Modification of Marine Transmission Lubrication System{3300} Caterpillar

A new lubrication system is used on 7251 and 7261 Marine Transmissions, effective with 74E2411 and 89B746. Formerly, lubrication oil flowed through the manifold to the junction between the manifold and the planetary housing. With modification, a new tube can be installed on the outside of earlier transmissions to send supply oil to the main output shaft bearings and the shaft bearings in the front cover. Installation of this system prevents leakage (caused by oil pressure) through the liquid gasket material used on the surface between the transmission top cover and the main case.

Parts Service

(2) If the former transmission housing is the new type (with the lube tube on the outside), remove 9F2247 Plug (1) and install 6P9677 Orifice Plug (2) and 9K2175 Plug (3). Other modifications to the replacement housing assembly are necessary; see the following procedure.

Necessary Parts For Modification

NOTE: Modification of either the 7251 or 7261 Marine Transmission is similar. The only difference is the drilling procedure for the rear housing assembly.

It is not necessary to remove the top shaft, but the rear housing must be moved away from the rear of the main case.

Modification Of 5L3313 Housing Assembly (7251) and 7L5169 Housing Assembly (7261)

(1) With a 7/16"-14 tap, make threads in existing oil supply hole (1) as shown. Put 9S3263 Thread Lock on the threads of 9K2175 Setscrew (2) and install it in oil supply hole (1). With a 60 (.25"0) drill, drill hole (3) in the lower part of the housing assembly as shown. This hole will release the oil pressure from against the O-ring seal. Hole (3) is shown as drilled directly under the center of the top shaft, but the hole can be off center if it is drilled without removal of the top shaft.

Modification Of 7L5644 Manifold Assembly (7251 And 7261)

(1) With a 5/16"-18 tap, make threads in existing oil supply holes (1) and (2) as shown. Put 9S3263 Thread Lock on the threads of two 8B7179 Setscrews (3) and install them in holes (1) and (2). On the right side of 7L5644 Manifold Assembly (4) and at the approximate location shown, drill a 140 (.56"0) hole (5) and make threads with a 3/8"-18 pipe tap (on the 7251) or drill an 180 (.719"0) hole (5) and make threads with a 1/2"-14 pipe tap (on the 7261). Through this hole, a tube and extra parts will send an oil supply to the rear bearing.

Modification Of 2N4344 Cover (7251)

(1) Remove 2N4344 Cover (1). Remove 5L9149 Oil Supply Tube (2), to keep metal drill chips from the output bearing.

(2) Make drill fixture (3) as shown. Drill two 170 (.656"0) holes (A) and one 140 (.56"0) hole (B) at the dimensions shown. Grind a flat area on housing (4) at location (C). Install drill fixture (3) on housing (4) with two 1A8651 Bolts (5), two 7D8299 Spacers (6), six 9S1319 Washers (7) and two 1D4720 Nuts (8). Install the drill fixture with bolts (5) in holes (D) on the housing. Drill a 140 (.56"0) hole (E) in housing (4) and make threads with a 3/8"-18 pipe tap. If the pipe tap hits bottom before the threads are deep enough to start the 1Y7452 Pipe Nipple, then grind the lead off a standard tap and make the threads deeper.

(3) Clean all parts to make sure that no foreign material is present, or can get into the transmission lubrication system. Again, install 5L9149 Oil Supply Tube (2), 2N4344 Cover (1), 7L5644 Manifold (4) and any other parts that were removed. Put 9S3263 Thread Lock on all connections with threads. Install 1Y7452 Pipe Nipple (9) and 4B2657 Fitting (10) in cover (1). Install 3B8997 Fitting (11) in manifold (4) as shown. Cut a length of 5P1201 Tubing (12) and bend it to fit between fittings (10) and (11) as shown.

Modification Of 7L5171 Housing Assembly (7261)

(1) Remove 7L5171 Housing Assembly (1). Also, remove the planetary gear carrier and output bearings, so drill chips are kept out of the bearings. Make drill fixture (2) as shown. Make a 5 (.18") fillet weld all around at location (A). Drill two 170 (.656"0) holes (B) and one 180 (.719"0) hole (C) at the location shown.

(2) Grind a flat area on housing (1) at location (D) as shown. Install drill fixture (2) on housing (1) with the same bolts and lockwashers that hold the 7L4844 Retainer to 7L5171 Housing Assembly; install the bolts in holes (E) on the housing. With an 180 (.719"0) drill, drill hole (F) in housing (1) to the depth shown; make threads with a 1/2"-14 pipe tap.

(3) Clean all parts to make sure that no foreign material is present and can get into the transmission lubrication system. Again, install housing (1), the manifold and any other parts that were removed. Put 9S3263 Thread Lock on all connections with threads. Install 3B7272 Pipe Nipple (3) in hole (F) of housing (1) and install 4K5740 Fitting (4) on nipple (3). Install 3B9386 Fitting (5) in the manifold. Cut a length of 5P1201 Tubing (6) and bend it to fit between fittings (4) and (5) as shown.