These questions come up every once in awhile:
What brand do I have:
Rounded upper with fin with hole DANA
Rounded upper with a chunk no hole DANA
Flat upper CHRYSLER DRIVE 90 and replacement housings
What model do I have:
Straight output shaft takes outdrive style props, SHIFT IN OUTDRIVE - MODEL 80
As above WITHOUT SHIFT IN OUTDRIVE - MODEL 81
Tapered output shaft takes inboard style prop, SHIFT IN OUTDRIVE - MODEL 90
As above WITHOUT SHIFT IN OUTDRIVE - MODEL 91
All the CHRYSLER units that I've seen were model 80 internal configuration.
In addition Model 81/91 came in 2 configurations:
R/R L/L and R/L L/R (engine/ outdrive) rotations.
There were 2 gear ratios available but unless you have a 440 its not an issue.
THE INTERNAL DIMENSIONS OF THESE CASES IS IDENTICAL AND ANY PARTS CONFIGURATION WILL FIT IN ANY CASE.
Clutch pump oil pressure. 300 psi +/- 25 psi. If you get a junk yard or GM replacement pump swap out the reservoir which has the heat exchanger built in and also the relief valve which has the proper spring to provide the 300 psi. Same rules apply if your boat was equipped with the Chrysler pump (rare)
They also built a model 60 but I have never seen one.
They built a few units where the bellows had a protector over it. I have only seen 2 of these.
These units were some of the toughest outdrives ever built. The reason they shift so smooth is the hydraulic clutch mechanism on the engine. If this is maintained properly these units will last forever.
Filling with oil. These units tend to get air locked and can fool you into thinking they are full. Operate them in foreward and reverse and check. These units hold 8 quarts of oil. If you have the extended length version they hold 9 1/2. Remove a capscrew out of the top of the shift lever cover when oil comes out you have the proper level. DON'T forget to put it back. Do not overfill because expansion can force out the top seal.
Hard shifting or clunking when shifting. hydraulic clutch not working - clutch plate stuck to flywheel.
Won't go into Foreward/Reverse. Springs or cotter pins in intermediate shift link missing or broken. (sometimes called shift assist link or shift booster) Note: make sure you use stainless cotters and springs for replacements.
No drive. splines stripped off primary shaft on clutch plate end. Always use spline grease or moly when installing the outdrive.
Rattling when turning. U joint shot. Look for same size Chevy joint, a lot cheaper.
Won't stay in gear or skips. Adjustment if your lucky, if your not Nubs are worn on clutch dog and gears.
Don't tell any body but these can be tig welded up and reground. Use something that comes out to about 50 rockwell hardness and grind to a 3 degree positive rake. Look in the yellow pages for CUTTER GRINDER SERVICE to do the grinding.
Marysville Marine in Marysville Michigan is a good source for help on these units as is Marine Parts.com The other Marysville Marine locations don't know these units exist.
Marine Parts.com for parts and manuals
If you get in trouble I have installation information with adjustment dimentions. However it will pay you to buy a manual..