Hurth transmission issue

[Helmsman]

I have a 2006 Hurth ZF 63 A - 2.7 transmission. I have a strong vibration that occurs when accelerating which continues at a lower rate when at speed. When I checked under the transmission, I noticed a few water drips underneath where the prop shaft leaves the boat.

I had to change out the heat exchanger on that transmission last fall. I don't think it has anything to do with the problem, but there was two small pools of transmission fluid on the bilge prior to taking it out the last time. When I brought it back in, there wasn't any on the floor.

Any ideas on what might be causing the vibration and the water leak?

[Viper]

Sounds more like an alignment issue than a tranny one. Did this just start or has it been like that for a while?

What type of shaft logs do you have? regular flax packing log or a dripless type? While the flax type are meant to drip a bit, it will drip more with a bad alignment. A bad alignment can also cause a dripless shaft log to leak.

A bad alignment will cause vibration at different rpm depending on how bad it is. It may also be a prop that needs to be tuned or a bent shaft, both will also cause a vibration.

Since you're in the water (I assume), I would start by checking the alignment. Someone who knows what to look for can tell from the results whether it's an alignment issue, a bent shaft, warped coupler, or warped tranny flange. All the above are potential culprits as well as fouled props, bad strut bearings, bad strut alignment, etc.

[Helmsman]

It is a dripless I believe. I tried to post a picture but it was too big. Here is what I got from the Internet (if this works). I found it under a search for dripless shaft log. It looks like this.

I have a mechanic coming by to look at it. The vibration is real heavy under acceleration load, and then calms down though you can still here a rhythmic vibration at 2500 rpm's.

It may be the prop. I looked at it with a small underwater fishing video camera but couldn't tell much. Nothing obvious was wrapped around it.

Will let you know what we find. Thanks for the help!

[Helmsman]

File attached

[Helmsman]

By the way, in answer to your question I first noticed after taking the first trip this spring.

[Viper]

Those logs use o-rings. Barring everything else being okay, they will leak if there is a wobble resulting from anything mentioned above.

I'm assuming you get hauled out for the winter. Did you notice anything when you first put it in gear when you left the slip? Not uncommon for there to be a lot of debris in the water after the ice thaws out. The debris I'm talking about is stuff like large branches and wood blocking dropped in at haul out or launch. Have seen folks need to do prop repairs at the beginning of the season because of this. Not to throw anybody under the bus but if the haul out crew didn't place the aft sling in the right location and went too far aft, she may have been picked up by her shafts. Seen that happen before though it usually results in a more sever symptom than what you're describing.

[Helmsman]

Viper, I live on Lake Chickamauga and don't haul out. We never get ice in the river. Logs and other stuff yes. It certainly could have been something I hit or that came down river and damaged the prop. I will probably jump in and take a look under the boat to determine if it is damaged or has something wrapped around it. If instead it is the O Rings can those be changed in the water?

[g36]

Qr Bbpost Viper, I live on Lake Chickamauga

sorry to hijack but i also am on lake chickamauga at pine harbor didnt realize i had any carver friends so close

[Viper]

Qr Bbpost ......If instead it is the O Rings can those be changed in the water?

Depends on the type. I've done some in the water. Do you have a spare assembly already mounted further up the shaft? If not, it can be done but you'll need to remove the shaft out of the coupler. The safest way is to do it with a set of slings under the boat in case something goes wrong....you know...the perfect storm.

[Helmsman]

Viper,

the raw water hose was loose in a couple of places. Which we think accounted for the drips. I am going to go through the engine room to insure we don't have others loose today!

A friend of mine is a boat mechanic. He and I took it out for a run this morning.

He first thought the engine was missing under pressure. However, after a couple of times rapidly accelerating, he is pretty sure that the keyway on the prop is probably sheared causing the prop to slip. I dove and did a visual inspection of the prop. I didn't see any noticeable damage on the prop.

Our next move is to remove the prop in shallow water by his shop, if the 3/8 x 3 stainless steel key is damaged, put a new one in, but also take the prop to the local prop shop to check it while it is out.

The other possibility is the transmission, but he didn't notice any rotation problem on the shaft under pressure.

He checked the shaft to see if it was warped, and it had a very, very slight out of round, around a thousandth of an inch, which he said was not anything to be concerned about.

I also read that those dripless shafts seals should be replaced or re-furnished every six years. This is a 2006 boat, so when I pull for bottom paint later this year, I plan to have them re-done.

I will let you know what we find in case others experience the same problem.

If you or others have any thoughts on what I am describing, please feel free to comment. The more information and thoughts we have , the more we can check. Thanks for the help. It makes a real difference in gaining an understanding of the boat.