Velvet Drive Problems Please Help!
Printed From: CorrectCraftFan.com
Category: Repairs and Maintenance
Forum Name: Boat Maintenance
Forum Discription: Discuss maintenance of your Correct Craft
URL: http://www.CorrectCraftFan.com/forum/forum_posts.asp?TID=19543
Printed Date: November-20-2024 at 12:30pm
Topic: Velvet Drive Problems Please Help!
Posted By: Illuma
Subject: Velvet Drive Problems Please Help!
Date Posted: September-23-2010 at 7:14am
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Apologies for the long post but I wanted to explain fully what I have done and what the problem is straight away.
I can’t work out why my clutch pack has failed? I have a Velvet Drive AS1-70C gearbox with a 2.1:1 reduction ratio it is coupled to a small diesel engine (54hp) and we run the engine at about 1000 - 1200 rpm to give us cruising speed (canal boat doing 3-4mph). We did a three hour run with no problems and moored the boat for the night, the next day I started the engine and there was a horrible grinding coming from the flywheel area, when I engaged forward we had little to no power same with reverse. I checked the oil and it was nice and pink but a little low, I topped it up but that did nothing. I removed the gearbox and saw the drive plate was broken but it looked like it had been for some time? When I opened the gearbox I instantly saw the reverse clutch had snapped in two and the internal teeth looked mashed! So I ordered a rebuild kit, a new oil pump (thought it was best to replace) and a new drive plate. The info in the 70C service manual is a little sketchy but I am no novice mechanically, so armed with my digital camera I stripped the drive and replaced all the seals, clutch plates and gaskets all went well. The only problem I came across was I could not figure out exactly how the forward clutch system worked? Looking at it in my opinion no matter how much the forward piston pushes the clutch spring it can’t put pressure on the plates because the snap ring bottoms out on the gear teeth of the ring gear? I called a place in the US and queried the snap ring that the clutch spring sits on, he said it looks weird but that’s how it works all he said was to ensure I put the thicker of the two springs in first which I did do. When I assembled the clutch spring compressed the top of the unit (forward piston) into the ring gear and inserted the last snap ring there was obviously pressure pushing down on the snap ring in the ring gear but you could easily move the clutch plates I would say there was about 1mm or more of play. In the 70C there is no rear snap ring and no mention of having to set any clearance with gauges. Totally baffled on how the clutch would bite I rebuilt the box, all looked well on the bench. I re fitted the gearbox back in the boat and got drive, I took the boat out for an hour to test the box and that’s when things got weird. Firstly moving forward 2mph all was well however put more power on and we slowed down, put the box in reverse (700rpm) and there was this loud constant clunking noise increase the revs (1200rpm) and clunking went, boat worked well in reverse apart from clunking. I checked the engine rpm with the gearbox output rpm and in forward at 700rpm I only got 280rpm out, then at 1000rpm I got 280, then at 2000rpm I got 280 out. Obviously for some reason the clutches were slipping? In reverse at 700rpm I got 330 out and at 1000rpm I got 480 out so apart from clunking all looked well there. I need to find out if I was given the correct ATF as it was supplied by the place I got the parts from but they re bottled it so I have no knowledge that it was totally correct but they do state it is for use in 70C, 71C, 72C borg gearboxes. I was careful checking the oil level and I know it was spot on so I was stumped. Today I decided to change the oil with some that I knew was Dexron II to see if the oil was the problem, I sucked the oil out and instantly saw bronze dust and discolouration as I got near the bottom of the fluid so I know the clutches have been slipping bad! With little to loose I started the engine to get the pump to shove as much oil back into the sump as I could so I could get more of the oil out, putting the box in fwd and reverse I noticed a strange thing, we obviously had no forward output but I did have reverse and it still looked good but the clunk had totally gone? Obviously I only ran the engine in total for about 10 seconds and moved through forward / reverse to get oil out. It worked and I took out another 0.5 litre. I re filled with new oil Dexron II and fired it up exactly the same problems as before? I am at the point where I will get a pressure gauge and read the pressures on the box to see what valuable info that gives me, then I will remove the box and replace the clutch plates again. Hopefully someone with greater knowledge can clear some of my problems up and clarify how the forward clutches work? What I don’t want to do is rebuild again and have exactly the same problem! Thanks in advance. |
Replies:
Posted By: Illuma
Date Posted: September-23-2010 at 2:12pm
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I got to test the pressure today, I don’t think it clears much up?
From the line port:- It read 135psi in neutral, 135psi in forward and 135psi in reverse. From the reverse port:- It read 0psi in neutral, 0psi in forward and 135psi in reverse. The max pressure I could get it to hit was about 170psi but then it would start to fluctuate so I guess that would be the pressure valve opening? Any help would be greatly appreciated. The company that supplied the questionable ATF fluid also came back and said it was Dexron II but I am still not sure I doubt they would admit if it was wrong?? |
Posted By: eric lavine
Date Posted: September-24-2010 at 10:14am
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these will run on water, it sounds as if you have the forward pack assembled incorrectly. it goes: with drum facing up
endplate, 5 clutches, 4 steels, endplate, thick snap ring (which does not fit in groove) spring, spring wear ring, piston and cylinder, then thin snap ring which will fit in outside groove. can you take a pic when you get it disassembled? ------------- "the things you own will start to own you" |
Posted By: eric lavine
Date Posted: September-24-2010 at 10:15am
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clunk is good, its a sign of a nice tight seal inside the trans ------------- "the things you own will start to own you" |
Posted By: eric lavine
Date Posted: September-24-2010 at 10:19am
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btw, you can air check the pack once assembled on the bench thru the 2 holes on the shaft end, it will give you a nice sound of engagement with a little air leak thru the bleedhole ------------- "the things you own will start to own you" |
Posted By: Illuma
Date Posted: September-24-2010 at 2:28pm
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Thanks for the info Eric,
My drive has three clutch plates and two steel plates it is a 70C is that correct? I am sure the clutch pack is correct but I will sure send some pics when I get the box out and apart again. Can you tell me if the forward clutch piston makes physical contact with the end plate? The one thing I could not work out was when the piston comes out how it put force on the plates to clamp them together, with the reverse it was obvious. Regards, Mark |
Posted By: eric lavine
Date Posted: September-25-2010 at 11:50am
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Ive only seen 1 transmission with the combination of 3 and 2 plates and were talking many, the belleville spring makes contact with the endplate, it fits between the fat snap ring and when the piston comes out it puts pressure on the spring also acting as a return spring....take some pics, i need to see the clutch hub and make sure it accomadates the 3 and 2 combo ------------- "the things you own will start to own you" |
Posted By: Illuma
Date Posted: September-25-2010 at 5:24pm
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Hi Eric
My belleville spring sits on top of my snapring and makes no physical contact with the end plate, and from what I could see when the piston puts pressure on the spring there is no way it can put pressure on the clutch plates as the spring bottoms out on the teeth in the ring gear before putting any pressure on the plates? I have just removed the drive, I am sure when you see some pics you will know whats wrong and where? I am usually very good at working out mechanical things as I am a mechanical / electrical and electronic engineer but this had me stumped as to how it would work? |
Posted By: Illuma
Date Posted: September-26-2010 at 8:45am
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Hi Eric
Here are the pics you can see where the gear has been scuffing the spring, looking at it now is the whole thing in backwards? ie the end plate with the raised bump is nearest the spring and not the other way round as it is in the pics? I am 99% sure this is how it came out as I laid each component out in order and the slight marking on the end plate I put nearest the spring that matched the snapring. This may account why forward was never too great when I got the boat? Only if I am right of course! If not I am still lost! Regards Mark     
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Posted By: eric lavine
Date Posted: September-26-2010 at 11:21am
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Ah my friend, you have the 2 endplates mixed up, the spring needs to ride on the plate with the rounded area on it... on the last picture, that endplate needs to go down in first against the ring gear ------------- "the things you own will start to own you" |
Posted By: eric lavine
Date Posted: September-26-2010 at 11:23am
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everything else looks correct, it will not work the way you currently have it stacked ------------- "the things you own will start to own you" |
Posted By: Illuma
Date Posted: September-29-2010 at 6:02am
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Hi Eric
Well I re-built the box and dropped it back in and checked for slipping, looked good at tick over with control lever disconnected so I re-connected the gear / drive lever and dropped it into forward, this used to give me about 2.5-3 MPH at about 1000 engine RPM's, fortunately there were no boats near us when I did that as we took off! I think I tore a new channel out in the bottom of the canal with the amount of mud we lifted, has anyone got a spare wakeboard? Looks like the box must have been re-built before and assembled wrong, then I simply copied how it was before. The only odd thing is prior to the failure if I put more revs on the boat did pick up speed but not allot, after rebuild one with more power I lost speed, and now after rebuild two I will have to lower the REVs because there is loads of power I think at 2000 RPM I could actually get rooster tails out the back! Thanks for all the help Eric, time to relax again at a nice slow pace. 
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Posted By: eric lavine
Date Posted: September-29-2010 at 9:45am
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good to hear, very common mistake along with leaving the fat snap ring out because the person rebuilding thinks because it doesnt fit in the groove, it doesnt belong ------------- "the things you own will start to own you" |