The history behind the modern strut type suspension has its origins in the United Kingdom. Henny Youngman would find a joke here. Something about Scotsmen, a Lotus, a spring, and a shock absorber. The punchline would be the MacPherson strut suspension. I love this crowd! The integral spring and shock absorber arrangement was pioneered by one Earl S. MacPherson. Since Mr. MacPherson worked for Ford at the time as the head honcho of engineering, the MacPherson strut first appeared up under the unitbody front fenders of a 1951 Ford Zephyr.
The MacPherson strut was just one part of the entire MacPherson suspension, which provided not only light weight but set the bulk of the suspension mass of the low on the vehicle. This placement improved handling. The integral strut and spring simplifies and lightens the front suspension by eliminating the need for an upper control arm and ball joint. The spring, shock absorber and wheel spindle are combined into one integral unit. Since this setup makes sense from a both a manufacturing cost and weight savings standpoint it is still used on many vehicles today.
Out in Front of the Back
Another suspension pioneer is credited for putting the same type of setup in the rear of a vehicle - namely a Lotus. Chapman Struts are named after Lotus engineer Colin Chapman, whose suspension and chassis building prowess put his name into the Formula One and Indy 500 history books along with forever cementing Lotus as a performance marque. Although Chapman Struts are very similar in design to MacPherson struts we'll be rolling stock for the purposes of this article. Building and installing coilovers along with higher performance adjustable suspensions will most certainly come around the Jalopnik later on.
Capture the Shock
One drawback of the MacPherson strut setup becomes apparent when it comes time to replace the worn out shock absorber at the center of the strut. The entire strut assembly must be dismantled to release the shock absorber section from its location within the strut housing. With a double wishbone or leaf spring type suspension the shock absorber can easily be removed without any major hassles, as it is usually not captured by the spring. More complicated still is that a good number of components often must be removed to get at the struts themselves. So it goes. Simplicity in design and manufacture brings complications in maintenance.
There is a simple solution to this vexing mechanical problem. Replacing the shock absorber or strut insert inside the MacPherson strut requires a tool known as a spring compressor. With the spring compressed and held in steel claws, the unit can be disassembled. The entire strut and shock absorber can then be easily serviced. Warning! Great care must be taken when using a spring compressor. The springs held captive inside the strut assemblies are designed to support the weight of the vehicle and passengers. Tremendous force required to compress even one of these springs. Great bodily harm can result if this force is suddenly released from the spring compressor in the form of a flying spring. Use extreme caution when it comes to using any type of spring compressor.
Remove and Replace
A good option for those living without spring compressor is to replace the entire strut with a ready made complete assembly. Instead of removing the used up shock absorber or strut insert from the assembly by way of a spring compressor, the entire strut assembly is simply be swapped out. Like a loaded brake caliper the strut assembly comes ready to install - no spring compressor required! Another advantage of these units is that as shocks wear out so do springs, and replacing both as a unit not only saves time, but can restore sagging rides. These assemblies are a fairly recent aftermarket innovation they not yet available for every vehicle on the road. As they will most likely never be available for the Mitsubishi Starion, at least not in this universe, away we go.
NOTE: As replacing struts is a complicated deal - we're breaking this procedure into two parts. This week removal. Next week install.
Stuff You'll Need:
· Repair or Service Manual
· Set of Replacement Strut Inserts (Shock Absorbers)
· Jack and Jack Stands
· Spring Compressor
· Air Powered or Electric Impact Wrench (Compressor Required for Air Tools)
· Impact Sockets
· Hand Tools
· Strut Bearings (if worn)
· Replacements for Rotten Rubber Parts (if worn)
· Penetrating Oil
· At Least Four Hours
With the vehicle secured on jack stands access the struts by removing brake calipers, rotors, hubs, or any other components specified in the suspension chapter of the service manual. This is a very simple rear-drive setup. Front wheel drive adds drive axles, complexity, and more swearing. Now is a good time to use some penetrating oil on potentially stubborn bolts and fasteners.
Remove the upper strut mounting bolts on top of the strut tower.
Remove the bolts that hold the ball joint knuckle arm and strut together. If the vehicle has a sway bar loosen the end-link bushings. This will provide more travel in the lower control arms. The impact wrench is great for removing bolts, but always put them back in by hand to prevent instant thread stripping. Use impact sockets. Regular sockets will disintegrate.
Use a pry bar to separate the strut from the ball joint knuckle arm. Note locating dowels.
Remove the strut assembly from the vehicle. Putting your foot down will work this time, and can help achieve the clearance required to remove the strut. A gentle push on the lower control arm is what needs to happen. If using this method with front or rear half-shaft axles involved, be wary not to yank the half-shafts out of the transmission or rear differential.
Mark the spring seat and spring to index components for reassembly. Use a grease or paint marker so that the marks don't rub off during ham-fisted disassembly.
Compress the spring using the spring compressor. Use hand tools and work slowly. Never use impact or power tools to compress or decompress a spring with a spring compressor. The sudden movement created by an impact wrench can cause the jaws to slip and send springs flying. Don't go nuts - compress just enough of the spring to relieve pressure on the assembly.
Here is where the impact wrench comes in handy. Use it to remove the top nut holding the strut bearing and strut together. The quick action will remove the top bolt in a hurry without disturbing the spring compressor. Gently remove the strut from the spring, being careful not to disturb the spring compressor. Think Wile E. Coyote and those humongous cartoon bear traps. Keep parts in order for removal and reassembly - which we'll cover next week.