Mercury MerCruiser 39899A1 Roller Bearing-to-Coupling Shim Set – TR / TRS Drive

The Mercury MerCruiser 39899A1 is a genuine OEM roller bearing-to-coupling shim set used to establish the correct internal spacing in selected MerCruiser TR and TRS sterndrive assemblies. The set contains four shim thicknesses — .002, .003, .005, and .010 in. (approx. 0.051, 0.076, 0.127, and 0.254 mm) — allowing the correct stack to be selected during assembly. The original 39899A1 has been superseded by current Mercury shim set 36178A02.

Compatible Applications

• MerCruiser 255 TRS — 1973–1974
• MerCruiser 280 TRS — 1975–1976
• MerCruiser II-TR — 1973–1976
• MerCruiser TR / TRS — 1977–1993
• Selected 215E / 215H applications — verify by drive serial number and parts diagram

Always confirm fitment using the sterndrive model, serial number, and the applicable Mercury parts diagram before ordering.

Where It Fits – Assembly Position

In TR/TRS drive-shaft-housing diagrams, this shim set is positioned between the roller bearing and coupling assembly. The correct shim stack is determined by measurement during the rebuild — it is not a fixed value that can be carried over from one service to the next without verification.

Kit Contents – Shim Thicknesses

• .002 in. (approx. 0.051 mm)
• .003 in. (approx. 0.076 mm)
• .005 in. (approx. 0.127 mm)
• .010 in. (approx. 0.254 mm)

Product Details

• Original OEM Part Number: 39899A1 / 15-39899A1
• Superseded By: 36178A02 / 15-36178A02
• Intermediate Reference: 36178A1 / 15-36178A1
• Earlier Related Reference: 23097A1 / 15-23097A1
• GTIN: 745061141643
• Factory Description: Shim Set – Roller Bearing to Coupling
• System: Sterndrive drive-shaft housing / gear and bearing assembly

Fitment Notice – Precision Setup Component

This is a precision setup part, not a universal spacer. The correct shim stack must be determined using the applicable Mercury service procedure for the exact drive assembly being rebuilt. Do not reinstall the same shim thickness without verifying the bearing-to-coupling setup, especially if bearings, gears, shafts, or housings have been replaced — any of those changes can alter the required shim selection.

When to Replace

Replace or reselect the shim set when:

• Rebuilding the applicable drive-shaft or gear assembly
• Replacing the roller bearing or coupling
• Bearing preload or internal spacing is being reset
• The original shims are bent, damaged, corroded, or missing
• Service measurements indicate a different shim stack is required

Installation Notes

Correct installation requires measurement and setup per the Mercury service manual:

• Keep all shims clean and flat — do not reuse distorted shims
• Measure the required stack thickness according to the Mercury service procedure for this drive
• Confirm bearing and coupling condition before final assembly
• Use only the thickness combination needed to achieve the specified setup
• Recheck bearing preload and endplay where required before closing the housing

Alternate / Superseded Part Numbers

• 39899A1 / 15-39899A1 — original Mercury number
• 36178A1 / 15-36178A1 — intermediate replacement
• 36178A02 / 15-36178A02 — current replacement
• 23097A1 / 15-23097A1 — earlier related reference

Related Parts

• Mercury MerCruiser Quicksilver Driveshaft Locknut 41527T
• Mercury MerCruiser Driveshaft Housing Water Seal 36557
• Mercury Quicksilver Driveshaft Housing Plug 64649
• Mercury MerCruiser Quicksilver Driveshaft Slinger Ring 30271 — 8M0214918

Parts Desk Insights

Best Use Case: This shim set is the right call during a full TR or TRS drive rebuild — specifically when the roller bearing or coupling is being replaced and the internal spacing needs to be re-established from scratch. It’s a measurement-driven setup step, so having the full range of shim thicknesses in hand before starting the job is the smart way to work.

Common Issues: The most frequent mistake is assuming the original shim stack can be reinstalled without re-measuring. Any time a bearing, coupling, shaft, or housing is replaced in this assembly, the required shim thickness can change — carrying over the old stack without checking can result in incorrect bearing preload and premature drive failure. Always measure first, then select the correct combination from the set.