Problems caused byworn or damagedsuspension bushingsare easy tomisdiagnose. Theseservice tips andbackground informationon bushing design willhelp you avoid somepotential bushinginstallation miscues.

Problems caused byworn or damagedsuspension bushingsare easy tomisdiagnose. Theseservice tips andbackground informationon bushing design willhelp you avoid somepotential bushinginstallation miscues.

24 June 2003

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BUSHINGBASICS

BUSHINGBASICS

BY SAM BELL

We see suspensionbushings manytimes a day inour service work,in a wide array

of applications. They rangefrom small sway bar cushions tolarge control arm bushings, inmaterials ranging from soft,rubberlike compounds throughalmost rigid, highly engineeredsynthetics. When they becomeworn or damaged, they can pre-sent symptoms that mimicproblems elsewhere in the sus-pension system. The trick is tobe able to correctly diagnosethe problems that stem frombad bushings.

25June 2003

What purpose do bushingsserve? The answers fall into threegeneral categories:

•They prevent wear to a moreexpensive or less easily replacedpart.

•They cushion or absorb someroughness or vibration that wouldotherwise be transmitted to the in-terior of the car or its occupants.

•They allow a small amount ofmotion, which could not be ac-commodated by a rigid joint.

Our understanding of the needfor bushings can be improved byconsidering things taken to theirlimits: If, for example, there wereonly a rigid connection between

the control arm and the frame,any irregularity in the road sur-face would virtually send us air-borne. Yet if the same control armwere connected only by a spring,we would bounce our way downthe road like some low-rider car-toon character.

Materials SelectionMany different elastomer formu-lations are used in OE and after-market bushings. A durometer isused to measure the rigidity of thebushing material. Materials with ahigher durometer index are morerigid than those with a lowerdurometer index. But rigidity is

not the only factor that’s consid-ered by the manufacturer whenselecting bushing materials for agiven application.

Bill Beard works on the DanaTech Line, where he dispenses in-formation and counsel on steeringand suspension service issues. Billstresses the importance of consid-ering the surrounding environ-ment when choosing the correctbushing replacement materials.

“For example, many Ford ra-dius rod bushings are exposed tohigh temperatures from nearbyexhaust and to oil spillage due tobeing located more or less be-neath the engine oil filter,” he

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BUSHING BASICS

Worn stabilizer bar mounting bushings may cause a clunk that’s hardto differentiate from a similar noise caused by a bad suspension strut.Check for play here with the vehicle’s weight resting on its wheels.

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says. “For an application such asthis, a synthetic material, such asAdvanced Elastomers Systems’Santoprene, will outlast more con-ventional materials.”

Yet in other instances, a materi-al can be too rigid. Lyle Burgessof Rare Parts, a suspension partssupplier, believes that some of theearliest polyurethane radius rodbushings developed for the per-formance aftermarket in the ’70swere so stiff they caused thethreads of the radius rod to fa-tigue and break off!

Many manufacturers of replace-ment urethane bushings requireinstallers to reuse the original pins

and sleeves. This can presentproblems if the pin surface is notsmooth enough. Chromed sur-faces work best where rotation is

desired or required, as in theseapplications. Some older urethanecompounds may also presentnoise problems at or below 40°Fambient temperature. Creaking,groaning or snapping noises mayaccompany rotation.

Energy Suspension, anotherbushing manufacturer, selects froma half-dozen proprietary polyure-thane compounds tailored to over-come these difficulties. Amongthese are graphite-impregnated ma-terials as well as bushings featuringgrease grooves and a Teflon-basedwaterproof grease where the elas-tomer meets the metal.

Clevite Elastomers’ Clevebloc

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BUSHING BASICS

Rigidity is not the onlyfactor manufacturers

consider when theyselect bushingmaterials for a

given application.They also look

at the surroundingenvironment.

The bright wear on this Plymouth Voyager’s stabilizer bar end link bushing is acry for help. The bushing I.D. has worn oversize and no longer grips the bar end.

design is another example of aurethane bushing that has over-come these potential disadvan-tages in control arm and idler armapplications. It consists of a waf-fle-pattern series of greased pock-ets molded into the urethane sur-face rotating inside a chromedsteel housing. These are expensiveto make, but hold up well.

Bushing ConstructionMany bushings now use hot-bonded construction, in which theelastic material is essentially melt-ed to the inner and outer metalsleeves. This contrasts with the“shot” type, in which the rubber

material (the elastomer) is inject-ed, then expands under pressureagainst the sleeves.

Burgess notes that shot prod-

ucts, if improperly installed (bytorquing the control arm bushingwith the arm hanging, for exam-ple), will twist through a greaterrange of motion before breakingfree from the sleeve (see “BushingService Timesavers” on page 38).In many instances, it will breakfree, slip and realign itself, thenlock into the correct position. Un-der the same conditions, a hot-bonded bushing will simply fail.

Energy Suspension’s Tanya Ox-ford notes that because polyure-thane does not bond to metal, itremains free-floating and allows agreater range of motion. In con-trol arm applications, this proper-

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BUSHING BASICS

It’s easy tomisdiagnose the

cause of a clunkingnoise. Often, a wornor damaged bushing

gets overlookedin the rush to

replace a moremajor component.

Hyper-Flex Master Sets from Energy Suspension include all the suspensionbushing parts for a particular vehicle in one set, with a single part number.

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continued on page 36

ty eliminates the need to weightthe wheels before the final fasten-er torque is applied.

Inspection & DiagnosisIt’s easy to misdiagnose the causeof a clunk or a thunk. In manycases, a worn or damaged bushinggets overlooked in the rush to re-place a more major component.Careful inspection of the entiresuspension system in both theloaded and unloaded positions isrequired for the kind of accuratediagnosis your customers deserve.

Most stabilizer bar mountingbushings can be correctly diag-nosed only with the vehicle’s weighton its wheels. One additional cau-tion: When inspecting stabilizer barlinks, both sides of the vehicle mustbe equally supported with theweight on the wheels. Otherwise,the torsion of the bar will load bothlinks, hiding any play. Most control

36 June 2003

BUSHING BASICS

Left: This Fordtruck radius rodbushing is still inserviceablecondition. Bad onesmake a big clunkingnoise, especiallyduring braking.

Above: Wheninstalling stabilizerlink bushings, don’t

overtighten theconnecting link nut.

When properlyinstalled, the

bushing rubbersshould not

protrude beyondthe washers.

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BUSHING BASICS

Bill Beard candidly volunteered that he may havemade installation errors on at least half the control

arm bushing jobs he completed during 20 years as aworking tech. He now works on the Dana Tech Line,fielding service questions on steering and suspensioncomponents from Spicer, McQuay-Norris, ACDelco andNAPA, and making sure others don’t make the samemistakes he did. Beard also teaches classes on the sub-ject. Here are some of his bushing service tips:

•When installing control arms or radius rod bushings,tighten the bushing bolts only finger-tight until the ve-hicle’s weight is resting on the wheels. Then torque thebolts to the recommended tightness. This prevents pre-mature wear to the bushing caused by improper cen-tering and bushing memory. In some cases, ride heightis also affected by an incorrect final torque sequence.

•When installing front or rear sway bar bushings,both wheels must be either hanging or weighted. Ifyou’re doing only one side with a floor jack, you’ll belooking at a comeback.

•Perform this test to inspect the track bar on a

Dodge Ram: With the vehicle’s weight resting on itswheels, have an assistant move the steering wheelwhile you look from below. Check for motion by theball-stud mount to the body.

•If a customer complains of a clunking sound fromthe rear of a Chevy Lumina—even after the rear struthas been replaced—check the upper strut mounting. Ifthe bushing is worn, it will appear to be off-center.

•A clunking front end on a Plymouth Voyager maynot be caused by worn front struts, mounts or balljoints. The actual cause may be worn stabilizer barmounts and end bushings.

•What if you’re replacing bushings on a Ford Rangeror Explorer 4x4 and the parts guys ask whether yourshas the Dana 35 or Dana 28 front differential? Thequick way to tell: The Dana 35 has a pinch bolt for theupper ball joint, the Dana 28 a castle nut.

•Does the Dodge Ram 4x4 in your stall have a Dana44 or a Dana 60 rear axle? If the wheels have eightlugs, it’s a Dana 60. Any other number and the rearaxle is a Dana 44.

Bushing Service Timesavers

arm bushings can be checked onlywith the wheels hanging or other-wise unloaded.

Service Tools & TechniquesMost factory service manualsspecify special tools for use asbushing drivers. That’s fine, but

most real-world techs don’t haveaccess to these tools. So they relyon a small set of dedicated bush-ing drivers and a large array ofsockets for most bushing R&R op-erations.

Both Bill Beard and LyleBurgess concur. Burgess, based in

sunny California, states that anappropriately sized socket orbushing driver and a good ham-mer are usually all it takes to re-place and reinstall a worn bush-ing. He cautions that if a bushingbegins to cock in its bore duringinstallation, it ’s important tostraighten it out immediately, toprevent damage to the bore.Beard, from the midwest, endors-es using a bench vise as a press forbushing reinstallation. Bothstressed the importance of prop-erly supporting the workpiece andcarefully selecting the appropriatedriver. “You don’t want to bendanything—especially the outersleeve or the flange—during in-stallation,” says Burgess.

In areas subjected to heavyroad-salt use, it pays to thoroughlyclean the bore before attemptingto install a new bushing. Use awire wheel, a flex-stone hone oreven a sandblaster to remove anyrust and corrosion. In some in-stances, a small amount of a non-permanent lubricant (like liquidsoap) may be needed to ease in-stallation. But remember, thebushing shell must be locked inplace, so use any lube sparingly.

ConclusionBushing problems are easy to miss.You must inspect the entire sus-pension system in both the loadedand unloaded modes. Select re-placement bushings based on vehi-cle use and the bushing’s environ-ment. Be careful to avoid damag-ing them during replacement. Andremember that the clunking noisefrom the rear of your customer’svehicle may not signal a strut job,just some worn stabilizer barmounting bushings.

39June 2003

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