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Tan
Tan, MerCruiser Certified Technician
Category: Boat
Satisfied Customers: 11052
Experience:  40 yrs. experience with complete engine repairs both inboard/outboard and MerCruiser Certified Technician.
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I have an older Mercury Thunderbolt 800 and I am re-installing

Customer Question

I have an older Mercury Thunderbolt 800 and I am re-installing the lower (I replaced the water pump).Now I can't get the transmission to work properly. It stays in forward, neutral and reverse aren't working. How do adjust it?
Submitted: 2 years ago.
Category: Boat
Expert:  Tan replied 2 years ago.
Hello. My name is***** you put the lower unit back on you need the control and the lower unit in forward gear. Drop lower unit back down. Shift into forward by rotating the shift rod on the lower clock wise till the prop locks when rotating the prop counter clockwise. Now be sure the control is in forward gear. Now while holding pressure CCW on the prop keeping the lower locked in forward install the lower. Install one bolt check shift does it shift correctly? Do you follow these instructions?
Customer: replied 2 years ago.

I have tried that except I didn't hold CCW pressure on th prop, I will try that now

Expert:  Tan replied 2 years ago.
Ok if you don't hold the prop the lower unit will slip out of gear. Post back with findings.
Customer: replied 2 years ago.

that didn't work, how far to the right of neutral should the shift rod be?

Expert:  Tan replied 2 years ago.
About 1/4 of a turn. Put the lower in neutral. Then start spinning the prop CCW while shifting when the prop locks that is in forward gear.
Customer: replied 2 years ago.

that didn't work, I'm sure I have the shift rod in the wrong spot. when it's not in neutral, the rod spins fairly freely on the back side of neutral position

Expert:  Tan replied 2 years ago.
Yeah you've gone beyond the shift. Can you rotate the shaft the other direction and get it to engage?
Customer: replied 2 years ago.

yes, it will engage all 3 F N R, just slips back into forward and stays locked there

Expert:  Tan replied 2 years ago.
You want it in forward when you install the lower. You want the control in for also. Do you have the shift cable disconnected at the motor? Maybe you shift cable is out of adjustment and not allowing the shift rods to align properly. Try putting the lower in a different gear and installing the lower. Be sure the control is in the same gear.
Customer: replied 2 years ago.

No, I have not disconnected the shift cable, I will try that

Expert:  Tan replied 2 years ago.
Ok
Customer: replied 2 years ago.

that didn't work either. Even when I assemble with it in reverse, it locks in forward

Expert:  Tan replied 2 years ago.
Well I'm out of ideas. I will opt out maybe someone else has an idea.
Customer: replied 2 years ago.

should I be able to spin the prop freely in neutral? or, will it still feel engaged at the prop?

Expert:  Tan replied 2 years ago.
Prop should spin freely in neutral. The prop must lock when rotating the prop CCW for forward and lock in rev when rotating the prop CW. Did the lower work before you removed it from the boat?
Customer: replied 2 years ago.

Yes, worked fine

Expert:  Tan replied 2 years ago.
Are you sure the shift rod is lining up correctly with the upper shift rod?
Customer: replied 2 years ago.

I guess it is, nothing binding when put a bolt on

Expert:  Tan replied 2 years ago.
The shift rod in the upper can slid off to the side and not engage the lower. You have to physically line the 2 up.We know the lower is good as it shifts correctly leaving the shift rods not aligning.
Customer: replied 2 years ago.

There is a rubber boot holding the shaft in place. Unless there is movement up and down, it should all be lined up.

Expert:  Tan replied 2 years ago.
There is some movement up and down. It can miss. When you have the lower unit on you should feel the same resistance on the shift at the top of the engine as you do on the lower unit when shifting it with lower unit off.
Expert:  Tan replied 2 years ago.
Something is not lining up correctly we know there is nothing wrong with the lower as it worked before. I have never had this much trouble installing a lower unit. Something just isn't lining up correctly.
Customer: replied 2 years ago.

Lol, I know and it's probably the guy doing the work

Expert:  Tan replied 2 years ago.
Make sure you have everything in the correct position. Now neutral is between forward and reverse on the front side not the back side. Try the lower unit in a different gear. Check that both the shift rods are lining up and engaging each other. You should feel the gears with the shift at the engine if it is lined up correctly.
Customer: replied 2 years ago.

I'll keep working at it, thank you

Expert:  Tan replied 2 years ago.
Ok your welcome............Thank you..........Tan If I think of something I will post it. But I covered everything it could be.