If you know the compatibility of your Johnson lower unit, there would be many advantages. In fact, having proper knowledge about it is a must at times. Starting from simple issues to a replacement, it is needed.
What Is Lower Unit?
ower unit is a component of an outboard motor. It is located at the bottom of the motor and houses the gears and bearings that transfer power from the engine to the propeller.
The lower unit also contains the water pump that circulates water through the engine to keep it cool. The Johnson lower unit is an essential part of the outboard motor and requires proper maintenance to ensure it operates correctly and efficiently.
So, What Is the Johnson Lower Unit Compatibility?
The Johnson lower unit compatibility goes with the Hp series, serial, drive shaft, and shift rod. The first series of each year goes with all Hp series except 6. And the rest goes with all except 10, 18, 20, and 25. But each series goes with a different sequence. So, the compatibility differs from one another.
You have come across a brief so far. Now, get into the detailed part that would cover your concern. We got here every detail.
So, get started now!
What Is The Johnson Lower Unit Compatibility?
To understand the compatibility of the Johnson lower unit, you must consider a few things. And those are the HP series, lower unit, drive shaft, and finally, shift rod.
Because without the compatibility, there would be many issues like Johnson fuel pump issues.
So, here we go with detailed compatibility of Johnson’s lower unit per year. Have a look-
1970
The lower unit of the year 1970 is compatible with all the HP series except 6. It would have the serial of 382574 or 390040.
The drive shaft and shift rod would be 381026 and 309582 respectively. However, the lower unit of 1970 has other compatibilities as well.
Like, some other versions are not compatible with 9.5,18, 20, and 25.
1971
The lower unit of the year 1971 is compatible with all the HP series except 6. It would have the serial of 382574 or 390040.
The drive shaft and shift rod would be 381026 and 309582 respectively. However, the lower unit of 1971 has other compatibilities as well.
Like, some other versions are not compatible with 9.5,18, 20, and 25.
1972
The lower unit of the year 1972 is compatible with all the HP series except 6. It would have a serial of 382574 or 390040.
The drive shaft and shift rod would be 381026 and 309582 respectively. However, the lower unit of 1972 has other compatibilities as well.
Like, some other versions are not compatible with 9.5,18, 20, and 25. Remember this sequence are same as the rest series.
1973
The lower unit of the year 1973 is compatible with all the HP series except 6. It would have the serial of 382574 or 390040.
The drive shaft and shift rod would be 381026 and 309582 respectively. However, the lower unit of 1973 has other compatibilities as well.
Like, some other versions are not compatible with 9.5,18, 20, and 25.
1974
The lower unit of the year 1974 is compatible with all the HP series except 6. It would have the serial of 382574 or 390040.
The drive shaft and shift rod would be 381026 and 309582 respectively. However, the lower unit of 1974 has other compatibilities as well.
Like, some other versions are not compatible with 9.5,18, 20, and 25.
1975
The lower unit of the year 1975 is compatible with all the HP series except 6. It would have the serial of 382574 or 390040.
The drive shaft and shift rod would be 381026 and 309582 respectively. However, the lower unit of 1975 has other compatibilities as well.
Like, some other versions are not compatible with 9.5,18, 20, and 25.
1976
The lower unit of the year 1976 is compatible with all the HP series except 6. It would have the serial of 382574 or 390040.
The drive shaft and shift rod would be 381026 and 309582 respectively. However, the lower unit of 1976 has other compatibilities as well.
Like, some other versions are not compatible with 9.5,18, 20, and 25.
1977
The lower unit of the year 1977 is compatible with all the HP series except 6. It would have the serial of 382574 or 390040.
The drive shaft and shift rod would be 381026 and 309582 respectively. However, the lower unit of 1977 has other compatibilities as well.
Like, some other versions are not compatible with 9.5,18, 20, and 25.
1978
The lower unit of the year 1978 is compatible with all the HP series except 6. It would have the serial of 382574 or 390040.
The drive shaft and shift rod would be 381026 and 309582 respectively. However, the lower unit of 1978 has other compatibilities as well.
Like, some other versions are not compatible with 9.5,18, 20, and 25.
1979
The lower unit of the year 1979 is compatible with all the HP series except 6. It would have the serial of 382574 or 390040.
The drive shaft and shift rod would be 381026 and 309582 respectively. However, the lower unit of 1979 has other compatibilities as well.
Like, some other versions are not compatible with 9.5,18, 20, and 25.
1980
The lower unit of the year 1980 is compatible with all the HP series except 6. It would have the serial of 382574 or 390040.
The drive shaft and shift rod would be 381026 and 309582 respectively. However, the lower unit of 1980 has other compatibilities as well.
Like, some other versions are not compatible with 9.5,18, 20, and 25.
So, this is the sequence it has come up to the latest series.
What Happens If The Compatibility Does Not Match?
It is very obvious that a mismatch of compatibility would have issues. So, you can not overlook this thing while you get one.
Now, you may wonder, what would be the issues for this mismatch! Well, there would be some common ones like the tachometer having issues.
However, there is more than you may know. So, here you go to understand those issues.
Problem 1: Gearcase Issues
The gear may make grinding noises if the compatibility does not match. Gradually, the gearcase would start wearing out.
As a result, it would be damaged eventually. And you need to replace it at a huge cost.
Problem 2: Less Efficiency
Due to the mismatch of compatibility, your boat would be less efficient. That is, the fuel consumption of the boat would be way higher.
You would notice that the fuel finishes way before you expect. As a result, the cost of fuel would increase significantly. And your fuel filter may also be damaged.
Problem 3: Sudden Stalls
You may experience sudden stalls due to the mismatch of compatibility. Along with that, the boat may suddenly give an irregular shake when you are riding.
However, your boat engine may also stall for other various reasons as well.
So, these are the common issues for the mismatch of the lower unit compatibility.
Problem 4: Forward Gear Bearings
There are differences in the forward gear bearings that need to be verified. The early models used a bronze bushing that was keyed to keep it in place, others had a needle bearing.
Comparing your motors OEM gearcase part number to other years and horsepower driveshaft numbers will alleviate this issue.
FAQs
Do Johnson and Evinrude join together?
Yes, Johnson and Evinrude joined together to produce outboard motors. These two companies are affiliated and have been making outboards stuff since 1986. However, they are competitors at first. And then they joined together to lower the competition and share profits.
Is there a way to identify the Johnson motor?
Yes, you can identify the Johnson motor easily. You just need to locate the code number of the motor. And you can find it on the outboard part. You would see a nameplate where it is mentioned. Once you identify the motor, it would be very feasible for you.
Is it worth it to use the Johnson motors?
Yes, it is worth it to use the Johnson motors. These motors are really appreciable for their quality and use. However, the Johnson motors are a bit oil-consuming. But if you can use it well then the motor would be very efficient. And the maintenance of these motors is easy too.
Are Johnson lower units interchangeable?
Yes, Johnson lower units are usually interchangeable. The majority of Johnson outboard motors from 1976 to 2006 use the same lower unit, so it is possible to swap the lower units from one motor to another.
However, in some cases, the lower units from different models may be incompatible, so it is best to check the documentation before attempting to swap out the lower units.
Some Johnson lower units from 1991 and later use a two-piece driveshaft which is not compatible with earlier models, so it is important to double check the compatibility before attempting to swap out the lower units.
How do I know if my lower unit is damaged?
Generally, there are several signs that indicate a lower unit may be damaged. These signs include grinding sounds coming from the lower unit, difficulty shifting the gears, water in the gear lube, metallic particles on the drain screw, and visible damage to the propeller, skeg, and lower unit.
If the boat is running slower than usual or is taking longer to accelerate, this can be an indication that the lower unit is damaged.
To be sure, it is best to have the motor diagnosed thoroughly to determine if the lower unit is indeed damaged.
The Final Words
The lower unit is an essential component of an outboard motor, and compatibility is crucial when it comes to replacement units. Always check the model number and specifications of a replacement lower unit to ensure compatibility with your motor.
And when in doubt, seek the advice of a professional technician to ensure that your motor runs smoothly and efficiently.
Now you know about the Johnson lower unit compatibility! We believe you have no more confusion regarding its compatibility concerns!
That is all from me. Good Luck!
I’m Liam Jackson, the proud owner and driving force behind KayakPaddling.net. Born somewhere in the expansive beauty of the United States, I’ve nurtured a lifelong passion for kayaking and fishing that has led me to explore the far corners of our nation’s waterways.
