The springbrake is the last element in an air brake system, converting air pressure into the force which actuates the foundation brake. It is also exposed to the most severe operating environment, being mounted on the unsprung axle assembly where exposure to vibration and road shock are worst. The spring section provides a failsafe backup against loss of pressure in the air system, so failure of the springbrake mounting can render both normal service braking and the backup emergency braking function totally ineffective. What's more, a springbrake which seperates from it's axle mounting poses a serious hazard to other road users, particularly if impact with the road damages the housing sufficiently to release the power spring.

The use of quality springbrakes from reputable manufacturers is an important first step - not surprisingly, we recommend TSE springbrakes, manufactured by TSE Brakes USA under ISO9001 quality standards. However, recent failures of a number of springbrake brands has also highlighted the importance of correct installation. Recommendations on springbrake mounting are included in the installation guidelines packaged in every Air Brake Corporation trailer brake kit, and relevant excerpts are copied below for reference, along with advice on what to look for in a quality springbrake. Failure to follow these recommendations can result in premature springbrake failure which is not covered by warranty.

We all want the best quality for the cheapest price. Springbrakes in particular have become a commodity item in recent years, but the old adage 'you get what you pay for' applies as much today as ever. The cheapest buy is rarely the best buy - a few dollars saved up front can cost dearly down the road when the product fails prematurely.

Unfortunately, it's not always easy to assess the quality of a product at the point of sale. The quality of internal component design and construction is often only proven in service, but there are some outward indicators of quality that can be easily checked. The following checkpoints should help you avoid inferior springbrakes that are designed to fail.

As eluded earlier, springbrake mounting is of foremost importance - if the springbrake falls off the axle, it obviously won't work! Installation procedures and operating environment can contribiute to mounting failure, but starting with a quality engineered springbrake is the first vital step. Look for the following in mounting design…

The mounting nuts should be positively locked against loosening under vibration ('prevailing torque' cone nuts are recommended), and the mounting washers should be of heavy gauge material, and preferably hardened, to prevent deformation under load and loosening of the springbrake. On a related note, the washer used under the release bolt should be of similar heavy gauge material, and comfortably larger in diameter than the release bolt hole in the rear of the springbrake - you don't want a caged springbrake letting go because the washer pulled through the hole!

The front mounting face should provide as much flat surface contact with the axle mounting bracket as possible, particularly in the vertical plane, to reduce the risk of 'rocking'. The mounting on the left with the 'cross' profile is less than ideal, as a large part of the vertical 'land' would float in the central void of many axle bracket designs. The one on the right provides maximum contact area regardless of bracket design.

The reinforcing pads under the mounting bolt heads should be generous in size, particularly in the vertical plane, and secured against loosening (EG: welded in position). 2430 models have a smaller mounting face than 3030 models, and consequently a smaller contact area with the axle bracket, which can make them more susceptible to 'rocking'. TSE 2430 models from Air Brake Corporation now have a full ring reinforcing plate to counter this reduced contact area.

Prior to springbrake installation, ensure springbrake is caged, pushrod is cut to correct length, & axle mounting bracket is free of excessive paint (less than 0.25mm thick), debris, burrs, & cracks, & flat within 0.5mm. Also ensure that bracket mounting holes align properly with springbrake mounting studs.

CAGING
Do not attempt to cage any springbrake with signs of structural damage or significant corrosion. Handle damaged springbrakes with extreme caution. Failure of a damaged springbrake can cause severe personal injury.

Apply minimum 600kPa air pressure to emergency port. Remove dust plug from release bolt access hole in rear center of spring housing. Remove release bolt from side pocket, insert through access hole into pressure plate, turn ¼ turn clockwise & pull to ensure cross-pin ears are properly engaged in pressure plate. Assemble washer & nut onto release bolt finger tight & release air pressure. Springbrake is now caged. NOTE: Do not tighten release nut more than finger tight. Over torquing nut can damage pressure plate, washer and/or spring housing, resulting in sudden release of main spring & severe personal injury.

PUSHROD
Springbrakes are supplied with a full length threaded pushrod to accommodate different axle bracket arrangements. Pushrod must be cut to correct length for a given axle prior to installation to obtain correct angle with slack adjuster when brakes are applied. Failure to do so can degrade braking performance & damage the springbrake. Pushrod length required is dependant on relationship between brake chamber axle mounting bracket & slack adjuster mounting. Axle supplier should be able to advise recommended pushrod length (if replacing springbrake, cut pushrod to same length as unit fitted). Install clevis jamnut on rod before cutting & remove after to restore thread.

MOUNTING
There may be multiple mounting holes on axle mounting bracket corresponding with multiple holes on slack adjuster. The ADR38 Compliance Plate Approval specifications for the trailer will indicate correct slack adjuster hole to use. Axle supplier should advise corresponding bracket hole (if replacing springbrake, use same springbrake size and same slack adjuster setting as unit fitted). Ensure that when mounted, springbrake does not foul or contact any frame or suspension components, & that full suspension travel does not interfere with springbrake.

Brake chamber axle mounting bracket must be free from excessive paint (less than 0.25mm thick), debris, burrs, & cracks, & flat within 0.5mm. Ensure that springbrake mounting studs align properly with holes in axle bracket. If studs do not pass through holes easily without binding, do not force or pull springbrake onto bracket by tightening nuts - rework holes for easy insertion or replace bracket. Clearance between holes & studs should not exceed 2mm. Mount springbrake directly to axle mounting bracket. Do not add or insert shims, spacers, washers, or reinforcing plates between chamber mounting face & axle mounting bracket.

Install mounting washers & nuts & torque to 150 to 160 Nm. Remove pin from clevis, adjust slack adjuster toward springbrake until appropriate hole aligns with clevis, & reinstall clevis pin. Consult axle supplier's instructions for correct slack adjuster alignment & end play adjustment.

Connect air lines & apply a minimum 600kPa air pressure to emergency port. Remove release bolt & secure it in side pocket with nut & washer. Install the dust plug into release bolt access hole in center of the spring housing. Springbrake is now uncaged.

Adjust brakes as per axle supplier's recommendations & check that angle formed by slack adjuster & brake chamber push rod is greater than 90 degrees when brake is in released position, & as close to 90 degrees as possible when brakes are applied.