Category Archives: Suspension

Rubber Soul – Looking after your Rubber-To-Metal Components

Rubber Soul – Looking after your Rubber-To-Metal Components

They’re not visibly prominent and many drivers won’t even be aware of their existence, but rubber-to- metal (RTM) components play a vital role in vehicle dynamics and safety. On occasions, workshops may need to explain this to a customer when justifying the replacement of damaged or worn parts that remain largely unseen. Take suspension strut and shock absorber top mounts as an example: in addition to preventing vibration and noise from intruding on passenger comfort, their condition directly affects steering, handling and braking characteristics.

What is RTM?

In simple terms, a rubber-to-metal component is a vulcanised rubber block bonded to metal (or plastic), used to join components or structures that must be isolated from noise and vibration – Fig 1 illustrates typical front axle locations. In practice, reaching an effective compromise between durability, safety and comfort involves many complex considerations when designing each individual RTM component to suit a specific vehicle model and purpose.

This leads to unique rubber/additive recipes and product designs to tune dynamic properties, while also meeting requirements such as high fatigue strength, resistance to ageing, temperature resistance, and recyclability. For this reason it is recommended to always use replacement parts from an original equipment manufacturer as fitted at the factory by many vehicle manufacturers. Parts from other sources that appear visually identical may for instance be constructed with rubber of unsuitable characteristics, e.g. hardness, or simply glued together rather than chemically bonded during vulcanisation.

The manufacturing process

Natural rubber comprises long polymer chains that can move independently of each other, allowing plastic deformation. To be suitable for RTM component construction it must be vulcanised to form an elastomer, which is both elastic and dimensionally stable. When making RTM parts, the rubber is also bonded to the metal substrate during the vulcanisation process. The metal is first primed, and then given a topcoat consisting of polymer solutions and other ingredients. The rubber/additives blend is then mixed with sulphur as a catalyst and moulded with the metal substrate under heat and pressure.

During the vulcanisation process, the metal interacts with the primer, the primer with the topcoat and the topcoat with the rubber. A very high modulus layer forms in the rubber next to the substrate, yielding a strong bond of only 10 to 20 microns in thickness. Meanwhile, polymer molecules in the rubber form cross-links, reducing the ability of the polymer chains to move independently. This allows the rubber to deform under stress but return to its original shape when the stress is relieved.

Safety, comfort and consequential wear

Shock absorbers must maintain tyre-to-road adhesion for good grip and braking. Worn top mounts reduce optimum tyre contact, resulting in longer braking distances and compromised handling, especially during critical avoidance manoeuvres. In addition, anti-lock braking and stability control systems can only function perfectly if all suspension components are in faultless condition.

Worn top mounts impair ride comfort, generating noise and transmitting vibrations into the vehicle interior. They also create higher loads on new shock absorbers and other suspension components such as drop links, which then wear more rapidly.

Top mount fault diagnosis

Wear in the top mounts may manifest itself through increased vibration, longer braking distances, or stiff/non-self-centring steering – symptoms that usually develop gradually and go unnoticed by the vehicle owner until a knocking noise prompts investigation.

Where possible without dismantling, visual inspection may reveal folds or cracks in the surface of the rubber (Fig 2) or the rubber detaching from the metal. Following strut removal, a thorough examination can be made and the top mount height compared with a new item (Fig 3). Although elastomer rubber does tend to settle under a static load, for a component in serviceable condition the height difference should be less than 2 to 3mm.

Workshop opportunities

At each service inspection, workshops should visually check the condition of the top mounts and for wear symptoms during a test drive, advising customers of any suspected faults. We recommend that top mounts are renewed each time the shock absorbers are replaced to ensure that vehicle safety and performance are maintained. No additional time is involved as the mounts need to be removed and replaced anyway, so this practice also boosts profit margins. Like shock absorbers, top mounts should always be replaced in pairs.

Active Suspension

Be Pro-Active – Active Suspension

The new Citroën C5 Aircross was launched in 2017, and KYB was selected as the Original Equipment supplier for the shock absorbers. The initial reviews in the automotive press described the behaviour of the vehicle as: “an ultra-comfortable hatchback with a unique personality”, with one commentator enthusing that “even before we’d driven our first mile, the improvements in comfort and overall refinement are little short of astonishing”.

Active suspension is starting to become a reality in passenger cars, and semi-active solutions are conquering more segments of the market. Thanks to the joint development between KYB and PSA, a suspension concept based on passive shock absorbers, capable of merging high performance with competitive costs, has been developed and applied to the Aircross. Citroën is calling the system Progressive Hydraulic Cushions.


Cutaway of shock absorber with double hydraulic stopper system.

The secret of this concept is a double hydraulic stops system. The total stroke of the shock absorbers can be divided into three differentiated parts, for which the shock absorber will provide different characteristics. The first part corresponds to the position around the center of the stroke. In this working area the conventional valving in the piston and the base valve provide the damping forces. The second and third parts correspond to the positions close to the end of the rebound and the compression strokes, with the hydraulic compression and rebound stops responsible for providing additional energy absorption.

This split allows the shock absorbers’ main valves to provide comfort and allows the hydraulic stops to take responsibility when more demanding situations are encountered. In order to achieve this effectively, both the rebound and compression stops have to be able to provide sufficient energy absorption and to have a very flexible response. The stops provide an unprecedented comfort level, and give what Citroën describes as a ‘flying carpet effect’, as the car feels like it’s flying over bumps and holes in the road.

KYB Europe’s General Manager for Aftermarket Product Management, Jean François Huan, explains: “This is another great example of the pioneering research and development that our OE engineers are famous for. I look forward to seeing how this new technology develops in the aftermarket”.

The challenges faced by KYB during the development of this double hydraulic stop system were reportedly huge. One important point was to keep the main damping law of the shock absorber invariable by the components that are part of the hydraulic stops. This goal was achieved by hydraulic and FEA calculations, and was verified by driving tests.

Another key requirement was to design the different components with sufficient robustness, in order that they withstand the high demands of the vehicle, even in the worst conditions. To be able to achieve this objective, KYB studied different material options and several geometries before reaching the optimal solution. Naturally, all components had to be built with the highest precision.

The working principle for the rebound stop is based on a reinforced plastic segment that is placed in the inner tube of the shock absorber through a deformation that defines the working area of the hydraulic rebound stop. When the rebound washer contacts the segment, a new oil chamber is created, meaning the oil is only capable of getting out of the chamber through the aperture of the segment. This controlled flow generates a hydraulic force that can be tuned with the adjustment of the segment opening. Additionally, the working area of this hydraulic stop can be tuned by changing the inner tube deformation length.

For the hydraulic compression stop, a similar principle is used. A new oil chamber is created by the interaction of a polymer component placed in the shock absorber piston and a metallic tube press fitted in the base valve assembly. The polymer part is built with some slots for the oil passage, which will allow tuning the efforts provided by the system. In order to achieve the desired maximum effort, a pre-compressed additional valve is placed in the base valve sub- assembly. The installation of the hydraulic compression stop enables the car manufacturer to simplify other suspension components, such as the compression bumper, as well as to redefine some structural parts, because of the lower efforts that will be transmitted to the vehicle chassis.

KYB was able to develop a system that combines robustness with a wide tuning range, which provides the vehicle with a soft damping when comfort is demanded and with excellent handling when control is needed. It is important to highlight that these features are met with a passive system, which assures an excellent response time and a competitive cost, according to the company. KYB is applying the double hydraulic stop system in other forthcoming vehicles in the European market – for instance the Citroën C4 Cactus – so keep an eye out!

Top Tips for Shock Replacement

Top Tips for Shock Replacement

It is recommended that three basic rules are observed when replacing shock absorbers:

  • Always replace in axle pairs, i.e. both front or both rear shock absorbers
  • Use original equipment (OE) quality replacements
  • Replace ancillary components of the shock absorber assembly at the same time

Always replace in axle pairs

The advice from OE manufacturers to always replace shock absorbers in axle pairs has been largely ignored by vehicle owners and workshops over the years, having been dismissed as a strategy to increase sales. The reality is that both shock absorbers on the same axle tend to do the same amount of work under the same environmental conditions and are subject to a similar degree of wear over time.

Gradual deterioration of a shock absorber’s performance with wear generally goes unnoticed by the driver. However, under heavy braking or during avoidance manoeuvres, there is a rough difference of 25% in damping force between a worn shock absorber and a new one on the same axle, which can lead to potentially dangerous consequences. The increasing complexity of newer steering and suspension designs means that minimising the variation in characteristics between components on the left and the right is even more critical in maintaining stability.

Use OE quality replacements

When advertising replacement shock absorbers, some manufacturers interpret ‘OE quality’ somewhat loosely in the descriptions of their products. In this case, it’s advisable to choose a brand that is actually supplied to the vehicle manufacturers as factory fitment.

OE shock absorbers may have different specifications for each engine size within the same vehicle model line-up to compensate for weight difference, and they are occasionally ‘handed’ (different left- and right-hand specifications). By contrast, many aftermarket parts compromise by covering an entire model range with the same shock absorber part number.

Replace ancillary components at the same time

In addition to new fasteners, three shock absorber-related items should be considered for replacement (Fig 1): the spring assister, commonly referred to as a bump stop, the gaiter, which protects the shock absorber piston rod from road debris, and the top suspension mount.

There is no additional work involved; all of these items are removed to gain access to the shock absorber.

Why is it important to replace these items?

The spring assister is certainly more important than ‘bump stop’ suggests; it supplements road spring compression at a predetermined point to prevent the suspension from bottoming out. More than a simple buffer, the assister’s material properties and design determine its behaviour at a vital time when the suspension is approaching its operating limit. It’s a crucial part of the shock absorber’s function and when it wears or gets damaged, the original operating characteristics of the vehicle are compromised.

Oil leaks from a shock absorber are a common reason for replacement. That leakage is likely to have been caused by road grit entering a split gaiter. When deposited on the shock absorber piston rod, it abrades the plating on the rod’s surface, causing roughness and creating the potential for corrosion. Either this and/or the grit itself tears the piston rod’s seal. Some of this oil and grit is retained by the spring assister, the structure of which subsequently degrades and attracts additional contaminants. Reusing this component on a new shock absorber is not recommended for obvious reasons.

A worn spring assister may separate into multiple segments (Fig 3). If only part of the assister is re-installed on the new shock absorber, the spring could become coilbound under extreme compression, transferring its energy directly to the vehicle structure and damaging the suspension turret or hub carrier. Detached spring assister fragments can also become trapped between the piston rod and seal, causing oil leakage.

We also recommend that the top suspension mounts are renewed whenever the shock absorbers are replaced. The top mount is a compliant rubber-to-metal component joining the shock absorber to the vehicle body (Fig 4).

It prevents suspension forces, noise and vibration being transferred to the cabin. Worn top mounts (Fig 5 & Fig 6) reduce optimum road contact, causing longer braking distances and compromised handling, as vehicle safety systems such as anti-lock braking and stability control programmes only function perfectly if all suspension components are in top condition.

How to Replace the Rear Shocks on a Peugeot Partner

Shocking Results: How to Replace the Rear Shocks on a Peugeot Partner

KYB provides a walk-through of how to replace the rear shock absorbers on two van models: Citroen Berlingo and Peugeot 5008/Partner.

This fitting guide runs through the process for replacing rear shock absorbers on: Citroen Berlingo/Berlingo Multispace (04/2008 onwards), Peugeot Partner/Partner Tepee (04/2008 onwards) and Peugeot 5008 (06/2009 to 11/2013). There are just fewer than 300,000 of these vehicle models on the road in the UK. The estimated fitting time for front shock absorber replacement is up to 90 minutes per side.

Remove the spare tyre. For the Peugeot 5008, you can find the special access tool just below the lip of the boot wall.

Remove the protection shields and rubber straps from the axle.

On the right hand side, remove the heat shield above the exhaust, to give access to the coil spring. Use a compressor to remove the coil spring.

On the left hand side, use a handheld compressor to compress the coil spring, in order to remove it from the vehicle. Remove the bolts on the mounting plate above the shock absorber.

Remove the bottom bolt, then remove the shock absorber and mounting plate.

Remove the mounting plate from the shock absorber.

Attach the mounting plate to the top of the new shock absorber.

Ensure the alignment is at 90 ̊.

Reattach the shock absorber and mounting plate to the vehicle. Replace the coil springs and heat shield, followed by the axle protection shield and rubber straps. Finally, replace the spare tyre. KYB recommends that shock absorbers and coil springs are always fitted in axle pairs.


INTERNAL REBOUND SPRING F.A.Q.s

INTERNAL REBOUND SPRING F.A.Q.s

“Why are some KYB shocks shorter than OE?”

This is due to the presence of a “rebound spring”. During the first mass production phase of a car, OE struts will often contain a rebound spring. It is at this point that the KYB aftermarket shocks are released, exactly matching this initial design.

After the initial mass production phase, some vehicle manufacturers are known to remove the rebound spring to reduce cost. This means when comparing a new OE unit with a KYB unit, there will be a noticeable distance in piston rod length- sometimes by up to 50mm. This can also be the case when comparing a KYB unit with a cheaper brand unit which does not contain a performance enhancing rebound spring.

It is worth noting the length of the piston has no effect on the ride height of the vehicle, this is determined by the height of the spring seat.

“What does a rebound spring do?”

It is a metal spring placed around the base of the piston rod inside the body of the shock absorber. The purpose of the rebound spring is to protect against potential damage from full extension of the piston rod. This also adds stability on cornering, and adds extra resistance during moments of heightened body roll, increasing comfort and safety.

The presence of the rebound spring makes it almost impossible to manually fully extend the piston rod from out of the body of the shock absorber. This is why there is a noticeable difference between units with and those without.

“When transfering the compressed coil spring and mounting kit to the new strut, the threaded stud doesn’t come through far enough”

On some applications, it is necessary to raise the axle or suspension slightly to attach the shock absorber mountings. This can be done either with a drive on ramp or by raising the lower control arm / axle so that it is not fully extended.

There are also tools on the market to assist with fitting shock absorbers that have a rebound spring. They compress the internal rebound spring sufficiently to be able to extend the piston rod to the required length to be able to thread the upper nut correctly.

TOYOTA RAV4 (Front)

TOYOTA RAV4 (Front)

When you replace the strut mount, you must check the shape of the piston rod. KYB shock absorbers 339031/32 have a flat surface and the strut mount must reflect this. These flat surfaces lock the piston rod in the installation position, allowing you to tighten or remove the nut. So, if you use the wrong strut mount, you are not able to assemble the parts correctly.

KYB shock absorbers 339031/32

DACIA Lodgy (Rear)

DACIA Lodgy (Rear)

Following a fitting test, KYB has found that this shock absorber must be fitted with the serrated surface against the car body – otherwise you may hear noise whilst driving.

Car body

Upper eye of KYB shock absorber

Fitting

Front Shock Fitment: Alfa Romeo

Step by step replacement guide for 01.11 Mito Model

With nearly 18,000 of these models on the road in the UK, the chances that your workshop will be faced
with a shock absorber replacement are fairly high. This job should take roughly one hour per side and should be undertaken following our expert instructions.

Getting started

Remove the tyre. Now release the ABS sensor cable from it’s clip, then the brake hose (see Fig 1).

Undo the clip on the left and keep it safely stored (see Fig 2).

fig3

Then undo the brake hose clip (see Fig 3).

fig33

Raise the height of the vehicle then remove the bottom two bolts from the strut (see Fig 4).

fig 4

Strut assembly

Under the bonnet, remove both windscreen wipers and the scuttle panel (see Fig 5).

fig5

Loosen the top nut and, whilst supporting the strut below, remove the nut and lift out the strut assembly (see Fig 6).

fig6

Use a good quality coil spring compressor to safely disassemble the unit.When assembling the new KYB shock absorber, coil spring, protection kit and top mount, check the end of the coil spring is aligned at the correct point on the spring seat (see Fig 7).

fig7

Gripping stuff

Ensure you tighten the top mount to the correct torque. It’s essential that you never use mole grips to steady the piston rod whilst assembling the unit – the grip can damage the smooth chrome coating on
the piston rod which will result in it not having perfect contact with the oil seal, causing premature leaking (see Fig 8).

fig8
The assembled suspension unit can now be offered up under the wheel arch and fixed in position from the top first, tightened to the correct torque. Use a small jack to support the wheel hub weight (see Fig 9).

fig9
Lower the vehicle and finish tightening the top nut to the correct torque. Then you can replace the bulk head, windscreen wipers and scuttle panel, not forgetting the small clip to the side of the bottom bracket see Fig 10).

fig10

Always fit in pairs!

KYB advises that you check the wheel alignment after the shock absorber is fitted to the vehicle and that shock absorbers and coil springs are always fitted in pairs.

VW Golf lV, Bora, Jetta IV; AUDI A3, SEAT Leon, Toledo; SKODA Octavia Front Suspension

VW Golf lV, Bora, Jetta IV; AUDI A3, SEAT Leon, Toledo; SKODA Octavia Front Suspension

Fitting video showing correct fitment of shock absorbers and coil springs to the front of:
Audi A3 2WD (09.96-05.03)
Seat Leon (11.99-06.06)
Seat Toledo II (04.99-05.06)
Volkswagen Golf IV 2WD, Variant (08.97-06.06)
Volkswagen Bora, Variant (10.98-09.05)
Volkswagen Jetta IV (10.98-09.05)
Skoda Octavia, Combi (09.96-06.04)

AUDI, SEAT, SKODA, VW – Front Suspension

AUDI, SEAT, SKODA, VW – Front Suspension

Video to show correct fitment of shock absorbers to FRONT of:

AUDI A3/A3 Sportback (05.03-)
SEAT Leon II (05.05-)
Alhambra II (06.10-);
Altea/Altea XL (03.04-)
Toledo III (04.04-05.09)