Mercury 850 thunderbolt control box issues

[bamaboy69]

been following iboats great site by the way........... first post ..... i have this motor and having issues with the control box i have taken it to a couple of marinas that has been in business for years both places have advised me that nothing in wrong with it at all .... i have replaced cables..... so the problem is that when i engage it into forward or reverse the warm up lever comes up also i have to hold down warm up lever to make it get correct throttle ... this is my first boat its been a project boat its an 77 challenger 16ft bass boat tri-hull...... looking at poss replacing control box and a couple more marinas said looking at 400 to update control box really that is more than i have in the whole boat itself don't care to spend the money if i need to .... but they also said that i would have to get a wiring harness for the updated control box but the current set up is without the wiring harness ... any help or advise will greatly be appreciated

 

[ajgraz]

Re: Mercury 850 thunderbolt control box issues

I believe the warm up lever has a roller that rides inside a groove in the "wheel" attached to the shift lever. It is designed to make the WU lever go down when you shift. If the wheel is outside the groove, it does the opposite, as you are seeing.

You'll have to take apart the control box to see what I'm talking about.

Edit: did you replace the control cables yourself?

 

[achris]

Re: Mercury 850 thunderbolt control box issues

That can also be an indicator that there is too much load on the shift cable. If you remove the shift cable at the engine end, does it still do it?

If so, then the problem is inside the box.

Chris........

 

[Jacket4life]

Re: Mercury 850 thunderbolt control box issues

I believe the warm up lever has a roller that rides inside a groove in the "wheel" attached to the shift lever. It is designed to make the WU lever go down when you shift. If the wheel is outside the groove, it does the opposite, as you are seeing.

You'll have to take apart the control box to see what I'm talking about.

Edit: did you replace the control cables yourself?

I can tell you from having messed with mine recently that it would be almost impossible to get the box back together with that roller not in the groove you're talking about. I'm more inclined to think Chris may be right, when you replaced the cables, you could have gotten the cable bent up or down binding it up, OR, you may need to go back and lighly grease the roller and shift plate assemblies. Could be as simple as the roller 'dragging' b/c it isn't lubricated.
Personally, no way I would spend $400 just to alleviate that problem.

 

[hereto]

Re: Mercury 850 thunderbolt control box issues

You are probably refering to the Mercontrol box used thru the 70's. The roller travels inside a face plate, eventually wears out and causes this problem. Before you try to run down this roller, I suggest you make sure your linkage is adjusted correctly. With shifter in neutral you should have a SLIGHT preload on your shift cable. This is a simple adjustment, but it must be right.(Check your manual) If it turns out you need that roller, let me know, I have an new one.

 

[Jacket4life]

Re: Mercury 850 thunderbolt control box issues

You are probably refering to the Mercontrol box used thru the 70's. The roller travels inside a face plate, eventually wears out and causes this problem. Before you try to run down this roller, I suggest you make sure your linkage is adjusted correctly. With shifter in neutral you should have a SLIGHT preload on your shift cable. This is a simple adjustment, but it must be right.(Check your manual) If it turns out you need that roller, let me know, I have an new one.

Hey hereto, you know quite abit about the controllers? If so, would you read my thread about forward/reverse shift probs? I've had two ppl tell me it could be an incorrect control box prob...

 

[achris]

Re: Mercury 850 thunderbolt control box issues

Hey hereto, you know quite abit about the controllers? If so, would you read my thread about forward/reverse shift probs? I've had two ppl tell me it could be an incorrect control box prob...

And you have checked that, and it isn't the problem....