Anybody have this problem before? Velvet drive issue

I just bought a 1979 Hershine 37' Trawler. 120 Lehman diesel / Borg Warner Velvet Drive. Left Eagle Harbor on Bainbridge Island, WA for 2.5 hour run. Tide with me all the way. Started out @ 8 kts +/-. After an hour or so speed kept dropping. Ended trip at 1.5 kts with same engine speed of 1500 rpm. Engine sounds beautiful. I was in a serious time jam up and left anchorage without checking trans fluid. When I noticed the radical GPS speed drop I first thought I must have read the tide tables wrong. Double checked...nope! Went back and looked at exhaust all seemed normal. Looked in hold briefly (boat was not in a position to stop due to rocks etc.) saw nothing amiss. Am suspecting clutch discs toast. Anybody run in to this kind of problem before?

What was the propeller shaft doing?
Was the transmission hot to the touch?
Was the fluid level low?
Was the wake normal?

And what color is the fluid?

High Wire said:

What was the propeller shaft doing?
Was the transmission hot to the touch?
Was the fluid level low?
Was the wake normal?

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These are all good questions. If I had a chance to stop the boat to look in the engine room I would have but I didn't realize I had a problem with the vessel itself until I got in a dangerous area. This was the very first run I ever made with the boat and didn't know its personality and "normal behavior" yet. I did look at the wake regularly throughout the trip when I was going by a smaller boat etc. and in retrospect I believe the wake was smaller during the latter part of the trip. Good thought! I did try lowering the throttle to 1000 rpms for a minute or two and the speed dropped to below 1 kt. Considering where I was, I raised it back to 1500 and only increased back to 1.5 kts or so. At the same time I was trying to investigate whether I made some mistake in reading the tide tables (no mistake) and if the tide was against me. My daughter was steering the boat for about half the trip while I walked around looking in the holds for water, things that might fall over, or anything else. Small vibration and rattle on initial throttle up in gear at start of the trip (suspect some lash in the flex plate). It ran so smooth after that and noiselessly too that I became more occupied with looking at tie up lines condition, and fly bridge gauge behavior (comparing to command bridge gauges) and trying to get used to the tiny plotter size. Was an hour late arriving in Eagle Harbor that I just left once anchored up and should have gone down and looked in ER at the trans while it was still potentially hot.
I figure if the forward clutches were slipping that much that it will be real obvious when I look at and smell the fluid. Reverse had normal power and response. My expectation is that either I have some water in the fluid allowing slippage, or the front clutch pack is slipping. It's just different than any other Velvet drive I've had over the years. I had a front clutch pack go out about thirty years ago and it went from full engagement to 5% in about 20 minutes and never regained full when it cooled down.
Am going back to the boat today to check it out. Will post findings

jleonard said:

And what color is the fluid?

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appreciate the response. Going to check it out this weekend. Was in too much of a hurry on the day of the trip to investigate. Was relieved to have made it in without towing it. My ride was in the car waiting for an hour and a half. Will post findings once I get to check it out. Have rebuilt one for myself and another for a friend before so hoping to find just front clutches bad and not water in oil too.

jleonard said:

And what color is the fluid?

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will be going to check out thoroughly this weekend.

I think you first need to determine whether there is slippage in the transmission, or somewhere else. It's also possible that the prop is not on securely and is slipping on the shaft. And possible that there is not secure coupling between engine and transmission. So first step is sorting out where the slippage is happening.

twistedtree said:

I think you first need to determine whether there is slippage in the transmission, or somewhere else. It's also possible that the prop is not on securely and is slipping on the shaft. And possible that there is not secure coupling between engine and transmission. So first step is sorting out where the slippage is happening.

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thats where I'm headed now... hopefully I'll find answers

Well it was definitely worth a look. The trans fluid was sweet smelling and absolutely clean. Probably Dexron II or III. No water in fluid. Looks freshly changed. No oil in bilge. Did find the heat exchanger hoses aimed parallel to water surface so a false oil level would be a factor. Oil level showed full on the stick but I think the heat exchanger could hold as much as a pint to pint and a half of fluid. Is it possible that there could have been air in the fluid that was skewing the pressure enough to allow approximately 50% slippage, that would still have enough oil to keep cooled down? Trans engages easily and responsively in both forward and reverse. Didn't take out for another run to test yet. Going to check if the shifter detent ball and the detent on the Morse control are in sync. Heard that if not fully engaged at the trans can cause less and less transfer due to restriction and lower pressure to clutches as it gets warmer. Not sure how valid that is but it kinda makes sense. Going to pick up a pressure gauge and test pressure in forward and reverse. Anyone know what control pressure there should be in the top port (non-reverse)? Just want to make sure the gauge I buy is high enough capacity. Since it runs in both forward and reverse I'm pretty sure the problem is not in the rest of the drive train.

Is there any way to determine the model of Velvet Drive without the numbers? The plate is missing completely. Original engine was 1979 Lehman 120hp diesel. Velvet drive in there now is original. My guess is a 71-C. I can't imagine they would put a 72C in it when there was no need for the high horsepower capability. 70 series I think were discontinued by early to mid 70's. The gear reduction bell is approx 7" inches long from the mating surface to the mating surface of the shaft coupler. Any idea how to tell reduction ratio with no numbers?

Is there any way to determine the model of Velvet Drive without the numbers? The plate is missing completely. Original engine was 1979 Lehman 120hp diesel. Velvet drive in there now is original. My guess is a 71-C. I can't imagine they would put a 72C in it when there was no need for the high horsepower capability. 70 series I think were discontinued by early to mid 70's. The gear reduction bell is approx 7" inches long from the mating surface to the mating surface of the shaft coupler. Any idea how to tell reduction ratio with no numbers?

A cheap photo tachometer will allow you to measure shaft revolution and engine revolution. Divide the two together will give you your ratio and an idea of slippage if any. https://www.harborfreight.com/digit...qJfj70Gbt-WJKUVxNuxw0muPZPM4VYssaAoT1EALw_wcB

A slipping clutch will really heat up the transmission, so that's something to check next time you run the boat. The photo tach is a good suggestion not only to establish the gear ratio, but it's also an easy way to check while underway to see if the shaft is turning at the expected speed. That will clearly identify any slipping between the engine output and the shaft.

The only other likely cause seems to be a prop that is slipping on the shaft. Is there anyone who can dive in the water and check the prop?

Cigatoo said:

A cheap photo tachometer will allow you to measure shaft revolution and engine revolution. Divide the two together will give you your ratio and an idea of slippage if any. https://www.harborfreight.com/digit...qJfj70Gbt-WJKUVxNuxw0muPZPM4VYssaAoT1EALw_wcB

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Yes it would. I bought one about a month ago for other reasons but will take it with me for next trip. Will have to have someone else drive boat while I compare rpms at start of the propshaft and same if speed slows down again. Found a hatch at the back of the engine room where I can get easy access. Great thought. It's so nice to have this much help making sure I don't overlook something by having tunnel vision.

twistedtree said:

A slipping clutch will really heat up the transmission, so that's something to check next time you run the boat. The photo tach is a good suggestion not only to establish the gear ratio, but it's also an easy way to check while underway to see if the shaft is turning at the expected speed. That will clearly identify any slipping between the engine output and the shaft.

The only other likely cause seems to be a prop that is slipping on the shaft. Is there anyone who can dive in the water and check the prop?

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Yes. I'm an experienced diver. I just didn't have my drysuit with me. Last dive I got a hole in my neck seal. A new seal should arrive this week. That thought about the heat generated really has me baffled. In every case in the past I have seen massive heat generated by slipping clutches, but in this case I see no signs of abnormal heat. Leads me to think it must be something else. A little gun-shy to take it on another long trip for fear it will act up again without finding the true issue. Hopefully, the next tests will find a smoking gun revelation. Thanks for all your help guys (and gals if any).

There is a pressure regulator valve comes up often that I am suspecting your problem is a slow loss of pressure.
I do not think the problem is unique to a model number.

SteveK said:

There is a pressure regulator valve comes up often that I am suspecting your problem is a slow loss of pressure.
I do not think the problem is unique to a model number.

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The problem is that if a rebuild is necessary, you need a model type to get the right kit. Is there a pressure relief valve on a Velvet drive? I was not aware of one. That could explain a lot if there is one.

liquidsands said:

The problem is that if a rebuild is necessary, you need a model type to get the right kit. Is there a pressure relief valve on a Velvet drive? I was not aware of one. That could explain a lot if there is one.

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I know that there is a spring controlled poppet in the control valve. Would this function as a pressure relief valve? I know the outfeed from that poppet goes directly to the cooling lines (no pressure). As a bypass valve I suppose it would function as a pressure control by default.

If the valve allows a bypass to take place because of a changed tension value (damaged or broken spring) that would explain the clutches surviving without burning up.

I attached a PDF, did you access it? The model may be different of course as I do not recognise yours compared to memory of the ones I had before. The relief valve controls pressure, not enough pressure and clutch does not engage fully. It talks about cleaning and polishing it. So far it makes sense why overheating is not occuring.

liquidsands said:

If the valve allows a bypass to take place because of a changed tension value (damaged or broken spring) that would explain the clutches surviving without burning up.

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I’m not so sure. I think low oil pressure means clutch slippage which means heat.

It is more likely than not you have worn clutch plates that are slipping. I would expect to see higher heat during operation but you would need a baseline for comparison. Shop will charge you min. $750 for clutch overhaul, you deliver transmission to them. It's a very simple transmission, easy to repair. YouTube videos are available. Clutch plates are the same for most 71 C's, no relation to gear ratio.

I would pull the control valve out for inspection prior to removal of the transmission to make sure oil passages aren't plugged.

SteveK said:

I attached a PDF, did you access it? The model may be different of course as I do not recognise yours compared to memory of the ones I had before. The relief valve controls pressure, not enough pressure and clutch does not engage fully. It talks about cleaning and polishing it. So far it makes sense why overheating is not occuring.

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I don't know how to find the pdf and download

SoWhat said:

It is more likely than not you have worn clutch plates that are slipping. I would expect to see higher heat during operation but you would need a baseline for comparison. Shop will charge you min. $750 for clutch overhaul, you deliver transmission to them. It's a very simple transmission, easy to repair. YouTube videos are available. Clutch plates are the same for most 71 C's, no relation to gear ratio.

I would pull the control valve out for inspection prior to removal of the transmission to make sure oil passages aren't plugged.

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I have overhauled 3 of them so far. It definitely is an easy task. The trick is identifying which model it is before opening it up so I can get the right kit when the tag is gone.

I`m probably saying something you know but there is a protocol for checking fluid level, from memory it`s immediately after engine shutdown. I had VDs on my last boat, dipsticks just had the one marking for hot and optimal check time but I believe some are marked for cold/just sitting as well.

liquidsands said:

I have overhauled 3 of them so far. It definitely is an easy task. The trick is identifying which model it is before opening it up so I can get the right kit when the tag is gone.

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The most critical overhaul thing is compressing the new clutch pack so you can measure for correct preload clearance.
The kit will contain a 'selective' snap-ring kit for the clutch drum to choose and hold the clearance.
Too loose reduces clamping force leading to slippage....too tight, shaft crawl in neutral.

liquidsands said:

I don't know how to find the pdf and download

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Can anyone tell me where to find the pdf SteveK sent?

liquidsands said:

Can anyone tell me where to find the pdf SteveK sent?

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Post 16 has the attachment. Just checked. Click, maybe double click on it and it pops up to be opened.
I do not know what else to tell you.

liquidsands said:

Can anyone tell me where to find the pdf SteveK sent?

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If you don't know how to use search engines to find a manual then you probably shouldn't attempt to tear apart your transmission. The pressure relief valve mentioned is part of the control assembly., a simple item to remove and inspect. I suspect your problem is worn clutch plates but checking the valve is a quick process.