Reply To: Shaking at High RPM Running 1955 Evinrude Fleetwin Aquasonic 7.5HP

[Don]

Have a look at the top of the lower driveshaft and its mating surface on the upper bushing/seal housing in the gearcase. You will see wear on the bushing/seal housing where the driveshaft has been rubbing/binding if the shock has expanded cause the lower driveshaft to grow in length. I just want to be sure you have found the issue…Usually, if the shock has been distorted, the symptom will be the engine just seems to bog down/lose power at high speeds because the lower driveshaft is binding on the housing. I have never heard of a damaged shock causing the engine to buck/vibrate wildly like you mentioned…But, I’m sure this could occur if the shock spring is actually broken.
Please check the prop shaft to make sure it is straight, look closely at the gears to make sure there are no chipped/damaged gear teeth. I just don’t want you to put this thing all together and still have the same issue.
Post some pictures of the various parts, perhaps someone will notice something…
And finally, post some pictures of the damaged propeller to help us understand your explanation of the damage…
Be sure to pressure test the gearcase once it is reassembled, you don’t want more water inside…
And finally, it is probably best to replace the lower driveshaft, unless you can successfully weld it in place. Remember, a used piece can have the same issue, so be sure to measure the driveshaft length before using/installing it…D