79 Mercury 150 Black Max slips when power is applied

[2muchfun?]

Happened last summer when pulling skier. Did OK all day then one time we hit the gas and it started to plane out then something started slipping. It was like you pulled back on throttle. Moves OK at idle and just a little above but something slips when more power is applied. Moter revs up fine.

 

[Bondo]

Ayuh,.... Welcome Aboard,.... Sounds like a blown prop hub,.... Pull the prop, 'n look it over,...

 

[2muchfun?]

Hate my PC. Had a reply ready but I don't thing it was sent. So will try again.
Prop hub was my first guess and changed it to my spare prop last fall but took it out fishing and it did the same thing. Worked great trolling but when you throttled up it slips so I gave up and let it set for the winter to see if it would fix itself. My spare prop was used so maybe it was bad as well. They both looked OK but is there an easy way to test hubs?

 

[Dukedog]

socket that fits tha flywheel nut, break over bar.. usin' a marker, put a line on both prop and prop shaft put tha motor in gear then turn tha flywheel and wedge a 2X4 between tha prop and gear case... try ta turn tha motor over using tha socket/break over with tha prop wedged......check tha marks if tha motor turns... if that doesn't work you can, put it in tha water and gas it till ya think its slippin'.. check tha marks again and hope that's what changed......

 

[2muchfun?]

I marked the splined part of the hub with the prop. I couldn't turn flywheel with the breaker bar using 2x4 between prop and housing. Finaly got some time to run it to the lake and it sliped again but the marks remained lined up. It doesn't sound or feel like gears are slipping or grinding and it goes all day at low-medium power but when more power is applied it starts to take off then it's like something starts slipping. Any other ideas before I try to pull it apart or take it to a shop?

 

[Dukedog]

sounds like crank or drive shaft splines.......more likely crank... its a little weaker.

 

[2muchfun?]

Thanks for your help on this but it's still got me puzzled.
Dropped the lower unit and the top spines of the drive shaft don't show any signs of spinning/slipping and looking with a flashlight up towards the crank spines everything looks fine. No sign of metal fillings in lower unit lube or anywhere. Any other ideas?

 

[Dukedog]

tha little pin stickin' outta tha top of tha drive shaft still intact? is it easy or very hard ta push in? can't think of anything that would not leave some kinda tell-tale sign except tha prop hub.......

 

[2muchfun?]

Pin is there but it will not move in or out. I thought it was pressed in until I just looked at the drawing in the motor manual and noticed it has a spring under it.

 

[racerone]

Measure the height of the transom.-Sounds like motor may be mounted too high.---That pin on top of the driveshaft has nothing to do with any slipping !

 

[2muchfun?]

I don't think it's the hight of the motor. Nothing has moved and we skied and tubed behind it for years. The last time we were out last summer my son was pulling me on the 3rd day at the lake (everything was fine until then) and the 2nd time I fell, it started to plane out and I was up and then it was like it cavitated or something and just dropped off. After that every time you start appling throttle it just slips or something but it revs up just fine. The first thing I thought of was the prop hub so I switched to my spare (used) prop but when we tested it at the lake last fall it did the same thing. Last week I marked the inner splined part with the outer part of the prop but when we tested it something slipped again but the marks stayed aligned. Works fine trolling all day and at about 1/4 throttle, lower unit lube looks fine and no metal on the drain plug magnet, so I don't think it's the pinion gear. Just has me stumped. Might put it back together and try the other prop with marks on it.

 

[Dukedog]

I marked the inner splined part with the outer part of the prop

one mark on tha prop and another on tha "prop shaft" (tha nut).........

 

[racerone]

If another prop does not help then measure the height of the transom and post that here.