Haldex extends ModulT range to cover 11-tonne trailer axles

Haldex’s hugely popular single-tappet ModulT disc brake range is being expanded to cover 11-tonne trailer axles, giving manufacturers access to one of the industry’s most advanced braking solutions, tailored to their specific needs, at a competitive price point.

For years, the default choice for heavier trailer axles has been to use truck brakes. The 9-tonne axle load has long defined the upper weight limit of purpose-designed trailer disc brakes, produced in high volumes.

In the past Haldex has provided its twin-tappet ModulX for higher trailer weight classes, but this best-in-class brake was not a high-volume product, meaning it was not commercially viable for all applications.

Now trailer OEMs have a new option, with the introduction of the ModulT for 11-tonne axles. “Until today, we have only delivered the ModulT up to 9 tonnes, the normal semi-trailer size,” says Charlotte Wall, product manager at Haldex. “From middle of this year, we will start to supply the 19-inch brake, and from October the 22-inch brake, for 11-tonne axles.”

The ModulT represents a different proposition from simply using truck brakes on trailers, delivering more bespoke design possibilities. Its 22-inch maximum size will serve the heavier trailer applications, with a standardised 430mm disc diameter effectively representing the ceiling for disc brake applications.

A key advantage of the single-tappet design of the ModulT, first launched in 2011, is that it allows the calliper to be optimised for the precise material volumes needed to handle brake torque and tension, without the constraints imposed by having to accommodate two tappets. “A single-tappet mechanism means you can further optimize the design of the casted parts related to required brake torque and tensions require,” says Wall. This translates into a lighter, more compact package, which is a benefit for trailer designers.

Part of the reason Haldex is now able to expand its ModulT range in a competitive way is that it shares some of its spare parts with the existing LT range, creating a modular design that enhances serviceability, reducing maintenance costs for customers.

Despite the common platform architecture, Wall is clear that there is no such thing as an off-the-shelf ModulT brake. Every application requires customisation of the carrier, which interfaces with the axle and the friction material, and must be developed in conjunction with the disc. The disc itself is owned by the axle or truck manufacturer, not Haldex, adding a further variable to the process.

“The carrier always differs because that takes the interface to the axle, and that is never the same for two customers” says Wall. The calliper may sometimes be shared across applications, she adds, and this is easier to achieve on trailers than trucks due to the tighter installation envelopes on the latter.

The new brakes will serve market demands for higher specifications on trailers that have qualification requirements that have moved considerably closer to automotive standards in recent years. “Trailer manufacturers now want evidence for testing, and they want full PPAPs and so on according to the automotive standards – this was not the case 10 years ago,” says Wall.

Questions of friction

For Jonas Benson, Haldex’s friction couple specialist, the main developmental hurdle in engineering the ModulT for 11-tonne axles was finding a friction material capable of surviving the demands of the 19-inch application.

“The 19-inch is more challenging for the friction material than the 22-inch,” says Benson. The reason is thermal mass: the larger 22-inch disc has more material to absorb and dissipate heat, while the 19-inch must handle equivalent braking loads and therefore equivalent energy in a smaller package.

In official testing, disc temperatures reached 690°C. The critical performance measure is the fade, which is the drop in braking effectiveness as temperatures rise. While legislation permits a 40% reduction in braking force between cold and hot conditions, real-world trailer designs require considerably more margin. “To build a brake system for a trailer with a high centre of gravity that puts a lot of brake load on the front axle, you need more margin than the legal demands,” says Benson. In practice, Haldex works to around 25% reduction, almost twice of the required amount.

Seven friction materials were screened for the application. Six failed the initial internal test, which mirrors the legal ECE R-13 standard. Only one made it through.

The survivor then faced an escalating series of tests. Two disc-crack tests are run concurrently over a two-week period, to assess thermal fatigue by repeatedly cycling the disc between hot and cold conditions, simulating the sustained braking loads of long mountain descents. ISO performance and wear tests follow, ensuring consistency between early prototype batches and serial production material.

Then came the Alpine test: a real-world validation carried out under extreme operating conditions in the Alps. During the test, sustained low-speed downhill driving pushed brake disc temperatures beyond 900°C. In some cases, these temperatures can even cause grease from wheel bearings to vaporize and ignite on contact with the disc. “It’s a spectacular test,” says Benson. And one that proves the durability of Haldex systems. “From a brake performance perspective, we find the calliper does what it did before the test and is still clamping with just as much force.”

With testing complete, an official authority test is conducted at TÜV, SAF's preferred testing partner, in Essen, before the most time-consuming phase of all – two years of field testing. In this project, 10 trailers fitted with 19-inch brakes and 10 with 22-inch brakes were deployed all across Europe, with inspections every three months. For a new friction material, the full process from initial screening to production release takes around three years.

Regulatory drivers

Looking ahead, Wall identifies regulation rather than pure performance as the primary driver shaping the next phase of disc brake development. The VECTO regulation, which governs how CO₂ emissions from heavy vehicles are calculated, and Euro 7’s forthcoming particle emission limits for brakes are both shaping Haldex's development priorities.

“Development of this kind of product is very much driven from regulations at the moment,” says Wall. Drag torque reduction, relevant to VECTO efficiency calculations, is one area of focus, while the phasing out of PFAS (per- and polyfluoroalkyl substances) from brake components is forcing a re-evaluation of materials across the product range.

With the 22-inch brake completing Haldex’s ModulT coverage up to the 11-tonne maximum the market requires, the company is in a stronger competitive position than at any point in its disc brake history. “It meets our demands and it meets customer demands,” concludes Benson.