1978 Volvo 280 Slipping Under Load

"Hoping someone can offer some

"Hoping someone can offer some help quickly as I have someone interested in buying my boat and trying to fix what I thought was a simple slipping prop problem but marked the nose cone and prop hub today and no change after taking it for a run. Am I right in assuming the nose cone is splined onto the prop shaft and shouldn't also slip if the prop was actually slipping on it's rubber hub?
The nose cone also has the center bolt attaching it to the end of the prop shaft.
Is there some other simple trouble shooting things I should check first that might be out of adjustment that would cause the slightly higher revs when under load. Occassionally it will sound like it just slipped completely out of gear when at top speed and I'll throttle back and throttle back up and it will revert to it's normal slightly higher revving routine while getting up to plane. No other strange noises coming from the out drive that would indicate problems and boat and motor well maintained with lot's of like left in the AQ140. Cruise around at slower speeds for hours and no problems what so ever.
Could a gear system be slightly slipping somehow and then occasionally totally slip? If it sounds like a overhaul of the leg I was contemplating just buying a used 280 for $700.00 and throwing it on just to get the boat gone now and then haul apart the old 280 over the winter and sell it come Spring. Thoughts anyone?
Thanks.
Glen"

"Two thoughts: 1) Is it po

"Two thoughts: 1) Is it possible that the problem is just the prop is spinning on its hub?; 2) The shift cable may need adjustment. Remove the shift cover in the leg, then remove the cotter pin 37 and the washer 38 and adjust the cube 36 so that the clutch can travel further towards the forward gear.


http://www.volvopentastore.com/INTERMEDIATE_HOUSING/dm/store_id.366--session_id. 606559579--cart_id.443433535--category_id.333012--list_time.1190803195--view_id. 325955"

"I got the feeling this is a c

"I got the feeling this is a cavitating/ventilating prop problem.
Fouled/hooked bottom, too much trim-out, (moove pin in)
de-formed prop-blades.
Take the prop to a shop and have them check/balance it."

"If you rule out that the prop

"If you rule out that the prop is not spinning its hub and your linkage is adjusted correctly, then I would give some thought to the upper gearcase slipping. I am haveing this exact problem on my 280 drive. I have been told that I need to tear down the upper and lap the face of the drive gears.

After spending all summer working on the boat, I am going to let this wait until winter and run my boat under the RPMs that cause slippage."