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Adjusting shifter linkage

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  • Adjusting shifter linkage

    How do you adjust the shifter linkage on a boat??? (Single control lever, mercruiser 120 I/O). My boats PO had installed new cables but the adjustment is off (in the water...on muffs if shifts fine..go figure). If this is too long or involved to explain here...Tell me to go buy a manual... I've got one coming just impatient and want to work on the boat.


  • #2
    Re: Adjusting shifter linkage

    I've owned a '70's era Mercruiser 120 for a year, and have struggled with the shift control problem, still haven't solved it completely, am eager for wise advice. Did buy a Sealoc Manual, but it is so badly written I want to toss it overboard, except that it's got a lot of other useful stuff. Extremely confusing about adjusting the shifting. Downloaded possibly useful advice from www.amarket.com, three pages of step-by-step instructions. Mechanics have told me the most common cause of difficulty adjusting shifting is that the cable running from the transom shift linkage down into the sterndrive is binding or too loose. I have removed that cable from the rear, and it seemed to be perfectly smooth and snug in its sheath. My boat's problem is that the ignition cut-out switch, designed to momentarily kill the engine when shifting out of gear, is actually killing the engine when I try to give any throttle when in reverse. Any old salts out there with good advice for us novice mechanics?

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    • #3
      Re: Adjusting shifter linkage

      I am about to get a 78 mercruiser 5.0, and I am new to inboards. I was wondering if the "ignition cut-out switch" you were referring to is the same as a "shift interrupt switch" or something like that. I have heard reference to it, but am wondering how it works and if a 78 5.0 has one. If you all could address this when you answer, I would much appreciate it. Thanks.

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      • #4
        Re: Adjusting shifter linkage

        Well, guys, I"ll try to explain shift setup....the book is a good place to start, but it doesn't give you what you need.... #1.. What do you want? No stalling into or out of gear....full gear engagement before rpm's increase... the same travel on the shift handle to go into forward or reverse [from neutral] 90% of the adjusting is done on the cable coming from the shift control box...the brass [or plastic] barrel is spun back and forth on the cable to vary the length....say your boat goes into forward well, but just grinds in reverse......adjusting this point 2 or 3 turns at a time will bring the adjustment closer to centered... Remember, anything you add to reverse you will be taking AWAY from forward...you are tring to hit a happy medium...by the way, ALL SHIFT ADJUSTMENT SHOULD BE MADE ON THE WATER! you need a load on the prop to make that cutout switch work properlyas far as that switch goes, it should only cut ignition when trying to come OUT of gear....any other time and we have poor adjustment as previous,[which will kill it in one gear or the other].. a too stiff cable from the shift plate to the drive,[ which will usually kill it in both gears].. or an overly sensitive switch...that roller on the switch should only cut ignition when it gets in the top 1/3 of the ramp, adjustment by bending the roller arm... if you end up with poor engagement in both gears after adjusting, you probably have some things worn out/bent in the drive...bent shift shafts from drive R&R's, or shift spools in the gearcase worn from poor shift adjustments.....good luck to you, if you succeed you have learned one of mercruisers 'black arts' LOL.......

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        • #5
          Re: Adjusting shifter linkage

          the reply from odd1 is close. I cut my teeth adjusting m/c shifters. Do it in the water with someone at the helm. Put the boat into forward gear. Adjust the cable coming from the helm station so it is as tight as you can get it without rocking the shift interupt switch. play with it a bit until you get it right. Next, go into reverse. you adjust reverse by using the slot which is cut into the arm which activates the reverse lock. if the slot is not long enough to get your adjustment, make the slot longer. The early m/c this slot was very long, but later they changed it to about 3/4 inch. your lower shift cable, the one going out to the lower unit must be in good shape, including the outer sheath. it usually will come apart just forward of where it threads into the housing, up near the u-joint bellows. starboard side. if you do end up fudging one way or the other, make sure that it gets into forward gear tight as this is the one that gets the most use, at least on my boat. hope this helps some of youeljay

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          • #6
            Re: Adjusting shifter linkage

            Thank you eljay and ODDD1. I think I'm getting closer to understanding the beast. But neither of you mentioned the non-negotiable six inches from barrel to post on the stern drive shift cable at the transom plate that I've read about. Is that important? And ODDD1, do you agree with eljay that the first step is getting the cable coming from the helm station "as tight as you can get it without rocking the shift interupt switch?" eljay didn't say whether the control handle should be pushed way forward, or just till it engages in forward gear. I'll bet both of you guys could adjust my boat's shift mechanism in a matter of minutes, as could the guys who wrote the Sealoc manual. The trick seems to be in explaining it unambiguously clearly to the naive but studious amateur, without leaving out crucial steps which, to you, seem glaringly obvious, but to us are not. If you have the patience, would either of you care to take it from the top and lead us all the way through to safe and happy shifting? One approach might be for you guys to check out the reference I made in my first posting here to this website: http://www.amarket.com/trakmerc.htm and see if you have anything to add or criticize. I smell success. Thanks for your input!

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            • #7
              Re: Adjusting shifter linkage

              Oops, sorry, correct web address for the shift linkage adjustment process is: http://www.amarket.com/help.htm

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              • #8
                Re: Adjusting shifter linkage

                Alright!!!! Well it is nice to know that 1) Others have the same problem I do. 2) People are nice enough to help out. I belive I understand (in theroy at any rate). I guess this weekend when I go to the lake I'll adjust some (hopfully I'll still get a day on the water and not on the trailer LOL). Thanks so much guys.

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                • #9
                  Re: Adjusting shifter linkage

                  Well, Michael JD, I do NOT agree that you should load the adjustment hard in either gear...by using up all the travel [and slack]you will force the shift spool in the gear case to rotate under load whenever the boat is moving...THIS WILL RAPIDLY WEAR OUT YOUR SHIFT SPOOL AND THEN YOU HAVE SLOPPY SHIFTING! the slot eljay refers to will give you additional travel on your lower shift cable...something you dont normally need, unless your SHIFT SPOOL IS WIPED OUT! it will help in a pinch, but ecsessive cable travel usually causes cutout switch activation, unless careful adjustment is done....and sometimes even ok shifting is not acheived...as far as your website, an interesting method, and one I have not {and wont] use..... the 6 inch dimension is so you dont run out of drive shift cable travel before you get full gear engagement in the drive.... it can be fudged, but only by a turn or two.... as far as a step by step hold-yer-hand, this is as far as I can go....put the boat in the water and put your hands on it.....seeing feeling watching will help with understanding....

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