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Old 15-11-2010, 17:58   #1
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Perkins 4-108 with Velvet Drive - Rotates Slowly in Neutral

Works fine in Fwd and Reverse, but very slowly rotates in Neutral. Anyone else ever experience this? Is it normal or a sign my velvet drive may be failing?

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Old 15-11-2010, 18:05   #2
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If very slowly then you're probably ok. If a lot then the clutches are going.

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Old 15-11-2010, 20:08   #3
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man is your question timely! i have the exact same setup as you plus a walther v-drive.

i just replaced the transmission cable after accidentally discovering the cover was pretty frayed. then i tried to adjust the cable. couldn't get the shaft to stop turning in neutral.

so i removed the cable from the transmission link and just manually moved it forward and back, trying to find a 'null' spot. there was none.

i could feel a 'clunk' as i pushed the link into forward, and the shaft began spinning much faster. same when putting it in reverse. but where 'neutral' should be there was still a small amount of shaft rotation, maybe 50 rpm or so.

i've decided to leave it alone.

but i do have an idea that i'd like to throw out there. could it be old or cold transmission fluid?? i'm thinking that when the fluid is thick it acts as a sort of clutch. maybe when the fluid gets hot and thin the shaft stops turning in neutral. i'll have to check that next chance i get......
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Old 15-11-2010, 20:36   #4
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My Islander 36 has a perkens 108 and velvet drive, It two may spin the prop very slow in neutral. I also get a (Click) like sound then engaged Fwd or Rev. The fluid looks good. I dont worry about it, Maybe I should.
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Old 18-11-2010, 06:47   #5
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You will get some "torque converter effect" in a transmission in neutral. The shear friction of the lubricating oil between a rotating clutch disc and an adjacent clutch disc will transmit a very small amount of torque, even with the clutch disengaged.
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Old 18-11-2010, 07:31   #6
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Mine does this as well. If I raise the rpm in nuetral it will stop spinning.
It's kind of like tearing up $100 bills while standing in a cold shower.
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Old 20-11-2010, 16:14   #7
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velvet drive

The clearance between the clutch plates in neutral is only a few thousands of an inch so the friction created by the oil is enough to cause a slow roll in neutral at idle. This is more noticeable when the oil is cold.
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Old 20-11-2010, 18:34   #8
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Perkins Sabre (4-108 IIRC, 75 or 82 HP) and Hurth transmission. Same thing, slowly rotates in neutral.

I'd bet that if you put your car (with automatic transmission) up on blocks, the wheels would spin slowly in when the car is in neutral.


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