40hp '94 Force Lower Unit Keeps stripping gears

matt323232

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I have a '94 force 40hp, bought used 6 months ago. When I first got it it would jump gear doing the famous "hitting a log feeling" bucking out of forward gear. Went from doing it every 5 minutes to 1 minute then every few seconds. I put a '88 50hp forward gear and it worked for about 5 hours then same problem. I can tighten the nut and sleeve on the linkage and it will work good, by the time I have adjusted it 3-5 times it will no longer have enough to reach reverse. What lower units will fit, I have found a mid 80's 35hp force lower unit but I noticed when I research the gears the 35hp has different gear part numbers inside lower unit. 40hp has forward gear # 817824a2 35hp is 819255a3. It works good when I rebuild the lower unit but it never last more than a few hours. Are the force motors known to have really bad lower unit or am I missing something. Thanks
 

Frank Acampora

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Re: 40hp '94 Force Lower Unit Keeps stripping gears

94 is a Mercury designed unit using Mercury gears. Anything earlier than 92 will not work. The 35 has 2-1 ratio gears and a smaller drive shaft.

The gears in the 94 lower unit need to be shimmed correctly when replaced.

Are you mistakenly "easing" the lower unit into gear? This wears the drive dogs rapidly and must be avoided. The engine must be "snapped" briskly into gear
 

matt323232

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Re: 40hp '94 Force Lower Unit Keeps stripping gears

I've made it a habit of shifting firmly into gear to not wear out the clutch dog. Is a little bit of wear(not chips) on the pinion, for/rev gears going to bother it that bad. I thought about just getting a dremel on the clutch dog and for/rev gears where they meet and squaring up the rounded edges, but this will be the forth time to rebuild. I thought '95 was when Mercury took over the lower units? How can I tell the difference in the for/rev gears from the 50hp '88 and 40hp '94? They look identicle. Thanks for the fast response
 

Frank Acampora

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Re: 40hp '94 Force Lower Unit Keeps stripping gears

104_7214.jpg104_7006.jpg104_7002.jpg

I do get a little mixed up on dates. If your engine does not have thru-hub exhaust, it is the old style lower unit and not Mercury. If it looks like this one, then, of course, the earlier gears will fit and you can use almost any lower unit from Chrysler on up.
 
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jerryjerry05

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Re: 40hp '94 Force Lower Unit Keeps stripping gears

Can't really tell from the side.
need a straight on pic?
 

matt323232

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Re: 40hp '94 Force Lower Unit Keeps stripping gears

Would the 80's 35hp force lower unit work? Even though the gears have different part numbers? ThanksScreenshot_2013-09-25-20-24-26.jpgScreenshot_2013-09-25-20-23-18.jpgScreenshot_2013-09-25-20-24-01.jpgScreenshot_2013-09-25-20-23-38.jpg
 
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Frank Acampora

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Re: 40hp '94 Force Lower Unit Keeps stripping gears

No, it will not work! The drive shaft is smaller diameter and the pinion therefore will not fit on the larger drive shaft you have. The drive shaft will not fit into your crankshaft. Since the gears are 2 to 1, you can not use your pinion with the 35 drive gears either.

From what I can see in the photos, your drive dogs on the dog clutch do not look worn enough to keep popping out of gear. Are the drive dogs on the forward gear in the same condition?

If so, look elsewhere for the problem. Is the clutch shaft free inside the propshaft? Does it move freely all the way to the end of its travel? Does the dog clutch slide freely on the splines? Can you slide it completely off the splines with no force (with the roll pin removed)? Is the shift rod yoke on the pivot pin correctly oriented? Do you have the correct shim in front of the forward gear?
 
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matt323232

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Re: 40hp '94 Force Lower Unit Keeps stripping gears

The drive dogs on the forward gear also look the same, decent shape not enough to be slipping. The clutch shaft seems to be moving freely, when I shift it manually when the lower unit is apart the clutch dog engages good. The shift rod seems good, shifts firmly because of the tight gasket. Shift rod yoke is correctly oriented, moves good, the small square piece that engages the clutch shaft is wore about a 1/32" because of gear jumping. Shim is correct on forward gear. Every time I rebuild it works great for a few hours then the gears start slipping and I start adjusting the shift rod until reverse goes out. Seems like the pinion needs a shim above the race, cause my gears keep getting wore out. Let me know what you think. Thanks
 

Frank Acampora

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Re: 40hp '94 Force Lower Unit Keeps stripping gears

It sounds like there is simply not enough movement of the shift linkage. This may be due to the cable and its terminations. Shift the engine into forward and note the position of the shift lever on the side. Disconnect the cable and see if the lever can be moved more.

It is time to check the control cables inside the control box AND at the engine. Is the groove in the end of the control cable firmly locked in place under the retainer? If the ball link is on a plate with multiple holes, is the ball in the correct hole? Is the end inside the box in the wrong hole? is the groove in the cable locked into the box?
 

matt323232

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Re: 40hp '94 Force Lower Unit Keeps stripping gears

GEAR FOR 3.jpgGEAR REV 3.jpgGEAR CLUTCH 3.jpgGEAR PINION 3.jpg Finally got large pics. Do the gears look reusable? My control box is good, I just added a new gear from where I pushed it to hard and broke it last time lower unit broke and I was trying to make it back to the boat ramp from a long ways out. I noticed on the engine where the shift arm meets the shift cable and pushes down the link, the cable has been mounted about 1 inch up, looks as if someone added a 1/4" bolt about 2" long and lifted the shift cable up 1". Im going to mount the shift cable back down. I already tried mounting it down before I took off the lower unit but the unit had already gone out so I figure the moving 1" down didn't make a difference. I'm going to disconnect the cable after shifting into forward and see how much the rod can move and let you know. Thanks
 
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Frank Acampora

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Re: 40hp '94 Force Lower Unit Keeps stripping gears

You can try re-using those gears--- BUT---If it were my lower unit, I would replace all of them. In the photos I can clearly see spalling and pitting on all three on a number of teeth. Service life will be reduced. How much? Can't tell.

Quite honestly, instead of trying to replace gears, you should really consider a whole used lower unit. What goes bad in lower units? Gears. AND, most people simply won't part out a lower unit. Besides, just buying gears will probably cost the same as buying a good used lower.
 

Frank Acampora

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Re: 40hp '94 Force Lower Unit Keeps stripping gears

Look at the next post down regarding 35-50. Apparently the later force 35 uses the same drive shaft as the 50 so gears should be interchangeable.
 

matt323232

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Re: 40hp '94 Force Lower Unit Keeps stripping gears

SHIFT ROD.jpgHeres the pic of the shift bracket where it looks as if someone added the top bolt? Wonder why they would add this? I noticed the 35 and 50hp use the same prop shaft but different part numbers on the gears? So are the gears the same ratios? Also I checked my shift linkage last night, on the rod on the side of the motor when I shift from forward to reverse the rod moves 9/16" up and down. Does that sound like enough to shift good, I got the lower unit all apart so I didnt get the chance to test the shift rod by hand. Also found a US Marine 50hp lower unit that is a Chysler, got it on my watch list. Thanks
 
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Frank Acampora

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Re: 40hp '94 Force Lower Unit Keeps stripping gears

I'm a little out of my league on these later force engines. Yours has Mercury controls. Who knows why the P.O. added the top bolt?

However, I have never seen the black plastic cylinder directly attached to a shift lever. The ones I have seen are in a holder in the front of the cowl and the movable end slips over a stud. Yours may be correct but it may be incorrect. At this point, you need someone on the forum to either say what correct attachment is OR supply the page out of a manual.

The 35 PROBABLY has a 2 to 1 gear ratio and that is not necessarily a bad thing. You can compensate by using a higher pitched prop.

In my older Force, the total movement of the shift rod is somewhere between 1/2 and 9/16 so you should have plenty of throw for total engagement of both forward and reverse.
 

matt323232

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Re: 40hp '94 Force Lower Unit Keeps stripping gears

I put in a new set of gears in my lower unit, I got the shifting between reverse and forward correct but at a high rpm somewhere over half it was slipping forward gear every 5-7 seconds. I tightened the shift linkage to where I no longer have reverse and then forward gear no longer slips. This is the THIRD time I have rebuilt it and I bought it this way so something is not right, I'm thinking maybe the shift cable to the throttle handle is bad, maybe. Any help would be greatly appreciated. Thanks
 

Faztbullet

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Re: 40hp '94 Force Lower Unit Keeps stripping gears

Pm me if you want a good unit ...
 

matt323232

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Re: 40hp '94 Force Lower Unit Keeps stripping gears

So I Installed new gears and the slipping in forward gear was still a problem, took it apart reassembled it still had the same problem. I then put in a new lower unit after checking the gears and making sure they looked new/good. I still have the slipping in forward gear. Is there something I'm missing. It goes together like it comes apart, I had a picture with parts diagram on it when rebuilding and it wasn't that complicated. Surely someone has had this problem with a Force 40hp motor or similar hp Force. I've spent a lotttt of time and $ on this problem please help. Thanks
 

Boatdoc58

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Re: 40hp '94 Force Lower Unit Keeps stripping gears

Do you have a one piece or a two piece lower unit ? Do you have the engine serial number. I have run it to this on many 90's Force motors.
 

matt323232

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Re: 40hp '94 Force Lower Unit Keeps stripping gears

It's a 2 piece lower unit, the power head has R467136. Is that the serial number or is it by the mount on a plate, if so I'll have to get it on my lunch break. So what have you run into on 90's force motors? Bad lower units? Thanks
 
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