Originally Posted by crazyguamboy
Thanks, motion30. That is what I am looking for. I heard that since the Jabsco model is faulty, the Johnson pump is the upgrade. But that's all the information they give. Do you know what the update is? Thanks again.
As Capt. Bill says, the potential failure is not with the Jabsco pump but wiith the Lehman drive coupler that connects the Jabsco pump to the engine's accessory drive. The drive tang on the end of the coupler's drive shaft is prone (eventually) to cracking and then snapping off.
However.... this failure is not connected to leaks so far as I know. The drive tang cracks, and when it finally shears off, the Jabsco pump stops pumping right now. The engine will overheat big time if the rise in coolant temperature is not caught right away and the engine shut down.
The way to eliminate the risk of the drive coupler's failure is to replace it and the Jabsco pump with a single-unit Johnson pump. I don't know the part number but a good diesel shop familiar with FL120s will. Or call Bob or Brian Smith at American Diesel.
If you hvae a leaking pump, the leak will most likely either be through the cover plate seal or the rear driveshaft seal. The Jabsco pump can be rebuilt with new seals, impeller, wear plate, etc. Or you can still buy a brand new one (I believe).
When we discovered the drive tang on the Lehman drive coupler of our port engine was starting to crack (at 2,000 plus hours) we elected to replace the raw water pump system on both engines with Johnson pumps. (see photo)
The failure of the Lehman drive coupler's drive tang is not tied ot any particular number of hours. They can crack after just a couple thousand hours, as on our engine, or they can go for many years and many thousands of hours with no problems. It's a total crap shoot.
The drive tang on our starboard drive coupler was fine, so we kept that coupler and its Jabsco pump to serve as a spare should we ever need one.