# 1840 Dunbier H3050 Mackay Hydraulic Coupling Master Cylinder | Marine Trailer Part

🔧 Product Description

  

Dunbier Hydraulic Override-Coupling Master Cylinder - Part Number: 1840

  

A replacement hydraulic master cylinder for compatible Dunbier override couplings. The cylinder converts coupling overrun movement into hydraulic pressure for the trailer disc-brake circuit.

  

⚙️ Key Features

  

• Trailer-specific hydraulic master cylinder

• Reservoir and piston bore configured for override coupling use

• Replacement for worn or leaking coupling cylinder

• Compatible with standard trailer hydraulic brake fluid system

• Mackay cross-reference H3050

  

📏 Specifications

  

• Mackay: H3050

• Application: Compatible Dunbier hydraulic override couplings

• Outlet thread and mounting dimensions must match the original

• Cap sold separately as Dunbier 1841 where not included

• Brake fluid type must follow the existing system specification

  

🔄 Cross Reference & Related Parts

  

• Dunbier: 1840

• Mackay: H3050

• Replacement cap: Dunbier 1841

• Related complete coupling master-cylinder/handbrake assembly: Dunbier 1029 / Mackay H3341

  

🚤 Trailer Compatibility & Application

  

• Suits compatible Dunbier/Mackay hydraulic override couplings

• Not for mechanical cable-operated brake systems

• Cylinder bore, pushrod stroke and outlet fitting must match the coupling

  

🔌 Function

  

Generates hydraulic pressure when the sliding override coupling compresses during vehicle deceleration.

  

Common signs of wear or replacement:

  

• Brake fluid leaks from the bore, boot or outlet

• Soft or ineffective trailer braking

• Piston sticks or fails to return

• Reservoir loses fluid

• Brake pressure remains applied after the tow vehicle accelerates

  

🛠️ Installation & Safety

  

• Brake work should be completed by a competent technician

• Flush contaminated lines and inspect calipers before installation

• Use only the specified brake fluid

• Bench-prime and bleed the system thoroughly

• Test braking progressively at low speed before road use

  

📦 Condition

  

• Genuine Dunbier Marine Products trailer component

• Brand new

• Supplied as one hydraulic master cylinder

• Supplied in original or equivalent packaging

## Details

- **Price:** 59.5 AUD
- **Vendor:** Dunbier
- **Tags:** Dunbier Boat Trailers | Marine Trailer Parts & Accessories

## Variants

| Variant | Price | Available |
|---------|-------|-----------|
| Default Title | 59.50 AUD | In stock |

## Images

- 1840 Dunbier H3050 Mackay Hydraulic Coupling Master Cylinder | Marine Trailer Part

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> Source: [Sawley's Auto and Marine](https://www.sawleysautoandmarine.com.au/products/1840-dunbier-hyd-coupling-master-cylinder-mackay-h3050)
> Updated: 2026-08-05