Volvo Penta SX clunk only in reverse (seperate from shift cable issue)

[Augoose]

At the end of last year, I started a thread under the same title. After a lengthy description, I received several suggestions of which all I followed during winterization this past winter (verify gear lube was/is not overfilled and ruled out shift cable issue).

I figured instead of reviving an old thread with several posts and conversations, I'd get straight to the point and talk about what I've done and what I'm experiencing.

My '99 SX-M drive clunks quite significantly but ONLY when going into reverse. Going into forward is silky smooth to the point you can't even tell if the lower unit is in gear or not until you throttle up and the boat actually moves.

In an attempt to isolate the problem, I've made the following observations:

1) At the lower unit, I removed the shift cable from the bellcrank slot so I could shift it manually. When on the muffs and running in the driveway, you can feel and hear a soft clunk only when going into reverse and manually rotating the eccentric pistol arm. The rpms are at about 650. The clunk is not bad at all, but noticeable when compared to the silence of shifting into forward.

2) Verified gear oil level - its high but not off the range area of the dipstick. Changed the lube over the winter and noticed no shavings or signs of water intrusion. Color was mostly green (same as when it went in) but had a little black to it as well - somewhat darker.

3) Today and when in the water and just coming down from speed (3,000 rpms sustained for about 5 minutes) I let the boat come to a stop and the idle to come down to about 650. I then tried to put the boat in reverse. The clunk was SIGNIFICANTLY louder and more aggressive (you can feel the shudder through the entire boat) than when I put the boat into reverse after letting it sit idling for about 3-4 minutes. The clunk when going into reverse after sitting for a few minutes is FAR less significant despite the rpm's still being at 650 in both cases. Why would that be?

I've done lots of searching and read threads where some folks say the clunk is normal while some say its not normal but the majority of threads deal with clunks while going into both forward AND reverse. I've found very few topics discussing a clunk only in reverse and none which deal with the clunk being MORE harsh shortly after running the boat at speed.

I took some video with my phone - not the best but I hope it helps describe what I'm talking about.

Here is the clunk when running on muffs - hardly noticeable. In the water its much more prevalent. However, you can tell the difference between reverse (early in video) and forward (later in video) - [video]https://onedrive.live.com/redir?resid=72FF8C9343022AF0!145&authkey=!ACKewFx__x_7gR4&ithint=video%2c.mp4[/video]

Sound and clunk after sitting idle for a bit - clunk not too bad - [video]https://onedrive.live.com/redir?resid=72FF8C9343022AF0!142&authkey=!AApbdMu4r-R1W7I&ithint=video%2c.mp4[/video]

Sound and clunk after running 3,000 rpm for 5 mins - pretty bad clunk and vibration - [video]https://onedrive.live.com/redir?resid=72FF8C9343022AF0!143&authkey=!ADUh6_d8CGAon_A&ithint=video%2c.mp4[/video]

Does anyone have a suggestion as to what else to check? Am I being overly paranoid? I keep expecting the shift into reverse to be as smooth as it is into forward. I'm also wondering why the clunk gets worse after running the boat, but then becomes less harsh after the boat idles for a few minutes.

 

[kelleyja]

Re: Volvo Penta SX clunk only in reverse (seperate from shift cable issue)

I have this issue as well. My clunk is in both directions, but reverse is slightly worse. On the muffs its barely noticeable but, you can hear/feel it in the water. The mating surfaces where the clutch engages are separate on the upper and lower output gear so it makes sense to me that they could wear differently and make different noise when engaging. Its annoying - I'm leaving mine as is until I have a winter to tear into the upper gear house.

Its odd that yours is louder when coming down from high RPM. It seems like it would be a gear oil issue since running it hard would heat up the oil and change its viscosity, then cooling it off for a few minutes would give it a chance to thicken again.

 

[skydiveD30571]

Re: Volvo Penta SX clunk only in reverse (seperate from shift cable issue)

I've had the "only in reverse" problem for a couple years now. Shifting forwards is almost inaudible, but reverse is pretty noticeably heard and felt. I've never paid attention to changes before and after running so I cannot comment on that. When I asked about it, Don S said basically the same thing as kelleyja...that parts can wear unevenly and make different noises in forward or reverse. It was his advice to not worry about it until there are obvious shifting issues. A couple years later and mine seems no different than when it first starting doing it, except I've gotten used to it and don't usually notice it anymore.

Out of curiosity, what gear lube and viscosity do you currently use?

 

[Augoose]

Re: Volvo Penta SX clunk only in reverse (seperate from shift cable issue)

Thanks for the reply's, starting to feel a little better about it. For lube I use west marine's synthetic 90w lower gear lube. Maybe I should try another brand?

 

[skydiveD30571]

Re: Volvo Penta SX clunk only in reverse (seperate from shift cable issue)

I've been using Amsoil 75-90 Marine Lube with good results. I honestly couldn't tell you for sure if it made a difference or not because I've learned to ignore the reverse clunk, but if I had to put money on it I'd say it did help a little. How much? Well that's anyone's guess. Not enough that I recommend a switch.

 

[Augoose]

Re: Volvo Penta SX clunk only in reverse (seperate from shift cable issue)

Thanks skydive. I'll try Amsoil next time I drain and refill. Not the first time I've heard positive things about it.