See full version: HOW TO: How the Shift Interrupt system works
As a trouble shooting note: If your shift interrupt switch is being activated going into either forward or reverse or coming out of gear when the boat is out of the water, then you have a problem with something binding from the lower shift cable to the drive itself. [links]
What happens with the shift interrupt system when moving the shifter from Fwd, or Rev back to the Neutral position goes something like this.
The lower gears (Both Forward and reverse) have a dog type clutch. These dogs are reverse cut so they try to hold themselves into gear, and will stay in gear even under heavy load. Even at idle they are under a fair amount of load and without the shift interrupt system, it’s almost impossible to get out of gear. You can see the undercut and how the shift dog fits in the gears in the picture below.
Usually in the spring and summer we get a lot of posts regarding the shift system for the MC-1 (falsely referred to as Pre-alpha drives) to the Alpha 1 drives. There are a lot of wrong ideas on how and why the system works and why it's there to begin with. Maybe this will help explain how it actually works and why it's needed.
The system is NOT designed to work when putting the drive into gear, or when the boat is out of the water and on muffs. Without the load on the prop, there is not enough resistance on the shift dogs in the lower unit to cause resistance to the shift cable and engage the shift interrupt system. [links]
The ONLY purpose of the shift interrupt system in the Mercruiser Alpha style outdrives is to get the drive out of gear (forward or reverse) when the engine is running and the boat is in the water with a load on the prop. here
MC-I, MR, Alpha One & Gen II (1978 & newer)
Brand new, genuine Mercury Marine / Mercruiser Shift Cable Kit. This is a factory original equipment item, not aftermarket. [links]
table.tableizer-table < font-size: 12px; border: 1px solid #CCC; font-family: Arial, Helvetica, sans-serif; >.tableizer-table td < padding: 4px; margin: 3px; border: 1px solid #CCC; >.tableizer-table th < background-color: #104E8B; color: #FFF; font-weight: bold; >RowClassPart NumberSS LevelDispDescription 1 865436A020ACTCABLE ASSY-SHIFT 2 19543A101SSCABLE ASSY-SHIFT 3 19543A82SSCABLE ASSY-SHIFT 4 19543A43SSCABLE ASSY-SHIFT 5 19543A24SSCABLE ASSY-SHIFT 6 41951A15SSCABLE ASSY 7 73679A26SSSHIFT CABLE @2 8 66065A17SSSHIFT CABLE @2 9 66069A28SSCORE WIRE
This product may contain chemicals known to the State of California to cause cancer, birth defects, or other reproductive harm. [links]
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Software Compatibility: more
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Mercruiser Exhaust Bellows 18654A1 Replacement Mercury Mercruiser 18654A1, 32734A3, 8M0124227 Fits all Mercruiser Alpha, Generation I and II, TRS and Bravo drives. Includes Clamps. Our bellows are supplied with 316 Stainless Steel Original Jubilee® Clamps Size. here
Gimbal Bearing - Non-serviceable / greaseable. Mercruiser: Replaces Mercruiser Part No. 30-879194A01, 30-879194A02, 60794A4, 862540A04, 862540A3, 862540T1, 879194A01, 879194A01&A02 Use with replacement Mercruiser gimbal oil seal 26-88416. Drives: Alpha One Gen I & II. more
Mercruiser Seawater Impeller 47-43026T2 Mercruiser part no. 21836, 25-21836, 430261, 430262, 430264, 43026B2, 43026Q02, 47-43026Q02, 47-43026T2, 8M0025709 Used on Mercruiser engines: Mercruiser Alpha One Generation 2 with serial number D494569 and. more
Lower Gear Aftermarket parts for Mercruiser Alpha 1 Gen 2 drives.
Trim Cylinders & Hoses for Mercruiser drives.