Hello I'm looking to identify my trans that are in my boat. They are attached to Detroit engines. Only numbers I can find on them are 9873b. Need to know what kind of oil goes in them.

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Don't hold me to this.... I've only worked on a couple. But "most of the gears" on the old detroits were Allison disc gears. Those units used the same oil as the engines. VERIFY this before you do it.  Also if you are losing gear pressure and it's an allison, there is a screen for the gear oil located on the Left top side with a large oil line attached. 3 bolts undo the cap, check the screen, make a new gasket and reinstall.   Lee

This site is great. Thank you. I'll look tonight.

I think the Allisons were on the 8V-71 and up engines.

Most of the 8v53 engines had the Twin Disc MG-506. I think this was because of the 8V53 not being offered in reverse rotation like all of the other Detroits.

The oil is specified as SAE 30w. CC or CD. Mutli-weight oils are not recommended.

Lee's advice about the filter screen and oil is correct.

Picture = 1000 words...more or less. ;-)

Absolutely right. I'm still figuring out how to post pics. I can't thank everybody enough


Just above the reply text box, there are some tiny icons. The first one is Link, the second one is for  pix.

Here are pictures from my transmissions


Definitely not an Allison...either way, that's one ugly duckling of a marine gear. Definitely no Michelangelos working in that engineering department.  lol

The transmission is a Twin Disc Mg 506 with a ratio of 1.93 to 1. The oil is Chevron Delo 100 30 weight. Which may be no longer available. Compare those specs to Texaco's  which is part of the same company. Minimum oil pressure is 300# at idle and minimum at cruising is 270#. Oil capacity is 1.2 gals. Check oil when idling in neutral.

I have noticed a whining noise once the trans is up to temp and I switch from forward to netruel. It lasts for 20 sec and goes away. Oil is good. Pressure is at 300. I'm thinking about a clogged screen. Am I on the right track?
Jerome Rahrig said:

The transmission is a Twin Disc Mg 506 with a ratio of 1.93 to 1. The oil is Chevron Delo 100 30 weight. Which may be no longer available. Compare those specs to Texaco's  which is part of the same company. Minimum oil pressure is 300# at idle and minimum at cruising is 270#. Oil capacity is 1.2 gals. Check oil when idling in neutral.

Sebastian My Twin Disc manual is in the boat 220 miles away. I'll be there late Thursday and look to see what it could be. I'm not on the site that often. I'll let you know what I find out. Jerome


Your idle oil pressure seems correct and if the "issue" only occurs when shifting from forward to neutral at idle, this has me thinking that it might not neccassrily be a problem. When you say a whine you didn't say how loud. Assuming that the whine is not very load in relation to the rest of the transmission noise at idle, it is very likely a normal situation. What you need to consider in troubleshooting this is that this is a wet disc clutch transmission. This means that when the clutch pack, which is made of several sintered bronze discs and steel drive plates forming the clutch pack, is compressed by a hydraulic piston when engaged. When you shift to neutral, the piston pressure is bled off and the clutches start to float. When the clutch discs are under pressure the oil is eventually forced out of the clutch pack until full engagement is reached. When you shift to neutral,the disc surfaces do rub lightly with the drive plates until the oil accumulates on the clutch discs and everything just kind of floats separated by an oil film. During this short time interval, there will be a certain amount of whine, until the discs are in full float. You should have the same noise when shifting from forward to neutral as when shifting reverse to neutral since the clutch packs are similar. Port and stb should also sound similar when shifted. If this is not happening and there is a distinct difference in sound between the two transmissions, then it is likely that the piston on the forward clutch pack is starting to exhibit signs of wear. What happens is that the piston slides inside of the clutch pack housing, the ID bore that rides inside of the clutch pack will wallow out slightly as it wears and causes slight jamming. The first sign is a longer release time and potentially a slightly louder whine during disengagement of the clutch pack. This condition can go for quite a while until eventually the piston might start to stick. This will also mean that occasionally that the clutch pack will hang in neutral for several seconds or engaged for several seconds.

If the whine is somewhat rough sounding and does not go away when in neutral and or reverse but is continuous until the transmission is put into forward, then you would probably have a bad bearing on the forward clutch. Bottom line if you have a bad bearing, you need to rebuild the transmission very soon. If it just a worn piston, then this condition could be tolerated for several hundred hours or more without damaging any of the transmission internals. It would help if you made a sound recording of the whine so that we can determine if it truly is clutch noise, gear noise, or bearing noise.

I've included the MG506 manual set in pdf for you.


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