From KC Marine:
- Propeller Size This is perhaps the most common issue that can cause clutch failure, i.e. too large a propeller. Factory WOT specifications should be adhered to, preferably toward the high end. Example: If your WOT specification is 4400 to 4800, 4800 RPM provides a less strenuous load against the clutch and will promote the longevity of the transmission.
The MercTrans has a relatively small oil capacity and cooling system. Also, pump pressure is relative to the actual surface area of the forward clutch assembly. Lower RPMs cause a substantially greater pressure/load gradient against the clutch and this can lead to slippage.
2 - Oil Type Modern synthetic ATF provides a lower operating temperature and subsequently a higher viscosity index relative to the oil quantity.
3 - Cooling System The factory outlet for the transmission cooler can be improved upon. A thru-hull bulkhead fitting provides higher output volume and unrestricted flow. This is very important. When a transmission has limited oil capacity, it must remain cool.
4 - Reverse The MercTrans design employs a reverse system which involves small eccentric gears in the planetary, i.e. when you shift into reverse, these eccentrics are turning an extremely high RPM. This equates into a potential overheating issue for the transmission. Reverse must be used prudently.
5 - Crankshaft Support of the Input Shaft The MercTrans system used a crankshaft support bushing. After doing an engine repower, this item is often ignored. The subsequent lack of support for your MercTrans input shaft can destroy the oil pump. This bushing is located in the end of the engine crankshaft. Be sure it is there. We can provide you with the proper bushing if yours is missing.
6 - Gimbal Alignment The TR drive is a real workhorse. However, it's size and weight can cause steering and alignment issues. Mercruiser's swivel kit, i.e. steering yoke, can cause problems if not maintained.
The clearance between the top of the gimbal ring and the gimbal housing should be no more than .005". If this dimension becomes larger, the subsequent strain can cause U-joint failure and/or breakage of the MercTrans output shaft.
7 - U-Joint Type The only U-joint that should be used in the MercTrans TR/TRS drive system is the Mercruiser part 75832T 1. There are plenty that will fit but no other can hold up under load and hours. Remember, U-joint failure and U-joint wear can affect your transmission. Never, never, never use U-joints from your local auto parts store!
8 - Output Housing The MercTrans output housing bearing bore must remain tight (see 6 and 7). The harmonic vibration caused by a loose bearing bore can break the output shaft. Misalignment and/or improper U-joints can cause this.
9 - Shifter Throw Unfortunately, the electric shift motor failure rate is rather high. This is due to age and certain internal design issues. Failure is failure, but, if the switch mechanism fails but still provides a partial alignment with the control valve passages, the subsequent loss of oil volume at higher RPMs can result in clutch failure.
The control box (usually dual lever) can cause the same problem with the mechanical shift system. Be certain all control box cables and bracket assemblies are tight.
Shifter throw is 60 degrees either side of neutral with a maximum variance of 5 degrees. In correct neutral postion, the shift shaft in the control housing, alignment pin on the shift shaft cam, and lower shift bracket mounting hole on the control housing will all align vertically. See picture.
10 - Engine Position In order to achieve proper output shaft spline engagement, it is crucial that the engine be installed properly. The MercTrans output housing must seat squarely against the flange in the gimbal housing. If the engine is mounted too far forward, output shaft failure will occur.