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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.

(My note: Having the rear mounting point slightly lower than the front actually increases anti-squat which is a good thing. I know Herb Adams use to run 150% anti-squat on his Trans Am car with no problems)

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. 

 

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.

  1. The factory rubber bushings in the lower control arms accommodate this rotation/twist by design;
  2. Poly bushings force the lower control arms to twist.
  3. Tubular or boxed control arms - with poly bushings - force the LCA mounting brackets on the chassis and axle to bend;
  4. 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.  
  5. 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. 
  6. 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.
  7. 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 PolygraphiteŽ 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. 

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:
    1. appearance - 'cuz they look cool
    2. added weight (some can be heavier than stock/1LE)
    3. aftermarket LCAs with spherical bushings (for racing)
    4. adjustable aftermarket LCAs with spherical bushings (for racing, FWIW)
    5. 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.
Wheel hop: I mention it here because many have commented how poly bushings have 'cured' their wheel hop problems.  Wheel hop occurs when the traction and torque applied to the drive wheels overwhelm the ability of the suspension to keep the tires on the ground.  The tire grabs, deforms, 'hops' up and comes down to grab again (and again, etc), with some forward/back motion as allowed by the bushings. As the bushings degrade over time, the problem worsens -- which is why 'upgrading' to poly seems to help, as the basic factory bushings can be worn out in as little as 30K miles.  Serious racers will go to rod ends, but for the street, to avoid the problems with polyurethane, the longer-lived 1LE bushings will suffice.  From my research and experience, good quality adjustable shocks can play a big role in eliminating wheel hop, as well as Air Lift air bags installed in the rear coil springs, which also allow preloading of the right rear tire at the strip.

References for this and other suspension topics:

  • Chassis Engineering by Herb Adams (ISBN1-55788-055-7)
  • How to make your car handle by Fred Puhn (ISBN 0912656468)
  • How to Tune & Modify Your Camaro 1982-1998 by Jason Scott (ISBN 076030436X)
  • My note: How to make you own LCA's and PHB. I want to make some just because they look so good, not to mention that fact they're cheaper to make than to buy.