# 25 merc won't shift into reverse - PROBLEM SOLVED



## 1 Brutus (Jul 27, 2007)

2003 merc 2 stroke tiller with side shifter. Randomly won't shift into reverse. When it does its smooth as can be. Checked all linkage under the hood. No conflict with anything jamming the shifter, shaft, or mechanism. Wondering if maybe the cam or follower pin in the front end of the prop shaft may be worn and causing it not to climb the cam into reverse. No obvious sign of excessive wear on the end of the pin or the stepped cam piece. Any ideas or has anyone ever had this problem? The shift shaft that goes down to the bottom end is straight, no wear, not bent. With lower end removed, I can shift it thru the gears by hand just pushing the shaft by hand, but it requires just a little force to pop into reverse.
Thanks.


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## 1 Brutus (Jul 27, 2007)




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## KaGee (Sep 8, 2006)

Idle too fast???


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## 1 Brutus (Jul 27, 2007)

Idle is fine. Even with engine off and turning prop by hand, it still will not shift to reverse. Then randomly, it will resume working normally. But when it's stuck, it's stuck.


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## Uncle Paul (Jul 10, 2004)

1 Brutus said:


> Idle is fine. Even with engine off and turning prop by hand, it still will not shift to reverse. Then randomly, it will resume working normally. But when it's stuck, it's stuck.


Brutus if your shift shaft when you drop the lower unit is a splined male into a female shaft you have worn parts that will be needed to be replaced, if it is a shaft that threads into a threaded coupling you can adjust it for the worn parts. The hard shifting with the engine not running is normal; it is designed to shift only when the engine is spinning but you won’t hurt it as long as you don’t force it


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## firemanmike2127 (Mar 17, 2013)

Just had customer in the shop with a similar issue on a 25 Merc. There aren't splined shift shafts connected to a shift cam that rotates as in other Mercury engines. The vertical shaft has a ramp (# 41) that pushes on a pin connected to the clutch dog. The prop shaft has a hole in the forward end that supports the connecting pin. My customer did a little diggin around on some forums & told me that he came up with a simple gear oil change as a fix. Sounded too easy to me but guess what ? We changed his L/U lube & put in Mercury High Performance gear oil (blue) & it shifted fine. His old gear lube was contaminated with some moisture due to crappy screw seals. He thought that his shift shaft seal (an o-ring) was leaking but his gearcase held 15 lbs of pressure when I tested it. Mike


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## Uncle Paul (Jul 10, 2004)

firemanmike2127 said:


> Just had customer in the shop with a similar issue on a 25 Merc. There aren't splined shift shafts connected to a shift cam that rotates as in other Mercury engines. The vertical shaft has a ramp (# 41) that pushes on a pin connected to the clutch dog. The prop shaft has a hole in the forward end that supports the connecting pin. My customer did a little diggin around on some forums & told me that he came up with a simple gear oil change as a fix. Sounded too easy to me but guess what ? We changed his L/U lube & put in Mercury High Performance gear oil (blue) & it shifted fine. His old gear lube was contaminated with some moisture due to crappy screw seals. He thought that his shift shaft seal (an o-ring) was leaking but his gearcase held 15 lbs of pressure when I tested it. Mike


Mike was talking about the upper end of the shift shaft and how it connects to the shift lever not in the lower unit sorry if I wasn’t clear. That gear lube trick was new to me learn something new every day, the High Performance is my go to lube whenever I can use it


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## fastwater (Apr 1, 2014)

For starters, would remove eng. cowl and closely inspect all shift linkages, especially where they attach via roll pins. Also inspect whatever linkages,clevis's and pins towards tiller handle. Would pull all pins one by one and check not only the pin itself for wear but the hole in the linkages to insure they were not worn and not egg shaped. Also inspect all mounting hardware and brackets securing linkages making sure bolts/screws,rubber/plastic grommets etc. are tight and in place.
While having the tiller handle linkage loose from the main shift linkage/rod at the top of the engine, thus eliminating any possible issues from the top of the shift rod out to the handle, try reaching in, grabbing top of main shift rod and manually shifting into reverse. If it goes into reverse, your problem is from either the adjustment at the main shift rod or an issue somewhere out to the tiller handle.


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## 1 Brutus (Jul 27, 2007)

This unit is a side shifter, not a tiller handle shifter. One thing I did, while it refused to go in reverse, was to release the clip on the horizontal shaft that connects to the vertical shift shaft: once disconnected, the shifter handle was totally free to move to the reverse position. This tells me the restriction is likely in the bottom end. Then I pulled the lower unit off. Once on the bench, I was able to stroke the shift shaft itself thru F-N-R with no issues, and the clutch dog was traveling as it should. Removed prop shaft and inspected all parts. Clutch dog is sliding freely. The push pin and mating ramp (or slide cog) show only minor wear.
I did however switch to sierra bottom lube coincidental to this problem. I'm thinking of replacing the ramp and pin, and switching to another lube.


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## firemanmike2127 (Mar 17, 2013)

My guess (without being able to inspect the internal components) would be the ramp. I'd recommend while you have it apart to give it a complete reseal as well, since you already have the labor time invested. The drive shaft & prop shaft seal lips should be showing some wear by now due to age/use. It looks like in order to change the shift shaft seals (2 o-rings) it required removing the prop shaft (unlike most older Mercs). The bend in the shift shaft didn't look like it would allow the seal housing to simply be slid off. The ramp retaining pin has to be removed first & then you should be able to separate the shift shaft from the seal housing. Since you've already got the prop shaft out now would be an excellent time to service the entire gearcase & then you should be trouble free going forward. Mike


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## firemanmike2127 (Mar 17, 2013)

BTW.....which Sierra gear oil were you using ? Is it conventional 80w90 GL-5 spec or something else.


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## 1 Brutus (Jul 27, 2007)

Sierra marine grade GL5 spec is what was in when the problem started. I now have Evinrude/Johnson HPF Pro gearcase lube installed, but issues remains. I'm gonna order parts tonight. Shift cam, shift pin that goes in prop shaft, and all shift shaft seals. Gearcase is tight, all driveshaft and prop shaft seals were new this winter and it holds pressure. But will change shift shaft seals since they're original. Case has always been clean and dry.


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## firemanmike2127 (Mar 17, 2013)

Sounds like a good plan. Please keep the thread updated with your progress & results. We might have a similar problem with my customer's gearcase down the road. I was going to share this thread with him next time we see each other. Good luck with your repair. Mike


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## 1 Brutus (Jul 27, 2007)

Problem solved! There was nothing wrong with any components or lube. When disassembling and removing the lower unit during the winter to install a new pump impeller, a small washer fell off of the top of the shift shaft. If you don't know it's there, it very easily gets knocked off when the shaft comes out of the housing. It rides on 2 pinched nub protrusions near the top of the shift shaft. These nubs can barely be seen in the first diagram about 2 inches from the top of the shift shaft. The washer serves to keep the loop of the lock down linkage from sliding over the aforementioned nubs. Without the washer, the nubs on shift shaft pull through the linkage loop when shifting to forward gear, then when you try to shift to reverse, which forces the shaft downward, the rod hangs up on the nubs, and the rod won't go down without extreme force to make the nubs pass back through the lock down linkage loop, or not at all. On the attached diagrams, the washer is part #30 at the top of the diagram. The lock down linkage mentioned is part #1 on the second diagram. 
The lesson here is be aware of the washer, be aware that it is easily knocked off when the lower unit pulled off, and assure it gets reinstalled correctly under the loop in the lock down linkage loop. Thanks for all the tips.


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## firemanmike2127 (Mar 17, 2013)

Good to see that you had an inexpensive fix & are back on the water. Mike


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## sherman51 (Apr 12, 2011)

good job getting it fixed.
sherman


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## bustedrod (May 13, 2015)

nice its always the little things good ur up and runnin


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## fastwater (Apr 1, 2014)

Way to stay with it until fixed.
And thanks for reporting back.
We all learned something....at least I did.


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