Shifting Question

I have a 73' Merc 850. Took it out today for the first time since I bought this boat. The motor runs great and shifts good into forward. Reverse is where the problem begins, it just grinds when trying to shift into reverse.
In the driveway, on the muffs, it shifts flawlessly--forward to neutral then reverse. I replaced the water pump this winter and checked the prop rotation in each gear. In forward the prop will ratchet clockwise and not turn at all counter-clockwise, In Neutral prop will spin freely in both directions, and in reverse the prop will only turn a little in either direction. So I "feel" pretty confident that I got the lower unit back together properly.
Any ideas on what I'm missing here?
Thanks

Re: Shifting Question

All the characteristics you're getting while checking the gear shift without the engine running are spot on.... Exactly what you should be getting...

The one thing I would however check first is the shift cable adjustment... It sound like you may have more bias towards forward than reverse.

If the adjustment is good, then I believe the problem may be one of slack/play in the shift system, most probably a worn control box.

You can check that by removing the cable at the engine end, moving the control box into gear (forward or reverse, doesn't matter) and pushing and pulling on the cable end. You should only get a few millimetres movement. Any more than that would indicate wear in the control box mechanism.

Given that the engine, and presumably the control box, are over 35 years old.....

Chris.......

Re: Shifting Question

Thanks for the reply. As I said,though, it shifts fine running on muffs in the driveway. I am going try running it in a drum, once I find one, to see if resistance of the water is causing issues. I disassembled the controls last night, wish I hadn't, but all looked fine.

Re: Shifting Question

egclassic said:

Thanks for the reply. As I said,though, it shifts fine running on muffs in the driveway. I am going try running it in a drum, once I find one, to see if resistance of the water is causing issues. I disassembled the controls last night, wish I hadn't, but all looked fine.

Click to expand...

The resistance of the water will make a difference.... As it is now the clutch teeth for reverse are only JUST grabbing. They are holding in enough for you not to be able to make it 'slip' out of gear (crunching noise) by hand, (or when the engine is running out of water, ie on the muffs) but when the power of the engine AND the resistance of the water get together, then the clutch is forced back far enough to make it 'slip'... grinding/crunching noise.

Chris.......

Re: Shifting Question

Had the same problem last summer. Appeared to shift fine in the driveway on muffs but couldn't reliably get reverse when in the water.

I found that in the driveway that it really wasn't engaged in reverse, but close enough to make the prop spin. I CAREFULLY used a piece of wood and could stop the prop from spinning when in reverse. Apparently only fluid friction in the gearcase was causing the prop to spin in reverse. Problem was a mis-adjusted shift cable.

Re: Shifting Question

Okay,
I put the motor in a barrel today and ran it. Shifted into forward just fine. Shifted back to neutral and when I shifted into reverse, there was a "slight" grinding noise and it went into gear. Apparently, this motor does not like to be "slammed" into reverse, rather babied. When I would "slam" it in, it would just sit there and grind, never seemed to go into gear. If I slowly pulled the control back, it seemed to go into gear(still a slight grind until it finds the gear). I adjusted the shift cable.
One thing I am not totally clear on is, when I had the lower unit off, there is a "reverse lock cam" on the lower shift shaft. I did not pay attention to its orientation the first time I dropped the LU, I did not know to look for it. My manual says if it comes off, shift the gear box into Neutral, face the high side of the cam forward..... How do you shift the gear box into neutral when it is off the motor?
Thanks!

Re: Shifting Question

GENTLY using a pair of pliers or a set of vice grips, turn the shift shaft....

Re: Shifting Question

At witts end! I dis-assembled the control box, with the intention of replacing the shift cable, only to find that it did not resemble the mercury style cable I bought or any of the others I've seen. The control box is a old style with IEKHAEFER- MERCURY stamped on the handle. I buttoned it back up.
I disconnected the throttle and shift cables from the engine. Started the motor and shifted with a long screw driver, pushing on the shift mechanism. Again, Forward(check), Neutral(check), reverse(sometimes would engage, sometimes just grinding.) The slower I pushed on the mechanism, the more often it would engage. But when I increased engine rpm's, it wanted to "pop" out of gear. Question of the day,
How much freeplay (up and down) should the upper shift shaft have?
I ask because it almost seems as though when the shifting mechanism is pushed towards reverse, the shift shaft raises up. I am wondering if it can raise up high enough to become disengaged from the lower shift shaft.
I have to be honest, I cannot confirm that this motor ever shifted properly as I acquired it this winter.

Re: Shifting Question

Problem could be that the alignment between the upper and lower shift shaft splines may be out one notch. Result would be that when moving the upper shift linkage (by cable or manually) that the lower shaft is not rotating far enough to properly engage reverse.

From the limited experience I have had with the lower units I remember that in forward gear there is LOTS of free play in the shift shaft and very little when in reverse. Neutral of course has only one positive detent location.

Re: Shifting Question

Today I pulled the prop shaft, bearing carrier and reverse gear out to take a look.
The clutch dog and reverse gear did not seem "too worn" to me, but I'm no expert. I took my dremel and carefully "sharpened" the edges of the reverse gear side of the clutch dog. I made sure as to not take off any more material than nescessary(I figure if it does not work, I was going to replace it anyway). I did find that someone else has had this apart, and they must have forgotten what went where. I found shim material that was supposed to be behind the reverse gear was installed between the bearing carrier and the lock nut. Also, there was no thrust washer installed for the prop. I have put it all back together and I will try it out again tomorrow.

Re: Shifting Question

Very ambitious of you EG . I am about to embark on pulling my lower unit apart in the next few weeks for a rebuild.

Did you find it easy to pull apart? Any special tools you used?

Re: Shifting Question

It was easy to pull apart, but pay attention to the positioning of everything in the lower unit when you remove it. I made the "first timer" mistake and got in a hurry. I did not need any special tools, except when I pulled the prop shaft I had to borrow a slide hammer from the mechanic at work.

Re: Shifting Question

Moody Blue said:

Problem could be that the alignment between the upper and lower shift shaft splines may be out one notch. Result would be that when moving the upper shift linkage (by cable or manually) that the lower shaft is not rotating far enough to properly engage reverse.

From the limited experience I have had with the lower units I remember that in forward gear there is LOTS of free play in the shift shaft and very little when in reverse. Neutral of course has only one positive detent location.

Click to expand...

Agree with this - put the motor in reverse with the remote control, then drop the lower unit again. Turn the shift rod counterclockwise until you are sure it's in reverse all the way, and put it back together.

Re: Shifting Question

Thank You, I'll give it a try.

Re: Shifting Question

Put her in the tank and ran it today. Seems to shift normally now. I know I just bought myself some time and the clutch dog will have to be replaced, but hopefully it will last long enough I can save the cash for a new reverse gear as well.
Thanks to all for the suggestions.