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Old 07-04-2014, 10:11 PM   #1
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Velvet Drive Output Shaft

Backing into the slip this afternoon and suprise! Nothing no forward or reverse. Managed to get tied up then took a look.



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The shaft has fractured at the spline to nut joint. Appears to have pulled apart while backing into slip. Now looking for parts and a rebuild kit. Any surprises I need to look out for?

Bonus is nice oily mess to clean up.
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Old 07-04-2014, 11:06 PM   #2
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Have we reached some sort of Armageddon or "Use By" date for BW Velvet Drive transmissions? They seem to be giving trouble, thread after thread . Touch wood mine are ok.
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Old 07-04-2014, 11:08 PM   #3
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Borgageddon!
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Old 07-05-2014, 02:34 AM   #4
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Looks like the shaft pulled out of the splines. How is the coupler retained in the tailshaft? There must be a fairly hefty retainer to stop the shaft from backing out when you go into reverse, or, on your transmission, not so hefty!
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Old 07-05-2014, 08:14 AM   #5
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Talk to Mike Vogt at Harbor Marine, Everett. Has the parts for sure. He's good on the phone and has made a career out of rebuilding marine transmissions.
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Old 07-05-2014, 08:32 AM   #6
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Reduction unit pulls off of gear easily, that is all that needs to be removed. Output shaft of reduction unit needs replacement. Gear can stay on engine.

Coupling nut may have been loose, and shaft alignment might have been off.
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Old 07-05-2014, 05:46 PM   #7
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If you have ever wondered what the output shafts looks like in two pieces. Here it is.

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Old 07-05-2014, 07:29 PM   #8
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Thanks for those photos - that explains a lot and shows me how the shaft is retained. I feel (some of) your pain.
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Old 07-07-2014, 05:57 PM   #9
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New output shaft, oil seal, nut and gasket from Harbor Marine in Everett, Washington was $299.00. If you need any part for a Velvet Drive, Twin Disc or Ford Lehman these are the guys to call. Went into the shop and it is crammed with parts. I delt with Mike Vogt, asked me if I knew all the tricks and then told them to me anyway!
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Old 07-07-2014, 06:11 PM   #10
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I'm sure he told you that fluid leakage can come down the splines as well as past the seal and that the splines need to be sealed too.

Looks to me that nothing really "broke" but that the shaft nut had been overtightened at some point in the past starting a fracture which ended the last time you went to reverse.
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Old 07-07-2014, 07:49 PM   #11
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An early sign of a leaking rear oil seal is a very fine line of oil spray on the area surrounding the coupling.
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Old 07-07-2014, 09:05 PM   #12
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It's tough to overtighten the nut when in the boat. 200 ft lbs. I know some use an impact wrench which could overtorque the nut easily.
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Old 07-07-2014, 09:17 PM   #13
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I'd guess it fractured not from being overtightened, but from being loose. Look for fretting marks where nut seated on inside of flange. Fretting means it ran loose. If it was tight, stress in shaft would be constant. Loose, stress varies with rotation and that sets up a fatigue scenario. could also mean tranny and prop shaft were misaligned.

Also, when putting it all together, pay particular attention to getting preload right on output shaft thrust bearings. I think those are opposed tapered rollers, and preload is critical.
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Old 07-08-2014, 01:00 AM   #14
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Preload is the most critical step. You are correct concerning the opposed tapered bearings. The proper preload is actually done with a torque wrench to check the amount of rotational resistance or by feel if you have done it enough times.

I used the torque wrench! Will be back in the boat tomorrow and off for a quick sea trial.
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Old 07-08-2014, 01:01 AM   #15
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Torquing to 200 ft lbs was a challenge. I ended up making a spanner out of some 1/4" stock to lock the flange then cranked her down.
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Old 07-08-2014, 06:34 PM   #16
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Update:

Nothing happens without a reason! After installing the new output shaft and housing I went to connect the flanges and they were nearly 1/2" out of alignment in the horizontal plane.

The cause of the misalignment was due to the front motor mount leveling nuts not being tightened after some insurance work by the PO. They had backed off completely to the base.

I have completely realigned the engine and shaft, torqued the mounts properly and checked everything associated with the drive train.

Wounder if these unusual problems will ever end?
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