Rubber over-haul

ss63

Member
I am getting ready to have my A-arm bushings changed. I got a kit of EnergySuspension polyurethane, the guy at the shop doesn't recomend me to use polyurethane for a daily-driver. He says they are too stiff and noisy (squeeky). Also any recomendations about bodymounts and ball-joints? Any imput on this items is greatly apreciated. :takethat
 

MileHiSS

 
Supporting Member 1
Here's some information on the case against poly bushings. I am not saying this is right or wrong, ( I use both rubber and poly), but I think it's good reading.

How the factory suspension and bushings work: The rubber bushings on most cars consist of a larger steel sleeve mounted in a control arm, with a smaller steel sleeve inside for the mounting bolt, held in place with rubber that was cast in place. The sleeve is fixed in the arm, and the inner tube held tight by the mounting bolt. As the arm moves, the rubber material gives to the shear forces, allowing smooth movement of the arm. There are no maintenance issues, and moving surfaces to wear/squeak/rattle, but over time, the rubber will deteriorate.

Bushings are placed at the pivot points of the suspension for some (not necessarily all) of these reasons:

Smooth movement - a nut and bolt aren't enough, but bearings overkill, or not applicable (bearings are made for circular motion, not back and forth movement)
Vibration isolation - rubber bushings reduce road noise
Deflection under load - when engineered into a system, this deflection can allow the suspension freedom of movement. See axle
The 4th generation f-body short-long arm (SLA) front suspension is designed so that the bushing deflection does not seriously impact the alignment, allowing for vibration isolation while preserving the steering geometry.
The 3rd and 4th generation Camaro and Firebirds have a trailing arm rear suspension that is susceptible to bind under some conditions. The lower control arms (LCA) are the key components, as they must position the axle front/back while handling acceleration and braking forces, while allowing the axle to move up and down and twist in relation to the chassis over bumps. The panhard rod (PHR) locates the axle side-to-side, handling the cornering forces. The torque arm is a nice feature in this setup, handling the torque from the driveline that normally would be taken up in the control arms or leaf springs (in older cars). Short of an independent rear suspension setup, this is probably as good as it gets.

Adjustable lower control arm (LCA) brackets: When you lower the car, the forward LCA chassis mounting point is lower in relation to the rear axle mount, causing the LCAs to slope down to the front mounts. This is not dangerous, but will hurt traction and increase squat and dive. These brackets allow the repositioning of the rear mounting point of the LCAs so the arms can again be parallel to the ground. If you picture the axle as pushing/pulling on the LCAs (when accelerating/braking), you want the forces to be horizontal to improve traction and minimize squat and dive. They are mounted on the axle (welded, but there are bolt in versions) and it is critical that the brackets are mounted parallel to each other, so as not to throw off the alignment of the rear axle. Note: If you alter the ride height after installing the brackets, and the rear mounting point of the LCAs are lower than the front, this will create dangerous handling at speed.

Adjustable panhard rod (PHR), for lowered cars, allows repositioning of the rear axle left-to-right in relation to the chassis. As the axle moves up and down, or when the car is lowered, the axle moves slightly left-right as the PHR swings in an arc. On most cars this is not an issue, but with larger tires and wheels some cars may need adjustment after the suspension has been lowered. After my car was lowered 2.5" in the rear, the axle was off 4 mm, not enough to worry about. You can measure this using a plumb line off the fender and a ruler against the wheel rim on each side.


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Suspension/bushing bind:

Bind occurs when the the pivot points of the suspension cannot move as intended. As it relates to third- and forth generation F-body car, bind is when the pivot points do not move smoothly under load (stiction, or static friction) or when the suspension moves outside its (or one or more of its components) design parameters (in this case, range of motion restricted by the lack of compliance in the polyurethane bushings)

Under hard cornering, bind can create dangerous handling conditions.

Polyurethane bushings:

Polyurethane (or 'poly' or 'plastic') bushings are popular, as they noticeably 'tighten up' the suspension, and the aftermarket arms look cool, but most purchasers to not understand how they work, or the problems they create. This is an old issue, but the recent popularity of poly-equipped aftermarket control arms has drowned out the proven drawbacks of this material, including stiction, binding, squeaking, harshness, and need for regular greasing.

Poly is used in place of the rubber portion of the factory bushings. Unlike the rubber bushings, they are not bonded to the inner and outer sleeve, and movement of the control arm will cause the internal surfaces of the sleeves and bushing to slide to accommodate the shearing forces. The two main issues:

Stiction (Static Friction): Under light loads, they may squeak as the arm moves. Regular greasing reduces the squeaking, but under high loads, especially cornering on uneven pavement, the "sticky" properties of polyurethane causes the plastic to "grab" the steel liner, adding harshness to the ride, as the steel sleeves can't slide smoothly over the poly bushing surfaces. At worst, when the suspension then cannot move as designed, the handling of the car will be affected and this can create unexpected and dangerous oversteer.

Binding: To complicate matters, the trailing arm type rear suspension in the late model f-body cars has bushings that flex or 'deflect' as a normal and required part of their function. As the solid 'live' axle moves to comply with an uneven surface, it (and the LCA mounting points) rotate in relation to the chassis. To illustrate:

Normal axle movement

The factory rubber bushings in the lower control arms accommodate this rotation/twist by design;
Poly bushings force the lower control arms to twist.
Tubular or boxed control arms - with poly bushings - force the LCA mounting brackets on the chassis and axle to bend;
Now that the car relies on twisting metal for suspension, it may at times bind, as the axle cannot move smoothly comply with bumps. The resulting oversteer condition can result in loss of control on high speed corners - not what you want in a high-power rear-drive car.
Subframe connectors (SFCs), added to brace the chassis, reinforce the forward LCA mounting points, but the twisting force is still there on the arms and rear mounts; poly bushings may seen to ride firmer after the addition of SFCs due to the more solid mounting of the LCAs.
Even for lower speed handling, the poly bushings increase the rear roll stiffness - something you should be tuning with the spring rates and sway bars.
Greasing the poly bushings does not help this issue.
Alternatives:

GM factory 1LE LCAs and PHR with higher durometer (firmer) rubber bushings. If you don't have a 1LE Camaro/Firebird (or earlier SS/WS6), the parts are available from GM parts counters, GMPartsDirect, SLP, and others. Don't pay extra for boxed versions of the factory parts. Reference: 1LE Part Numbers (Note: GM discontinued the use of 1LE bushings in the WS6 and SS packages a couple years ago, so may/may not apply to your car)
Spherical bushings - very noisy, harsh, meant for race cars. No deflection or stiction problems, but can loosen and rattle with wear over time.
Dispelling other myths:

Why isn't Polyurethane a good bushing material?

"...virtually no deflection..." (cut and pasted from their web page). As mentioned above, the engineers that design these cars employ rubber bushings because deflection is required in most locations.
"But I lubed them well, or I used Polygraphite® bushings": You are asking the poly material to act like metal bushings, and it can't. Lubing will temporarily reduce the squeaking and stiction. The graphite-impregnated versions are just 'pre-lubed', and once the graphite has worked its way out, the bushings will squeak and require regular lubing like the others. Lubing does nothing for the binding problem.
"They get quieter over time": Poly will cold-flow, meaning it will deform under pressure and not return to normal, as it lacks the elasticity of the rubber bushings. Over time, they will loosen and then rattle. Check out the shape of your swaybar's poly end-link bushings after only a few months. This cold-flow issue can also lead to alignment problems on the front control arms, as the bushings deform.
"But everyone sells them". Well, yes, and the manufacturers of Slick 50 and the makers of 'ultra/super white' bulbs could line up a long list of satisfied customers, but what would that mean?
"Testimonials are everywhere!" but they don't convey the facts. Don't' believe everything you read in a glossy brochure or web page. Ever watch those late night infomercials? Like those other automotive miracles, wouldn't the large manufacturers pick up on this stuff if it really lived up to all it's claims?
"But lots of other people use them!" As mentioned above, trailing arm suspension requires deflection in order to work, and when poly bushings are used, the required deflection is still there -- in the bending of the arms, mounting points, and flex of the rear tires. This is why these bushings appear to work fine for street applications.
 

MileHiSS

 
Supporting Member 1
Are Factory control arms strong enough?

"They are just stamped steel". They are more than strong enough for a 1LE car on R compound tires. The stress loads are all longitudinal. They do not support any side loads, so they don't need strength in those directions.
"They twist, especially with poly bushings in place." Of course - if you take out the bushing compliance with poly, something must give. This twisting does not effect the alignment or placement of the rear axle.
"Boxed arms are better". There is no gain to be had from boxing the factory lower control arms. This is done by welding flat plates on the underside of the stamped steel arms. If fact, allowing them to twist will compensate for the poly bushings if you have them.
"Boxed (or rectangular) tubing will resist lateral loading better than tubular". There are no lateral loads on the LCAs or PHR.
"Tubular arms are stronger". Tubes are the strongest design for resisting twisting forces - but since this is not a problem in F-body trailing arm setups, tubular arms should be purchased for:
appearance - 'cuz they look cool
added weight (some can be heavier than stock/1LE)
aftermarket LCAs with spherical bushings (for racing)
adjustable aftermarket LCAs with spherical bushings (for racing, FWIW)
spending excess cash.
Also, the strength of the tubular arms, combined with poly bushings on each end, will affect the roll stiffness of the car (turning the axle into an second swaybar) and transfer the twisting forces into the LCA mounting points on the chassis and axle. This is not good.

Many people that swear by poly bushings simply do not understand how the suspension on these cars work. BMR, a popular F-body aftermarket supplier, is a good example of this, with a FAQ that contains glaring errors regarding the specific duty of each of the F-body suspension parts.


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MileHiSS

 
Supporting Member 1
Well you asked:roll

I didn't retype this just for you. This was a reply I made to the same question a couple of years ago on the tri five chevy forum which I spend tiime on. The question kept coming up, so I took time to do some research. Take what you like and leave the rst.

dave
 

Ronnie Russell

Well Known Member
Supporting Member 2
Holy cow, Dave !!! Why don't you answer the question? :roll:roll:roll Everything a guy needs to know about bushings. Great job.
 

Phil Reed

Well Seasoned Member
Supporting Member 10
I was going to say the same thing Ronnie!! Well..........sorta of.........

Holy Crap Dave!!!!!!!!!!!!!:roll:roll:roll

I think you ought to be in Washington as our new Treasury Secterary!!!! If you have that good of insight and ability to research a subject.................you could get us out of this "recession" by next Wednesday!!!!!!!!!:roll:roll:roll

Great subject matter!!!!
 

rstreet

Well Known Member
Supporting Member 17
wow great work. Dave do you also write electrical specifications and water pipe fittings.
robert
 

MileHiSS

 
Supporting Member 1
Aw, shucks guys.

I don't know a lot about anything, but I know a little, about a lot of things. I just try to learn something new every day.

Here's an example.In all my years of playing with cars, I have never known much about flathead engines. Just last night, I got hands on experience taking one apart, and learning about them from a true expert. But these guys won't be around, all that much longer. My fear is that we are going to loose all of this great car knowledge that is in your heads. It isn't getting passed down like it used to be, and our kids will be full of misinformation. I love forums like this, that help me get to the truth.

wow great work. Dave do you also write electrical specifications and water pipe fittings.
robert

Funny, funny Robert! I've learned that we are all experts about one thing or another. No water pipe fittings, but if you ever need help with windows and doors, now that's were I might just have some pertinent knowledge.:)

dave in denver
 
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