2004 VP 5.0 with SX-M slipping with slight revs

[MNBrent]

2004 Glastron GX205SF with VP 5.0 GL-E with SX-M 1.6 outdrive

Ive experienced some slipping this year under a few conditions:

1) Loaded boat with 4 adults and 4 kids under way, 15mph or so, just under plane, and suddenly get slipping, like cavitation where RPMs go up quickly, but boat slows down. I can throttle it back and recover. In this case, the outdrive and prop are under considerable stress as I'm trying to accelerate to get on plane.

2) Going a slow 5mph towards a dock, after a full day of boating, and almost idling will get slipping if I give the boat any throttle. there is just a free rev up as though the boat went into neutral, but I've been in gear for a long time. Its intermittent, but will recover by going back to neutral. In this case, much reduced stress on the outdrive or prop.

Does this sound like cone clutch slipping or prop hub slipping or ?
What is a good way to go about isolating these down?

Thanks, Brent in Mpls

 

[jerryjerry05]

Re: 2004 VP 5.0 with SX-M slipping with slight revs

Prop.
Take it off and mark the hub.
Then go for a ride and see if the line moves.
The dive full of oil?
No water?

 

[skydiveD30571]

Re: 2004 VP 5.0 with SX-M slipping with slight revs

What jerry said, also, what kind of gear lube are you using? There have been reports of drive gear slipping when using "limited slip" gear lube. SX drives should not have "LS" gear lube in them.

 

[dypcdiver]

Re: 2004 VP 5.0 with SX-M slipping with slight revs

Interestingly LS gear oils have a friction modifier added to increase the friction, so should in effect increase the friction between the cones, as is the case in the LS Differentials that employ clutch discs it was originally designed for. Puzzling eh?

 

[mandmj]

Re: 2004 VP 5.0 with SX-M slipping with slight revs

As for the gear oil, I recently contacted mobil about the LS 75w90 vs what VP specifies in the service manual for my DP-SM (mobil 1 SHC 75w90). Evidently the synthetic 75w90 at most autoparts stores is not what is recomended. Mobil replied that we should use Mobil Delvac 1 75W90 in the outdrive, which looks spec wise to be nearly identical to the euro named Mobil 1 SHC 75w90.

Also, regarding the LS label on the autoparts store items, based on another reply from Mobil, the product wasnt changed when they changed the label to LS 75w90 a few mos/year or so ago (I had seen this question arise on another thread about the oils). They simply added the LS to the labeling to make it more clear that the product was intended for limited slip diffs.

Both are API GL-5 lubes, but the indepth specs on the websites differ quite a bit. Based on a quick glance at the amazon prices, it is cheaper to get the VP branded oil over the delvac. I havent tried other sources as of yet tho.

edited for clarity

 

[MNBrent]

Re: 2004 VP 5.0 with SX-M slipping with slight revs

Im using VP synthetic gear oil 75W-90 for gear case. Is there a better recommendation of a limited slip additive that should now be used?

Also I did put on a new prop this year. I'll mark the hub. Thanks for that.

Is there also a rubber dampener, similar to the prop hub, between the engine and outdrive spline shaft?

 

[dypcdiver]

Re: 2004 VP 5.0 with SX-M slipping with slight revs

To answer your question, yes there is a damper it is part No. 3858437 and called a "rubber coupling" fixes to the flywheel, generally very reliable.

 

[BRICH1260]

Re: 2004 VP 5.0 with SX-M slipping with slight revs

I would bet on the prop hub slipping.

 

[skydiveD30571]

Re: 2004 VP 5.0 with SX-M slipping with slight revs

To answer your question about the gear lube you are using, if it is the VP branded lube then you are fine. As mentioned above, Mobil 1 75W-90 found at most auto parts stores is limited slip which is why Mobil 1 does not recommend it.