MercTrans and TR/TRS Repair, Design and Modification Experts

Oil capacity, in conjunction with the original oil cooling system, is something that boat owners need to be aware of. The two quart capacity of the MercTrans requires far more frequent oil changes than stated in the original Mercruiser service manual. The low operating temperature of modern synthetic Type F fluid is a helpful contributor to MercTrans longevity. Keeping the oil clean and cool is perhaps the most important issue for long transmission life, as standard Type F, ATF, begins to breakdown at a relatively low temperature and is not recommended. Rerouting the MercTrans cooler outlet to thru-hull can and will make a huge difference in maintaining lower operating temperatures. The oil cooler is a single pass system and cannot be restricted in any manner. If the cooler outlet and/or internal passage become restricted the transmission “will” fail. 
The electric shift mechanisms, although convenient in houseboats and vessels with prohibitively long cable runs, is a ticking time bomb. Fact is that internal switch failure is rampant due to both design and age. Full failure results only in inconvenience (if another shift motor can be located), but partial failure can cause internal mechanical damage, especially if the switch mechanism decides to provide partial throw or oscillation. The resultant loss of oil volume at higher RRM, can and will, cause damage. KC Marine strongly advises conversion to mechanical shift. This is easy to accomplish with only a few hand tools and takes approximately 30 minutes. Conversion provides a permanent fix. Replacing the shift motor only delays another inevitable failure and increases the probability of MercTrans internal damage. 
About the Mercruiser MercTrans
Mercruiser originally contracted with BorgWarner Corporation to supply the transmission for its TR/TRS drive series. This arrangement was short lived, and Mercruiser went to the design table to construct a shorter lighter transmission to compliment the drive series and allow boat builders more latitude in design configuration (MercTrans engine package is approximately 9” shorter in overall length). There were, however, compromises in the design of the MercTrans. The compromises do not affect performance or longevity if one is aware of them. First would be the actual surface area of the forward clutch. It is not as large as the BorgWarner, but the issue is easily overcome with “Kolene” base plates and the correct composition clutch plates (metal type plates do not hold the cohesion ratio at relative MerTrans oil pressure levels).
Correct propeller sizing in reference to load vessel size and actual usage parameters make the smaller clutch surface an academic issue only. Reverse in the MercTrans is entirely different in function than the BorgWarner. Reverse engagement is accomplished by gear reversal in the planetary by means of a large reverse band stopping planetary rotation and the eccentric gears changing shaft rotation. This is problematic only in terms of heavy use. The heat that builds during prolonged loaded reverse use (via small eccentrics turning at extremely high RPM; relative to actual output RPM), can cause substantial damage. However, if one is aware of the issue and use of reverse is delegated to docking and slow maneuvers, reverse will last a lifetime. We provide Kevlar reverse bands for all overhauls here at KC Marine and reverse band failure rates are 0%. The Kevlar prevents planetary external wear, and will provide more stable and reliable engagement. 
There are also several published internal design changes along with several unpublished design changes. The particular combination and application of these design “options” are specific to vessel type, usage, and more importantly holding the correct mechanical “judgment” in order to apply this information. KC Marine can do exactly what is appropriate for your particular boating preference. Keep in mind that any mcm a,b,c,d and e are exactly the same insofar as internal case dimension. Point being…just because the case says “a” does not indicate that it does not hold “e” internals. Unless the entire transmission history is known, the only way to obtain certainty as to which design(s) of internal components a particular MercTrans has; is to “gut” it on the bench. 
The horsepower capacity of the MercTrans is a frequently asked question and an irrelevant question at that. In a planing application, the correct denominator is “load” not horsepower. Actual maximum clutch load is reached at breakover point, and not on a planing step.  Cooling becomes the central point of concern at high horsepower.
The TR/TRS sterndrive can also affect the transmission. KC Marine also specializes in sterndrive repair, and internal modification for high horsepower applications. The TR/TRS sterndrive can be easily modified for high horsepower applications. The TR/TRS sterndrive can be easily modified for longevity. Please keep in mind that modern oil makes original preload specification obsolete and counterproductive.

About Mercruiser MercTrans

Oil Cooling System

Oil capacity, in conjunction with the original oil cooling system, is something that boat owners need to be aware of. The two quart capacity of the MercTrans requires far more frequent oil changes than stated in the original Mercruiser service manual. The low operating temperature of modern synthetic Type F fluid is a helpful contributor to MercTrans longevity. Keeping the oil clean and cool is perhaps the most important issue for long transmission life, as standard Type F, ATF, begins to breakdown at a relatively low temperature and is not recommended. Rerouting the MercTrans cooler outlet to thru-hull can and will make a huge difference in maintaining lower operating temperatures. The oil cooler is a single pass system and cannot be restricted in any manner. If the cooler outlet and/or internal passage become restricted the transmission “will” fail.  We highly recommend Amsoil Super Shift Racing transmission fluid SAE 10. It's been tried and tested and it's our preferred tranmission fluid.

Electric Shift Mechanism

The electric shift mechanisms, although convenient in houseboats and vessels with prohibitively long cable runs, is a ticking time bomb. Fact is that internal switch failure is rampant due to both design and age. Full failure results only in inconvenience (if another shift motor can be located), but partial failure can cause internal mechanical damage, especially if the switch mechanism decides to provide partial throw or oscillation. The resultant loss of oil volume at higher RRM, can and will, cause damage. KC Marine strongly advises conversion to mechanical shift. This is easy to accomplish with only a few hand tools and takes approximately 30 minutes. Conversion provides a permanent fix. Replacing the shift motor only delays another inevitable failure and increases the probability of MercTrans internal damage. 
About the Mercruiser MercTrans

Transmission

Mercruiser originally contracted with BorgWarner Corporation to supply the transmission for its TR/TRS drive series. This arrangement was short lived, and Mercruiser went to the design table to construct a shorter lighter transmission to compliment the drive series and allow boat builders more latitude in design configuration (MercTrans engine package is approximately 9” shorter in overall length). There were, however, compromises in the design of the MercTrans. The compromises do not affect performance or longevity if one is aware of them. First would be the actual surface area of the forward clutch. It is not as large as the BorgWarner, but the issue is easily overcome with “Kolene” base plates and the correct composition clutch plates (metal type plates do not hold the cohesion ratio at relative MerTrans oil pressure levels).

Reverse

Correct propeller sizing in reference to load vessel size and actual usage parameters make the smaller clutch surface an academic issue only. Reverse in the MercTrans is entirely different in function than the BorgWarner. Reverse engagement is accomplished by gear reversal in the planetary by means of a large reverse band stopping planetary rotation and the eccentric gears changing shaft rotation. This is problematic only in terms of heavy use. The heat that builds during prolonged loaded reverse use (via small eccentrics turning at extremely high RPM; relative to actual output RPM), can cause substantial damage. However, if one is aware of the issue and use of reverse is delegated to docking and slow maneuvers, reverse will last a lifetime. We provide Kevlar reverse bands for all overhauls here at KC Marine and reverse band failure rates are 0%. The Kevlar prevents planetary external wear, and will provide more stable and reliable engagement. 

Design Changes

There are also several published internal design changes along with several unpublished design changes. The particular combination and application of these design “options” are specific to vessel type, usage, and more importantly holding the correct mechanical “judgment” in order to apply this information. KC Marine can do exactly what is appropriate for your particular boating preference. Keep in mind that any mcm a,b,c,d and e are exactly the same insofar as internal case dimension. Point being…just because the case says “a” does not indicate that it does not hold “e” internals. Unless the entire transmission history is known, the only way to obtain certainty as to which design(s) of internal components a particular MercTrans has; is to “gut” it on the bench. 

Horsepower

The horsepower capacity of the MercTrans is a frequently asked question and an irrelevant question at that. In a planing application, the correct denominator is “load” not horsepower. Actual maximum clutch load is reached at breakover point, and not on a planing step.  Cooling becomes the central point of concern at high horsepower.

Sterndrive

The TR/TRS sterndrive can also affect the transmission. KC Marine also specializes in sterndrive repair, and internal modification for high horsepower applications. The TR/TRS sterndrive can be easily modified for high horsepower applications. The TR/TRS sterndrive can be easily modified for longevity. Please keep in mind that modern oil makes original preload specification obsolete and counterproductive.