• Borg Warner 71C V-Drive and Transmission Disassembly

    It was a nice Sunday morning as we eased up to our friend to tie off and enjoy the day in one of our favorite coves. There was a light breeze causing his Crownline to swing a bit so I had to approach a little steeper than usual. As I moved the port engine from forward to neutral the engine stalled. I quickly restarted the engine and shifted the transmission to reverse and Lucy continued forward. Something was amiss!

    Once the boat was secure I began to troubleshoot the issue. I opened the hatch and disconnected the shift cable at the transmission. Using the shift lever on the side of the transmission I shifted to forward and the prop spun forward, so far so good. I moved the shift lever to neutral and the prop shaft continued to spin, uh-oh. I shifted the transmission to reverse and the prop shaft slowly stopped but I could hear a tapping sound in the transmission, at that point I felt a pain in the wallet.

    I was hoping that my problem was the somewhat less expensive "welded clutch" issue that is common to these drives but as you will see from the pictures I was not that lucky. I ordered a full rebuild kit for the transmission and v-drive and when they arrived I began to tear down the assembly with the intention of doing a rebuild. About halfway through the project I realized I would be better off getting a rebuilt transmission since the costs of replacement parts was going to be quite high.

    The series below shows the teardown process that you will use to replace the clutches if that is the problem. I also show the v-drive disassembly since I had to flush it and check it for damage.

    Preparing the transmission assembly for removal took about 1.5 hours and I began by pumping all of the fluid from the reservoir. Next I removed the electrical connections to the neutral safety switch and the transmission temp sending unit. With a bucket handy the transmission cooler lines were removed and more fluid was drained. Don't forget to undo both lines, the return line also has a metal loop securing it to the side of the v-drive that has to be removed.
    Attachment 629
    I scribed a mark on both the v-drive coupling and the prop shaft coupling to allow me to assemble them in the same orientation. Once that was done the propeller shaft was disconnected.
    Attachment 630
    At this point I began to break loose all of the bolts that secure the transmission assembly. There are 4 bolts located along the top and then there are two studs with nylon nuts near the bottom. I also loosened the four bolts that hold the v-drive to the motor mounts. My intention was to remove as little as possible and try not to disturb the engine alignment. This process worked well since the motor mounts when unbolted from the v-drive will slide right out of the way.

    Now we were ready to support the engine to prepare for the final removal steps. This process took about 2 hours as it took us a bit of time to figure out how to best tackle the situation. The engine is supported by two motor mounts located aft and two motor mounts attached to the v-drive. We used a chain to lift the driveline end of the engine slighty and finished removing the bolts from the v-drive motor mounts. Now we lifted the engine an additional inch and slid a piece of wood under the oil pan for support. We lowered the engine to rest on the wood and then used the lift with a chain to connect to the v-drive. With the v-drive supported by the chain we removed the remaining bolts securing it to the engine bell housing. At this point we lifted the transmission assembly clear of the boat.

    Note: We removed the whole transmission assembly as one piece and it was quite a bit to handle at around 210 pounds. When we installed the assembly back into the boat we installed the transmission and secured it to the bell housing, then installed the v-drive which proved much easier.

    With the transmission assembly back home on the work bench it was time to break it down.

    Attachment 631
    Remove the shift lever bolt. Be careful there is a steel ball and spring behind the lever that you don't want to lose.

    Attachment 632
    Shift lever components.

    Attachment 633
    Now move to the other side of the transmission and remove the neutral safety switch.

    Attachment 634
    The neutral safety switch is screwed into the control valve cover plate assembly. With the safety switch unscrewed remove the bolts and the cover plate.

    Attachment 635
    With the cover removed, you will remove the switch cam. The switch cam has a metal tab that fits into a slot on the bottom of the control valve assembly. When you are putting this back together ensure that the transmission is in neutral and make sure the control valve assembly's slot is at the bottom, the switch cam tab fits in that slot (see service manual).
    Attachment 636
    Now move to the other side and lightly tap the shift lever shaft with a rubber mallet driving the control valve out the other side.

    Attachment 637
    This will push the control valve out the other side to allow removal.

    Attachment 638
    Now it is time to remove the oil pump. Prior to removal you will note that the pump has the words "TOP" and an arrow pointing one direction at the top of the pump and another "TOP" with an arrow pointing the other direction located at the bottom of the pump. This pump can be mounted in two positions 180 degrees different from each other and the correct position depends on the rotation of the engine. If you install the pump incorrectly you will not have oil pressure and could damage the transmission. Pay close attention to this orientation. This is referred to as "pump indexing".
    Attachment 639

    Now remove the four bolts and remove the oil pump.

    Attachment 640
    Now remove the pumps drive gear and key.

    Attachment 641
    Remove the four star bolts holding the forward/reverse adapter in place.

    Attachment 642
    Now begin to separate the forward/reverse adaptor housing, use caution when removing the clutch springs and dowel pins will fall out.

    Attachment 643
    Now you can see the orientation of the springs and dowels.

    Attachment 646
    Now remove the reverse clutch pressure plate to gain access to the reverse clutch pack.

    Attachment 647

    Remove clutch cylinder snap ring.

    Attachment 680

    Remove sealing ring.

    Attachment 681
    Remove ring gear assembly.

    Attachment 682

    Remove bronze thrust washer.

    Attachment 683

    At this point I discovered the pinion carrier assembly was damaged.

    Attachment 684
    Remove pinion carrier assembly.

    Attachment 685
    At this point I decided to order a rebuilt transmission so I did not disassemble the forward clutch pack, but the following pictures will show some key components.

    In the following picture note the tab on the thrust washer and the sealing rings on the pinion carrier shaft.
    Attachment 686
    The following picture shows the slot that the thrust washer tab fits in on the transmission case.

    Attachment 687

    V Drive Disassembly
    This series of pictures will show the disassembly of the V Drive to check for damage and to flush it out. To begin remove the nuts from the studs holding the V Drive to the transmission.

    Attachment 688
    With the V Drive separated from the transmission, note the orientation of the coupler.

    Attachment 689
    Remove the output shaft nut, don't forget to order a new one.

    Attachment 690
    Remove the flange and bolts in the bearing case.

    Attachment 691

    Remove the bearing cap.

    Attachment 692
    Remove the output shaft bearing.

    Attachment 693
    Remove bolts from the V Drive case and separate the halves.

    Attachment 694
    Input, output and intermediary shafts.

    Attachment 695
    Case cover with bearing cups.

    Attachment 696
    Once everything was inspected and flushed a new gasket was installed and the output shaft was aligned.

    Attachment 697

    A new oil seal being installed in the bearing cap.

    Attachment 698
    The bearing cap was installed with a new gasket, next came the output shaft nut torqued to 225 ft/lbs.

    Attachment 699
    Next the case bolts were installed and torqued.

    Attachment 700
    Once the rebuilt transmission arrived the oil pump was indexed to match the old one.
    Attachment 701
    I had originally ordered my clutch pack rebuild kit from Transmission Marine Inc in Ft. Lauderdale, Florida (MarineGears.com) and when I discovered the extent of the damage I decided to contact them about a rebuilt unit. Those folks are great! They immediately shipped me a rebuilt unit and once it arrived I pulled the necessary components off of the old tranny and slipped it into the box along with the clutch pack rebuild kit to return to them. They gave me credit for the clutch pack kit and were more than eager to answer any questions I had concerning the installation over the phone. They were even kind enough to email me a pdf file of the transmission service manual. Kudos to those guys.

    Click HERE to download the 71C v-drive manual!
    patch41 and patches42 like this.


    Comments 3 Comments
    1. patch43's Avatar
      patch43 -
      When you say you raised the rear of the engine one inch to put the blocks underneath , Did you have to loosen anything on the front engine mount or was you able to raise the rear of the engine one inch without doing anything to the front engine mounts, Thanks.
    1. TimG's Avatar
      TimG -
      There was enough play in the mounts to allow the engine to be raised slightly without loosening the mounts as they sit in huge rubber bushings.
    1. patch43's Avatar
      patch43 -
      Quote Originally Posted by TimG View Post
      There was enough play in the mounts to allow the engine to be raised slightly without loosening the mounts as they sit in huge rubber bushings.
      Thank you for the reply TimG, I followed your great instructions the only thing left is to raise the engine, And i am taking your advise separating the v-drive from the transmission, I have a 30ft
      twin engine sea ray fly-bridge and there is not much room, But i am hopeful once i separate them i will be able to haul them out with a come-along, Thanks again.
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