Transmission clunks in gear?

[Escapade]

Running a 05, 390 dancer w/ 8.1 gas in fresh cold water Lake Michigan. Just hit 1000 hours. I have always heard a clunk when shifting in to gear. It seams the clunk is louder then normal. I'm high and dry now but, want to do all I can prior to next season. It shifts great. Runs well No other symptoms.
I did not check fluid levels at haul out. Mid Season was fine. Will change fluid and the filters.
Could this clunk be dampening plates springs over time loosing tension? Maybe mount pads loosen up? Anyone gone through this?

 

[JimG]

Did you check your idle RPM? Should be around 600...

 

[Escapade]

The idle speed is 650- 660. Years back I've had it drop below 650 and got clicking before it shifted. The plugs were fouled. Replaced plugs, idle speed back back and clicking gone. This is a thud. a single thud. Does it for Port and Starboard.

 

[Island Time Buffalo]

May be unrelated, but I have clunking into gear as well, especially reverse. In my case I also have slippage at high rpms and have a tranny replacement scheduled for this winter. Hopefully you are not in the same situation. But if it's happening on both tranny's it may be "normal ....ish" for the age.

I know it's not preferred, but you could try changing the fluid with the high-mileage type with leak sealants and see if it changes the symptoms.

 

[Escapade]

What identified the Slippage at High RPM. I cant say I have ever come across slippage to know any better.

 

[ttmott]

Does your engine to transmission coupler have rubber dampers?
If so they may have failed.

 

[LG111]

It's the dampener. I lost my port zf gear this Summer. The new one and new dampener now makes that clunk. Kinda like an outdrive. It's not hurting a thing. Some do it, some don't.

 

[cfd95]

Could be the damper springs are worn or the splines on the coupler are worn.
Did you check the cutlass bearing too
I have a knocking noise on the starboard trans at an idle that goes away when i raise the rpm's
I'm suspecting a broken spring on mine.
There is no rubber in the coupler
You can probably pull the starter and rotate the engine with a breaker bar and look in the starter hole at the springs.
The ZF Hurth trans uses its own coupler plate which is expensive i've found them new for $700

 

[Escapade]

I will have mechanic check transmission coupler rubber dampers. Thanks for all the input.

Mike

 

[Island Time Buffalo]

What identified the Slippage at High RPM. I cant say I have ever come across slippage to know any better.

When pushing the throttles up, once it hit approximately 3200 rpms, it would (1) shudder a lot, (2) make a rumbling noise while shuddering, (3) the rpms would shoot up about 300-400 ticks, and (4) immediately l could feel momentum slide off. The rpms jumping is the biggest clue that it's slipping. I had to isolate the engines to identify that it was port.

In my case the previous owner had this unit rebuilt for the same issue. I think there is an issue with the core, this time I sourced a brand new unit in Michigan.

 

[FootballFan]

If a dampener is failing most of the time you will see a rubber dust in the bilge around where the transmission mates with the engine.

I have had it occur before - did not have a "clunking".

Seem to remember a friend had a similar symptom a year or so ago on a gas motor - turned out to be plugs/wires - something along that line. Was not a transmission or dampener issue.

 

[Escapade]

No symptoms of slippage. I will check under trans / engine mate to see if I can find any rubber.

 

[FootballFan]

My experience with adapter failure: may be isolated.

First started seeing a fine black powder around the area of the transmission. Watching it, over the next 20-40 hours of run time, powder got heavier, then tiny particles, bigger than the dust. A few almost to the size of pencil lead.

Never experienced any symptoms related to performance or shifting in and out of gear.

Mark