Occasional transmission noise while steaming

[noworries]

Our boat has the M35 engine.  Occasionally when underway there will be a loud noise from the tranny.  It's hard to describe but kind of like the noise you would make if you had something caught in your throat.  It's a lower frequency grinding type noise... not a whine.  When this happens I kill the throttle and it goes away, then I bring it back up and it's fine.

This happened 2-3 times on a 30NM cruise under power.  When I arrived I checked the tranny oil and the dipstick was dry.  So I added oil to get it up to the proper level.  On the way home it only did it once, but I was hoping for none.

Anything I should do or be worried about?

Boat is overpropped and cruises at 6.5-7 knots in good conditions at 1500 RPM.  I know I need to address the prop issue and it's on my list... but my list keeps growing.  Had the damn jabsco macerator fail (the 4 little bolts that hold it together rust out and then the pump comes apart, dumping crap in the bilge--UGH) so that's getting swapped out as soon as the new shurflo pump arrives.  That only leaves 2 pumps left on the boat I haven't replaced... the water and bilge.

[Ken Juul]

I know it is a fairly new boat to you.  Have you previosly checked the trans oil level? 

If yes, and it was ok, then the first step is to figure out where it leaked.  Only a few places; input & output shaft seals, shift shaft seal, drain (probable source)/fill plugs, and or any gaskets where the case goes together. 

If no, it is normal for a small amount of leakage from all the shaft seals.  With normal servicing, not a problem.  Over time it drained the trans.

Condition 1, fix asap, see flushing procedures below.

Condition 2, fill the trans to max, rotate the shaft a couple revolutions, then drain.  Repeat, this will get any friction plate residue out of the trans.  Use a new crush washer on the drain bolt.  Refill to normal level.  Clean the exterior and shaft area well.  Use the boat monitoring the trans to figure out where the leak is.

[Steve Sayian]

I had an situation on my previous C-30 where the transmission dip stick vent hole on the top of the hex head had clogged which caused an overpressure in the transmission case and the fluid was pushed through the shifter lever seal.
Once I figured out the problem, no more leak.  Might want to give that a check.

[Ron Hill]

No : To properly check your transmission dip stick - remember there are 2 holes that should be open. 
One in the hex nut head and one in the top of the dip stick just under the threads.

If you drain the transmission from the bottom - remember that the Al washer is a one time crush washer. 

A few thoughts

[noworries]

I never checked it since we bought it.  I'll check it again next time I'm down there.  Assuming it's not leaking, I guess I should try flushing it as you described?  When I checked the fluid I just used the dipstick, I didn't see any mention in the manual about opening a second bolt somewhere?

The boat sat for probably 2 years so that may be why it's dry?

[Ron Hill]

No : I never use the bottom drain plug as it's easier to suck out the fluid from the top hole that has the dip stick -- then refill to correct level. 

I'd recommend that you change the fluid.  The normal maintenance for a boat that's in storage for over 6 months is to fill the transmission all the way full (per owners manual).

[scotty]

The "turkey baster" method works really well for filling or changing tranny fluid.  I just did it and it was amazingly easy!  It's on the website on the forum http://c34.org/bbs/index.php/topic,5757.0.html
and also on the FAQ section
http://www.c34.org/faq-pages/faq-transmission-oil.html