4.3 OMC slip in forward gear

[danjohn4]

I have a 1991 4.3 OMC cobra outdrive. When I accelerate slowly especially under load (skiing/tubing) the boat will speed up and then (for lack of a better word) “clunk” as though it is slipping out of gear and then engaging back into gear again. I’m not sure if the forward gear is engaging properly. Is there any adjustment for this? What needs to be done to repair this problem?

 

[whywhyzed]

Re: 4.3 OMC slip in forward gear

http://www.hastings.org/~stuart/cobra/index.html <br /><br />probably the best place to start reading.... unfortunately your lower unit would not survive coming out of gear under load...sorry

 

[danjohn4]

Re: 4.3 OMC slip in forward gear

Thanks for your info. I'm reading and trying to figure out if my problem is the cable or if the gears are bad. I just bought the boat and had the upper unit gears re-done by a marina who is supposed to be OMC experts. I assume they adjusted the shift cable properly when they installed the stern drive. Therefore, I'm concerned the problem in not the cable. In addition, OMC had many of the cable problems diagnosed prior to my 1991 unit being sent out. What can I do to identify if the problem is the gears as opposed to the cable or something else?<br /><br />Danjohn4<br />

 

[KaGee]

Re: 4.3 OMC slip in forward gear

Normally you would suspect a bad prop hub first. But, you mentioned a "clunk" and that's not what a bad prop would normally do.<br /><br />You need to drain the oil in the lower unit and inspect for shavings. My wild guess from your description sounds like your clutch dog may be worn. If so, you are looking at replacing it and the lower gear set. Clutch dogs go bad by shifting at too high RPM and/or improper shift cable adjustment or stretched out cable.<br /><br />Another possibility is a worn engine coupler. I would have hoped that in doing the upper re-build, they would have inspected the drive shaft for possible wear. <br /><br />I would fix the problem now. If something detonates in that lower unit it's moocho buckos.

 

[danjohn4]

Re: 4.3 OMC slip in forward gear

Thanks for the info. Keith<br />When I drained my oil, there were small pieces of metal on the plug magnet. Is this normal or acceptable? I have about 6 hours on the new upper gears. Could the new gears be the cause of the metal?

 

[DHPMARINE]

Re: 4.3 OMC slip in forward gear

If you just had the drive worked on,STOP doing things to it and take it back to the people you paid to work on it.<br /><br />DHP

 

[KaGee]

Re: 4.3 OMC slip in forward gear

Good advice DHP.<br /><br />No Dan, the upper and lower are seperated. Their oil do not interchange. I would not expect the upper work to be related, unless, like mentioned above, the shift was not properly adjusted.

 

[seahorse5]

Re: 4.3 OMC slip in forward gear

Originally posted by KaGee:<br />No Dan, the upper and lower are seperated. Their oil do not interchange. [/QB]

On a Cobra drive, the upper and lower housings share the same gear oil.

 

[seahorse5]

Re: 4.3 OMC slip in forward gear

Originally posted by danjohn4:<br /> I have a 1991 4.3 OMC cobra outdrive. When I accelerate slowly especially under load (skiing/tubing) the boat will speed up and then (for lack of a better word) “clunk” as though it is slipping out of gear and then engaging back into gear again.

It definately sounds like it is jumping out of gear. On a 15 year old rig like yours, it could be a combination of wear, cable adjustment, or even poor shifting habits.<br /><br />Since you mentioned upper gear service just prior to the problem, perhaps the shift adjustment wasn't performed when the outdrive was reinstalled. There is also a shift rod height adjustment that should be checked and that could have been overlooked when the upper and lower housings were reassamebled. It is possible that when the units were apart, someone inadvertantly turned the shift shaft, changing its measurement.<br /><br />Either way, once a unit jumps out of gear under load, the clutch dog and forward gear lugs get rounded and most likely have to be replaced.<br /><br />Have a knowledgeable Cobra mechanic check the shift linkage, cables, and adjustments, then try the boat. If you are lucky, everything will work fine for now. Either way, eventually you will need new fwd. gear and a clutch dog.

 

[KaGee]

Re: 4.3 OMC slip in forward gear

Originally posted by seahorse:<br />

Originally posted by KaGee:<br />No Dan, the upper and lower are seperated. Their oil do not interchange.

On a Cobra drive, the upper and lower housings share the same gear oil. [/QB]

My bad... I always thought the lower was self contained simular to the Stringer. Even looks that way in the drawings.

 

[lakelivin]

Re: 4.3 OMC slip in forward gear

Originally posted by KaGee:<br /> ..... My wild guess from your description sounds like your clutch dog may be worn. If so, you are looking at replacing it and the lower gear set. Clutch dogs go bad by shifting at too high RPM and/or improper shift cable adjustment or stretched out cable...... <br /><br />I would fix the problem now. If something detonates in that lower unit it's moocho buckos.

Is replacing the lower gearset & clutch dog something that could reasonably be done by a non-professional? Let's assume one has the correct OEM manuals, time & patience, but no special OMC tools. My understanding is that rebuilding the upper drive would be beyond the scope of most 'non-pros' (special tools needed, etc.) but I haven't heard about the lower unit....

 

[danjohn4]

Re: 4.3 OMC slip in forward gear

Thanks for all the info. Does anyone know if it is possible to get the special OMC tools to rebuild the lower unit?

 

[danjohn4]

Re: 4.3 OMC slip in forward gear

Is it possible to measure for the shim material on the lower unit driveshaft w/out the special driveshaft holding tool P/N 314438?