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OMC Electric shift Stringer outdrive design

Stringer years 1962 to 1977

  • Early models with Buick Motors
  • Outdrive technical specifications
  • Press on ball gear shaft
  • Electric shift lower unit engineering
  • Exploded View Drawings
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By author Trish Dougherty

Outboard Motor Corp. designed

Began production of the stern drive in 1962 with their first model. The first model; known as the Stringer outdrive - was produced between 1962 and 1968. The lower cases had a bullet style housing which later changed to a more conventional shaped lower unit. First generation Stringers made from 1962 to 1963 came with an 80 or 90 hp. engine; and in 1964 manufactured a slightly heavier duty lower unit powered by Chevy and Buick engines. These models came powered by either a 120 hp. Chevy in-line 4 cylinder, 150 hp. V6 Buick or a 200 V8 Buick. The Buick motors were discontinued in later years; and in 1969 the 5.0L 305 Chevy V8 was added along with a modern 4.3 Liter 262 Chevy V6 in 1973. Ford 5.0L 302 and 5.8L 351 V8 engines were added 2 years later. During that early stern drive era of engineering - Mercruiser (Mercury) and Volvo designed their drives to be mounted in the traditional transom mount style. OMC came up with a mounting design where the motor and outdrive were attached to the boats stringers hence the name stringer. The unit was mated with the intermediate housing which was sealed with a large, rubber transom seal.

Stern Drive Stringer

Stern Drive Stringer

At the time, Volvo and Mercury (MerCruiser) used a u-joint design which allowed the drive to be run when tilted up and turned. OMC engineers opted for a less conventional design (due to patent restrictions owned by Volvo); and decided to use ball gears instead of u-joints for the power transfer from engine to outdrive. One press on ball gear was on the end of the intermediate drive shaft coming out of the engine coupler for years 1969 to 1972. The other gear on the upper case driven shaft. This odd design from motor / coupler to stern drive allowed both to mate fully when the drive was tilted down a hundred percent; but when tilted up at any degree, the knuckle gears would only mesh with each other on certain spots on the knuckles which typically lead to premature wear which would call for the gear to be replaced sooner than their engineers had predicted.

Press on ball gear 1969-1972

Press on ball gear 1969-1972

The drive shaft and press on ball gear with plug was only sold as one piece unit up to 1972. Replacement cost for one with shaft-retainer seal assembly in 1972 was over $500.00 and average life span was 250 hours on V8 225 hp. engines. In 1973 they redesigned unit to bolt on with a taper and nut with replacement cost of $60.00. Stringer models used an innovative shifting system in which the lower unit contained magnetic coils which engage the lower unit into forward or reverse. MerCruiser and Volvo used a traditional mechanical shifting system at the time. The electric shift shifting system used current that was sent to electromagnetic coils when the operator would engage the drive into gear. The clutch springs spun freely around the hub when in neutral; when the operator would select a gear – the forward or reverse the electromagnetic coils would cause either the forward or reverse spring to immediately lock onto the hub forcing it into gear. The unit did have some design flaws other than the ball gear system. The clutch springs were relatively thin; and tended to break on the end if too much force was put upon them. This could be caused by engaging the drive into gear with the RPM above 650 or reckless shifting. A lower viscosity thinner type C oil had to be used in the lowers. The upper case up to the year 1972 used a longer drive shaft and water impeller shaft. These upper housings were sometimes called high profile models. In 1973 and early 1974 the upper unit was redesigned to use a shorter drive shaft (4.6”) and impeller shaft (5.6”). These updated upper housings were sometimes called low profile to distinguish them from the earlier higher profile models. OMC stopped production of the electric shift lower unit in 1977. To continue reading about the history of the 400 and 800 models Click here