I own a 1993 370 searay express...

[jimromer]

I own a 1993 370 searay express cruiser. With two 7.4L MerCruiser engines. Heard rattling type noise. My mechanic said "tranny" and friend said replace "damper plate" also. Mechanic fully agreed. So I did and even purchased a new tranny ( not rebuilt). After many of labor we started engine and the same noise was present. In order to eliminate the noise you have to push the idle to.900 rpm. Nothing changed I could have eliminated sound before I did repair by increasing idle speed. Noise still present with a new tranny and damper plate. Any suggestions. Would anyone have an idea on the amount of labor hours involved in doing entire job from damper plate back?

Thank you.

Jim

[wingless]

The damper plate idle rattle is a known issue.

The transmission fluid can improve the condition, as shown in this service bulletin. This suggests swapping from Dexron 3 transmission fluid to 15W40 motor oil.

https://teamtalk.mastercraft.com/attachment.php?attachmentid=95164&d=1368844409

If I were to do that swap then my five zone high volume / high pressure oil change system would be very useful, as my installation included replacement of the transmission drain plug w/ a hose barb, to suck from the bottom of the transmission sump.

https://live.staticflickr.com/4745/40465168062_560799e07e_c.jpg

My suggestion would be to not turn another bolt for this "issue". According to the linked service bulletin: "Although the noise can be irritating, this is a normal condition with these transmissions that in no way affects the durability or reliability of the unit."

[Bow_Tie]

Damper plate as Wingless stated. Leave it alone and enjoy the boat. I had a 370 EC years ago, same issue, I had the boat 8 years and never did anything about it and never changed anything, know issue on the Velvet Drive Borg Warner.

[Bow_Tie]

Known issue.