Monday, December 3, 2012

Suspension Work

The suspension on your car is ironically, largely made of rubber.  A Macpherson strut (blue) on a 1995 Ford Taurus.  The spring (black) is mounted above the strut.  Control arms tie the bottom of the strut to the car.  The whole thing is attached to the car through rubber bushings.

I just completed another suspension overhaul, this time on the X5.  Automotive suspensions haven't changed much in the last 40 years, but cars are lasting longer and longer.   And often, when your suspension wears out, it makes the car difficult, if not unsafe to drive.

And repairing your suspension can be expensive and difficult.   If you don't have the right tools, such as a spring compressor, well, you really can't take apart a MacPherson strut, at least not safely.

But what does your suspension comprise? And why does it wear out?   Well, you may not believe this, but a lot of it is rubber - and what causes it to wear out is your driving style.

Most cars today use MacPherson struts up front, and then a control arm arrangement in the back with coil springs and shocks.  This sort of design became popular in the 1970's, and pretty much started to dominate the market by the 1980's.

Prior to that time, most cars used a dual-control-arm setup to provide independent front suspension.  Your old Chevy Caprice had this, and many sporting cars (e.g., Corvette) continue to use it today.

Most postwar cars adopted independent front suspension which used dual control arms (black), a coil spring (red) and a hydraulic shock absorber (yellow) such as shown in this 1981 Fiat.

Prior to that, of course, cars had solid front axles.  Unless you drive around in a Model A Ford, that really isn't relevant to the discussion.  And your old '68 Caprice had a live axle in the back - a solid once-piece design that soldiers on in pickup trucks today.  Most modern rear-wheel-drive cars today have an independent suspension, with axle-shafts and CV joints, much like the front suspension of a front-wheel-drive car.

Modern independent front suspensions have a number of wear points.  First are the ball joints, which connect the control arms to the wheel spindle assembly.  These joints are necessary as the spindle assembly has to move up and down and also rotate, so the car can steer.  So a joint than can move in three dimensions is required.

Ball Joints - Ball joints are present in both types of designs, with the dual-control-arm designs having both upper and lower joints, while MacPherson struts generally have only one per side.   These wear over time, and eventually get a little loose, making the steering and handling seem more vague.   Originally, these were greased every 15,000 miles with a grease gun.  But in the early 1960's, manufacturers would dispense with the "zerk" fittings and offer "sealed for life" ball joints.   This meant that "chassis lube" jobs were no longer necessary.  However, it also meant that ball joints needed to be replaced at about 70,000 to 100,000 miles, particularly in early cars.

Two things can damage a ball joint and cause it to fail prematurely.  First is the rubber boot tearing, allowing dirt to get in.  This can occur if you run over some road debris, such as sharp metal or the like.  The second is to strike a curb - hard.   Ball joints are usually bolted to the control arm or spindle on  one side, usually with two bolts, and then the other side pressed into the spindle (or forged control arm, on a MacPherson strut arrangement).  On some cars, such as Mercedes, the ball joint is pressed in on both sides.

Although there is a large nut on the ball joint, this is used merely to snug the tapered shaft into its mating tapered hole at the mounting point.  It is the mating of these tapered surfaces that holds the ball joint in place, not the nut.  In fact, the nut would not have enough strength to hold the ball joint in, should the taper joint fail.

And when you hit a curb, often what happens is that this tapered hole in the spindle or control arm becomes egg-shaped.  As such, the tapered shaft no longer seats, and the ball joint works loose.  Eventually, this pulls out the nut and the suspension will come apart, likely while you are driving, often with catastrophic results.

The only solution is to replace both the ball joint and the spindle assembly.  Usually the latter can be had from a junkyard.  On more modern cars, the tapered hole may be on a forged steel control arm, and these can be bought from a parts source.

Merely replacing the ball joint will not work, as the egg-shaped hole will ruin the new ball joint in short order.

Ball joints are cheap enough (about $30) but the labor to install them is pretty steep.  The entire suspension needs to be disassembled, in many cases, and this is time-consuming.

Ball joint wear, of course, can be accelerated by hard cornering, sudden stops, hitting speed bumps and curbs, and the like.

Rubber Bushings - But what holds the other end of the control arms to the car?  On both MacPherson Strut and dual-control-arm designs, usually a bushing is used to allow the control arm to move up and down in two dimensions.  These bushings are often made of rubber, and thus absorb shocks from road bumps.   A friend of mine once decided to replace the bushings in his car with bronze ones that he machined on a lathe.  His thought was, it would provide better handling.  When he was done, the car was basically undrivable, as you could feel every tiny bump in the road and the noise was deafening.

The problem with suspension bushings is multifold.   First, they are a pain in the ass to replace, as you have to take apart the entire front end to get at them.  Often they have to be pressed in to the control arms, which is not easy to do.  Second, they are made of rubber, and after a decade, they rot out and fall apart.  Usually, you notice sloppy handling and perhaps vibration at highway speeds, as the failing rubber allows the front-end alignment to wander all over the place.  Aggressive driving, hard stops, hard cornering and the like, really wear on these bushings as well.

Under normal usage, the bushings in a modern car can last 150,000 miles or so, without too much trouble.  But as the car gets older, these may start to be problematic, and combined with wear in other suspension components, result in a car that handles oddly or feels "loose" and harder to drive.

Many manufacturers sell the entire control arm, with the bushing already pressed in, which saves a lot of time and doesn't cost a lot more than just buying the bushing by itself.   But it still is not an easy job, and installing them requires some careful thought, as they need to be torqued in place when the car is sitting on the ground, not airborne.  The bushings are directional, and have to be installed and tightened in a certain orientation, or the handling will be weird, to say the least.

A new and old tied rod end for a 1997 BMW 328iC, removed from the car.  On the right side is the outer end, which attaches to the spindle and has a tapered shaft.  The inner end screws into the rack and pinion unit, and is covered by an accordion bellows.

Tie Rod Ends - Tie rod ends, or tie rods, as some people call them, are just ball joints that attach your rack-and-pinion steering (or recirculating ball-gear, if you have a really old car) to the front spindle.  These also wear and can be damaged in the same manner as ball joints.  And like ball joints, if they fail, the results can be catastrophic - one wheel will become detached from the steering and decide to go its own way.  Again, back in the 1960's and before, these were lubricated with a zerk fitting, as part of a "chassis lube".  Today, they are sealed for life, and by life, I don't mean yours.   They start to wear and get loose by 70,000 miles.   They can last the life of the car, but the steering will feel looser and looser as they wear.

And like ball joints, sudden impacts with a curb or the like can egg-shape the tapered hole in the spindle, resulting in the tie rod end coming loose.  The threaded nut on the tie rod end is not sufficient to hold it in place.  When it separates, catastrophe can occur.

Upper Strut Bearings:   I used to make these, as well as integrated spindle assemblies, for GM.   The top of the strut assembly attaches to the bodywork of the car though a bearing that is set in - you guessed it - a rubber bushing.  These bearings allow the strut to rotate, so the spindle can turn and your car can steer.  They are remarkably thin bearings, often with steel races inserted into plastic housings.   Yes, the entire weight of the front end of your car rests on a couple of plastic rings and a rubber doughnut.

A strut bearing for a 1995 Ford Taurus, disassembled.  The bearing has a plastic housing with thin metal races in it.  The rubber bushing is shown at the upper right.  It bolts to the strut tower with three bolts, and the strut shaft bolts through the center.

Strut bearing rarely wear out, but if they do, you would notice the steering getting difficult or feeling grinding noises from the front when you steer.  The rubber bushing in the strut bearing might wear out over time (crack, degrade).  Many mechanics recommend replacing these when replacing the strut cartridge, but often it is not necessary.

MacPherson Strut:  A MacPherson strut is a combination of spring, shock absorber, and suspension link component.  By making three components into one, assembly is made easier and overall cost is less.  So of course, it was invented by a Scotsman.   While these are ubiquitous today in most cars, MacPherson struts do cause some camber change as the car suspension moves up and down.   A dual control arm setup, like in the Fiat photo above, keeps the wheel perpendicular to the ground as it moves up and down.   A MacPherson strut setup, is more like a tripod, and as the strut expands and contracts, the camber (the amount a tire leans in toward the car) changes.

To some degree, this is not a problem, as sometimes you want camber changes when the car is, for example, cornering.  This can actually improve handling.  And many manufacturers tweak how the strut changes camber to work this to handling advantage.

One problem with MacPherson struts is that on most cars, you can't adjust the location of the strut, and thus cannot adjust camber.  In fact, on most cars today, the only thing you can adjust, in terms of a front-end alignment, is the toe-in, which is adjusted by rotating the tie rod ends in and out.

Strut tower on a Ford Taurus SHO.  The mounting plate for the strut is tack-welded in place, but can be moved, as in this picture, to alter the camber adjustment.   Camber adjustments may be needed if you are using sport springs or different sized tires.  Most cars do not provide for this adjustment, unless you go to aftermarket camber plates or strut bearings.

The problem with a MacPherson strut, of course, is that if the shock absorber part wears out, you have to remove the strut, disassemble the strut, and then install a new shock absorber part (which is either a cartridge, or comprises the entire strut body) and then reassemble and re-install.  In a dual-control arm setup, such as the Fiat shown above, the shock absorber can be removed with a couple of bolts, and a new one installed - in a manner of minutes.

So, changing a MacPherson strut can be a pain-in-the-ass.  How much of a pain-in-the-ass?  This link shows how much.   And while changing shocks is something a shade-tree mechanic can do in an afternoon with just a Sears socket set, rebuilding strut assemblies requires a lot more tools (such as a spring compressor) and a lot more risk.

Some backyard mechanics attempt this without the right tools, sometimes with tragic consequences.  They try to take apart the strut using the weight of the car as a compression tool, and if the spring lets loose, well, it can take your head off.  There is a lot of energy stored in a compressed car spring.

The good news is, the shock cartridges in MacPherson struts can outlast the car.  Many last 150,000 to 200,000 miles or more.  This is pretty amazing as 40years ago, a set of shocks might last only 30,000 miles, if that.  Better seal technology is one reason they last longer.  But again, how long they last depends a lot on how you drive.  Hit the speed bumps at 50, and no, they won't last long (and your bushings will be shot as well).

The odd thing about modern cars is that in the past, shocks would wear out, but springs seemed to last forever.   Today, we do hear about car springs "wearing out" - usually by sagging excessively to the point where the car has weird camber angles and handles funny.  It doesn't happen often, but it can occur.  If your car is taking on that "low rider" look, worn springs may be the reason why.

A rack and pinion unit from a 1997 BMW 328iC.  Note the "trombone" tubing for the power steering fluid - this acts as a cooler for the fluid.  Old unit is in the back and was removed because the shaft seal started leaking.  Note sway bar in the back.

Rack and Pinion:  Not really a suspension component, but a primary part of the steering gear, the rack and pinion unit steers the front end via those tie rod ends mentioned above.   Rack and pinion units don't wear out and get loose like old recirculating ball gear or worm-gear steering "boxes" of days gone by.  But they can start to leak over time, as the shaft seals wear.  And usually, the only thing to do is replace them, which is expensive and time-consuming.

I replaced one rack on a car I owned, and I suspect that the reason the shaft seal started to leak was that one tire was getting old and hard, and started to vibrate when we drove.  It is possible that this vibration worked on the shaft seal over time.  It was not that hard a job to replace, but I am in no hurry to do it again.

Most folks never change their power steering fluid.  It is hydraulic fluid (usually ATF, Dextron III or the like) and it does not "wear" out per se.   However, heat does break down hydraulic fluid over time, and I notice that on my BMWs, the fluid does turn from bright red to black after 30,000 miles or so.  I change the fluid at about that interval, usually by removing some fluid from the reservoir and then refilling it, making sure not to get air in the lines.

Sway Bars & Sway Bar Bushings:  Independent suspensions allow each wheel to "do their own thing".   A sway bar is the step back in the other direction.   Essentially a giant torsion bar, it ties the two wheels of the car together so that if the car is swaying in a corner, some of this energy is transmitted to the other side, resulting in flatter cornering.  Sway bars rarely wear out, but they attach to the suspension using small ball joints and are tied to the car with (wait for it) rubber bushings.  Over time, if you horse the car around, these components can wear as well.

Wheel Bearings:  These bear mention in that while not part of the suspension per se they a critical part of the car - they are what makes your car roll. In the olden days, repacking your front wheel bearings was something every boy learned to do in High School.   Most cars had tapered Timkin roller bearings up front, and you could take apart the hub from the spindle with little more than a screwdriver and a pair of channel-lock pliers.  Pay $1 for a tub of grease, and you could have the whole thing taken apart, cleaned and regreased in about an hour.  If a bearing actually failed, it was a simple matter to put a new one in, and the cost was only a few dollars.

Today, only trailers have such wheel bearings.  Most modern cars have integrated spindle assemblies or cartridge bearings that have to be pressed in at a machine shop.  To reduce rolling resistance, most manufacturers have moved to ball bearings.  They are sealed-for-life, and that life is not yours.  And these bearings can be easy to damage if you attempt a "DIY" repair.

Hard cornering and overloading can damage wheel bearings over time.  You will notice a "roaring" noise from the bearings when they start to fail.   Usually they give you plenty of warning when they are about to let go.  For most folks, the only choice is to take the car to a shop to have a new bearing pressed-in.

Tires: I saved the best for last.  Tires are part of your suspension - in fact, most of it.  Tires make the car - providing the handling, ride, braking, traction, and acceleration. How a car handles and feels is 90% the province of the tires.  Buy crappy tires, you will have a crappy car.  And yet, a lot of people try to go cheap on tires.  And given the staggering cost of tires today, it is not hard to figure out why.  But while shopping around on price and comparing treadwear ratings is a good idea, buying used tires or recaps is probably a bad bed for a passenger car.   And I say this with firsthand experience, as dry-rotted used tires can ride like a steamroller and often be unsafe.

And how long your tires wear is a direct function of how you drive.  Hard cornering, hard braking, peeling out, and the like can shorten tire life considerably.   Keeping tires inflated to proper pressures is also essential, as low pressures can increase tire temperatures, causing excess wear (at best) and a blowout at speed (at worst).
* * * 
Modern cars rarely need serious suspension work until they hit the 150,000 mile mark or so - perhaps later.  You may never replace a strut on a modern car, during your period of stewardship.   However, as a car creeps up to the 150,000 mile mark and beyond, replacing these and other expensive suspension components may be necessary.   And oftentimes, the cost of such replacement can exceed the resale value of the car - or comprise a significant chunk of it.

Throwing $2000 to $3000 at a used car worth only $5000 or so is often not a good idea.  Yet a used car needing new struts, brakes, tires, and a few other things (CV joints) can run up such a bill in a real hurry.  This is why it pays to have a used car inspected before you buy it.   And this is why it pays to think hard before you throw money at a used car on the premise that you are going to get into the Subaru 300,000 mile club.

And it also points out why hot-dogging your car can really wear it out.   And yet most people do this on a daily basis, without thinking about it.  When you slam on your brakes at a stop sign (as opposed to anticipating your stops ahead of time) you are throwing 4,000lbs of car onto some thin rubber bushings - and multiplying that weight by the rate of deceleration.   This type of treatment can shorten the life of your suspension - easily in half.

It is, your choice.