Hydraulic Assembly Lubricants in Aviation: Why MCS-352B Matters for Skydrol Systems
The most common consumables for aircraft maintenance shops and line maintenance teams are oils, greases, and hydraulic fluids. While these are the items most likely to be bought in bulk, they are far from the only items necessary for a well-rounded supply point.
Greenwood Aerospace lists nearly one thousand items on GSA Advantage, the vast majority of which are not oils or lubricants. One product in that category is adjacent to hydraulic fluid, and a commonly used one is hydraulic assembly lubricant; this lubricant seals during component assembly to keep unwanted foreign debris out of the component.
Let’s take a look at this and why it matters, and where you can source it for your hydraulic back shops.
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Why Hydraulic Assembly Lubricants Matter in Aviation
Even though hydraulic assembly lube is used within the hydraulic systems, assembly lubricants serve a completely different purpose and are not interchangeable. Hydraulic fluids like Skydrol are engineered for power transmission, thermal stability, and long-term system circulation.
Assembly lubricants are formulated for temporary protection during the assembly process of hydraulic components. This is the time when seals, O-rings, and packings are most likely to be damaged.
Why MCS-352B Is Specified for Skydrol Systems
MCS-352B is a viscous assembly lubricant engineered specifically for Skydrol hydraulic fluid systems. Its viscosity is carefully balanced to stay in position during assembly. For example, packing, O-rings, and even check balls are often used in hydraulic systems, and they must remain in a specific position during assembly. Once the component is assembled, the assembly fluid is mixed into the hydraulic fluid.
Unlike conventional greases or oils, MCS-352B is formulated to coexist with phosphate-ester hydraulic systems, allowing it to serve its temporary protective role without compromising long-term system performance. It is also used to reduce the introduction of foreign material, which is always one of the highest risks of component overhauls.
Technical Characteristics That Make MCS-352B Effective
One of the key performance characteristics of MCS-352B is its thick, gooey consistency. It stays exactly where you put it during assembly. Unlike thin fluids that migrate or drip away, MCS-352B stays on seals, O-rings, and mating surfaces, lubricating throughout the installation process. This sticky behavior keeps seals in place as components are inserted, reducing the risk of rolling, pinching, or cutting elastomeric parts when pressed into tight bores or housings.
MCS-352B’s purple color is a functional feature, not a cosmetic one. During assembly, technicians need to verify that seals and surfaces are evenly lubricated before installation. The visible color indicates that the lubricant has been applied, even on dark elastomers or metal surfaces. When you need parts to seat properly and reduce foreign contamination with a viscous liquid, assembly lubricants are the way to go.
Lubricating Seals During Assembly: Why This Step Is Critical
Seals must remain lubricated during assembly; a thin fluid, such as aviation hydraulic fluid, will lubricate them but will not hold them in place. These pieces must be held in place without assembly tools during assembly, so they rely on chemical components to do the work, and they must also be lubricant-approved to work with hydraulic fluids.
Also, many of the minute parts in hydraulic assemblies are designed to sit in place only during installation, or, like an O-ring, to sit in a small groove and be easily moved out of position when disassembled.
Common Assembly Tasks That Require MCS-352B
Here are a few of the most common tasks that require a hydraulic assembly fluid for parts that use Skydrol aviation hydraulic fluids:
- O-ring installation in hydraulic fittings and actuators
Provides lubrication to prevent O-rings from cutting, rolling, or extruding during installation and torque-up. The viscous, sticky fluid keeps the seal in its groove during assembly and prevents silicone or petroleum contamination in Skydrol systems. - Assembly of components with sliding O-rings
Reduces friction during O-ring sliding across bores and mating surfaces, reduces installation force, and minimizes wear. High viscosity keeps the lubricant in place during assembly, preventing it from washing away too soon. - Seal and fitting installation in Skydrol-wetted components
Designed for equipment using Skydrol aviation hydraulic fluids. Limited solubility (5% by volume at 24 °C) allows gradual dilution after system activation without haze, residue or fluid incompatibility. - Assembly tasks requiring temporary hold and controlled tackiness
The thick, purple liquid shows you when you’ve applied it and has enough tack to hold seals and components in place during alignment, fastening, and closing. Low acid number is compatible with seals and metal parts.
Greenwood Aerospace Supports Hydraulic Teams & Backshops
Backshop hydraulic teams go through a lot of consumables. From O-rings in brake assemblies, assorted packings, check balls, gaskets, the list goes on and on. Greenwood Aerospace is the trusted procurement partner you need to keep your hydraulic shop bench stock fully stocked. Make sure to check out our full lineup of hydraulic fluids, too. We carry MIL-PRF-5606 and MIL-PRF-83282 fluids, hydraulic assembly fluid, gaskets, packing, seals, and more!
As a U.S. Department of State ITAR-registered company, Greenwood Aerospace is defense contracting certified. We have AS9120B QMS and ITAR DDTC Export Compliance.
Company IDs:
UEI: KVSUYYSJS174
DUNS: 604006874
Cage Code: 2Y735
NAICS: 488190, 336413, 332722, 336411, 336413, 481212, 532411
Need help with product availability, bulk orders, or expedited shipping? Contact us at gsasales@greenwood.aero or 580-865-6000 / 833-GSA-EBUY (833-472-3289).
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