Vehicle Suspension Systems

1. Suspension Systems

2. Purpose of Suspension Systems • isolate passengers from pot holes & bumps • support the weight of the vehicle and its’ load • maintain tire contact with road surface

3. Suspension System Components

4. Suspension Springs • springs sit between the frame or body and the axles • the spring absorbs irregularities in the road surface a) torsion bars b) coil springs b a

5. Types of Suspension Springs c) leaf springs • oldest form of suspension spring • can be multi-leaf • or single, fiberglass “mono-leaf” d) air bags • now obsolete in automotive use • “hot rods” & custom cars often use air bags • used on many tour buses and highway trucks & trailers c d d

6. Control Arms • control arms act as pivot points for the steering knuckle • control arms or strut rods also prevent fore/aft movement of the tire during braking, acceleration and turns • the inner end of the control arm mounts to the frame or body • mounted via a rubber or urethane bushing • the other end is attached to the steering knuckle through a ball joint

7. Shock Absorbers • shocks are dampers • springs actually absorb shock • shocks DO NOT support the weight of the vehicle • without shocks, springs would compress & rebound many times • spring oscillations are slowed by forcing hydraulic fluid through tiny passages • this is the principle of fluid displacement

8. Gas Charged Shocks • gas charging is not a required part of a shock absorber • gas charging is an improvement to a conventional shock • gas charging minimizes aeration of the hydraulic fluid • nitrogen gas compresses the hydraulic fluid • this prevents the oil and air from mixing and creating foam • foam affects performance because air can be compressed - fluid cannot • with aeration reduced, the shock is able to react faster and more predictably, allowing for quicker response time and helping keep the tire firmly planted on the road surface

9. Adjustable Shocks • some aftermarket shocks can have the orifice size adjusted • this adjusts how easily the fluid can move from one chamber to the other • this alters the shock’s dampening rate • this adjustment can be done electronically or manually

10. Anti-roll Bars • anti-roll, stabilizer or sway bars help limit body roll during cornering • made of spring steel • can be used on the front only, or front & rear suspension

11. Front Suspension System Types • suspension pivotpoints, springs & shocks can be arranged in various configurations…

12. Short-long arm suspension aka “double wishbone” • uses upper & lower control arms • used on many rear-drive domestic cars • equal length arms would cause tires to scrub across the road Coilover suspension

13. Twin I-Beam suspension • rugged construction, high unsprung weight • sprung weight: everything supported by the spring • unsprung weight: everything below the spring • used on many Ford trucks

14. MacPherson strut • compact, light, low unsprung weight • very popular suspension design • used with unibody construction • modified strut • used by Ford

15. Torsion Bar suspension • one end fixed to the frame or body structure • other end fits into the lower control arm • torsion bar twists with control arm movement causing control arm to return to its original position • ride height is adjustable – not possible on coil or leafs

16. torsion bar suspension…

17. Multi-link Suspension • variation of the double wishbone suspension • each arm of the wishbone can pivot independently • helps to keep the tire tread planted on the road

18. Rear Suspension System Types

19. Solid Axle Suspension • may utilize one of the following spring arrangements… • coil springs with control arms (figs. a & b) • pan hard bar prevents left-to-right axle movement • what happens to one tire is transmitted to the other tire • leaf springs suspension (figs. c & d) b d a c

20. Solid Axle Suspension • air spring suspension • lighter than a coil spring = lower unsprung weight • no friction • has also been used on front suspension • used on transit and tour buses and many semi trailers

21. Semi-Independent • axle beam flexes to minimize movement from one side to the other over bumps & holes in the road • used with MacPherson struts • used on some front wheel drive vehicles • improved ride & handling over solid axle suspension

22. Independent – Trailing Arm Suspension • no tire scrubbing – arms positioned front to back • takes up a lot of space

23. Independent Long-Short Arm Suspension • short-long arm suspension with coilovers • used on some rear drive performance vehicles

24. Suspension System Repair

25. Shocks • check for oil leaks • bounce test car on the ground • should bounce once or twice, then stop • age of vehicle & # of km?

26. Sway Bar Bushings • check sway bar mount bushings & outer link kits for wear • worn bushings will lead to clunking noises

27. Control Arm & Strut Rod Bushings • visually inspect bushings for deterioration • use a pry bar to check for looseness

28. Testing Ball Joints • check ball joint sockets for wear • follow specific inspection procedure in Mitchell • does the vehicle have lower joint only or upper & lower? • they can break & cause tire to “kick out” • leads to loss of control & vehicle damage • when replacing ball joints, they can be… • threaded into the control arm • pressed into the control arm • riveted to the control arm

29. Broken Springs • coils, leafs or torsion bars that are weak or broken will cause the vehicle to sag on the affected corner

30. Removing/Replacing Springs • follow proper spring removal procedures! • use proper spring compressors • spring’s stored energy can injure or kill!

31. Compressing McPherson Strut Springs NEVER loosen/remove the nut at the top of the strut until spring tension has been released by the coil spring compressor!!! the spring should rotate freely when compressed before the nut is removed