Harley-Davidson X440 / X440 OBDII Rear Brake Fluid Reservoir OEM | HDH43550AAZ310

Replace a cracked, leaking, faded, or damaged rear brake fluid reservoir with this genuine OEM reservoir assembly for Harley-Davidson X440 series motorcycles. Part number HDH43550-AAZ-310 is listed in the genuine parts record as RESERVOIR COMP RR. In buyer language, this is best understood as the rear brake fluid reservoir, rear brake oil bottle, or rear master cylinder reservoir.

This is the small fluid reservoir used with the rear brake hydraulic system. If the original reservoir body is cracked, the plastic is damaged or discolored, fluid is leaking, or the reservoir is being replaced during brake system repair, this OEM part helps restore proper fit and fluid storage for the listed applications.

This listing is written to be easier for customers to understand. Instead of only using the factory term RESERVOIR COMP RR, it also uses the common buyer names: rear brake fluid reservoir, rear brake oil bottle, and rear master cylinder reservoir.

This part is confirmed for the following applications based on your genuine parts applicability screenshot:

• Harley-Davidson X440 (Sept 2023)
• Harley-Davidson X440 OBDII (May 2025)

Not confirmed in the provided evidence: X440T, X440X, and Hero Mavrick 440. Please do not assume wider fitment unless your old part, VIN, or EPC reference confirms the same part number.

This listing is for one rear brake fluid reservoir only. Do not assume it includes the master cylinder, hose, cap, bracket, rear caliper, or a complete rear brake assembly unless separately stated.

Key Features

• Genuine OEM rear brake fluid reservoir
• Part number: HDH43550-AAZ-310
• Factory description: RESERVOIR COMP RR
• Buyer language: rear brake fluid reservoir, rear brake oil bottle, rear master cylinder reservoir
• Confirmed for X440 and X440 OBDII
• Used in the rear brake hydraulic system
• Useful for replacing cracked, leaking, or damaged reservoir units
• Helps maintain correct brake fluid storage and OEM-style fit
• Important distinction from master cylinder and full rear brake assembly
• OEM-style fit for the listed applications

Compatibility

What's in the Box

• 1 x HDH43550-AAZ-310 – Rear Brake Fluid Reservoir (RESERVOIR COMP RR)

Installation & Maintenance Notes

• This listing is for one rear brake fluid reservoir only.
• Please match your old part number, shape, and hose connection before ordering.
• Do not assume this includes the rear master cylinder or cap unless separately stated.
• Inspect hose condition, mounting area, and brake fluid level/system condition during replacement.
• Brake work should be done carefully and correctly. If unsure, use a qualified mechanic.

Before You Order

Important: This is the OEM part identified as RESERVOIR COMP RR, presented in buyer language as the rear brake fluid reservoir. It is not the complete rear master cylinder and not the rear caliper.

For X440T, X440X, or Hero Mavrick 440, fitment is not confirmed in the provided applicability record. Please verify by VIN / EPC / old part match before ordering.

Why Buy From Under The Hood

• Buyer-friendly naming for technical OEM brake parts
• Clear explanation of what the reservoir actually is
• Helpful distinction between reservoir, master cylinder, and full brake assembly
• Useful for owners and workshops ordering exact brake hydraulic parts

FAQs

1. What is HDH43550-AAZ-310?
It is the OEM part listed as RESERVOIR COMP RR, best understood in buyer language as the rear brake fluid reservoir.

2. Which bikes is this confirmed for?
This part is confirmed for Harley-Davidson X440 and Harley-Davidson X440 OBDII.

3. Is this the complete rear master cylinder?
No. This listing is for the rear brake fluid reservoir only, not automatically the full rear master cylinder assembly.

4. Will it fit X440T?
Please verify by VIN / EPC / old part match before ordering. X440T is not confirmed in the provided applicability list.

5. Will it fit Hero Mavrick 440?
Please verify before ordering. Mavrick 440 is not confirmed in the provided applicability list.

6. When should this part be replaced?
Replace it when the reservoir is cracked, leaking, damaged, discolored, or no longer serviceable during brake repair.

7. What should be checked before ordering?
Please confirm the exact bike variant, old part match, and whether you need only the reservoir or a larger rear brake repair assembly.