Sterndrive gimbal bearings: Alpha, Bravo, OMC and Volvo identification, seals and tools
A sterndrive gimbal bearing supports the drive shaft near the transom assembly; it is not the propeller-shaft cutless bearing, a universal joint or the upper-swivel-shaft seal. Identify the drive and transom serial numbers before choosing a part. Engine displacement alone, such as 3.0, 4.3 or 5.7 litres, does not establish the correct bearing.
On this page15 sections ⌄
What the bearing does, and which parts are different
“Gimble bearing” is a common spelling in searches; the sterndrive component is normally called a gimbal bearing. Do not confuse it with a camera gimbal or with an unrelated inboard shaft support.
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| Part | Role | Common confusion |
|---|---|---|
| Gimbal bearing | Supports the sterndrive shaft at the transom-side assembly | Not the transom steering pivot bearing |
| U-joints | Allow angular movement in the drive train | U-joint wear can also cause noise or vibration |
| Engine coupler/alignment | Connects the engine output to the drive shaft | A freely turning bearing does not prove correct alignment |
| Bellows | Protect the relevant flexible connection from water entry | A new bearing does not repair a leaking bellows |
| Propeller-shaft cutless bearing | Water-lubricated shaft support in a strut/stern tube | Different construction and lubrication |
Quicksilver application references: keep A01 and A02 separate
These are Mercury’s published application summaries. Check the exact drive/transom serial and current service parts listing before installation; a summary is not a universal interchange certificate.
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| Quicksilver part | Published application summary | Important qualification |
|---|---|---|
| 879194A01 | Alpha One Gen II: 1998 and newer; Bravo and Vazer transom assemblies: 1996 and newer | Do not extend to all Gen II production years |
| 879194A02, Perma-Lube | MC-1, R, MR and Alpha: 1974–1997; Bravo One: 1988–1995; OMC Cobra also listed | Retain the Perma-Lube description and exact application check |
| 8M2005029 | Upper-swivel-shaft seal kit for select R, MR, Alpha and Bravo transom assemblies | Not a gimbal-bearing part or a generic internal bearing seal |
Which bearing fits my MerCruiser 3.0, 4.3, 5.0 or 5.7?
The engine size is insufficient. Identify the drive family and transom serial and the original part. The table cannot assign one bearing to every boat using that engine.
Does Alpha One Gen II always mean 879194A01?
No. The cited A01 application starts at 1998. Confirm the exact serial-controlled application, rather than dropping the production boundary.
Sierra 18-2100: declared cross-references and greasable construction
The following relationships are Sierra’s aftermarket manufacturer references. They are not an independent claim that every listed assembly accepts any bearing sharing the same external dimensions.
Sierra lists OMC Cobra and King Cobra applications. Its MerCruiser notes include 120/140 hp serials 2791957–6225576 with a gimbal trim sender, and 165 hp from serial 2763442. These qualifiers matter; horsepower alone is not the lookup key.
The Sierra page also contains packaging dimensions. Those are not bearing bore, OD and width, so they are not inserted into BearingScope’s dimensional bearing search. Exact bearing dimensions must come from a bearing drawing or specification.
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| Reference owner | Numbers listed by Sierra | Scope |
|---|---|---|
| MerCruiser | 30-60794A2; 30-60794A4; 30-60794B4; 30-879194A02 | Manufacturer-declared aftermarket reference |
| OMC | 3853807; 983937 | Manufacturer-declared aftermarket reference |
| Volvo Penta | 21752712; 3853807 | Check exact Volvo assembly and serial |
| Sierra construction | 18-2100: Link Belt, greasable | Do not treat it as having identical lubrication instructions to Quicksilver Perma-Lube |
Alpha, Bravo, Cobra, SX and DP: what to record
Keep uncertain applications open rather than forcing them into the nearest part number. A previous owner may have changed the drive or transom assembly. The exact installed configuration controls the lookup.
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| Search description | Useful next identifier | What this page does not infer |
|---|---|---|
| Alpha / Alpha One / Gen I / Gen II | Drive and transom serials, generation and bearing reference | One part for all generations |
| Bravo One / Two / Three | Exact drive and transom serial-controlled parts list | A Bravo One historical listing proving every Bravo variant |
| OMC Cobra / King Cobra | Exact transom assembly and original part; check Sierra/OEM distinction | A Volvo part based only on a shared name |
| Volvo SX / SX-A / SX-M / DP variants | Complete drive designation, product/serial and original bearing | One 3853807 replacement for every Volvo drive |
| Volvo 280 / 290 or an unidentified older drive | Assembly drawing and the actual shaft-support arrangement | Modern SX gimbal construction on a different drive design |
| A boat make or engine displacement | The installed drive/transom identifiers | Fitment from the boat badge or litre figure alone |
Sealed / Perma-Lube vs greasable: service the actual bearing
Mercury calls 879194A02 Perma-Lube; Sierra calls 18-2100 greasable while listing 30-879194A02 as a reference. That is exactly why a cross-reference must preserve service-design differences. Do not invent a single grease recommendation for both.
Lubricant compatibility, seal orientation and any grease-passage alignment are version-specific. If the exact service document is unavailable, those requirements remain unverified instead of being guessed from photographs or a similar drive.
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| Condition | Correct distinction | Do not do this |
|---|---|---|
| Permanently lubricated replacement | Follow its specified service requirements | Inject grease through seals because an older assembly had a fitting |
| Greasable 18-2100 or other identified version | Follow that bearing and drive’s specified grease path, grade and interval | Copy a universal amount or interval from another part |
| External fitting on the transom | Identify which component it serves and the fitted bearing design | Assume the fitting proves every replacement bearing is greasable |
| A kit containing bearings, seals or bellows | Identify each part and its application separately | Treat every item called gimbal seal as the bearing seal |
Grinding, rumbling or vibration: a diagnostic checklist
These are inspection directions, not a remote diagnosis or permission to operate a damaged drive. Do not approach a rotating shaft or propeller to locate noise. Follow the service procedure for controlled testing; stop for significant vibration, overheating, water entry or damage.
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| Observation | Possible checks with the system isolated | Why it is not a diagnosis by itself |
|---|---|---|
| Rumble or grinding | Bearing roughness, corrosion, shaft contact and other rotating components | Sound can travel through the transom |
| Vibration that changes with steering or trim | Gimbal bearing, U-joints and the prescribed alignment checks | Angular-load changes can affect more than one component |
| Water or rust in the bearing area | Bellows, seals, mating surfaces and the entry path | Replacing the bearing does not stop the leak |
| Roughness after replacement | Correct seating, installation damage, lubrication version and alignment | A new part can still be incorrectly installed |
| A smooth bearing removed from a noisy assembly | Continue checking U-joints, coupler, shaft and drive | Do not replace parts solely from an online sound comparison |
Puller, driver and alignment tool: different jobs
Primary tool-maker examples. The tool’s listed application is not approval of a particular replacement bearing or a substitute for the drive service procedure.
Removal needs a secure puller engagement and supported reaction. Installation needs a correctly sized driver acting on the intended bearing surfaces. Alignment is a separate check. A homemade bar with an approximate diameter cannot be assumed to perform all three jobs.
This guide does not publish guessed alignment-bar dimensions, universal insertion depth, puller force or a drill pattern. Obtain those from the applicable service/tool drawing. Do not strike a bearing through its rolling elements or omit required alignment checks to avoid using the specified tool.
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| Tool | Published function/reference | Selection boundary |
|---|---|---|
| Marine Tech Tools AMT0040 | Locks into the gimbal bearing for removal; Alpha, Alpha 1, MR, Bravo, OMC, Cobra and Volvo families listed | Verify the reaction surface, access and exact tool instructions |
| AMT0040 maker cross-references | Sierra 18-79820-1 / 18-79820; Mallory 9-79820; WSM GBP-1-PL | These are tool references, not bearing numbers |
| Marine Tech Tools K1008 | Two-piece alignment/installation kit; bearing and seal driver; maker lists 91-30366T reference | Confirm the required reach and geometry for the actual drive |
| Complete alignment procedure | Checks the drive/engine relationship using the specified equipment | A driver seating the bearing is not by itself proof of engine alignment |
Replacement checklist and unresolved specifications
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| Before removal | Before installation | Before return to service |
|---|---|---|
| Secure vessel; isolate power; support drive | Verify original and replacement reference | Check the prescribed alignment |
| Record bearing orientation and retaining arrangement | Inspect housing and shaft; address damage | Verify sealing and correct lubrication design |
| Inspect water-entry evidence and bellows | Use specified driver, depth and procedure | Reassemble with exact fastener and service requirements |
| Confirm correct extraction tool | Keep parts clean and avoid installation damage | Complete the equipment’s inspection/test sequence |
Can I replace it without an alignment tool?
Do not omit a required alignment check. Whether a particular tool or procedure is required depends on the exact drive manual; a bearing that feels free is not evidence that the engine and drive are aligned.
Does this page give a full Alpha/Bravo/Volvo workshop procedure?
No. It answers identification, reference and tool distinctions. Exact torque, seal orientation, seating depth, grease grade and drive-removal sequence remain controlled by the applicable service instructions.
Does BearingScope sell these parts or perform the repair?
No. BearingScope is an independent technical lookup and comparison resource. Product and tool examples are reference records, not sales offers or service claims.
What the evidence can — and cannot — tell you
| Observation or context | Interpretation to consider | Verification needed |
|---|---|---|
| Identity | Drive family, transom serial, original part and revision | Alpha, Bravo and Volvo names include different assemblies. |
| Bearing design | Exact greasable or permanently lubricated version | Do not infer serviceability from boat age alone. |
| Condition | Bearing, bellows, U-joints, shaft, housing and alignment | Noise alone does not identify a failed gimbal bearing. |
| Installation | Specified puller, driver, alignment procedure and manual | Tool compatibility is not replacement-bearing interchange. |
Plan the work safely
Identify and record
Record the drive/transom identifiers, original bearing number and installed lubrication arrangement. Match them to the current equipment parts and service documentation; do not identify the bearing from engine capacity alone.
Check the context
Secure and isolate the propulsion system and follow the exact drive-removal procedure with appropriate lifting support. Inspect the bearing, water-entry evidence, bellows, U-joints and associated shaft and housing surfaces.
Verify before acting
Use the specified puller, bearing/seal drivers, orientation, seating and lubrication instructions. Apply force through the approved bearing surfaces and stop if seating or tool reaction is incorrect. This reference does not supply universal torque or depth values.
Keep the decision traceable
Complete the prescribed alignment and reassembly checks before service. Verify lubrication and sealing for the actual version; investigate the cause of water entry or misalignment rather than treating a replacement bearing alone as a complete repair.
Capture the information a model search cannot guess
Keep this checklist with your inspection or comparison. Checking a box only records that you have collected the item; it does not certify the bearing.
0 of 4 information groups recorded.
Technical basis & editorial scope
Original BearingScope workflow, written for catalogue research and comparison. Manufacturer material is used to check principles, not copied as a product endorsement or substituted for model-specific instructions. Reviewed 1 October 2026.
- Mercury Marine / Quicksilver 879194A01 application listing — Exact manufacturer, product family and document scope only. Technical reference, not a vessel-fitment approval.
- Mercury Marine / Quicksilver 879194A02 Perma-Lube application listing — Exact manufacturer, product family and document scope only. Technical reference, not a vessel-fitment approval.
- Mercury Marine / Quicksilver 8M2005029 upper-swivel-shaft seal kit — Exact manufacturer, product family and document scope only. Technical reference, not a vessel-fitment approval.
- Sierra 18-2100 greasable gimbal bearing: manufacturer cross-reference and application notes — Exact manufacturer, product family and document scope only. Technical reference, not a vessel-fitment approval.
- Marine Tech Tools AMT0040 gimbal bearing puller: tool compatibility and references — Exact manufacturer, product family and document scope only. Technical reference, not a vessel-fitment approval.
- Marine Tech Tools K1008 alignment and installation kit: manufacturer description — Exact manufacturer, product family and document scope only. Technical reference, not a vessel-fitment approval.
Source addresses and collection status are retained in the internal audit. No unpublished dimensions, torque settings, service intervals or interchange approvals are inferred.