Since the serial numbers on Merc drives are decals...it's easy to have several different Bravo I upper and lower units that are tough to tell apart unless you KNOW...and I don't. I purchased 2: uppers and a lower on the Swap Shop ( another total fiasco story) here earlier this year and nothing matches up. Seems that I have 1: early upper with pressed gears and another with threaded gears. Neither match up with the lower I have which doesn't have the matching oil drain hole. Has any one ever read anything that explains the differences, what to look for and what matches up with what? I totally trust the guys that I am working with now but I want to educate myself as to what the design change process was on Bravo Drives for the first 10 years anyway. I am listening to explanations about what is compatible with what and I might as well be listening to Chinese.

Now...what I think I know is that the Bravo was introduced in '88 and modified in '92 and again in 2002?. The '88~'91 drives did not share drive oil between upper and lower gear cases...everything '92 and later did. A '92 and later lower gear case cannot be used on an earlier ('88~91) upper gear case unless the oil drain hole at the to p of the newer lower is plugged. An early pre '92 lower can only be used with an upper gear case earlier than '92...period. Now I'm not sure...but I'm thinking that the press in upper main gear was used in '88~'91 and it was threaded after that. The '92 and later gear design is stronger.

Is there someone here that can explain this to me in any more detail or send me to a source that I can read and understand?

Thanks in advance.

Damn...I stumped the Forum!!

Where did you hear that the 88-91 don't share oil between the upper and lower? I have a drive that falls into the category, it most certainly does share oil between the two.

I think the early ones don't use an external reservoir but they do share oil between upper and lower

Some guy at the marina...I asked how is that possible? the answer was because the early ones don't have the drain hole.

That.s why I'm asking. Also...some shops won't take pre '95 uppers or lowers for an exchange core because they are obsolete.... so I am trying to get some input here.

i believe the 89 was the only one without the oil hole,send a pm to mr gadgers,im sure he knows the answer and will help you in any way he can.

This should help with some of your older questions for identification purposes,
http://www.boatfix.com/merc/Bullet/91/91_20.pdf

Along with pages 3A-10 through 3A-16,
http://www.boatfix.com/merc/Servmanl/11/11a3r5x.pdf

For the newer drives, you should be able to find updated info in an mercruiser service manual #39 i believe in and around the same pages as service manual #11 linked above.

If you don't have #39, try googling it, i believe it's out there somewhere on the internet at one time or another.

Hope this helps, Good luck.

THIS is exactly what I was looking for... thank you!!

I have an 88 Baja and it doesn't have the drain holes and external reservoir. And i've seen other 88 Baja's that do have the external reservoir. I was told it was only the first of the first Bravo's that didn't have the reservoir. Consider it a defect. Without the reservoir the drives tend the seap oil and suck in water with excessive expansion and contraction due to heat.

I understand...according to Mercruiser...

A. BRAVO DRIVE UNIT/HOUSING COMPARISON AND IDENTIFICATION
Models
MCM 5.7L/7.4L/454Mag/502Mag/HP465/HP525SC/D183 Turbo/D219 Turbo/D254 Turbo
Changes
The latest production and service replacement housings will have an internal casting change to allow for an
oil recirculation system on all 1991 and newer Bravo drive units, both Bravo one and Bravo Two models. The
oil recirculation system is unique in that it causes the oil to flow from the lower gear case up through the driveshaft
housing to the universal joint pinion gear bearing set. Oil also pumps up into the top cover and returns
to the lower gear case from the back side of the drive shaft housing, through the lower drive shaft needle bearing
to the gear case. Besides improving lubrication this oil movement helps the drive unit run cooler.

This is very helpful when shopping around for these drives.