Normal
axle movementThe internet is a great source of information -- but it is swamped with opinions and misinformation, and finding the facts can be tricky, as I found when I started doing my research for my own projects. This page has been created in an attempt to dispel some some of this, and as this could obviously become huge, it has been limited to automotive subjects, specifically those that relate to my own vehicles. References are included - well worth reading.
Trailing Arm Suspension - how it works:
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
How the factory suspension 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.
Rubber bushings are placed at the pivot points of the suspension for some (not necessarily all) of these reasons:
The 3rd and 4th generation Camaro and Firebirds' trailing arm rear suspension has inherent benefits and shortcomings (as installed in these cars):
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 pivot 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.
Lower control arm (LCA) relocation brackets: When you lower the car, the forward LCA chassis mounting point becomes much 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, increase squat on acceleration and and dive when braking, and increase wheel hop under hard braking. These brackets allow the repositioning of the rear mounting point of the LCAs so the arms can again be parallel to the ground (or slightly higher in at the rear mounting points). 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. The brackets are mounted on the axle (usually welded, but there are bolt in versions) and it is critical that the brackets are mounted parallel to each other, and the holes perpendicular to the ground, so as not to throw off the alignment of the rear axle. Do not mount the brackets so that the additional mounting holes are forward or rearward of the factory holes.
Myth - the bottom holes are the best to use for everyone: Reality - for drag racing purposes, some use the lower mounting points on the LCA relocation brackets to provide an aggressive anti-squat geometry (the LCAs sloping upwards to the chassis mounting points), but be aware that this reverses the rear-steer issue (becoming rear-oversteer), creating potentially dangerous handling at speed.
Myth - the rear mounting holes should be 'in an arc' centered on the front mounting point: Reality - this was a sales pitch from one company that wanted customers to use factory length LCA and the lower bracket holes without having the (effectively shorter) LCAs move the axle forward within the wheel well. The problem with this was that this only worked for cars at the factory ride... if you lowered the car later you had to cut the brackets off or you were forced to buy expensive adjustable LCAs to correct the positioning of the rear axle.
Myth: Polyurethane is a great bushing material. Reality - they are cheap to make and sell well, but actually create problems in the suspension.
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.
Under hard cornering, bind can create dangerous handling conditions. Since this relates to roll stiffness, an otherwise stock vehicle will encounter this problem in the form of sudden oversteer. Vehicles with higher roll stiffness (upgraded springs, sway bars) will suffer the same symptoms, closer to the limit.
Why isn't Polyurethane a good bushing material?
Are Factory control arms strong enough?
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.
Misleading FAQs and forum discussions: Many companies that sell and swear by poly bushings simply do not understand how the suspension on these cars work. There are popular F-body aftermarket suppliers with FAQs that contains glaring errors regarding the specific duty of each of the F-body suspension parts; their stuff still sells... and then sometimes their stuff breaks. Look for race-proven parts when putting your money down. Also remember that race cars are inspected before each race.... are you prepared to check your suspension on a regular basis to look for problems?
Adjustable panhard rod (APHR): the PHR locates the axle left-right within the chassis, and as the axle moves up and down the axle moves slightly left-right as the PHR swings in its arc. On most cars this is not an issue, but with larger tires and wheels some cars may need adjustment for proper clearance through the full range of suspension travel.
Myth: the adjustable PHR is you can centre the axle left-to-right within the wheel wells at any given ride height, and you need to re-adjust it if you lower or raise the car later. Reality - the most important thing about the positioning of the rear axle is that your tires do not contact chassis or bodywork anywhere throughout its full range of movement - particularly when the suspension bottoms out - so this is where you need to adjust it, with the rear springs out and the axle lifted up into the body. If there is enough clearance to allow for further centering of the axle at a given ride height, use it. If you center the axle without checking for tire clearance, you may cut the tires when you bottom out and they hit the car, an expensive lesson learned.
Myth: coil-overs allow you to drop the car to whatever ride height you want. Reality: the adjustable spring perches are only for fine tuning the ride height - shorter spring with higher rates are what's needed to lower a vehicle, otherwise you may end up with a car that crashes on the bump stops over every bump. The front alignment would need adjustment each time the ride height was changed.
Wheel hop: 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. 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 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:
Myth: The SS Camaro is a more powerful model, built by an aftermarket tuner for GM, with ram air induction, low restriction exhaust, better suspension, more standard options, and is individually numbered by the builder. Reality:
Myth: F-body convertibles have lower electronic speed limiters than the coupes. Reality: the speed limiter is set solely based on the speed ratings of the tires the car is ordered with from the factory. The base tires and wheels save money (the convertible is an expensive model) and give a more compliant ride, so this may be a more common option for the drop-tops.
Myth: F-body convertibles come with subframe connectors from the factory. Reality: this was promoted by retailers that only had SFCs for the coupes. The factory installs additional bracing in and under the door sills, but aftermarket SFCs are definitely worth the investment.
Myth: You can't buy OEM SS hoods without a proper VIN. Reality: this only applies to 96/97 parts that came from SLP. The '98+ SS parts are now over-the-counter parts. I'm just glad that I could get the hood without having to buy the entire SS package.
Slick 50 and other Teflon-based oil additives are still out there. Don't waste you money on this snake oil. More info on the legal action taken against Slick 50.
Ultra White or Super White bulbs are popular, but many don't realize you do not improve visibility by filtering the light. More info.
Armor-All:
quote:
Somewhere I heard that Armor-All is bad for your interior because it contains silicones or something. Is this true?
The more I read the bottle, the more I wondered - It says not to get on paint, clear plastics (it does ruin clear plastic), or fabric. Is this stuff safe for interiors or not?
From the Armor-all web page: "It works by penetrating the surface and combining with the molecular structure to keep it soft and pliable". Until an expert on polymers can explain how you can mess with the molecules in a polymer with no risk of damage, I would be cautious. But if it ruins clear plastic, then it is suspect on other plastics.
Take testimonials with a grain of salt. Just because it sells well doesn't mean it's better. Are you in the market for any oil additives? How about some polyurethane control arm bushings?
Do you need it at all? (I will withhold my opinions on the glossy finish left by this product, as I don't see why you would want your tires to look 'wet'). I've had 10 year old cars with new-looking dashes. I do live above the 49th parallel, and my cars are usually garage-kept. I don't smoke. Consider a dash mat and window tinting to keep the sun off the interior surfaces, and look for protectants that are cleaners/UV protectants, and do not claim to affect to the plastic -- "safe on all surfaces" sounds better to me.
Read the ingredients. If in doubt, look elsewhere.
Last edited Wednesday, October 15, 2003
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