All about Haldex foundation brakes

Today, thousands of trailers around the world are now being controlled by the Haldex ModulT trailer disc brake. Since it entered European markets more than ten years ago, it has proven to be reliable in the field, suffering from very few support issues, the company reports, a statistic that reflects well on both the brake’s design and manufacture. 

Here, four specific examples of design features supporting longevity of the Haldex ModultT brake are picked out. First, although the disc brake design is open enough to allow for cooling and drainage, a folded bellows mechanism protects moving parts from impact by stone chippings, salt and surface water kicked up from the road. 

Second, Haldex is the only brake OEM to fit stainless steel pins in the brake for the caliper to slide on during operation. This impervious material provides a second layer of defence (in addition to protective metal caps) against the risk of binding due to rust. To simplify maintenance, composite trailing-edge bushings prevent the need for manual lubrication. 

Third, the cast body of the caliper has been designed specifically for strength and integrity, at an absolute minimum of weight. Modern computer software can design parts around the forces imposed on the component during operation, adding supporting material in areas of greater stress and removing metal where it is not needed. As such designs cannot necessarily be made in real-world production processes, casting experts further refine the design. One particularly important issue is the taper, the transition between thick and thin areas, since the ratio of surface area to volume determines cool-down time. Haldex ensures that no taper is too extreme, since cooling times could differ so greatly that they could lead to structural imperfections.  

Fourth, Haldex brake calipers are produced in an extremely automated process. That means that the manufacturing process repeats from one brake to the next in batches running into thousands; any variations in an individual part will be detected automatically by in-process measurements at each production station and prevented from progressing further (supplemented by random production sampling regimes). 

Other design features enable ModulT to function efficiently at a minimum weight. For example, the brake features a single, rather than a double, tappet mechanism between the brake chamber and the disc thrust plate. Although this design reduces the number of parts in the brake and makes it lighter, the risk is that it might not evenly distribute force to the pad, producing uneven wear that might require more frequent pad changes. To prevent that possibility, Haldex’s ModulT brake incorporates a very wide mechanism to provide even force distribution through the mechanism.  

Also, as disc brakes are moving assemblies, they could potentially suffer from hysteresis, the loss of braking force due to frictional losses. Haldex minimises the risk by fitting back-to-back double roller bearings. 

To improve the ease of routine servicing, ModulT requires no tooling for the regular task of changing the pads. Which is not to say they are not secure; pads need to be held in place to guard against the risk that they might fall out (with potentially disastrous consequences for the loss of braking power). Haldex’s retaining clip however does not need a special tool to remove. Instead, the pad retainer is removed by sliding it out from the caliper after compressing a spring clip. Despite the simplicity of the toolless brake change, every Haldex aftermarket pad kit contains an instruction sheet. Haldex gets the message across to technicians across Europe by using pictures rather than words showing the correct process (indicated with a green tick) as well as the incorrect process to avoid (highlighted with a red cross). 

Also, the toolless connection avoids some of the risks caused by bolted connections, which are only repairable when the tool is available at the point of service, and only secure once the correct bolt has been reinstalled at the correct torque. That means that the integrity of the brake depends on not losing the bolt or tool; they are also vulnerable to damage by overtightening. 

Of course, drum brakes use pads as well. While Haldex has never produced drum brakes, it is now part of axle supplier SAF, which does offer a drum-braked axle. To those, Haldex supplies automatic brake adjusters. Although the ModulT (and in fact disc brakes in general) adjust the gap between pad and disc automatically, drum brakes do not include any adjustment mechanism, and rely on the adjuster to mechanically take a new grip inside the brake adjuster mechanism. 

For more than 50 years, Haldex has supplied automatic brake adjusters for drum brakes, and still produces its traditional model, AA1, alongside its latest model, S-ABA, which is specified for new products since around the millenium. The principal difference between them relates to installation. AA1 has a specific reference point, which means that obtaining the designed gap between lining and the drum requires a perfectly correct installation. S-ABA does not require that, but instead will find its own zero-point after a few brake application. 

Turning to the future rather than the past, one new modern trend in braking is connectivity; providing brake-related information, such as temperatures or wear, to help improve operational safety or streamline maintenance practices to schedule repair tasks. Haldex offers two systems for brake monitoring: a simple wear indicator that only activates when the brakes are completely worn (or nearly so). It also offers a continuous sensor for constant brake wear monitoring, for greater oversight. Such a scheme is often popular for tractor and truck brakes. 

Compared to trailer disc brakes, truck brakes tend to be larger and stiffer, to compensate for the greater braking force required. Although both are expected to last for the same amount of time, their design is required to actuate much more often; double in fact (2.5 million compared to 1.25 million), partly because of parking brake actuations.  

Next year, Haldex will begin series production of 17-inch and 19-inch brake calipers for a medium-duty truck. Both the cast parts and the pad designs will be new. It isn’t Haldex’s first truck brake – that would be a special 21-inch disc brake for the Mercedes-Benz Unimog, which have been produced for a few years. But it is an exciting development of a platform for truck brakes. 

Haldex continues to expand its product portfolio of commercial vehicle products. The proven operational reliability of existing products like ModulT demonstrate how the Haldex brand continues to provide its customers with high quality.