Something slips in the driveline

[Rabbitdawghunter]

I have been working on a 1987 3.0 liter Mercruiser with an Alpha One outdrive. I installed a new forward gear and clutchdog about 2 weeks ago. The owner came back with the boat claiming that it was still jumping out of gear. Lake test revealed that it was not jumping out of gear but rpms would go way up especially in a tight turn. The lower unit was still fully engaged in gear because it was still pushing the boat steadily about half speed. I'm suspecting the engine coupler is bad. I have removed the cap off of the upper drive housing and checked those gears. I have pulled the outdrive and inspected the driveshaft splines that go into the engine coupler and also the female splines of the engine coupler, they all looked good. I am just not seeing the smoke and the smell of rubber burning that I experienced with the last bad coupler I dealt with. Is there a way to isolate the coupler as the source of the problem without pulling the engine to get a look at the coupler?

 

[Rabbitdawghunter]

Re: Something slips in the driveline

Forgot to mention I have already tried a new prop and there was no change.

 

[DHPMARINE]

Re: Something slips in the driveline

Could the answer be in that the customer calls it 'jumping out of gear" and says it stills <br />is,and you say it is 'slipping' ? The clutch dog and forward gear should fix jumping,but do little for slipping.So you've got to speak the same language with him.<br /><br />Props don't last long when slipping.Neither do couplers.I have seen lower gearcase to upper gearcase splines do this,but generaly not on Mercruisers.<br /><br />DHP

 

[Rabbitdawghunter]

Re: Something slips in the driveline

The boat came to me the first time for a genuine jumps out of gear condition, it would stop dead in the water once the cluth dog disengaged. This is different. The edges of the gears were rounded off. That was fixed with the rebuild and it was shimmed to factory spec with the correct factory manual. I tried a new prop so wouldn't that put the prop issue to rest.

 

[DHPMARINE]

Re: Something slips in the driveline

Tell us more about slipping and going at half speed,if you can.<br /><br />DHP

 

[Don S]

Re: Something slips in the driveline

Yes, it's probably the coupler. It's the only other thing in an Alpha setup that could slip.<br />When I say slip, I mean the rpm's will go up, but the boat slows down.

 

[jlshields]

Re: Something slips in the driveline

Props will sometimes ventilate in a turn if you're trimmed up just a little too much.<br />Even a Bravo3 will do it, at least mine does.

 

[Rabbitdawghunter]

Re: Something slips in the driveline

I played with the trim quite a bit and it would keep happening even when trimmed completely in to the point that the bow was plowing and hard to turn the boat.

 

[Rabbitdawghunter]

Re: Something slips in the driveline

Hey Don, how many hours do you usually have in changing a coupler. I was estimating 8 hours labor and 275.00 for the coupler.

 

[DHPMARINE]

Re: Something slips in the driveline

I'm not stepping in for Don,but the coupler price is in the zone,and the labor okay depending on the boat configuration.Even those 4's can sometimes be a real hard pull.<br /><br />Have you given thought to replacing the u-joint shaft splines as well ? I always replace as a set.Worn steel splines in a new aluminum coupler probably won't break-in well,and will have early failure.<br /><br />DHP

 

[Rabbitdawghunter]

Re: Something slips in the driveline

Thanks DHP, Don and everybody, the guy does not want to spend the money right now. I guess I'll see him back with that sad look on his face when it overrevs enough and the engine pukes.

 

[Don S]

Re: Something slips in the driveline

Shouldn't take long if it's a coupler problem. Once they start slipping, the next trip it may not move at all.

 

[whywhyzed]

Re: Something slips in the driveline

remind the customer that when the coupler fails, his water pump stops...

 

[trog100]

Re: Something slips in the driveline

i just changed the coupler on my 88 3.0L merc alpha one unit.. the drive just instantly went and it didnt fail at speed either.. the boat just failed to move away from idle.. the aluminum splines in the coupler ripped out..<br /><br />if i did it again i recon no more than four hours.. half an hour would see the engine out and half an hour would see it back.. half an hour to pull the drive.. half an hour to put it back.. an hour to change the coupler.. an hour to fit the new yoke..lets say four hours in total..<br /><br />assuming u dont hit any major snags u could do two in eight hours.. my engine has a removable cover (doghouse) and is easy to get at.. <br /><br />the new mercruiser flexy/plate couplings come fitted with a grease nipple and have steel splines a far better arrangement than relying on a smear of grease as the old (no grease nipple) ones did..<br /><br />cos of the grease in the boat idea a new yoke is needed with a groove for an o-ring to stop the grease from just coming out as u pump it in..<br /><br />they come as a kit.. coupler and yoke.. the only difference tween the new and old yoke is the o-ring groove..<br /><br />four hours is working at an easy pace.. i recon if i tried hard (on my boat) i could do it in three..<br /><br />it took me a little longer cos i had to cut down and redrill a coupling for the now standard (after 2000) 14 inch flywheel.. the earlier 3.0Ls came with a 12-3/4 inch one.. after 2000 it seems all the GM cast iron boat engines come with the bigger 14 inch flywheel..<br /><br />hard to believe but the main mercruiser UK dealers didnt have the one i wanted and one would have had to be shipped in from belgium of all places.. they quoted me 14 days which i didnt believe so i cut the bigger one down.. just for interest the two couplings 12 and 14 inch are exactly the same except for the hole centers and the three fingers stick out further.. a drill and a grinder soon made the big one into a little one..<br /><br />also just for interest.. it seems these coupling splines get more wear at low trolling speeds than they do at normal speeds.. i assume its cos the engine especially a four banger dosnt run smoothly at low rpm and the coupling splines get lots of side to side rattling about type movement.. its that type of movement that causes the spline wear.. not when the boat is under heavy load and going faster..<br /><br />trog

 

[Rabbitdawghunter]

Re: Something slips in the driveline

OK, I finally talked the guy into changing the coupler. Everything went smooth, but when I lake tested the same problem. The thing that I can't understand is it takes about 10 minutes of hard runnning (flawlessly) before the slipping shows up. I guess the next thing I am going to try is a third prop to be sure that the second used one that I robbed from another boat was not spun as well, beyond that I think I'm goin into the upper drive to see if the splines there are gone. I can't see how metal to metal parts could exhibit the slipping like a prop hub or coupler gives. I would think that gears and splines would just go crunch and come apart. I can still come off the throttle to idle then throttle back up and everything is fine until the first hard turn. Let's hear your thoughts?

 

[Rabbitdawghunter]

Re: Something slips in the driveline

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[mlslocks]

Re: Something slips in the driveline

since the coupler replacement did not repair the problem do you still charge?

 

[Rabbitdawghunter]

Re: Something slips in the driveline

This one is strictly for educational value at this point, I'm trying to maintain my sense of humor!

 

[KaGee]

Re: Something slips in the driveline

Wouldn't a quick oil check for metal let you know if the splines in the upper were rounded?

 

[Cptkid570]

Re: Something slips in the driveline

Couldn't you test the coupler by painting a line on the shaft and the coupler,, then after a suspected coupler failure, see if the lines are still together? I don't understand why the coupler had to be changed in order to test it.