Complete Gear Solutions for Eaton FSO4405 and FSO4505 Transmissions

1. Introduction

The Eaton FSO4405 and FSO4505 5-speed transmissions are widely used in medium-duty and regional haul trucks. In daily operation, their durability, shift quality, and ease of maintenance directly affect vehicle uptime and operating costs.

Over the years, transmission rebuilders and parts distributors have consistently faced the same challenge: when overhauling these gearboxes, it is difficult to source Eaton FSO4405 parts and Eaton FSO4505 gearbox parts that are truly reliable, dimensionally accurate, and capable of matching original OEM performance.

As a precision gear manufacturer focused on commercial vehicle drivetrains, PairGears has developed a complete range of gears, shafts, and synchronizer components for these two transmissions. All components are engineered as true drop-in replacements, helping workshops and fleets restore gearbox performance with confidence using high-quality aftermarket gearbox components.

2. Why Aftermarket Components Matter in Eaton Transmission Overhauls？

In real-world transmission repair, problems rarely exist in isolation.

What initially appears to be a single damaged gear often reveals additional wear once the gearbox is disassembled. Inconsistent truck transmission gears, worn synchronizer interfaces, or shaft tolerance deviations can quickly result in noise, hard shifting, or premature failure after reassembly.

Typical risks include:

• Inconsistent gear tooth geometry causing unstable meshing

• Degraded Eaton synchronizer performance leading to gear clash

• Shaft tolerance mismatch increasing bearing and gear loads

• Reduced service life under normal operating conditions

For this reason, PairGears develops aftermarket gearbox components with a strong focus on system-level compatibility, rather than treating each part as an isolated replacement.

3. Key Engineering Considerations in Our Development Process

During the development of each gear and synchronizer component for Eaton transmissions, we focus on several critical engineering factors:

• Accurate gear tooth geometry

Ensures stable meshing of truck transmission gears under varying loads, minimizing abnormal noise and impact.

• Proper Eaton synchronizer cone angle matching

Allows faster and smoother speed synchronization during shifting, reducing the risk of gear clash.

• Heat treatment aligned with load and wear conditions

Balances surface durability with core toughness instead of simply maximizing hardness.

• Strict control of shaft runout and concentricity

Prevents small deviations from being amplified during long-term gearbox operation.

Before release, every Eaton FSO4405 and FSO4505 component is verified against OEM samples and assembled transmission units.

4. Eaton FSO4405 – Complete Gear and Synchronizer Coverage

For the Eaton FSO4405 transmission, PairGears has developed a comprehensive portfolio of Eaton FSO4405 parts, including gears, shafts, and Eaton synchronizer components commonly required during overhaul and rebuild work.

These components are designed to support:

• Smooth and precise shifting

• Reduced gear impact during engagement

• Stable torque transmission under load

• Long-term durability in commercial truck applications

▶FSO4405 Transmission Exploded View

Eaton FSO4405 gearbox parts exploded view-PairGears

The exploded view illustrates how the Eaton synchronizer assemblies, shafts, and truck transmission gears interact inside the FSO4405 gearbox.

▶FSO4405 Parts Summary Table

No.	PairGears No.	OEM No.	Part Name	Mating Gear	Online Product Page
1	PGEA123	3361224	Synchronizer 5A		View product
2	PGEA547	3344765	Synchronizer 3/4		View product
3	PGEA548	3344755	Synchronizer 1/2		View product
4	PGEA132	3344768	Synchro Ring 3/4/5		View product
5	PGEA129	3344778	Synchro Ring 3/4		View product
6	PGEA130	3344534	Synchro Ring 1/2		View product
7	PGEA103	3344701	3rd Speed Gear - Mainshaft	3341184	View product
8	PGEA102	3344769	5th Speed Gear - Mainshaft	3341107	View product
9	PGEA108	3344777	Reverse Gear - Mainshaft	3341182	View product
10	PGEA120	3344260	Input Shaft	3341109	View product
11	PGEA114	3344641	2nd Speed Gear - Mainshaft	3341390	View product
12	PGEA107	3344522	1st Speed Gear - Mainshaft	3341390	View product
13	PGEA117	3341164	Mainshaft		View product
14	PGEA112	3341107	5th Speed Gear - Countershaft	3344769	View product
15	PGEA116	3341109	Drive Gear - Countershaft	3344260	View product
16	PGEA101	3341184	3rd Gear - Countershaft	3344701	View product
17	PGEA118	3341390	Countershaft	3344522/3344641	View product

The parts summary table allows rebuilders to quickly cross-reference OEM numbers and select the correct aftermarket gearbox components for repair or spare-parts programs.

3344755 Synchronizer for Eaton Gearboxfor FSO4405

3361224 Synchronizer for Eaton Gearbox FSO4405

3344778 Synchronizer Ring for Eaton Gearbox FSO4405

5. Eaton FSO4505 – Precision Components for Consistent Shifting

Although the Eaton FSO4505 shares a similar architecture with the FSO4405, it operates under different load profiles and duty cycles. PairGears has therefore developed a dedicated range of Eaton FSO4505 gearbox parts, optimized for reliable engagement and long service life.

Our FSO4505 components focus on:

• Stable gear meshing under variable torque

• Improved Eaton synchronizer response during upshifts and downshifts

• Direct fitment without additional modification

▶FSO4505 Transmission Exploded View

Eaton FSO4505 gearbox parts exploded view-PairGears

▶FSO4505 Parts Summary Table

No.	PairGears No.	OEM No.	Part Name	Mating Gear	Online Product Page
1	PGEA109	3361064	5th Gear - Countershaft	3361400	View product
2	PGEA105	3361067	Drive Gear - Countershaft	3361436	View product
3	PGEA113	3361063	3rd Gear - Countershaft	3361402	View product
4	PGEA119	3361300	Countershaft	3361295/33610	View product
5	PGEA131	3361096	Synchro Ring 3/4/5		View product
6	PGEA133	3361091	Synchro Ring 1/2		View product
7	PGEA125	3361397	Synchronizer 5		View product
8	PGEA122	3361396	Synchronizer 3/4		View product
9	PGEA127	3361242	Synchronizer 1/2		View product
10	PGEA121	3361436	Input Shaft	3361067	View product
11	PGEA104	3361400	5th Speed Gear - Mainshaft	3361064	View product
12	PGEA106	3361398	Reverse Gear - Mainshaft	3361058	View product
13	PGEA111	3361402	3rd Speed Gear - Mainshaft	3361063	View product
14	PGEA115	3361295	2nd Speed Gear - Mainshaft	3361300	View product
15	PGEA110	3361075	1st Speed Gear - Mainshaft	3361300	View product
16	PGEA128	3361073	Mainshaft		View product

By combining the illustration with the parts list, technicians can accurately identify Eaton FSO4505 gearbox parts and avoid mismatched replacements.

OEM 3361063 Gear for Eaton Gearbox FSO4505

OEM 3361242 Synchronizer for Eaton Gearbox FSO4505

OEM 3361096 Synchronizer Ring for Eaton Gearbox FSO4505

OEM 3361436 Shaft for Eaton Gearbox FSO4505

6. Designed for Direct Replacement

All PairGears components for Eaton FSO4405 and FSO4505 transmissions are manufactured according to original OEM dimensions, tolerances, and load requirements. As a precision gear manufacturer, we ensure that our aftermarket gearbox components provide:

• Direct installation without rework

• Full compatibility with existing transmission housings

• Reliable performance comparable to original Eaton parts

Whether replacing worn Eaton synchronizers, damaged truck transmission gears, or transmission shafts, each component is designed to integrate seamlessly into the original gearbox assembly.

7. Typical Applications

PairGears Eaton transmission components are widely used in:

• Truck transmission overhaul and repair workshops

• Fleet maintenance operations

• Commercial vehicle spare-parts distributors

• Medium-duty truck remanufacturing programs

These aftermarket gearbox components help extend transmission service life while controlling maintenance costs.

8. Custom Support Beyond Standard Parts

If a required Eaton FSO4405 part or Eaton FSO4505 gearbox component is not listed, PairGears also supports custom manufacturing based on drawings or physical samples.

Our engineering team can assist with:

• Reverse engineering of OEM Eaton components

• Material selection and heat treatment planning

• Small-batch or project-based production

9. Conclusion

By systematically developing Eaton FSO4405 parts and Eaton FSO4505 gearbox parts, PairGears provides gearbox professionals with reliable, precision-engineered solutions for real operating conditions.

As an experienced precision gear manufacturer, we support transmission overhaul, repair, and long-term spare-parts programs with stable-quality truck transmission gears and Eaton synchronizer components.

If you are planning an Eaton transmission rebuild or aftermarket supply project, feel free to Contact Us to discuss your requirements.

FAQ

1. Are PairGears parts direct replacements for Eaton FSO4405 and FSO4505 transmissions?

Yes. All PairGears components for Eaton FSO4405 and FSO4505 are engineered as drop-in replacements, manufactured according to original OEM dimensions, tolerances, and load requirements. No additional modification is required during installation.

2. What types of Eaton FSO4405 and FSO4505 parts does PairGears supply?

PairGears supplies a complete range of truck transmission gears, shafts, and Eaton synchronizer components, including mainshaft gears, countershaft gears, input shafts, synchronizer assemblies, and synchro rings commonly required for gearbox overhaul and repair.

3. How do PairGears synchronizer components help prevent gear clash?

PairGears Eaton synchronizer components are designed with proper cone angles and controlled friction characteristics, allowing gear and shaft speeds to synchronize smoothly before engagement. This helps reduce gear clash, improve shift quality, and protect gear teeth from impact damage.

4. Are these aftermarket gearbox components suitable for heavy-duty or high-mileage applications?

Yes. These aftermarket gearbox components are developed for real operating conditions found in medium-duty and regional haul trucks, including frequent shifting, variable loads, and long service intervals. Material selection and heat treatment are optimized for durability and stable performance.

5. How do PairGears gears compare to original Eaton parts?

As a precision gear manufacturer, PairGears designs its gears to match OEM geometry and performance expectations. Our truck transmission gears focus on stable meshing, controlled noise, and consistent load distribution, providing performance comparable to original Eaton components in overhaul applications.

6. Can I identify the correct part using OEM reference numbers?

Yes. Each Eaton FSO4405 part and Eaton FSO4505 gearbox part is listed with corresponding OEM reference numbers in the parts summary tables. This allows rebuilders and distributors to quickly cross-reference and select the correct replacement components.

7. What if the required Eaton transmission part is not listed?

If a specific Eaton FSO4405 or FSO4505 component is not listed, PairGears can support custom manufacturing based on drawings or physical samples. Our engineering team offers reverse engineering, material selection, and small-batch production support.

8. Who typically uses PairGears Eaton transmission components?

Our components are widely used by truck transmission repair workshops, fleet maintenance teams, commercial vehicle parts distributors, and remanufacturing programs that require reliable aftermarket gearbox components for Eaton transmissions.