Bent Suspension Components
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DIAGNOSING AND REPAIRING BENT SUSPENSION Issue 12/2017 COMPONENTS SHOCK ABSORBER, SUSPENSION, BRAKES, TOWBARS AND WHEEL ALIGNMENT SPECIALISTS Diagnosing Bent Steering and We do this by making use of alignment angles to effectively divide the suspension into two halves. Suspension Components Using The alignment figures will tell us in which half of the Steering Geometry Angles suspension the fault will be found. Camber is one of the most commonly adjusted alignment The alignment angles we use to do this are Camber, geometry angles and 95% of all faults are corrected by S.A.I. (Steering Axis Inclination) and I.A. ( Included Angle). normal alignment methods. However in the other 5% S.A .I., also known as King Pin Inclination (K.P.I.), is the of cases, location of damaged components can prove angle between the true vertical and a line drawn through difficult and time consuming. More importantly, incorrect the centre of the strut’s top pivot (or upper ball joint) diagnosis and repair of the camber faults may lead to and the lower ball joint. It is sometimes difficult to obtain far more serious ramifications. This issue of Tech Stop, an OE specification on S.A.I. and so we recommend shows how alignment angles can be used to indicate keeping a record of SAI angles to obtain an average where the damaged component is, what to replace and figure which becomes your specification for a particular how to achieve correct alignment geometry angles. vehicle. There are a number of potential causes of camber faults I.A is the angle between the S.A.I. and camber line when including movement within the bushes; wear in the viewed from the front. We cannot measure I.A. directly joints; ride height changes; flex from within the chassis; and so we calculate it by adding or subtracting the actual or a combination of the above. camber from the S.A.I.. This explains the term ‘Included Angle’ as you need to include camber with the S.A.I. to As we have mentioned, normal adjustment will correct get the I.A.. When camber is positive, add it to the S.A.I. the great majority of these faults. Our purpose here is to angle. If camber is negative, subtract it from the S.A.I. to show how the use of alignment angles, can make it easy obtain the I.A.. to identify problems. Here are two examples: S.A.I. + Camber = I.A. 1. S.A.I. = 9° Camber = + 1° I.A. = 9° + 1° = 10° 2. S.A.I. = 11° Camber = -1° I.A. = 11° + -1° = 10° Example 1 Example 2 Straight advice, specialists you understand and... The S.A.I. and I.A. are very good wheel alignment geometry angles to use as diagnostic tools for vehicles that are not producing alignment figures consistent with the O.E. specifications. It helps you determine if a component is bent and where it is located. DIAGNOSING AND REPAIRING If the S.A.I. is at the OE specification, (on averageBENT 13° to 14°), we SUSPENSION can be certain that the problem is outboard of the steering axis pivots. If the S.A.I. is greater or less than the OE spec, then the problem will lie inboard of the steering axis pivots, one of the pivots has moved (or both). Issue 12/2017 COMPONENTS In twin lateral arm suspension the steering axis pivot is the centre line drawn between the upper and lower ball joints. On a MacPherson or Chapman strut suspensions,SHOCK ABSORBER, the steering SUSPENSION, axis pivot BRAKES, is TOWBARSthe centre point of the top pivot bearing and the centre of the lower ball joint.AND WHEEL ALIGNMENT SPECIALISTS Example 1. The S.A.I. and I.A. are very good wheel alignment The Included Angle on the LH side is within OE specs, geometry angles to use as diagnostic tools for vehicles but the RH side is 2° out. Because the RH side S.A.I. is A car with MacPhersonthat are not producing Strut suspension alignment has figures the followingconsistent camberto readings: specification but its Included Angle is incorrect, we with the O.E. specifications. It helps you determine if a know that the fault exists outboard from the steering axis RH = -1° componentLH = +1° is bent10' andOE where spec =it +1°is located. pivots. The vehicleIf wasthe S.A.I. involved is at the in OE an specification, accident and (on we average need 13°to determineThe components what damage that arehas outboard been done from tothe the steering to 14°), we can be certain that the problem is outboard axis pivots are the ball joint stud, the strut shaft, the strut alignment . ofA thevisual steering inspection axis pivots. reveals If the no S.A.I. difference is greater between or less the leftbody and and right the forged suspension stub axle components. or the knuckle assembly. than the OE spec, then the problem will lie inboard of We know that the fault does not exist inboard from the By checkingthe the steering S.A.I., axis the pivots,following one ofwas thenoted: pivots has moved (or steering axis pivots. Thus the following components will both). RH = 7° 15’, LH = 7° 00' OE spec = 7° be in correct alignment: the ball joint seat, lower control In twin lateral arm suspension the steering axis pivot is arm, lower inner bush, chassis rail, strut tower and top The S.A.I. onthe both centre sides line are drawn within between specs. the upper and lower ball bearing plate. joints. On a MacPherson or Chapman strut suspensions, From the camberthe steering and S.A.I. axis pivot read isings the, centrewe can point calculate of the topthe pivotIncluded Example Angle. 2. bearing and the centre of the lower ball joint. A vehicle with twin lateral arm suspension has the RH 6° LH 8° 10' following wheel alignment specifications: Example 1. The IncludedA carAngle with MacPhersonon the LH sideStrut suspensionis within OE has specs,the but the RH side is 2°RH out. BecauseLH the RH sidOEe S.A.I. is to specificationfollowing camber but readings: its Included Angle is incorrect, we knowCamber that 2°the faul20’t exists outboard-0° 20’ from the-O° l5’ steering axisRH pivots. = -1° LH = +1° 10’ OE spec = +1° S.A.I. 5° 55’ 8°30’ 8°35’ The componentsThe vehicle that arewas outboard involved in from an accident the steering and we axis need pivots areI.A. the ball joint8° 15’ stud, the8° strut 10’ shaft, the8°20’ The S.A.I. and I.A. are very good wheel alignmentto determine geometry angles what to damage use as diagnostic has been tool dones for vehicles to the that are not producing alignmentstrut figures body consistent and thewith forgedthe O.E. specifications.stub axle orIt thehelps knuckle you determine assembly. if a This vehicle obviously has a camber problem, but the alignment. A visual inspection reveals no difference component is bent and where it is located. Included Angle is to specification. Because of this we between the left and right suspension components. know that all the components between the two steering If the S.A.I. is at the OE specification,We know (on thataverage the 13° fault to 14°) does, we notcan beexi certainst inboard that the fromproblem the is steering axis pivots. Thus the following components outboard of the steering axis pivots.willIf be the inS.A.I. correctBy is greaterchecking alignment: or less the than S.A.I., the the OE theball spec, following joint then the seat, problemwas lower noted: will liecontrol arm,pivots lower and inner the wheelbush, arechassis in correct rail, strutalignment. tower inboard of the steering axis pivots, one of the pivots has moved (or both). and top bearingRH = plate.7° 15’, LH = 7° 00’ OE spec = 7° This means the problem is inboard of the steering axis In twin lateral arm suspension the steering axis pivot is the centre line drawn between the upper and lower pivots. The possible faults are a bent chassis, incorrectly The S.A.I. on both sides are within specs. ball joints. On a MacPherson orExample Chapman strut 2. suspensions, the steering axis pivot is the centre point of the positioned ball joints, stretched top arm, bent lower arm, top pivot bearing and the centre of the lower ballFrom joint. the camber and S.A.I. readings, we can calculate worn upper or lower pivot bushes. Example 1. A vehicle withthe Includedtwin lateral Angle. arm suspension has the following wheelalignment specifications: RH 6° LH 8° 10’ A car with MacPherson Strut suspension has the following RH camber LH readings: OE RH = -1° LH = +1° 10' OE spec = +1° Camber 2° 20' -0° 20' -O° l5' The vehicle was involved in an accident and we need to determine what damage has been done to the alignment . A visual inspection S.A.I.reveals no difference5° between55' the 8°30'left and right8°3 suspension5' components. By checking the S.A.I., the following was noted: RH = 7° 15’, LH = 7° 00' OEI.A. spec = 7° 8° 15' 8° 10' 8°20' The S.A.I. on both sides are withinThis specs. vehicle obviously has a camber problem, but the Included Angle is to From the camber and S.A.I. readspecification.ings, we can calculate Because the Included of this Angle. we know that all the components between the two steering pivots and the wheel are in correct alignment. RH 6° LH 8° 10' Example 1 Example 2 The Included Angle on the LHThis side ismeans within OE the specs, problem but the RHis sideinboard is 2° out.