Velvet drive skipping under heavy load?

[biggsie]

Finally got out to set up surf wave with some friends and more ballast. Waves were starting to look great with 750 in rear corner 400 next to motor cover and another 400 up front. Just when I thought "sweet let's try it" the boat skipped and shuttered and I could feel the boat slow like the prop stopped spinning for a split second. Wtf was that!!!

Note: originally the fluid was milky so I replaced the cooler and flushed twice. Boat has had about 4 hrs of runtime since with no milk.

When checking fluid after the issue the cap kinda popped off like there was some pressure buildup. Shouldn't it be vented?

Added some ATF and emptied ballast and it was fine. Tried surfing again and the same thing happened.

I'm obviously thinking I need new clutches or something but the drive seems great without ballast even on WOT pulls.

Any help here ??


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[csuggs]

Could be the damper plate.


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[Cusefan78]

My bet is the drum is cracked. Pretty common problem. Had to change mine when I changed out my clutch discs

[lively]

My bet is the drum is cracked. Pretty common problem. Had to change mine when I changed out my clutch discs

Please tell me how a cracked splined drum would cause the velvet to slip in forward gear ? How many of these drives have you personally rebuilt ? It is not common for the drum to crack , now if you run it low on fluid and don't add then yes the pressure would build and things would give way .

In his case the fluid is hot and his friction disc are worn , thus causing slipping in forward gear . 4 hours with a rebuild kit and should have no issues


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[biggsie]

I have removed the pop-off vent and replaced it with a vent hose. Flushed fluid one more time and will try it again. Really hoping I don't have to pull tranny in the middle if summer.


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[Cusefan78]

Mine was slipping it did have worn discs. Talked to Vince at skidim and he told me drum cracks are common and will prematurely wear the discs. Sorry for giving my opinion I'll just but out, clearly you are the transmission man here. Oh and just a heads up a cracked drum will cause pressure loss which will make the discs slip. But once again I'm clearly an idiot and you are the man.

[biggsie]

Just out of curiosity, what does a "slip" feel like to you guys? All the clutches I've ever felt slip feel like the power isn't coming in strong enough and it's a smooth low power feeling.

This feels like a jerk into neutral to me.


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[Cusefan78]

Mine felt like cavitation when i tried to get out of the hole or turned hard. You'll know if it's slipping

[biggsie]

I guess that's what I was feeling then.

Think I can get through the season without it getting worse if I just don't surf?


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[Cusefan78]

I tried that, got 1/2 of another weekend. I think once they start to slip they degrade quickly.

[chris young]

It's a long shot, but it is a possibility. I thought mine was slipping last year. I haven't used the boat enough this year to be 100% sure, but in my case it looks like the prop was slipping. I was similar to the sypmptoms you're describing. I was skiing, not driving when this happened, but to the skier, it felt like the boat lost power momentarily out of the hole, and when you got to about 34MPH the motor would rev quite high but the boat wouldn't go any faster. It got worse near the end of the summer and I was preparing myself to pull the tranny and do it over the winter. Then, my wife backed off the throttle when she was dropping me at the dock, and we lost the prop.

I'm pretty sure what happened was that the nuts backed off and when you went in reverse it would pull the prop back and then when you went forward, push the prop back up the shaft. The key fell out, and so the shaft would slip until the force on the prop caused it to seat. Finally when the nut fell off completely, and my wife pulled the throttle, the prop just fell off.

Long story, but it's definitely worth taking a look, if it happened to me it could happen to someone else.

I've only had the boat out a couple of times this summer, but so far it seems to pull a lot better, and it tops out at 37MPH with a brand new Acme 541.

[wotan2525]

Mines been slipping for years. One of the seals leaks and I go through about 3/4 of a quart per summer. When it gets low, the pressure drops and it slips (revs suddenly but boat doesn't go anywhere.) A little splash of fluid and it's good to go again. A little bit of a pain but nothing that has made me want to pull the tranny, yet.

[lively]

Mine was slipping it did have worn discs. Talked to Vince at skidim and he told me drum cracks are common and will prematurely wear the discs. Sorry for giving my opinion I'll just but out, clearly you are the transmission man here. Oh and just a heads up a cracked drum will cause pressure loss which will make the discs slip. But once again I'm clearly an idiot and you are the man.

No harm done , I was questioning your knowledge on the drum cracks to better my knowledge . Don't get your panties in a wad . I'm from Texas we are a bit blunt round here . Sorry for that


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[lively]

Now one thing you can do is run a pressure test on the water to see what is going on . Two Allen heads by the selector shaft are for forward gear and the other Allen head is on the the front pump housing is for reverse .

Verify pressure forward
Big Allen head is measuring the main body (drum,front pump) plum into that to see total pressure

The little Allen head measures how much fluid is actually getting selected buy the selector shaft .


Reverse is measured the same way . When I rebuilt mine I did this on the bench and on the water to give me some notes to go buy . Also the PDF of the velvet drive will have all specs and how-too .


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[biggsie]

Lively, how did you bench test it?


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[lively]

Drill motor (drill) and a PVC rubber coupling with 4 hose clamps . The rubber coupling slips over the chuck of the drill and the spline of the trans . And then go get a cheap pressure gauge and plum into those access ports described above


1" couplings work the best . Make sure to tighten down good so it doesn't slip


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[lively]

http://youtu.be/8ePCVGDxle0


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[Cusefan78]

Np I'm Italian so I go off easily. The pressure test you described is the way to do it you'll see if there are any leaks