Eaton FSO4405 & FSO4505 Transmission Gear Solutions

When rebuilding or servicing 5-speed synchronized manual transmissions like the FSO4505, shift quality and durability depend on synchronizer condition, cone geometry matching, and stable gear tooth accuracy. We supply aftermarket replacement gears, shafts, and synchronizer components cross-referenced by OEM numbers—supported by quality evidence for repeatable assembly outcomes.

Key Facts:

Transmission family: 5-speed synchronized light-duty manual transmission; model includes FSO-4505.

Shift system note: FSO-4505 has five forward speeds and synchronized gearing; misuse can accelerate synchronizer wear.

What we supply: gears, mainshaft/countershaft parts, synchronizer rings & assemblies (OEM-number cross reference).

Send us your OEM part number / photo / drawing for a fast cross-reference and quote.

1. Customer & Application

Customer type:

A regional transmission rebuilder and parts distributor needed a stable source of replacement components for Eaton FSO4405 and FSO4505 units used in light/medium-duty truck fleets.

Application:

5-speed synchronized manual transmission rebuilds focused on restoring smooth engagement, reduced gear clash, and reliable torque transfer. Synchronizers are designed to match shaft and gear speeds to enable smooth shifts.

2. Customer Pain Points (What they asked us to solve)

2.1 Hard shifting / gear grinding after service.

2.2 Uncertain interchange: wrong cone angle / incorrect mating fit leads to rework.

2.3 Inconsistent life: unstable heat treatment or surface integrity can accelerate wear.

2.4 Need OEM-number ordering to reduce mistakes in procurement.

3. Product Scope (OEM-number cross reference)

We cover common service parts for both transmissions, including:

• Gears (countershaft/mainshaft, 1st–5th speed related items)

• Shaft parts (mainshaft, countershaft related)

• Synchronizer components (rings, assemblies, hubs, sleeves)

▶FSO4405 Transmission Exploded View

▶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

▶FSO4505 Transmission Exploded View

▶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

4. How We Delivered

Pre-production

• Confirm OEM number mapping and mating gear pairs to avoid incorrect interchange.

• Identify critical geometry (tooth accuracy, cone angle, fit interfaces) that affects shift feel and assembly success.

In production

• Control tooth geometry consistency to reduce abnormal noise and premature wear.

• For wear-critical transmission components, case hardening such as carburizing is commonly used to achieve a hard surface with a tougher core.

• Where specified, shot peening can introduce beneficial compressive residual stress at the surface.

Post-production

• Provide inspection reports and drawings upon request.

• Pack and label by OEM No. to reduce receiving mistakes for rebuilders.

5. Project Challenges & How We Solved Them

Project Challenge	What Could Go Wrong	How We Solved It
Synchronizer cone / friction-surface matching	Hard shifting, gear clash, or grinding even after parts replacement	We treated cone angle + friction-surface fit as a key acceptance point, verified incoming samples against the mating parts, and locked the control points into our process to keep results consistent.
Tooth profile & lead consistency	Abnormal noise (whine) and rough meshing after assembly	We defined profile/lead inspection items (e.g., lead, profile, runout as applicable) and standardized them into a redacted outgoing inspection report for repeatable assembly results.
Heat-treatment stability	Early wear, pitting, or surface distress in service	We controlled surface hardness and case depth as the core CTQs and, when needed, added redacted metallographic verification to confirm the hardened layer and microstructure.

FAQ

1. Do you supply parts for both FSO4405 and FSO4505?

Yes. Share your OEM number list (or photos), and we'll confirm interchange and matching pairs.

2. Are these parts drop-in replacements?

They are manufactured to OEM-number cross reference and intended for direct replacement; final results depend on gearbox condition and correct rebuild practices.

3. What information do you need for a quote?

OEM No., quantity, target lead time, and any special requirements (material/heat treat/inspection).

4. Can you provide inspection reports and drawings?

Yes—redacted inspection reports and drawings can be provided for review (project-dependent).

5. Do you support small trial orders?

Yes. We can support sample or pilot quantities before ongoing supply.

If you're rebuilding Eaton FSO4405/FSO4505 units and want stable shift quality and repeatable fit, send your OEM part numbers for cross-reference and quotation.