Assessment down to the smallest detail
When the caliper arrives, it is checked several times for defects and damage. To do this, it is disassembled into all its individual parts and cleaned. In this way, cavities and hard-to-reach areas can be better controlled and the current state can be assessed more precisely.
This can be a difficult undertaking. So the pistons may be seized and not move a millimeter from the spot. We try to set the pistons in motion with special tools and / or high-pressure hydraulic presses. When opening the fixed caliper, tight screws can make it difficult to separate the two halves of the caliper. In addition, torn off ventilators often have to be removed with great effort, if possible without damaging the thread and the valve bore in the housing. All of this is very complicated and time-consuming, and requires the routine work of our technical team. From time to time our team also holds combination calipers with an integrated parking brake (piston mechanism) in their hands. With an experienced eye, you can see immediately which pressed-in covers or which Seger rings can be opened.
Some internal mechanics or adjustment units shouldn’t be removed. In such cases, dismantling is carried out individually and in consultation with the customer. Everything that can be removed from the case is removed. The components are carefully examined, recorded and checked for reusability. In the case of components that are no longer reusable, the availability of new parts is queried. Wear and rubber parts are generally replaced. We keep many items in stock. If parts are not available, we will obtain corresponding offers from our partners.
The documentation comprises the following three core areas:
Inventory of the caliper housing
The cast housing made of cast iron, cast steel or aluminum – mostly the material gray cast iron (GG) – is examined in detail for crack formation, material breaks, the effects of corrosion, material wear and possible damage to cavities.
The brake caliper housing is seriously damaged if broken valves or e.g. the expansion screws get stuck in the fixed caliper, the contact surfaces of the caliper halves can no longer be “smoothed” and the area of the screw connection is too corroded. Or, however, if the cylinder bore has been worn away so severely by extreme rust or excessive honing that the tolerances for the space between the piston and cylinder bore are exceeded. If there is no longer any prospect of refurbishing the caliper housing, it may make sense to manufacture the caliper housing again after detailed material determination and measurement.
On the piston, attention must be paid to broken edges, broken groove flanks, sharp-edged areas, as well as cracks, grooves, dents and flaking chrome coatings. Excessive scoring on the piston (but also on the cylinder bore in the housing), deeply recessed areas of rust and scratches, or extensive pitting and surface corrosion, already hinder the piston movement in the cylinder interior and lead to tension and displacement of the piston and the sealing ring. Back then it was not uncommon to use honing to repair the running surfaces of the cylinder bore in the event of severe rust and to adapt the pistons accordingly. With today’s tight tolerances, such interventions on the brake caliper are no longer carried out. The manufacture of brake pistons has changed over time. Initially, cast pistons were manufactured using a gray cast iron process and machining. Then they started to manufacture steel pistons in non-cutting forming processes. Various processes are used such as: deep drawing, extrusion, compression molding, folding the contact surface, rolling groove and shoulder and much more. Deep-drawn steel pistons are lighter and have thinner walls than cast pistons. Weight savings could also be achieved with aluminum pistons. These expand more under heat and transmit heat from brake linings more strongly than conventional steel pistons. Such piston designs devised by the manufacturer should not be changed and therefore the pistons must be exchanged exactly according to vehicle-specific specifications. This is even more necessary with pistons made of plastic. In order to improve the low thermal conductivity of the thermoset material and to avoid thermal overloading of the brake pads and the piston, metal inserts or metal accessories are integrated. In addition, plastic pistons (phenol pistons) are very susceptible to cracking in the event of extreme overheating. Heat damage that cannot be seen with the naked eye forms in the material. A purely visual inspection cannot detect this internal damage caused by heat, age-related material degradation or side impacts. That is why we generally change plastic pistons. If an old cast piston can no longer be saved by grinding, coating and polishing and is no longer available as a replacement part, a customer-specific new production on CNC milling and lathes can help. This is done in consultation with the customer.