Hydraulic Clutch Slave Cylinder Piston — Aluminum Alloy for Forklift Clutch Release System

This is the aluminum hydraulic piston that operates inside the clutch slave cylinder on forklifts with hydraulically actuated clutch release systems — a completely different component from the release bearing itself, which is what this piston pushes against. In a hydraulic clutch system, when the operator depresses the clutch pedal, brake fluid is pressurized by the master cylinder and sent through a high-pressure line to the slave cylinder mounted on the transmission bellhousing. This pressurized fluid enters the slave cylinder bore and pushes this piston outward, which in turn pushes the release fork (or directly presses the release bearing) against the diaphragm spring fingers, disengaging the clutch. The aluminum alloy construction is deliberate: it must be light enough so that the return spring can push it back rapidly when the pedal is released (to prevent clutch drag), corrosion-resistant against DOT 3/DOT 4 brake fluid which is hygroscopic and acidic, and thermally stable so the piston-to-bore clearance does not change as the transmission housing heats up from normal operation.

The most common failure mode of this piston — and the reason it must be replaced rather than cleaned up and reinstalled — is pitting corrosion at the seal groove lip. When moisture contaminates the brake fluid (inevitable in high-humidity warehouse and outdoor forklift environments), the water reacts with the glycol-ether base fluid to form acidic compounds that concentrate in the seal groove dead space where fluid circulation is minimal. Over time, this creates microscopic pits in the aluminum surface at the exact location where the cup seal must create a leak-free hydraulic seal. You cannot polish out these pits without reducing the groove width below tolerance (which makes the seal fit too loose and blow past immediately), and you cannot weld-fill them on aluminum without distorting the piston diameter. The only correct repair is piston replacement. A second failure mode is piston bore scoring from contaminated fluid carrying abrasive particles — the scored piston surface then acts like a file against the slave cylinder bore seal, destroying the seal and causing an external fluid leak at the push rod boot within hours.

Compatible with Heli CPCD20-CPCD35, Hangcha CPCD20-CPCD35, TCM FD20-FD35, Toyota 7FD/7FG 20-35, and Komatsu FD/FG 20-35 hydraulic-clutch models. Always verify the piston diameter (typically 19mm or 22mm for 2-3.5T forklifts) and overall length against your existing piston before ordering — the same slave cylinder housing can use different piston sizes depending on the clutch clamp force requirement. Replace the piston seal kit simultaneously (cup seal, dust boot, push rod boot), flush the hydraulic system with fresh DOT 3 or DOT 4 fluid, and bleed thoroughly after installation. For the complete slave cylinder assembly, browse our transmission parts category. Reference OEM specifications at Heli official website.

Technical Specifications

• SKU: CLUTCH-PISTON-AL
• Key Differentiator: Hydraulic slave cylinder piston — NOT a release bearing or housing. This is the internal piston that converts fluid pressure to mechanical force. Aluminum alloy with seal groove for DOT 3/4 fluid.
• Material: Aluminum Alloy — Corrosion-Resistant for DOT 3/DOT 4 Brake Fluid
• Type: Hydraulic Clutch Slave Cylinder Piston
• Common Diameters: 19mm or 22mm (Verify Against Your Existing Piston)
• Application: 2-3.5 Ton Hydraulic Clutch Forklifts — Heli, TCM, Toyota, Komatsu
• Warranty: 12 Months

Compatible Forklift Models (Hydraulic Clutch)

Kingstream clutch pistons are individually oil-wrapped in VCI paper and packed in rigid cartons. QC: diameter measurement, seal groove dimensional check, surface finish inspection. 12-month warranty. Contact us with your slave cylinder bore diameter for fitment verification or bulk pricing.