Velvet Drive chatter in neutral

[tomschauer]

Hello, just di a sea trial on a 1998 355 today. Motors ran great, greats shift quickly and smoothly. The starboard trans has some chatter only in neutral, port is quiet. Engines and gears only have about 230 hours.
Does anyone have any experience with these Borg Warner gears?

Any help would be appreciated.
Thanks
Tom

[Viper]

Are they EFI engines? What RPM are they running at idle? Too low can cause a chatter. If the engine isn't tuned properly, it could cause a chatter in the tranny. You may not notice a dead cylinder while the engine is running, but the imbalance will cause a jerking action that will transferr to the tranny resulting in gear chatter. I assume you've checked the fluid level and condition of the fluid. Is it clear or burnt? Is it the recommended fluid?

[tomschauer]

Viper, they are 7.4 mpi merc's. standard 320hp's. They run smooth and quiet at idle, and pulled to 4400 rpm without issue, cruised at about 3300 for 20 minutes, sound great.
Fluid looks clean and clear dextron. No noise in either forward or reverse, just neutral?

[tomschauer]

Idle about 700 per tach.

[Lyndon670]

The tacs are never really "accurate". Sounds to me like the issue is that the idle is just below the sweet spot and should be turned up marginally. The 502's in my Silverton were both like that when I bought it and bumping the rpms up a touch is all that was required.

[mjk1040]

Our 1998 has 7.4 Crusaders EFI's, and u have to clean the throttle bodies occasionally, I think its the throttle positioning sensor that gets gummed up causing idle issues which could be the cause of the improper idle speed. I've seen this same problem in others boats, they paid big bucks to change out the tranny's only to find out that a rough running engine was causing all noise problems in their transmissions. Our mechanic has been in this 30/+ years and his knowledge is invaluable. He said that almost all these tranny's are almost bullet proof. I'd tend to agree with all the other's input here, to make sure check engines are running smoothly at idle and rpm's are in the sweet spot before suspecting the tranny. Hopefully it's something simple. Please let us know what you find out. Mike

[Viper]

Source of the post Viper, they are 7.4 mpi merc's. standard 320hp's. They run smooth and quiet at idle, and pulled to 4400 rpm without issue, cruised at about 3300 for 20 minutes, sound great.
Fluid looks clean and clear dextron. No noise in either forward or reverse, just neutral?

I am still leaning toward an engine related issue rather than a tranny one. Will the tranny rattle as you increase rpm in neutral? When was the last time the engines were serviced, a tune-up done, etc.? Does the engine hunt at idle by any chance (rpm up and down)? Have you started her up cold or was she warmed up just before you arrived for the sea trial (old trick)? A tip to potential purchasers; tell the seller prior to the sea trial date that you do not want them to warm up the engines prior to your arrival. Then for assurance, as soon as you get on board, feel the engines to ensure they are not warm prior to starting them. If they ignored your request and you find them warm anyway, walk away and book another sea trial date with a warning not to warm them up again next time. They may be trying to hide something.

Along with the TPS noted above, IACs cause idle issues also, sometimes undetectable by ear. The little idle air filters in these are also know to cause problems (if it's even there anymore). I'd get a tech to hook up Merc's diagnostic software to see if it pulls any useful info including stored faults. While there, they can perform a couple of tests including a cylinder drop test.

This could be anything from something as simple as a little filter to something more complex like an injector or worse. It's not impossible for it to be a tranny issue but chances are it's not. In any case, you must rule out the engine first.

[tomschauer]

Thanks for the tips. The boat was "really cold" when I got there. I actually hadn't been run in over two years. we pumped out the old gas and put in new gas and filters. They seemed to run smooth at idle, quiet, no "jumping" around like a miss. Trans was quiet until after it ran an hour or so. Who knows, maybe the new gas sloshing around the tanks stirred up some gum and such? I will dig a bit deeper. I didn't think a rough idle could cause noise at the output of a hydraulic tranny.
Thanks for your help.

[Viper]

Actually, I forgot to mention above that I though the hours were kind of low for that age of boat. Depending on the circumstances, this is usually a red flag for me. While low hours may seem beneficial, engines like/need to be run to prevent some negative effects of being laid up for extended periods. Nothing worse for an engine than not being run, that's why so many owners have genny issues. If they just run them every week for a while, they'd run better for many years. Along with the engine itself, there are other concerns such as the one you've mentioned from non-use. While the fuel can be easily pumped out, it's harder to get rid of the junk old fuel leaves behind.

By the way, are you sure it's the tranny rattling and not the engine's flex plate? It's an easy oversight because of their proximity to each other.

[tomschauer]

Viper, I am not 100% certain its not the plate, but it really seems as the noise is coming from the "tail" of the trans.