Volvo-Penta Drive

[coopanabi]

Need some help ! I have a 1996 Donzi with a VP DP sterndrive (280 Hours) - when you shift into gear (forward or reverse) it really slams - whole boat shudders, run. Marine service has worked on it , 1st is was a thrust washer - nope, next it was the cone clutch - nope. Now they say I need a new upper unit. Anuy suggestions? Thanks

[redtech]

I'm sorry to say that I've faced this problem my self
after many long nights of not getting paid and turning this thing inside out and backwards I broke down and did a rebuild (shifted like butter afterwards) was not able to find something truely wrong that I could blam turned out to be a freeby.(not very happy, no broke no pay)
I've stumped VP techs on this one at the time but have never got an answer on what was wrong my thoughts are not worth the two cents but I believe that high shift ratios are behind the problem
I think that a reshim and lapping in the cone clutch to the gears and shift shoe will fix the hard shifting
very sorry i don't have an answer for you one way or the other but if someone has please respond i've always been proud to go ten rounds on and engine or drive and even though bloodied know that its been fixed but this ones kicked my ass
ps.i have tried just about everything from props to engine speed to rebuilds

[coopanabi]

Thanks for the info - yea, my tech is stumped as well after many hours and as you say, all freebie. The Volvo Tech is also lost as to the fix. Guess I'll have to go the re-build way. Appreciate the reply.

[gonzo]

A rebuild by a mechanic that can't find the problem is a bad deal. Do you know what kind of clutch you have? There were some made at that time that have a black coating. They are mainly for skiing and are supposed to shift hard. What are the RPM at idle? What kind of gear oil are you using? Are there any metal filings in the gear oil? Are the gears and cone clutch scored?

[redtech]

gonzo, having to go as far as a free rebuild even after a month with two volvo reps was pretty hard to swollow. with that said leading up to the rebuild was adjusting idle speed even below specs lapping in a new clutch, replacing the shift shoe, replacing and reshimming the shift housing, checking engine alignment, engine coupler, check lower unit shimming, everything that would or would not make a hard shift
this was a stock dp-sm cone clutch no metal in the oil and no scoring between the clutch and gears and no scoring on the shift shoe
i would have been thankful for any tell tails that would have given me something to blam the shift on but it looked good
the only thing that really stood out was the drive had a extremly high shift ratio on it still think that that may have something to do with it but haven't come across another yet
thank you for the questions still looking for what i missed if you have some more shoot them my way you mite ask the one to answer this mystery

[gonzo]

What is the gear ratio?

[redtech]

1.95 or 1.65 don't remember for sure but 1:95 stands out in my mind

[Frosty]

I am not farmiliar with Volvo legs --however I know that cone clutches were very bad at snatching.

I would imagine that you could only use a cone clutch in a wet (oiled) stuation.

[Karl2]

If it is a DP drive you probarbly have a 1.95 gear ratio. I'm assuming that the problem you describe is a hard engagement not that a hard effort is required at the shift handle.

With a coneclutch you rely on prop torque for engagement. The shallower nummerical ratio or a bigger propset will make the engagement harder. A high idle rpm on the engine will also, greatly, affect this. Check your idle setting.

Having said all of this the clutch will, and is supposed to, engage with a pronounced thump or bang. If you have a smooth engagement (Like that of a hydralic reverse gear) you have a problem. A smooth engagement means that the cone is slipping during engagement. This, usually, means that sooner or later (More often sooner) the cone will start to slip over a wider range of rpm and eventually stop engaging all together.

Within reason a pronounced bang during engagement is good - Silent shift is bad.

Karl

[Frosty]

[quote=Karl2;140791
Having said all of this the clutch will, and is supposed to, engage with a pronounced thump or bang. If you have a smooth engagement (Like that of a hydralic reverse gear) you have a problem. A smooth engagement means that the cone is slipping during engagement.

Karl[/QUOTE]

Isnt that what the clutch was meant to do, engage smoothly.

If a bang when engaging is what you like then hey just put a dog clutch in there.

[Karl2]

I have worked on these drives for thirty years and when I don't hear or feel the engagement I get worried.
There is, of course, times when an engagement is too hard and there is a problem. There are also differences between different model drives - The cone itself has changed many times over the years: from brass to steel to "Nedox" coated brass back to brass to steel to brass again etc. etc.

And as I stated in previous post, application makes a big difference. In a 18000 lbs boat designed for 20 knots using a 4.3L V6 with a 2.15 ratio and swinging a 15x15 single prop you may have a very "smooth" shift. The same cone and shift components in a 5000 lbs boat doing 55 knots with a 8.1L bigblock, 1.68 ratio and swinging C7 duoprops will result in a very hard engagement.

What the issue is in this case is difficult to trouble shoot this over the www.

Karl