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
coil springs are made of spring steel rods that are heated & wound in the shape of a spiral
the spring is also carefully tempered to achieve proper tension
spring rate: how many pounds it takes to compress the spring one inch
Torsion Bars act just like springs because they twist with varying load forces. The response time for torsion bars are slightly faster than with springs and there is no bouncing effect.

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
Nitrogen is used as the gas.

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
What a sway bar does is counteract the action of body roll during cornering by transferring spring rate from the inside wheel to the outside wheel in a corner.
This means that you don't actually get any added spring rate; you just subtract it from one side and add it to the other.
This has the ultimate effect of transferring load from the inside tire to the outside, which has the visual effect of compressing the suspension on the inside of the turn and expanding the suspension on the outside of the turn (thus limiting body roll).
The bar is made of spring steel and is designed so that when one wheel is forced up in a turn, such as the left wheel in a left turn, the bar pushes down on the right wheel counteracting the body roll. Thereby keeping the car as level is possible under all driving conditions.

11. Front Suspension System Types
suspension pivot points, 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
The disadvantage of an SLA design is that it is slightly more complex than other systems like a MacPherson strut.
SLAs are very common on front suspensions for larger cars, pickups, and SUVs
Coil-overs allow the car to be lowered
The main purpose and advantage of the coil-over design is to allow independent ride height adjustability of each corner of the car. This ride height adjustability allows manipulation of the center of gravity of the car.
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
Although it is a popular choice due to its simplicity and low manufacturing cost, the design has a few slight disdavantages, with regards to the quality of ride it provides and how it affects the handling of the car.
Geometric analysis shows that it cannot allow vertical movement of the wheel without some degree of either camber angle change, sideways movement, or both.
It is not generally considered to give as good handling as double wishbone suspensions, because it allows the engineers less freedom to choose camber change.
The wheel tends to lean with the body, leading to understeer.
Another drawback is that it tends to transmit noise and vibration from the road directly into the body shell, giving higher noise levels and a "harsh" feeling to the ride compared with systems such as double wishbones, requiring manufacturers to add extra noise reduction or cancellation and isolation mechanisms.
Also, when the internal seals of the shock absorber portion wear out, replacement is relatively expensive compared to replacing a simple shock absorber.

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
The main advantages of torsion beam suspension are easy adjustability of ride height, and small profile along the width of the vehicle.
It provides a longer travel than leaf spring systems, and takes up less of the vehicle's interior volume compared to coil springs.
A major disadvantage is that torsion bars, unlike coil springs, usually cannot provide a progressive spring rate, forcing designers to compromise between ride quality and handling ability - progressive torsion bars are available, but at the expense of durability since they have a tendency to crack where the diameter of the bar changes.
In most torsion bar systems, especially Chrysler's, ride height (and therefore many handling features) may be adjusted by bolts which connect the torsion bars to the steering knuckles and require nothing more than crawling under the car with a wrench in hand.

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. Air Spring Suspension
read warnings in Mitchell/AllData before servicing vehicles with air suspension
air pressure can be in the 100psi to 200 psi range

22. 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

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

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

25. Suspension System Repair

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

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

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

29. 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

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

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

32. 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