30-803099T1 Transom Repair Bellows Kit Fits MerCruiser Alpha One Gen II 1991 & Up

30-803099T1 Transom Repair Bellows Kit — Fits MerCruiser Alpha One Gen II 1991 & Up, Replaces Sierra 18-8206-1

Full Gen II transom repair kit — Compatible with MerCruiser Alpha One Gen II
(1991–current, serial 0D469859 & up). Bundles three Gen II bellows, gimbal bearing,
housing gasket kit, water hose, O-rings, and clamps so you finish the whole seal job in one pass
while the drive is off. Gen II redesigned the transom in 1991: flat U-joint (no ridge) and a
rubber exhaust bellow instead of the Gen I exhaust tube. Drive-off labor is expensive —
replace the worn set together. Bearing still solid and you only need rubber → 18BK003
(already on GHMarine.com).

What is in the box?

Three bellows + gimbal bearing + gasket kit + hardware for a complete Gen II transom service.
Each bellow also sold individually on GHMarine.com.

Component	OEM Part No.	GH SKU (single)	Qty
U-joint bellow (flat, no ridge)	816431A1	17B1007	1
Exhaust bellow	18654A1 → 8M0124227	17B1003	1
Shift cable bellow	74639A2	17B1005	1
Gimbal bearing	30-60794A4	18MB001	1
Bell housing gasket kit	27-94996-2	20GK002	1 set
Water hose 3/4"	32-41725-33	19H1002	1
O-rings + clamps	25-25439 / 25-33504 / 54-38863	—	as packed

 

Which kit is this?

OEM kit 30-803099T1 for Alpha One Gen II. U-joint 816431A1 is flat —
Gen I uses ridged 60932A4, Bravo uses 86840A05. Serial 0D469858 or below →
Gen I kit 17B3005 (full) or 17B3001 (rubber only). SN 0L100040 & up (1998+)
→ confirm greaseable bearing before ordering.

Signs your transom needs service

·       Water in the bilge after launch — any of the three transom bellows may be torn or de-bonded.

·       Gimbal bearing howl or grinding when turning the wheel — bearing may be rusted or worn.

·       Hard shifting — shift cable bellow may have pulled off its nipple.

·       Visible cracks, dry rot, or soft rubber on any bellow — replace all three while the drive is off.

·       Milky gear oil — water is getting past the drive shaft seals into the gearcase.

·       Spring inspection or scheduled transom service — drive already off, do it all at once.

Will it fit my drive?

Gen II 1991 & up. Serial 0D469859 & up. Greaseable bearing variant 1998+
(SN 0L100040+). Match the drive serial plate — HP alone does not prove fit.

Brand	Model / Drive	Rated HP	Stroke	Years	OEM Part No.
MerCruiser	Alpha One Gen II (standard)	135–300	4-Stroke	1991–1997	30-803099T1
MerCruiser	Alpha One Gen II Greaseable	135–300	4-Stroke	1998 & up	30-803099T1 / Mallory 9-72904

 

OEM & swap numbers

30-803099T1 / Sierra 18-8206-1 / GLM 21960 / Mallory 9-72900 /
PROmarine 68398.

Type	Brand	Part Number	Notes
OEM	Mercury / Quicksilver	30-803099T1	Primary OEM — full transom bellows kit Gen II
Aftermarket	Sierra	18-8206-1	Transom Seal Kit — 1:1 replacement
Aftermarket	Sierra	18-8218	Alternate Sierra packaging
Aftermarket	GLM	21960	Transom Service Kit Gen II
Aftermarket	Mallory	9-72900	Transom Seal Kit — 1991–97 (SN 0D469859–0K999999)
Aftermarket	Mallory	9-72904	Transom Seal Kit — 1998+ greaseable bearing (SN 0L100040+)
Aftermarket	PROmarine	68398	Transom Service Kit Alpha Gen II

 

Wrong kit? Read before you order

·       NOT for Gen I kit 30-803097T1 — U-joint is 60932A4 (ridged); see 17B3005 (full) or 17B3001 (rubber only)

·       NOT for Bravo kit 30-803100T1 — U-joint is 86840A05; see 18B5001 (full) or 17B3003 (rubber only)

·       NOT a single bellow — this is the full kit with bearing, gaskets, and hose

·       NOT 18BK003 — that is the rubber-only sibling (same OEM 30-803099T1, lighter box)

·       NOT Gen I exhaust tube 78458A1 — Gen II uses exhaust bellow 18654A1 / 8M0124227

·       NOT Gen I ridged U-joint 60932A4 — Gen II flange needs flat 816431A1

What ships in the box

·       1 × U-Joint Bellows 816431A1 (flat, Gen II type) with clamp

·       1 × Exhaust Bellows 18654A1 / 8M0124227 with clamps

·       1 × Shift Cable Bellow 74639A2 with clamps

·       1 × Gimbal Bearing 30-60794A4

·       1 × Bell Housing Gasket Kit 27-94996-2

·       1 × Water Intake Hose 3/4" (32-41725-33)

·       O-Rings & spare clamps as packed

·       Bellows adhesive — sold separately

·       Bellows expander tool 22ET001 — sold separately

·       U-Joint sleeve driver 21B1001 — NOT required for Gen II (no aluminum retainer ridge)

Install tips while the drive is off

Work in a ventilated area. If unsure, use a marine shop. Drive removal = heavy — use a stand.

1. Remove sterndrive per shop manual. Drain gear oil. Mark shifter position.

2. Scrape off old adhesive from all flanges — any crud left = future leak.

3. Apply bellows adhesive inside both ends of each bellow. Let tack up 10–20 min.

4. Install shift first (trickiest access), then U-joint, then exhaust last.

5. Use expander 22ET001 when seating the exhaust bellow onto the bell housing.

6. Gen II U-joint has no ridge — flange fit is simpler than Gen I. No aluminum sleeve required.

7. Replace gimbal bearing using a bearing driver. Do not nick the housing bore.

8. Torque all fasteners to spec. Run on muffs in neutral, check bilge.

9. If SN is 0L100040+ (1998+), confirm you have the greaseable bearing variant.

Kit or singles?

Get this kit if: bearing howl / gasket weep / two+ bellows aged / planned overhaul while the drive is off.

Get a single instead if: only one boot failed and the rest + bearing are fresh —
17B1003 / 17B1007 / 17B1005.

Sold separately either way: bellows adhesive · expander 22ET001
(Gen II does not need sleeve driver 21B1001).

FAQs — the bros want to know

Will this fit my MerCruiser sterndrive?

Yes — for Alpha One Gen II drives 1991–current, serial 0D469859 & up. This is the FULL transom service kit: 3 bellows + gimbal bearing + gasket set + hose + O-rings + clamps. If your serial is 6225577–0D469858 (Gen I), you need kit 17B3005 instead. Confirm your drive serial on the decal — horsepower alone is not enough.

What is in the box?

Three bellows: U-joint 816431A1 (flat), exhaust 18654A1 (→ 8M0124227), shift 74639A2. Plus: gimbal bearing 30-60794A4, gasket kit 27-94996-2, 3/4" hose, O-rings, and clamps. Adhesive and expander sold separately.

How is this different from the rubber-only kit (18BK003)?

18BK003 = same three Gen II bellows only — already on GHMarine.com. 17B3007 = bellows + gimbal bearing + gasket kit + hose + O-rings + clamps. Bearing solid and you only need rubber → 18BK003. Full transom service while the drive is off → 17B3007.

Should I buy one bellow instead of the kit?

Only one cracked and the other two + bearing are fresh → buy that single (17B1003 / 17B1007 / 17B1005 — all already on GHMarine.com). Two or more aged, bearing play, gasket weep, or planned overhaul → 17B3007. Drive-off labor usually costs more than the missing pieces.

Do I need Gen I or Bravo kit instead?

Gen I 1983–1990 (SN 6225577–0D469858) → 17B3005 full or 17B3001 rubber only. Bravo 1988+ → 18B5001 full or 17B3003 rubber only. These are NOT interchangeable — the U-joint bellow is different on every generation.

What about the 1998+ greaseable bearing?

Gen II from 1998 (SN 0L100040 & up) uses a greaseable gimbal bearing — this kit covers that variant via Mallory 9-72904 cross-ref. Confirm your current bearing type before ordering.

What tools do I need?

Marine bellows adhesive (buy separately), expander 22ET001. Gen II U-joint has no ridge — you do NOT need sleeve driver 21B1001 (unlike Gen I). Gimbal bearing driver recommended. Shop manual strongly advised.

Please note

Aftermarket replacement kit. Not OEM. Not affiliated with engine manufacturers
referenced above. Always confirm fit with your drive serial
(0D469859 & up = Gen II).