Difference between revisions of "Transmission"

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The transmission was also used by Lotus in the Esprit up through 1987, and the Maserati Merak (all types). The gearbox cases differ in these uses.  The Merak engine spins the same way as the SM engine but is forward of the transmission.  Therefore, to have five forward gears, the crown wheel was changed to the opposite side of the pinion.  This necessitated casting a new differential case.  The Lotus Esprit engine spins the opposite way from the C114 engine used in the SM and Merak.  Like the Merak, the Lotus engine is forward of the transmission.  Therefore in order to have five forward gears, the entire transmission spins backwards, with the pinion driving the coast side of the crown wheel when the vehicle is moving forward.
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The 5-speed manual transmission was also used by Lotus in the Esprit up through 1987, and the Maserati Merak (all types). The transaxle cases differ slightly in each.  The Merak engine spins the same way as the SM engine but is forward of the transmission.  Therefore, to have five forward gears, the crown wheel was changed to the opposite side of the pinion.  This necessitated casting a new differential case. The Merak transaxle is easily distinguishable from the SM transaxle because the breather is on the opposite side as the SM breather.  The Lotus Esprit engine spins the opposite way from the C114 engine used in the SM and Merak.  Like the Merak, the Lotus engine is forward of the transmission.  Therefore in order to have five forward gears, the SM transaxle is used without any internal modifications.  Instead, the entire transmission spins backwards, with the pinion driving the coast side of the crown wheel when the vehicle is moving forward. The Lotus transaxle can be distinguished from the SM transaxle by the bell housing, which has external fluted reinforcing ribs and a cast-in bore for the slave cylinder.  
  
The transmission is very strong (Jerry Hathaway's land speed car used a stock transmission).
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The transmission is very robust for its applications (Jerry Hathaway's land speed car used a stock transmission).
  
Problems in the Lotus were likely caused by powering the forward gears of the car on the coast side of the crown wheel.  The coast side of the crown wheel not only is less robust than the drive side but running the transmission backwards also causes the thrust vectors of the helical gears to augment, rather than counteract, the thrust vectors of the pinion to crown wheel. This causes excessive stress on the pinion thrust bearings.  Harry Martens Limmen in the Netherlands now offers a mirror image crown wheel and pinion for Lotus which at least solves the problem of driving on the coast side of the crown wheel.
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Problems in the Lotus were likely caused by powering the forward gears of the car on the coast side of the crown wheel.  The coast side of the crown wheel not only is less robust than the drive side but running the transmission backwards also causes the thrust vectors of the helical gears in the transmission itself to augment, rather than counteract, the thrust vectors of the pinion to crown wheel. This causes excessive stress on the pinion thrust bearings.  Harry Martens Limmen in the Netherlands now offers a mirror image crown wheel and pinion for Lotus which at least solves the problem of driving on the coast side of the crown wheel.
  
 
== Specifications ==
 
== Specifications ==
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== Modifications ==
 
== Modifications ==
  
* The vent opens to the top. It's possible to put a small hose on it to prevent water and dirt from falling in.
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* The vent is threaded M9 x 1.25 and opens to the top. It is possible to tap a brass fitting to M9 then put a small U-shaped hose on it to prevent water and dirt from falling in.
  
 
== See also ==
 
== See also ==

Revision as of 16:29, 6 August 2020

The 5-speed manual transmission was also used by Lotus in the Esprit up through 1987, and the Maserati Merak (all types). The transaxle cases differ slightly in each. The Merak engine spins the same way as the SM engine but is forward of the transmission. Therefore, to have five forward gears, the crown wheel was changed to the opposite side of the pinion. This necessitated casting a new differential case. The Merak transaxle is easily distinguishable from the SM transaxle because the breather is on the opposite side as the SM breather. The Lotus Esprit engine spins the opposite way from the C114 engine used in the SM and Merak. Like the Merak, the Lotus engine is forward of the transmission. Therefore in order to have five forward gears, the SM transaxle is used without any internal modifications. Instead, the entire transmission spins backwards, with the pinion driving the coast side of the crown wheel when the vehicle is moving forward. The Lotus transaxle can be distinguished from the SM transaxle by the bell housing, which has external fluted reinforcing ribs and a cast-in bore for the slave cylinder.

The transmission is very robust for its applications (Jerry Hathaway's land speed car used a stock transmission).

Problems in the Lotus were likely caused by powering the forward gears of the car on the coast side of the crown wheel. The coast side of the crown wheel not only is less robust than the drive side but running the transmission backwards also causes the thrust vectors of the helical gears in the transmission itself to augment, rather than counteract, the thrust vectors of the pinion to crown wheel. This causes excessive stress on the pinion thrust bearings. Harry Martens Limmen in the Netherlands now offers a mirror image crown wheel and pinion for Lotus which at least solves the problem of driving on the coast side of the crown wheel.

Specifications

  • Manual Transmission is similar to 5-Speed DS transaxle. It is a fully synchromesh design with a spiral bevel (not hypoid) ring and pinion. Consequently, the transmission does not need GL5 oil and, in fact, because of the brass synchros, GL5 oil should be avoided in favor of GL4 oil. There have been reported incidences in which the 5th gear became loose on the ouput shaft, resulting in a failed transmission. To check this, remove the DIRAVI governor and the front cover. The spedometer drive gear (which holds the 5th gear in place) should be tightened to 200 ft-lbs and staked in place.
  • Automatic Tranmsission is a Borg Warner Type 35, similar to the DS BVA transmission. On 1972 models, the transfer gear set is geared quite low and for this reason 1972 BVA are the least desirable of all models. On 1973 models the transfer gear set ratio is much better suited to the engine. It is possible to fit a later tranmission to an earlier model car if replaced as an entire set including the later torque convertor and flex plate. In the USA the automatic transmission developed a reputation for being unreliable, due in no small part to the failure of many owners to adjust the brake bands (which must be manually tightened every 10,000 miles - a simple operation, but if left undone will lead to early failure.) It is important to use only Ford Type "F" fluid - never Dexron in the transmission. Use of Dexron AFT in any Borg Warner type 35 will lead to early transmission failure.

Modifications

  • The vent is threaded M9 x 1.25 and opens to the top. It is possible to tap a brass fitting to M9 then put a small U-shaped hose on it to prevent water and dirt from falling in.

See also

Transmission Oil