Shock mount questions

[PeteandGigi]

I purchased a 77 Johnson, 35hp. Runs great (thank you) but there seems to be a problem with the rubber shock mounts (at least I think there's a problem). We have this motor on a 17 ft pontoon, it is a long shaft that at rest is about 2 inches deep to the anti-cav plate. When under high throttle conditions it produces an erratic THUMP, A VERY LOUD THUMP. I can see it is the motor jerking the top end forward. I have looked at the rubber mounts and the two top are pretty old, I will be replacing those. What about the rest of the expensive little buggers? Should I replace them all? The two I plan to replace are on the rear left and right sides. Looking at a parts breakdown I see there is a TOP FRONT MOUNT that I didn't see. The lower mounts all seem to be in reasonable condition. Any one replaced these? Suggestions? Advice? Most importantly, do you think that's what is causing the very nerve racking thud? Thank's for your help.

 

[F_R]

Re: Shock mount questions

I purchased a 77 Johnson, 35hp. Runs great (thank you) but there seems to be a problem with the rubber shock mounts (at least I think there's a problem). We have this motor on a 17 ft pontoon, it is a long shaft that at rest is about 2 inches deep to the anti-cav plate. When under high throttle conditions it produces an erratic THUMP, A VERY LOUD THUMP. I can see it is the motor jerking the top end forward. I have looked at the rubber mounts and the two top are pretty old, I will be replacing those. What about the rest of the expensive little buggers? Should I replace them all? The two I plan to replace are on the rear left and right sides. Looking at a parts breakdown I see there is a TOP FRONT MOUNT that I didn't see. The lower mounts all seem to be in reasonable condition. Any one replaced these? Suggestions? Advice? Most importantly, do you think that's what is causing the very nerve racking thud? Thank's for your help.

Duplicate posting . See the other one for the answer.