspension, soon to be six, and the number one comment I get about in car video is "WTF is broken in your suspension?".  You don't really notice the suspension clunking and banging when you're driving it because you tune it out, but still... wow there's a lot of clunking and banging.  New ends are quiet for, literally, a day or two, then they start to speak their mind.

Never understood why you would replace a bush that doesn't wear with one that does.  Bragging rights for a couple of months until the wear becomes significant, after which both your bushes and potentially your suspension is wearing together.

The fairly stiff rubber bushes, particularly the bonded Metelastic versions, will work well unto the rubber gives up in 20+ years. Other than no bragging rights, there isn't any downside to them.

I've seen a number of cars with solid bushings fitted that were ignored afterward which resulted in needing replacement A arms etc.  Unless you are racing, forget about it.

wspohn said:

Never understood why you would replace a bush that doesn't wear with one that does.  Bragging rights for a couple of months until the wear becomes significant, after which both your bushes and potentially your suspension is wearing together.

The fairly stiff rubber bushes, particularly the bonded Metelastic versions, will work well unto the rubber gives up in 20+ years. Other than no bragging rights, there isn't any downside to them.

I've seen a number of cars with solid bushings fitted that were ignored afterward which resulted in needing replacement A arms etc.  Unless you are racing, forget about it.

I wouldn't be so quick to abandon the idea of poly et al in some cars. For instance with MGBs every single replacement rubber suspension bushing you can buy is pure Chinese garbage. Some people have them fall apart in as little as a couple months.

I'm interested in experience of those who have used sphericals or rod ends. I've always been under the impression that the really good (read really expensive) sphericals of the proper size and maintained well should last quite a long time. Airplanes use them all over the place and most of those are tiny compared to what would be used on cars.

In reply to freetors :

A lot of cars have spherical bearings in the suspension.  Toyota Camrys with rear struts have used them in the rear suspension's rear lateral links for a while, and Subaru uses them in the front suspension, first in the STI a few years back, and more recently the WRX.

Clearly they have figured out how to make them not wear out.  Mazda used them in the FD RX-7 and there were several parts updates for suspension clunks until they figured it out, or gave up trying.

I hasten to point out that the commonly used ball joints/tie-rod ends are de-glorified spherical bearings, but they have the somewhat dubious advantage of being mounted in single shear, so they can use some form of spring tension on the other side.  At one point I wanted to redo the rod ends in my suspension with tie-rod ends just so maybe the links would last longer...

jimbbski said:

carguy123 said:

Thanx.  Isn't 8.8 & 10.9 AN?

Those numbers are the bolts strength rating. 8.8 could be said to be like SAE grade 5 and 12.9 is more like grade 8.

10.9 is somewhere in between.

 

8.8 is similar to grade 5, 10.9 similar to grade 8. 12.9 is stronger, similar to a socket cap screw. 

I've installed a mix of both rubber and poly on my cars. 

For MINI's, the go-to solution for the front LCA rear bushing is to replace the oil-filled OE bushing with PowerFlex poly bushings.  I've seen the OE bushings puke out their oil in literally less than 10K miles.  However, they do seem to need some level of regular maintenance. The design is slightly different than other poly bushings. There is a large bushing pressed into the carrier mounted to the body and a second bushing that slips onto the hexagonal part of the LCA. The latter rotates inside the former as the suspension cycles. Strangely, PowerFlex provides what essentially looks like copper anti-seize to be the lubricant, which while sticky as hell, I've understood to actually be anything but a lubricant when viewed under a microscope.  When I install these bushings, I use the sticky green poly grease I've received with different poly bushings kits. 

On Spitfires, poly front control arm bushings are a popular "upgrade" but I agree keeping them lubricated can be a challenge.

I know one caveat about rubber bushings is they need to be torqued down when the car is weighted.  Tightening the bolts with the suspension drooped can cause problems.  Unfortunately, this is easier said than done on some cars.

Ian F said:

I know one caveat about rubber bushings is they need to be torqued down when the car is weighted.  Tightening the bolts with the suspension drooped can cause problems.  Unfortunately, this is easier said than done on some cars.

^This is a great point.  You should torque all your bushings with the car resting on it's wheels.  If you don't, especially with rubber bushings, you'll introduce binding or preload until the bushing is dead....that won't take very long.

Poor man's solution is an open deck trailer or wheel cribs.  If you want to get fancy, a drive-on lift/alignment rack.

carguy123 said:

And I've never had luck with spherical joints.  NOISE, NOISE, NOISE plus they wear out faster than I can replace them.  I think there are 26 joints on this car.  I am going to leave the spherical joints for the pushrods & inboard shocks but I am replacing them everywhere else.

Knurled. said:

10-4 on the rod ends.  Teh RX-7 has two rod ends in the rear suspension, soon to be six, and the number one comment I get about in car video is "WTF is broken in your suspension?". 

What make/model/size of sphericals/rod ends are you each using in the various locations?  Have you gone so far as to specifically request only the tighter fit units for the given make/model of sphericals/rod ends?  If even the best teflon and/or injection molded race (nylon based) rod ends have proven to be insufficient, have either of you looked into or considered the off-road originated heavy duty products, like Johnny Joints and the ilk?

freetors said:

I personally don't like the theory behind OEM rubber bushings having to twist because it ultimately makes your suspension less supple and limits free movement. 

I can't say that I am inclined to agree with this assessment. 

The only real drawback I see with bonded rubber bushings is the geometry change when they deflect under lateral load, which I expect the geometry can be designed to largely take into account. 

Beyond that, 0 stiction is only a benefit, as a digressive stiffness is going to be inherently harsher feeling than a progressive stiffness.  And as long as the bushings full range of intended motion is greater than that of the suspensions (shocks) mechanical range of motion, then there I don't see any real detriment to a relatively small progressive rate contribution from the bushings...In fact, I can even see how it could be used to the suspension designers advantage, including in conjunction with the bumpstops that many modern cars are utilizing during normal suspension operation to intentionally increase the progressiveness of the suspension.

My experience with aftermarket (both polyurethane and Delrin) on my Fox chassis car is that the center metal sleeve is actually too short to allow proper torquing of the fastener. My first fix was to loosen the fastener, and apply a jam nut, but, in time, the holes got oblonged. The real fix was to add metal to the metal sleeve so that they were longer than the bushing material, which let me torque the fastener to spec, while still allowing the arm to move freely. My Fairmont's front control arms will slowly fall until they point at the ground when the rest of the suspension is unhooked. 

Driven5 said:

freetors said:

I personally don't like the theory behind OEM rubber bushings having to twist because it ultimately makes your suspension less supple and limits free movement. 

I can't say that I am inclined to agree with this assessment. 

The only real drawback I see with bonded rubber bushings is the geometry change when they deflect under lateral load, which I expect the geometry can be designed to largely take into account. 

Take into account?  There is a whole engineering subfield dedicated to how to vary suspension geometry under various loads with engineered bushing compliance.  Kinematics.

Knurled. said:

Driven5 said:

freetors said:

I personally don't like the theory behind OEM rubber bushings having to twist because it ultimately makes your suspension less supple and limits free movement. 

I can't say that I am inclined to agree with this assessment. 

The only real drawback I see with bonded rubber bushings is the geometry change when they deflect under lateral load, which I expect the geometry can be designed to largely take into account. 

Take into account?  There is a whole engineering subfield dedicated to how to vary suspension geometry under various loads with engineered bushing compliance.  Kinematics.

I'm going to write a book: "10000 ways to worsen the handling of your BMW with aftermarket parts for less than $500."  

Driven5 said:

What make/model/size of sphericals/rod ends are you each using in the various locations?  Have you gone so far as to specifically request only the tighter fit units for the given make/model of sphericals/rod ends?  If even the best teflon and/or injection molded race (nylon based) rod ends have proven to be insufficient, have either of you looked into or considered the off-road originated heavy duty products, like Johnny Joints and the ilk?

Well I began with Aurora ends and then went up from there.  I've never looked into off-road stuff because I didn't think it was any different.  Is it?