no speed, feels like slipping

HELP PLEASE, got a 1988 268DA with a 7.4 magnum (454), bravo 1 outdrive. 3 weeks ago the boat ran great, last week, we took it out and it sounded like a transmission slipping. runs fine in slow speeds, go to push on the throttle, at about 3000 rpm it start to Rev up, but doesn't go anywhere. marine mech. said to switch out prop 1st. said it may have spun the hub, did, made no difference. he took the boat out, pulled up the engine cover, no rubber smell, he then pulled the outdrive, no metal shavings near the coupler. decided that it had to be the cone clutch in the upper part of the outdrive. he sent it to a certified mercruiser tech. he rebuilt the upper half of the lower unit. put it back on yesterday, same thing. while the outdrive was off he put a tool into the coupler, and a pipe on the end of it, and a big wrench in the front of the motor, he couldn't turn the coupler, that's when he said it had to be in the upper half of the outdrive. Now, he says that he has no answer, he's called other techs, and they say that they have no clue either. PLEASE, ANY IDEAS
thanks,
Matt

I believe it has to be the coupler or the prop. I also believe the coupler could still slip at high speeds/torque and you would not be able to duplicate that in the shop. Just my opinion.

I'm a little disturbed regarding the "cone clutch". The 1988 268's still had the Alpha drives. It is my understanding that the Bravo drives were not put behind the big blocks until 1989..

Could it be prop cavitation??? Does it continue to rev up even when you trim the lower unit down??

in 1988 some big blocks that had problems, with the alpha drive were fitted with the bravo 1. I'm sure it's a bravo 1, the water pump is on the front of the motor, not in the outdrive. the top half of the lower was rebuilt, I have the old parts. the prop was changed (thought it might be slipping in the hub). Have not changed the coupler, but, we can't make it slip out of the water.

Deleted.
(wrong thread)

I'm going to say coupler also. A 454 makes a lot of torque, would be hard to duplicate that and the heat associated with running using a wrench and pipe. I know you have to pull the engine to do the coupler, but what other options do you have? I'd get an SEI drive before I put any more money in repairing your OD. You will get a warranty and if it isn't the problem, you can sell it.

Do you have a hand held temp gun? Before yanking the engine for what looks like a coupler, did you allow it to slip for long or immediately shut it down? A 7.4 will quickly replenish the air in your engine compartment at 3000 rpm. I would allow it to slip for a bit and then look for a quick temp increase in the coupler. If not, then more than likely it's not your problem. Have not heard of it happening myself but wonder if it possible that the exhaust flappers in your Y pipe have failed and are restricting the upper ports in the transom assembly. This may allow enough exhaust to flow in front of your prop causing it to slip. Just thinking outside of the box.

Take a paint pen and put a line on the coupler down to the input shaft. Take it out and if the coupler is slipping, the paint line will be broken. Time for a new coupler.


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Who rebuilt the drive ? May have done a shoddy job. Exactly what did he replace ? If he replaced the clutch cone only and the cup on the gear is glazed or worst it could still be your drive.

thanks everybody. it was the coupler. 1st. the moron that owned the boat before me told me that he had replaced the coupler. so I didn't think that it was the problem. Everything kept pointing to the coupler. Pulled the motor out, it had the triangular plate coupler on it. NOT FOR A 454. it had the rubber balls on it. HE had the balls to tell me that he put that one on because the bellhousing was broke, and the one that he found, had the smaller hole in it. So that's what he used.

Here is an update, a year later. Replaced the coupler, the correct one needed the larger hole cover plate, found one at a boat boneyard. I have a skinny friend that works on boats. Within an hour he had everything disconnected and we pulled the motor. Sat it on a stand, than drank beer. Next day we we replaced the parts, cleaned up stuff that is too hard with the engine in. The put the motor back in. Hooked everything back up, hoisted it back up, sat it in the water, started right up, took it for a test, came right up on plane, cruised for about an hour, went back to the club, docked it, then drank a lot of beer. A year later, still runs great.