A rubber silent block in a suspension arm that breaks down in one season on bad roads drags along play, knocks, and unscheduled chassis diagnostics. Replacement once a year becomes a habit, even though the arm itself is intact. A polyurethane silent block holds the suspension geometry many times longer and is not afraid of oils or reagents. Let me break down which polyurethane exactly this part needs, how to match the hardness to the suspension type, and why the polymer is pushing rubber out of the running gear.
What a silent block does and why the material is critical
A silent block is a suspension joint that connects the arms to the body and damps vibration and impacts from the road. It determines how precisely the chassis geometry holds and how much noise is transmitted into the cabin. So the material of a silent block has to both damp oscillations and hold the load without residual deformation.
Rubber was historically the main material for this part, but it has two weak spots: it wears out quickly under alternating load and ages under the action of oils, ozone, and temperature swings. In the cold a rubber silent block stiffens and cracks, and from contact with technical fluids it swells. Because of this the part loses its resilience and starts to develop play, throwing off the camber and toe.
Polyurethane solves both problems. It keeps its elasticity in a wider temperature range, is not afraid of oils, and has a service life many times greater than rubber. That is exactly why suspension makers increasingly switch to polyurethane silent blocks in repair and reinforced solutions.
It is important to understand the difference in the material’s behaviour under load too. A rubber silent block gains residual deformation over time: rubber does not fully return to shape after compression cycles, and play appears in the joint. Polyurethane, thanks to its higher resilience and tensile strength, holds the original geometry longer, so camber and toe drift less between services. For the driver this shows up as more stable car behaviour on the road throughout the service life of the part.
Which polyurethane is needed for silent blocks
For silent blocks a medium-hardness polyurethane is used, which combines the ability to damp vibration with resistance to load. The overall hardness range of TIMOL polyurethane runs from 50 Shore A to 70 Shore D, and for suspension joints a value in the middle part of this range is chosen. Too soft a grade sags faster under constant load, too hard a one makes the ride stiff and damps small impacts worse.
The choice of a specific hardness depends on the suspension type and the driver’s priority. For a comfortable ride a softer polyurethane is taken, which feels closer to rubber but lasts longer. For a sporty or loaded application a harder one is chosen, which holds geometry more precisely and gives sharper handling at the price of a slightly stiffer ride. The plant’s engineer helps determine the optimum for a specific assembly.
Regardless of the chosen hardness, a polyurethane silent block beats rubber in its bond with the metal sleeve. A properly prepared surface and adhesion layer practically eliminate the peeling that happens in rubber as it ages. This directly affects the longevity of the joint.
The idea that polyurethane suits only sports cars with stiff suspension is mistaken. The same material at a lower hardness gives comfort close to stock rubber, but with a much greater service life. That is why polyurethane silent blocks are fitted on everyday civilian cars too, where the main goal is rarer replacement and stable chassis geometry, not sporty handling.
Engineer’s tip: do not chase maximum hardness in the hope of service life. Too hard a silent block transmits all impacts to the body and the arm itself, accelerating their wear and spoiling comfort. For most civilian suspensions the optimum is a medium hardness: it gives a noticeably longer service life than rubber without losing ride smoothness. Harder grades are justified where precision of geometry under high load matters.
Comparison table: polyurethane versus rubber for silent blocks
The figures are taken from standard engineering references (DIN 53516, ISO 4649, ISO 37, Matweb) and explain the difference in service life and durability of the joint.
| Parameter | Polyurethane (TIMOL) | NBR rubber | SBR rubber | Natural rubber |
|---|---|---|---|---|
| Abrasion (DIN 53516), mm³ | 38-39 | 80-150 | 100-200 | 60-130 |
| Operating temperature, °C | -60…+100 | -30…+100 | -40…+80 | -50…+70 |
| Hardness | 85A-95A | 40A - 90A | 40A - 80A | 30A - 80A |
| Tensile strength, MPa | 39-87 | 10-25 | 8-20 | 20-30 |
| Oil resistance | excellent | good | low | low |
For a silent block the two most important rows are abrasion and oil resistance. Polyurethane loses 38-39 mm³ per DIN 53516 against 80-200 mm³ for various rubbers, meaning it wears 2-5 times more slowly under alternating load. In oil resistance, polyurethane and NBR are ahead, while SBR and natural rubber degrade quickly from technical fluids. The wider temperature range of polyurethane (-60 to +100 °C) means the part does not stiffen in the cold, when rubber has already lost its resilience.
Installation and maintenance of polyurethane silent blocks
Installing a polyurethane silent block differs little from a rubber one, but has its nuances. The part is pressed into the seat of the arm, and the inner sleeve is tightened to the stock torque. It is important not to over-tighten the fastener and to tighten the joint in the working position of the suspension, when the car stands on its wheels rather than hangs. This way the polyurethane works in its designed deformation range and does not take a constant skew that shortens its service life.
Polyurethane silent blocks often have a split design of two bushings, so they can be replaced without pressing out the whole arm. This simplifies maintenance and makes repair cheaper. Some solutions include lubrication grooves: greasing reduces friction between the sleeve and the polyurethane and removes the squeak that sometimes appears in dry joints. If a silent block starts to squeak, it is not wear but a lack of grease in the friction pair, and the problem is solved without replacing the part.
How to order silent blocks from the TIMOL plant
To order, provide a worn silent block as a sample or a drawing with dimensions: outer and inner diameters, height, and the type of fit for the sleeve. The engineer takes the measurements, selects the polyurethane hardness for your suspension type and operating conditions, after which the part is cast by open casting with controlled properties. The finished silent block replaces the stock one without any rework of the assembly.
Polyurethane silent blocks are in demand not only in passenger cars. They are fitted into the suspension of trucks, trailers, buses, and special machinery, where loads are higher and downtime is costlier. For heavy machinery the choice of polyurethane is especially justified: the service life of the joint directly affects the maintenance schedule of the machine, and resistance to oils and reagents reduces the number of unscheduled repairs.
Manufacturing is possible both one at a time, for the repair of a specific car or machine, and in runs, for service stations and suspension makers. The range of polyurethane products for running gear is gathered in the catalog, and more about the material and its properties can be read in the reference information section. To select the hardness and order a part for your assembly, reach out through the TIMOL plant contacts: our specialists will help with the calculation and manufacturing.