# 1841 Dunbier Hydraulic Master Cylinder Cap Suits 1840 | Marine Trailer Part

🔧 Product Description

  

Dunbier Hydraulic Master-Cylinder Reservoir Cap - Part Number: 1841

  

A replacement reservoir cap for Dunbier master cylinder 1840. The cap closes the brake-fluid reservoir, supports the venting arrangement and prevents dirt and water entering the hydraulic system.

  

⚙️ Key Features

  

• Direct replacement for Dunbier 1840 master cylinder

• Brake-fluid-resistant cap material

• Protects reservoir from contamination

• Maintains the specified venting arrangement

• Service replacement for lost, cracked or damaged cap

  

📏 Specifications

  

• Application: Dunbier 1840 / Mackay H3050 master cylinder

• Cap seal or diaphragm is included only as supplied

• Thread or bayonet profile must match the reservoir

  

🔄 Cross Reference & Related Parts

  

• Dunbier: 1841

• Master cylinder: Dunbier 1840

• Complete hydraulic coupling assembly: Dunbier 1029 or 1030 where applicable

  

🚤 Trailer Compatibility & Application

  

• Suits the Dunbier 1840 master-cylinder reservoir

• Not universal across all trailer master cylinders

• Confirm the old cap profile before replacement

  

🔌 Function

  

Seals the brake-fluid reservoir while allowing the designed pressure equalisation as fluid level changes.

  

Common signs of wear or replacement:

  

• Cap is cracked, swollen or missing

• Brake fluid leaks around the reservoir

• Water or debris is visible in the fluid

• Threads no longer tighten securely

• Vent is blocked and causes brake drag or poor return

  

🛠️ Installation & Safety

  

• Clean the reservoir opening before fitting

• Do not allow dirt or water into the brake fluid

• Replace damaged diaphragm or seal components

• Tighten only enough to seal

• Bleed or flush the system if contamination has entered

  

📦 Condition

  

• Genuine Dunbier Marine Products trailer component

• Brand new

• Supplied as one replacement master-cylinder cap

• Supplied in original or equivalent packaging

## Details

- **Price:** 6.75 AUD
- **Vendor:** Dunbier
- **Tags:** Dunbier Boat Trailers | Marine Trailer Parts & Accessories

## Variants

| Variant | Price | Available |
|---------|-------|-----------|
| Default Title | 6.75 AUD | In stock |

## Images

- 1841 Dunbier Hydraulic Master Cylinder Cap Suits 1840 | Marine Trailer Part
- 1841 Dunbier Hydraulic Master Cylinder Cap Suits 1840 | Marine Trailer Part
- 1841 Dunbier Hydraulic Master Cylinder Cap Suits 1840 | Marine Trailer Part

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> Source: [Sawley's Auto and Marine](https://www.sawleysautoandmarine.com.au/products/1841-dunbier-hyd-master-cylinder-cap-to-suit-1840)
> Updated: 2026-08-03