Massive clunk on hole shot. Mechanic can't find issue. Please help-thanks.

[took-the-red-pill]

Hi there,

First of all, thank you to those of you who lend your valuable time to help the rest of us work through our problems.

1988 OMC Cobra, 175 Horse on a 16.5 foot Campion, 2BBL Carb. We do skiing and tubing.

On hole shot, we put it into gear, listen and feel that it is engaged, then give 'er. About 1/2 the time, there is a massive CLUNK about 1.5 seconds in, as it's accelerating, that you can feel throughout the whole boat. The boat starts, runs, performs in every way perfectly other than that. Once you're going, pulling a tube or a skier, it's great, with no hitches, glitches, or hints of any issues throughout the whole power band.

The mechanic has it apart right now(finding someone who will work on these old dogs in Alberta Canada is a huge pill). So far he has checked and says the U joints are good and the gimball bearing is fine(done 2 years ago) and he can find nothing out of the ordinary. He's going in deeper this afternoon, but I'm just wondering if anyone has any experience with this happening, and what it was.

Note: The shifter was very stiff, and I have read that this is a harbinger of doom for these legs, so I've told him that as well as repairing the leg, he needs to adjust it until it shifts with two fingers.(I have read the information here, and printed it out for him to adjust it.) The old shifter was hooped, so I got a used one on ebay that he will install. Do you think the old shifter being stiff could possibly have caused this second clunk? I haven't read anything about that specifically on the OMC information published on this forum.

Thanks for any insights on this.
Cheers
Keith

 

[bajaunderground]

I'm only adding my $.02 worth...given the new format of iboats, it might not get answered as quickly as previous!

There's a few things I would have my mechanic check-out before replacing shifter...given that he's checked the gimbal bearing and joints and that they are "good".

1) Check (with engine running if possibly?) that the shifter is engaging the drive all the way? Meaning the added force of movement might be shifting it the rest of the way in to the Forward position once underway/power?

2) Check alignment of drive...the drive coupling could be worn and/or loose and gives and initial "clunk" until it catches under load?

Good Luck with the diagnoses...the boating season is soooo clooosseee!!!

~Brett

 

[bruceb58]

Your lower shift cable has failed and your dog clutch is likely also damaged enough that it will never hold anymore. This was a common problem when the Cobra first came out. Happened to my boat but fortunately OMC was still in business and fixed my drive under warranty.

You can replace the cable, adjust it properly with the tools and see if it still does the clunk but once it does that one or two times, the dog clutch teeth are rolled over and they won't hold anymore.

You need to read this:
http://www.hastings.org/~stuart/cobra/

 

[took-the-red-pill]

Thank you. I have passed this information on to my mechanic. I will try to report back as to what happens for future users.

Regards
Keith

 

[Idlespeedonly]

Unfortunately I second the dog failure. They usually cant be adjusted to hold anymore.