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Fitting
Air Disc Brake Caliper Mechanism Fitting is a pneumatic brake fitting that joins the air line to the caliper body and seals it with a gasket. Read the guide
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What is Air Disc Brake Caliper Mechanism Fitting?
Air Disc Brake Caliper Mechanism Fitting is the fitting on pneumatic disc brake calipers of trucks and buses that joins the air line to the caliper body and seals the joint with its threaded body and gasket set. Because it is the first connection point through which compressed air reaches the piston chamber inside the caliper, a large share of air leaks in the system start here. The part that wears most in the field and loosens over time is the contact surface between the fitting threads and the body, together with the gasket and O-ring set above it. Workshops often call this part an air fitting or air inlet fitting.
How does Air Disc Brake Caliper Mechanism Fitting work and what does it include?
Air Disc Brake Caliper Mechanism Fitting is not a moving part; it stays fixed to the caliper body and does its job in place. When the brake valve opens, incoming air passes through the fitting first into the body and then into the piston chamber. The elements found in this group in the field are:
- Fitting body: the main part where the air line is connected, screwed into the caliper body.
- Threads: the threaded section that secures the fitting to the body and forms the first sealing surface.
- Gasket: prevents compressed air from escaping at the joint between the threads and the body.
- O-ring: provides additional sealing at the opening of the fitting to the air passage.
- Air passage: the internal channel that carries air from the fitting to the piston chamber in the caliper body.
Air Disc Brake Caliper Mechanism Fitting types
- Straight fitting: used where the air line enters the caliper body directly and without an angle.
- Elbow fitting: used when the hose must turn in a tight space around the body.
- Short-body fitting: chosen when space around the caliper is tight and the fitting must not protrude too far.
How to choose the right Air Disc Brake Caliper Mechanism Fitting?
Selection should be made from the removed fitting. First note the connection angle, the direction the hose exits and the thread type. Then inspect the seat in the caliper body and check the seating depth. Even within the same model series of Mercedes-Benz, MAN, Scania, Volvo and DAF, different layouts can exist, so choosing by model name alone is a mistake.
| Criterion | What to check | Why it matters |
|---|---|---|
| Thread | Thread type and fit with the body seat | A wrong thread damages the body and breaks the seal |
| Angle structure | Straight or elbow design, and the hose direction | Prevents kinking and friction on the hose |
| Gasket and O-ring | Shape of the old ring and signs of tearing | The most common source of air leaks |
| Material | Body material and surface condition | Determines resistance to corrosion and breakage |
| Seat depth | Whether the fitting sits fully in the body | A loosely seated fitting can blow out under pressure |
Installation and maintenance points
- Thread check: before fitting, make sure the thread is clean, burr-free and undamaged.
- Gasket replacement: a removed gasket or O-ring should not be reused; a new ring must be fitted.
- Controlled tightening: over-tightening damages the threads and body; leaving it loose lets air escape.
- Hose direction: the hose must connect to the fitting without rubbing or pull tension.
- Leak test: after assembly, pressurize the system and apply soapy water to the connection points to look for leaks.
Common faults and solutions
- Air hissing around the fitting: loosened thread or worn gasket; tighten in a controlled way and replace the gasket.
- Pressure drop and delayed braking: constant leak at the connection point; clean the fitting and reassemble it with a new gasket.
- Scratched body thread: wrong fitting selection or over-tightening; repair the thread, and replace the caliper body if the damage is advanced.
- Uneven braking: leak difference between two calipers; check the connectors on both sides together and replace the leaking part.
Frequently Asked Questions
Do I always need to replace the whole Air Disc Brake Caliper Mechanism Fitting if it leaks?
Not always. The leak source is often only the gasket or O-ring. If there is no damage to the threads and body surface, renewing the gasket set solves the problem.
What should be considered when removing the fitting?
Empty the air line completely before removal. Turn the fitting without forcing it or damaging the thread, and note the connection angle.
Should the gasket be replaced together with the fitting?
Yes, this is the recommended approach. If the old gasket damaged during removal is reused, the leak may return from the same point.
Should the air hose connected to the fitting also be checked?
Yes. If the hose end shows cracks, swelling or rubbing marks, the leak can continue even after the fitting is replaced. Cut the hose end cleanly and reconnect it.
How is a leak identified after assembly?
After the system is pressurized, apply soapy water to the connection points. A point that forms bubbles or produces a hissing sound is the leak source.