I have standard Bravo 1s with IMCO shorties on my 2000 Fountain Lightning. I'm a stickler for maintenance and almost seasonally I open them up, replace what's needed. They've both had gears, shafts, etc. I started with a problem 2 seasons ago, the starboard drive pushed the pinion seal (I think it may be called a driveshaft seal) out, and filled the bellows and then the bilge. My mechanic replaced the seal with the "new" style seal. Lasted 30-40 hours, and happened again the beginning of this season. Once again had it replaced and watched him do it. No funny business, I saw a new seal, saw it drove in place, etc. Did it for a second time this season, same solution and it's held so far. In my mind I figured that possibly the case, and the area that the seal sat, may have been out of spec from the numerous rebuilds and that maybe this wasn't allowing the seals to stay put. That train of thought lasted until my port drive did it all of the sudden at the end of this season. What gives? I don't have reason to believe that run hot, or that gear lash is wrong, or that bearings are bad... everything I "think" is pretty damn good. It's beyond frustrating. Any ideas? Words of wisdom?

BTW: Run the Merc Hi Perf fluid, nothing but Merc parts in rebuilds, and just standard 500EFIs

Verify that you have pinion bearing preload. No preload can let the pinion wobble inside the seal.

I think somebody makes a seal retainer (the part the seal presses into) that has a flange to keep the seal from moving. Shouldn't be necessary but a nice add.
Have the input shaft (seal area) flamesprayed with ceramic. Install a new seal.
Done

Sounds like you have the old style retainer. The new version has a lip on it so the seal can't come out. Mercury part number 841026A2

Marc, he mentioned B1's, we have to assume it is the old style retainer and seal. That part number is for the X - XR case, which wouldn't fit in the standard B1. Not trying to step on anyone here..
My question would be, how easy did the seal press in? Was the seal staked after if was installed? Shouldn't need it but sometimes it helps. Was red loctite used on the edge of the seal? How much heat is the drive seeing. Heat makes pressure that could push the seal out. No mention of drive showers.
Just some thoughts, hopefully they help??
I think there are some aftermarket retainers with the lip for the standard B1, but I have never had to use them to solve a seal problem.

Dick

Oops - I missed the B1 part. Geez I have never seen that happen on a B1

Maybe you just need to clean valves , rubber hose and plastic canister for oil . That is what i usualy find as a problem . Oil somehow fills the sterndrive up to the top but when it gets warm oil needs space to expand , and since it cant expand so fast to canister it pushes u-joint seal out and u-joint cuts the seal .

I thought that was what happened, Marc. I spotted the B1 and like you say, not very often that seal is an issue. I did have one that didnt press in very tightly, so I replaced the retainer.

As babalu said, does the canister drain when you drain the drive? Could be a blockage in that system, causing pressure in the drive.
What process do you use to fill the drive, that air space is needed in the top of the drive.

Thank you guys for the responses. As best I know, the valve that closes when the drive is removed works properly. When I push on it, fluid leaks out, when I let go it seals up. I do run drive showers, just standard IMCO units. I don't have any reason to believe the drives are getting very hot, they seem to turn over well by hand, I assume are shimmed and setup properly, etc. Whenever I've watched my mechanic fill the drive he pumps the unit full through the drain in the carrier, then tops the bottles off.

Clean valves , rubber hose and plastic canister for oil , and you should be ok . Bravo drives are bit dirty , they like to make some dirt ( oil becomes greasy ).

When I fill a drive, I fill it until I see it come out of the top plug. I then put the plug in and continue to fill it until I see it come into the bottom of the bottle. I let it equalize and put the bottom plug in and then top off the bottle. I run it and check the level several times until the level stabilizes..