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Author Topic: Dinghy 3.5 hp outboard will not shift into forward after changing impeller  (Read 95 times)

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Rortega46

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I have a 3.5 hp Mercury/Tohatsu dinghy outboard. While changing the impeller I accidentally lifted the water pump housing assembly and the shift linkage and drive shaft unseated from their connections in the lower unit.  IĎve successfully reattached the lower unit to the engine, but now it will not shift into forward.   Maybe the drive shaft or shift linkage is somehow not connected to each other or the propeller correctly.   I donít think itís an upper linkage adjustment because after detaching the lower unit a second time, the propeller would not engage gears when manually lifting the lower unit linkage. Does anyone have suggestions regarding how to troubleshoot and get it to properly shift into forward?
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Randy & Karla Ortega
2001 MKII Hull # 1532 M35BC
S/V Yat
New Orleans, LA

Dave Spencer

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Randy,
You'll likely have much better success getting a good answer searching on a Mercury or Tohatsu small outboard forum (I'm sure there will be one). 
However, my faint recollection from years ago when I was working on a 1970's era 7.5hp Mercury was that the shift lever had to be in a certain position when the lower unit is remounted.  You may have to remove the lower unit again and fiddle with the shift lever to get it in the right position.  As I recall, there were two shafts that extended from the engine to the lower unit on my ancient Mercury; one to transmit power and one to select which gears were engaged in the lower unit.  (F, N or R).  My circa 2008 3.5 Tohatsu only had F and N so it may be totally different.  Plus, your engine is likely 35-40 newer than the old Merc I was dissecting. 
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Dave Spencer
C34 #1279  "Good Idea"
Mk 1.5, Std Rig, Wing Keel, M35A Engine
Boat - Lion's Head, Ontario
People - London, Ontario

Rortega46

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Dave, thanks for the comments.  I have been unable to find a good owners repair forum for Mercury or Tohatsu outboards.  You are right in that the shift lever should be in neutral when the lower unit is removed and reassembled.  Iíve done this 3 times without success. There are 2 shafts (drive and shift) and a water hose extending from the engine to the lower unit and all 3 appear to be reconnected correctly.  The problem is likely somewhere beneath the water pump housing and the propeller shaft.  This area was supposed to be off limits when changing the impeller, but Murphy intervened.


FYI, Its much simpler to change the impeller on my C34ís OB water pump than the impeller on the little 3.5 Mercury outboard!
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Randy & Karla Ortega
2001 MKII Hull # 1532 M35BC
S/V Yat
New Orleans, LA

Dave Spencer

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Randy,
Youíve likely already tried this but if the shifting shaft gets out of phase, youíll never be able to shift into F. Have you tried placing the shift lever in F instead of N and reassembling?  Try shifting the lever and watching what the shift shaft does. Likely itís a slight rotation. Then figure out how the shift shaft movement changes gears in the lower unit. Since you have 2 shafts down to the lower unit, it was sounds like your configuration my not be radically different from my old 7.5. Good luck. I still think Dr Google or Professor YouTube is your friend for things like this.
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Dave Spencer
C34 #1279  "Good Idea"
Mk 1.5, Std Rig, Wing Keel, M35A Engine
Boat - Lion's Head, Ontario
People - London, Ontario
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