Identify That Drive at Sterndrives.Com

With many different models and changes it's important to get the right parts for the right unit.

"R" or #1 Drive

The "R" drive is also known as a #1 (number one) drive.
It is often referred to as a "Pre-Alpha" drive as it was made
before the newer Alpha One Drive.

The Older style of the the "R" drive is evidenced by several things.
1. Crowned, rounded driveshaft housing where the unit mates to the bellhousing.
2. Rear end of cavitation plate is rounded off.
3. Ribs on sides of driveshaft housing.
4. Top cap has a lifting ring.
5. Pre-load pin on top of lower driveshaft.

 This is a typical R Drive shaft housing assembly
"R" Style Driveshaft Housing

Not ALL "R" drives will have the lifting ring on the top cap.
It MAY be that someone fitted a newer style cap to the "R" drive!

The BEST way to I.D. the drive is to remove the upper from the lower and
inspect the top of the lower driveshaft.

 See the pin? Then it's an R Drive!

If the shaft has a pre-load pin at the top then the
LOWER gearhousing is definatly an "R" Style.
Notice that I said the "LOWER" gearhousing is an "R" Style?
That's because you COULD have an Alpha Upper bolted to an "R" lower!
Yep, the Alpha Lower will bolt to the "R" upper as well an
"R" Lower will bolt to an Alpha upper.
See, there is really no difference between the guts of an Alpha and "R" upper.
The REAL difference is in the Lower Gear Case Assemblies.

The "R" Lower had the gear teeth at a different angle and the driveshaft bearing set up
was such that it required the pre-load pin.
This worked OK for years but Mercruiser found a stronger method of design.

Really, it doesn't make sense to even buy an "R" lower any more.
If you have an "R" and need a new lower then you might as well get the
stronger and newer Alpha Lower.
If you need to have your "R" rebuilt then you MUST use "R" parts.

Important! The water pump base is NOT the same as an Alpha!
We always reccommend

Please Email us at
Back to the Index Page