1984 Gulfstar 49 trans iissue

[kreagsman]

So bought the boat a few months ago and just now getting to take it out. 6V71 Detroit’s have 1200hr and 1100 hrs. Smokes bad but cleans up after warmup. Treated the fuel with Lucas fuel treatment. Had issue with starboard engine cutting out but think it is getting better. Transmission initially worked fine but after a hour or so it seems to not engage fully or slipping in forward. Reverse seems fine. Not familiar with this trans so am needing some advise. The transmissions were serviced a few months before I bought boat. It shifted fine and all when we left marina but when engine started cutting out on me I ran engine (starboard) for a while without trans in gear to try and get the Lucas worked through which seemed to help as engine started running better but when I went to engage that trans in forward to help with navigation it didn’t seem to engage or seemed like it was slipping which is a definite after more testing. Don’t works fine in reverse but doesn’t lock up in forward. The prop shaft turns but is like half speed of the port engine. Is my linkage out of adjustment or help me understand the process. I am a diesel mechanic for years. Heavy equipment and trucks. Rebuild JD power shift. Alison. So not ignorant of hyd systems but am not at all familiar with this transmissionnnor do I know what brand or model. Any help would be greatly appreciated. Thanks Adam

 

[Comodave]

If you don’t know what model the transmission is it will be very difficult to give advice. There is usually a plate with the manufacturer, model and gear ratio on the transmission. See if there is one.

 

[kreagsman]

I have been doing more research and think it is Alison MGear. Maybe a 20. 2:1 ratio
I think it is curious that I lost forward but reverse is good but maybe not uncommon. More research. Thanks

 

[kreagsman]

Hey guys here is a pic of the port engine transmission plate. Like I said I am very unfamiliar with these so any help identifying this is appreciated. Remember I lost forward gear but reverse works. The oil is black. Could it be as simple as strainer screen? Prolly not since reverse works. Any ideas? Thanks

 

[Comodave]

Can you clean up the data plate and get a better photo of it. I can’t read it, but my eyes aren’t that great…

 

[kreagsman]

Let me try and blow it up. I am no longer on the boat and it was very hard to get in to see this much. It is a M20L which I assume the L means left gear. So the PO had oil changed and filter in gear before I bought. The oil level with engine idle is slight over full like 1/4 in. When I initially started up and did warmup on both engines we left marina and all went well for 15 minutes the starboard engine stalled. I restarted and it stalled again. Since they haven’t been run in a while I assume it needed some major run time and the only option I had since we were on the Cumberland was to keep the engines going and make our way up river which was working ok. I kept starting starboard engine and after a while of running it at different rpm’s decided to put gear in forward again and did so noticed it did not seem like it was pulling equal with port. We came to conclusion that it was slipping and ended up shutting that engine down. We used port engine and made our way to Nashville and spent night at dock there and in morning headed back downstream. We got boat back in slip and this is where that story ends. Looking for advise on possible problems other then a complete rebuild. Thanks again appreciate any help. Adam

 

[Deano]

I had an issue with a twin disc. Search my posts for twin disc shifting issues. The fix was easy.

 

[heysteve]

Consider joining BoatDiesel.com as they have a section dedicated to Allison transmissions. I looked briefly and in response to a shifting issue one poster suggested calling Acadian Marine Transmission in Broussard, LA. No experience with them... just passing on the info.

 

[divert00]

So bought the boat a few months ago and just now getting to take it out. 6V71 Detroit’s have 1200hr and 1100 hrs. Smokes bad but cleans up after warmup. Treated the fuel with Lucas fuel treatment. Had issue with starboard engine cutting out but think it is getting better. Transmission initially worked fine but after a hour or so it seems to not engage fully or slipping in forward. Reverse seems fine. Not familiar with this trans so am needing some advise. The transmissions were serviced a few months before I bought boat. It shifted fine and all when we left marina but when engine started cutting out on me I ran engine (starboard) for a while without trans in gear to try and get the Lucas worked through which seemed to help as engine started running better but when I went to engage that trans in forward to help with navigation it didn’t seem to engage or seemed like it was slipping which is a definite after more testing. Don’t works fine in reverse but doesn’t lock up in forward. The prop shaft turns but is like half speed of the port engine. Is my linkage out of adjustment or help me understand the process. I am a diesel mechanic for years. Heavy equipment and trucks. Rebuild JD power shift. Alison. So not ignorant of hyd systems but am not at all familiar with this transmissionnnor do I know what brand or model. Any help would be greatly appreciated. Thanks Adam

Easy stuff first. Remove linkage at transmission and shift by hand and test tranny to see if linkage needs adjustment. You mentioned oil is black. This should not be. Dirty oil fouls the strainer and reduces pump effectiveness. Flush and fill tranny with fresh oil and test for tranny improvement. If oil turns black again you’ve got a problem with contaminaton of the tranny oil (likely engine oil).