Bonded Pistons
A bonded piston is a steel piston with the seal moulded and chemically bonded straight onto it. Inside an automatic transmission it applies a clutch pack hydraulically, with no separate lip seal to twist or dislodge on assembly. SES holds the range as an authorised SKF distributor, covering construction Rubber-to-metal bonded assembly; function Hydraulic actuation piston with integral sealing; materials NBR, HNBR, ACM, FKM on pressed steel; media Automatic transmission fluid. Executions include clutch apply pistons, brake band and brake clutch pistons, lock-up clutch pistons, balance and centrifugal cancel pistons. It is specified most often into automatic transmission clutch packs in commercial vehicles and powershift transmissions on loaders and dozers. Every part is genuine SKF through official channels, with designation, specification and options confirmed against your duty before it ships — supplied from Kolkata and our branch network, with breakdown cover that does not sit in an inbox.
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From integrated steel plants to power utilities and EPC majors — the works that cannot afford a counterfeit part specify through SES.
Construction
Elastomer bonded to a formed steel piston
Duty
Hydraulic clutch and brake application
Media
Automatic transmission fluid
Advantage
No separate seal to install or displace
Where it runs.
You will find Bonded Pistons in the parts of a plant where this particular duty actually occurs. In practice that means automatic transmission clutch packs in commercial vehicles, powershift transmissions on loaders and dozers, torque converter lock-up clutch assemblies, and equally tractor powershift and creeper units, industrial gearbox clutch actuation, off-highway machine transmission overhauls. What links them is the duty rather than the machine name — construction: Elastomer bonded to a formed steel piston. If your installation is not on that list it matters less than you would think: the operating condition decides the specification. Send us the load, the speed, the running temperature and the environment it runs in, and we will match it to the right execution in the SKF range and confirm what is in stock.
Specify it against the duty.
Specification here follows the operating condition, not the catalogue. The transmission uses a synthetic or specification-specific ATF — Confirm elastomer compatibility with that fluid. Bonded elastomers swell or harden with the wrong ATF and the clutch then applies late. Shift quality is soft and slipping under load — Check the piston seal lip for wear before condemning the clutch plates. Pressure lost past the piston looks exactly like worn friction material. The transmission sees heavy stall and torque converter heat — A compound rated for that sustained temperature. Bonded seals cannot be replaced separately, so the whole piston is the wear item. Where two of those apply at once, specify for the harsher of the two — under-specifying is what puts the part back on the bench a month later. Send us the duty and we will confirm the execution.
Ordering this from SES.
Lubricate the bore with clean ATF and enter the piston square. A bonded lip that catches a snap ring groove on the way in tears in a place you will never see once the drum is assembled. Send the designation off the failed part and we will confirm the SKF equivalent and stock position.