Borg Warner — Shift Spool O-Ring Velvet Drive 71C 72C — 4804H
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The Borg Warner / Velvet Drive 4804H is a small but important control valve shift spool O-ring used in classic Velvet Drive hydraulic marine transmissions. It seals the shift valve spool inside the outer control head assembly and is commonly replaced to correct transmission fluid weeping from behind the external gear-selector shift lever. This O-ring is a practical service part for leak repair around the selector shaft area on many Borg Warner and Velvet Drive 71C, 72C, and related marine gearboxes.
Key Features
- Part number: 4804H
- Component type: Control valve / shift spool O-ring
- Standard size reference: BS210 / AS568-210 style imperial O-ring
- Approximate dimensions: 3/4" I.D. x 1/8" cross section
- Metric reference dimensions: 18.64 mm I.D. x 3.53 mm cross section, approximately 25.7 mm O.D.
- Application location: Internal hydraulic shift valve / control spool spindle
- System location: Transmission outer control head / gear-selector assembly
- Material type: Oil-resistant rubber compound such as nitrile or Viton, depending on supplier
- Service purpose: Helps stop transmission fluid leakage at the external shift lever area
Transmission Compatibility
This O-ring is commonly associated with classic Borg Warner / Velvet Drive hydraulic-shift marine transmissions, including many:
- Velvet Drive 71C
- Velvet Drive 72C
- Velvet Drive 73C
- 1004 series marine transmission housings
- 1005 series marine transmission housings
- 1013 series marine transmission housings
- 1014 series marine transmission housings
- 1017 series marine transmission housings
- 1018 series marine transmission housings
Fitment should be confirmed by transmission model, control head layout, and parts diagram before ordering.
Fitment Notice
Confirm the transmission model tag, control head style, and selector-valve parts breakdown before installation. This O-ring fits the shift spool/control valve location and should not be confused with the neutral safety switch plate gasket, output seal, input seal, pump gasket, or full transmission overhaul seal kit.
If the transmission has been rebuilt, converted, or fitted with a non-original control head, compare the old O-ring and spool dimensions before reassembly.
When This Part Needs Replacement
Replace this O-ring when automatic transmission fluid weeps from the shift lever/control head area, leaves red oil staining around the selector shaft, or returns after cleaning the outside of the transmission. It should also be replaced any time the control valve or neutral safety switch plate is removed for service.
A hardened, flattened, cut, swollen, or brittle O-ring can no longer seal the shift spool properly and may allow fluid to migrate out behind the external shift arm.
Installation Notes
Use care when removing the external shift arm and control head components. The selector mechanism may contain a small detent ball and spring that can fall out during disassembly. Work over a clean tray or protected bilge area so small parts are not lost.
After removing the shift arm and neutral safety switch housing plate, the shift control valve can be moved carefully to expose the O-ring. Lubricate the replacement O-ring with clean transmission fluid before installation and avoid cutting it on sharp edges. Do not reuse the old neutral safety switch plate gasket if the cover has been removed.
Inspect the shift shaft, control spool bore, mounting plate gasket surface, detent spring, ball, fasteners, and neutral safety switch components while the assembly is apart.
Alternate/Cross-Reference Part Numbers
- Borg Warner / Velvet Drive: 4804H
- PCM / Crusader reference: R047010
- Alto reference: 010210B
- O-ring size reference: BS210 / AS568-210
- Related gasket often serviced at the same time: Neutral safety switch plate gasket 11006 / L4-147
Parts Desk Insight
This is a small part, but it is often the source of a very visible Velvet Drive leak. If the oil is coming from behind the shift lever rather than from the input, output, or pan area, the shift spool O-ring is one of the first service points to inspect. Pairing it with the neutral safety switch plate gasket helps avoid having to reopen the control head for a second leak.
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Shipping information
In-stock and OEM parts: ship same or next business day.
Locally warehoused items: ship within 3–4 business days.
Special-order items: timeline confirmed after order.
Returns & warranty
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