I started my GT 31 on the trailer to do some checks and discovered a roaring noise when I engaged the clutch. I've got grease in the belt housing so I'm sure the front seal is blown. The lower unit is practically new. I replaced the grease after the initial 15 hours and have since applied fresh grease after every use (with the plug screw removed). Usually three or four pumps after I have grease coming out. The lower unit has barely 25 hours on it. The noise is only heard when the clutch is engaged, but I can't locate the exact location it's coming from. Checked for play in the prop in every direction, it's solid...no movement on the shaft at all and it turns freely.

Is there a bearing in the clutch or am I only looking at the lower unit as the culprit? No oil or any sign of leakage around the crank case or drive shaft.

Is it unusual for a bearing to go bad so quickly?

Apparently, the front seal blew when I replaced the grease. How do I avoid having it happen again?

Thanks in advance.

Update: Made a stethoscope out of water hose and took a good listen to everything. The noise is coming out of the lower unit, but the weird part is that after the thing warmed up good, the sound is almost un-noticeable. Turning the prop by hand (engine off) doesn't generate any concerning sounds at all.

If it growls typically that means a bad bearing. Upon all of my new bearings I install I pack the bearing full of grease upon installation. Then I pack the cavity between the bearing and seal. Knock seal in (make sure the lips are lubed) then put snap ring on followed by pulley.

Do you have Thrust movement in the prop shaft? (in/out)

Can anyone tell me their procedure for changing out grease in a GT straight tube lower unit? I'm about to replace the seals and bearings. When changing/adding grease, do you engage the clutch first and let it spin a while to warm everything up or just go at it cold? I want to try avoiding a seal failure from just adding grease. I tried it cold the first time and am pretty sure that's when the seal failed.

I personally pump grease into the zerk and when clean grease comes out of the bleed screw I usually hold my finger over the hole and put 1-2 pumps extra then spin the prop shaft a few turns then I put the bleed screw back in. Typically after 15 -20 hours pull the screw give it a few pumps until you see good grease again, then re install the screw and you are good to go.

Before I assemble I pack my bearing and seal cavities with grease.

I just had the same noise on my 2014 MB 3500. Pulled the lower unit apart and found the drive bearings bad. Specifically the one closest to the belt opposite of the prop. Strange thing was, they were relatively easy to pull out of the housing. Was able to get them out by hand. Be calling Boat DR in next hour for bearings.

You can add grease how ever often you would like, But make sure you remove the plug. Also when I said I held my finger over the hole and pumped the extra squirts, By the time I put the screw back in the pressure equalized by letting some escape.
I always added when the unit was cold.

I would pull the back housing off and check the needle bearing/race and see if its good, and change at least the back 2 seals, then change what needs to be swapped up front. I ill take pics of a rebuild tonight as I am fixing a customers LU this evening.

Pack roller bearing and tap into housing then install snap ring


Pack seal cavity with grease tap seal in bore and install next snap ring

Install shaft, wear sleeve, taper lock pulley , and tighten front nut.
I then pump grease through shaft without rear bearing housing installed until I see good grease out the bore. Install needle bearing race and o rings on shaft. Next install new seals and bearings in housing. Slip the wear sleeve into the bearing then screw bearing housing into the shaft and thread it into the hosting bore.

Install prop. Then I pull the bleed screw and pump until clean grease is there and re install lower unit and prop.




Sent from my iPhone using Tapatalk

Thanks Maxx. I think I just may be able to do this with your instructions.