Clunking in reverse and motor lifts up

[udusted]

I have a 1976 Glastron T166 with a 76 Mercury 850. When I put it in reverse it makes a clunking noise and the motor wants to raise up out of the water. Even though I have power trim. With the boat trailered and boat off if I put the boat in neutral the prop spins fine both ways. If I put in forward gear it spins forward but when I put in reverse it doesn't spin in reverse. I checked oil in lower unit and not really any metal flakes only like glitter. Not sure how to fix issue or what is going on. Thanks for your help

 

[smokeonthewater]

Well the symptoms sound contradictory.

"Wants to raise up" indicates an issue with the power trim system.

The "glitter" in the oil and the prop not reacting correctly to reverse gear indicates the likely need for a replacement lower unit....

What's odd though is that if it didn't engage reverse it wouldn't "raise up"

Possibly you have multiple problems... Your shift cable may not be properly adjusted.

The trim pump for those old motors has a valve on it that must be closed if high throttle is needed in reverse.

Thinking about this as I type the best theory I can come up with is that you aren't engaging reverse fully and then as you throttle up the gears violently engage making the motor tilt....

I say adjust the shift cable and change the oil.... If it seems to work them change the oil again after about an hour or so of run time....

Good luck.

 

[scrapper042000]

hey guys don't forget to check the reverse lock (knurled thumb screw )on the trim/pump/reservoir under the back of the boat inside ,should be a tag on the unit that says for reverse turn in or out all the way

 

[scrapper042000]

ive noticed a few of those old merc controls for the 80 and 85s starting to not get enough response or movement from the shift cables and or the remote ,last one I had to open the cowling and manually slide the shift rail with a screwdriver to see if the lower unit had a solid reverse before I would even waste anytime on it

 

[scrapper042000]

ooops sorry kevin looks like you covered the reverse lock ,maybe he will need to also check the reservoir and add some oil before cycling it up and down down all the way ...typical hydraulic cylinders with possibily of air in them ...these poor boats don't get used in some areas very much let alone the normal boater probably has not checked the oil reservoir on these old school systems as long as it has been working for raising and lowering the motor

 

[MTboatguy]

If it is wanting to lift out of the water when you get it in reverse, then I would guess you have bad seals in the power tilt system, if it is clunking and you have metal shaving, then it needs to be taken apart cleaned and put back together and adjust cables and such to ensure you can shift it smoothly, well as smoothly as you can expect on an older system.

 

[Frank Acampora]

Remember also that with Merc lower units if you put it in forward gear and turn the prop in the forward direction it will click and turn. If you turn it backwards (which is the load direction) it will lock up. However, reverse will lock in both directions.