Brake & Clutch Cylinder Types

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One programme, five product lines

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Every hydraulic brake and clutch cylinder on a vehicle does one of two jobs: it creates pressure, or it uses it. Getting which one right is the first step; getting the bore and the port thread right is the second. Here is the honest comparison of the four cylinder families and the repair kits we supply, including where each one is the wrong choice for your market.

All five lines are available under our own reference numbers or as private label with your branding. Bore, port thread and mounting distance are confirmed per part number, in writing, before production.

01 — Brake master cylinder

Brake master cylinders (BMC)

The pressure source of the whole braking system. Tandem and single-circuit versions, cast iron and aluminium bodies, integrated or remote reservoir.

Design & materials

A cast iron or aluminium body with a stepped or straight bore, an EPDM cup seal set on an aluminium or steel piston, and either an integrated reservoir or a remote reservoir fed by a hose. Tandem units carry two pistons so the two brake circuits stay independent.

How it behaves

The pedal pushes the primary piston; the trapped fluid pushes the secondary piston, so both circuits see pressure together. Tandem design means a seal failure on one circuit still leaves braking on the other — which is why the part number, not just the bore, has to match. Bore size sets the trade-off between pedal travel and pedal effort: larger bore, shorter travel, more effort.

Watch out: this is the most mis-ordered part in the category. The bore, the port thread and the reservoir interface all have to match — never confirm one from a vehicle name alone.

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02 — Brake wheel cylinder

Brake wheel cylinders (BWC)

The actuator inside a drum brake. Supplied as matched left and right hand pairs, in cast iron or aluminium, with EPDM cup seals and dust boots.

Design & materials

A short cast iron or aluminium body with one or two pistons, an EPDM cup seal at each end, dust boots on the outside and a bleed screw. Machined with a two-bolt flange that matches the backplate, and made in distinct left-hand and right-hand versions on most applications.

How it behaves

Hydraulic pressure enters at the inlet port and pushes both pistons outward, which forces the brake shoes against the drum. It is the simplest part in the system and the most exposed: road salt, brake dust and heat all attack the dust boots, so seal failure is the normal end of life. A weeping cylinder contaminates the shoes, and the symptom is a wheel that drags or grabs rather than a pedal problem.

Watch out: never sell one side of a drum axle on its own. A matched pair is a higher-value order and it removes a comeback in the same visit.

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03 — Clutch master cylinder

Clutch master cylinders (CMC)

Converts pedal travel into clutch pressure. Because the fluid volume is small, bore accuracy here matters more than anywhere else in the range.

Design & materials

An aluminium or cast iron body with a single bore, an EPDM cup seal, a pushrod that connects to the clutch pedal, and a reservoir that is either mounted directly on the body or connected remotely. The outlet feeds a rigid or flexible line down to the slave cylinder.

How it behaves

Pedal travel is converted into a small volume of fluid at pressure. Because the fluid volume is small, bore accuracy matters more here than anywhere else in the range: a fraction of a millimetre changes where the clutch bites. The classic failure is internal bypass — the pedal slowly sinks while held, with no external leak at all.

Watch out: the classic failure is internal bypass — a pedal that sinks while held, with no external leak at all. Sell it with the slave cylinder when the system is more than a few years old.

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04 — Clutch slave cylinder

Clutch slave cylinders & concentric (CSC)

External units that move the release fork, and concentric units that sit on the gearbox input shaft and act directly on the release bearing.

Design & materials

The external type is a compact aluminium or cast iron body with a pushrod acting on the release fork, with a dust boot and an integral bleed screw. The concentric type (CSC) is built around a bearing carrier that sits on the gearbox input shaft and acts directly on the release bearing, with the hydraulic connection made through the gearbox casing.

How it behaves

Pressure moves the piston, which moves the fork or the bearing, which disengages the clutch. The concentric version removes the fork and the external linkage entirely, which makes it more precise but unforgiving on installation: it must be bled on the bench or with a pressure bleeder, and any misalignment damages the seal on first use.

Watch out: a CSC cannot be repaired and must be bled with a pressure bleeder, not by pumping the pedal. If a workshop fits the cheaper external part on a CSC vehicle, the job comes back.

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05 — Repair kits

Cylinder repair kits

Cup seals, dust boots, pistons, springs and snap rings for every cylinder family we supply — the line your workshop customers ask for by name.

Design & materials

A matched set for one cylinder: cup seal, secondary seal where fitted, dust boot, piston, return spring, snap ring and, on the wheel-cylinder kits, the bleed screw. Rubber parts are moulded in EPDM and SBR to hold their dimensions in DOT 3 and DOT 4 fluid.

How it behaves

A rebuild only works if the bore is still true. The kit restores the sealing surfaces, but a scored or pitted bore will destroy the new cup seal within a few hundred kilometres — which is why we tell workshops to measure the bore before selling them a kit, and to fit a new cylinder instead if it is out of tolerance.

Watch out: a kit restores the seal, not the bore. Tell your workshops to measure the bore first — selling a kit for a worn cylinder is how comebacks start.

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