Gearbox question - advice please.

[asteven221]

I have a pair of Twindisc gearboxes on Volvo TAMD61A 306hp engines. One blew up about three years ago which I replaced with a new one at great expense and hard work!! They seem to be working fine, except I have noticed they make quite a loud grumbling noise in reverse when they are hot. When cold and reversing out my berth I can't say I have noticed any noise, but on return I definately notice it - even on the flybridge. I have never really bothered about this before, but now I am wondering if this is actually normal or not. Unfortunately I can't recall how long this noise has been going on, or even if one made the noise before the other. The only way I can describe the noise is it sounds like the kind of grumbling you get when there is no lubrication in ball bearings. My thoughts are maybe it's caused by the oil thinning when hot. I am using the oil recommended by the manufacturer which is SAE30CD, however it's from a wholesaler who assures me it's the correct specification. Should I change to say Volvo oil to be on the safe side? I appreciate anyones advice who has experience of marine transmissions. Maybe I am concerned about nothing. Thanks.

 

[volvopaul]

Dont bother with volvo oil ,my mate has an oil company and refines his own, he had there oils checked and at that time they were buying gulf oil, he said it was cheap and nasty.
Volvo dont market sea 30 if I can remember correctly, any 30 grade will do the job, what boat do you have? as some lightweight boats like a princess the twin discs will last years on the other hand if its in a heavy displacement or semi then they do tend to make noises after a few years, also the drive coupling do make a chattering sound, check engine alignment and shaft coupling and bolts for distortion, as years get on the rear engine mount will sagg this puts pressure on the shaft, stern gear, cutlass bearings which in turn puts pressure on the rear gearbox bearing.
Some years back I had to fit a new cutlass bearing on an old princess 385 with volvo 61a in, to get the prop off I had to slide the shaft back with meant disconnecting the coupling bolts at the rear of the gearbox as soon as the shfaft slid back the engine dropped nearly half an inch.
Problem sorted by realignment of mounts etc.

 

[asteven221]

Thanks for the advice volvopaul. I called the Twindisc distributers where I bought the recent gearbox from. The chap there was very helpful and made some suggestions to try and isolate the problem. From what he said it doesn't sound too sinister and seems to echo what you have said.
Thanks again.