2000 40hp Mercury slips in reverse at high rpm

I am no mechanic but here goes....
2000 40 hp Mercury 2 stroke 2 cylinder
Remote steering

I can use reverse fine at low rpms. If I add fuel to get off the trailer or hard reverse I can hear and feel the lower unit slip. ONLY IN REVERSE.

Took to marine repair place to have it checked. They told me that a spring that goes inside the prop shaft was probably bad.(Is that a possible cause?)
I disconnected the shift shaft and you can feel it lock in to F and N. When I put it into R it does not click and when I let it go it comes right back up.

Any ideas....?

I have the lower unit off and tore down right now. Spring looks to be in one piece. Ordered a new one today so that I would have something to compare it to.

I also have a new seal kit. I am going to change all of the seals as I go back together.

Any Ideas would be more than appreciated. Like I said this is all new to me. Never been inside a lower unit before. Dont really know what to look for. Thanks in advance!
Jason

Re: 40 Mercury slips in reverse at high rpm

The spring (and there are two of them) doesn't sound right.

The springs are there to move the clutch out of reverse back into forward. If the springs were weak or broke you would most likely end up stuck in reverse, it wouldn't slip out of reverse.

If the reverse gear and the clutch look ok where the two mate up it's more than likely just an adjustment problem with the shift cable (or it's streached out of shape etc).

This is just a recent problem? or you have just acquired the motor so you don't know if it's been doing it for a while??

(should have added)

The other issue could be a worn shift cam - it's kinda like a wedge at the bottom of the shift shaft. To get reverse the (wide) part of the wedge is needed to push the pin that moves the clutch into reverse. So if it's worn, it won't fully engage.

(see my doctored diagram below which should help with my explaination of the shift cam)

Re: 40 Mercury slips in reverse at high rpm

Galamb
I took the whole torn down assy to a reputable outboard shop here in town.
This is what he told me:
Gears look better than new
Clutch dog assy looks great no wear.
Shift cam looks fine.
cam follower spring looks fine.
Howerever I now have to replace my prop shaft carrier b/c I dropped it and broke one of the ears off of it. DOHE!
I also have to replace the shift shaft retainer. Broke it pulling it out. DOHEx2!!
Last but not least I have to replace the water pump base assy. It just looked bad. It is a conical aluminum part that sits at the base of the drive shaft where it goes into the gear housing. Just figured that since I was there might as well change it out.

I was told that the motor never had this prob before. Boat had been sitting for 2 years. He replaced the water pump and took it for a ride. Said he did not notice it. It only did it in hard reverse. I am merely speculating.....
The shift linkage where the upper and lower shafts go together were not adjusted properly. That is just a guess. the only thing that still stumps me is that even when the lower unit was removed it would not "CLICK" into reverse. The shift shaft would just go down a little bit and when you took pressure off it would come right back up....?
Any input?

Re: 40 Mercury slips in reverse at high rpm

I'm not overly concerned with "no click".

Since you have seen all the "guts" you can see that the forward and reverse gears are always being turned by the pinion - so both are kinda (in gear) all the time.

That click can be a combination of the shift linkage at the powerhead end (has 2 pieces of spring steel that kinda locks the lever into whichever position you have selected FNR (called a detent and backing spring - but made from flat steel, not the spring you are used to seeing) and the sound of the clutch smacking into the the gear face plus that pin that moves the clutch (inside the propshaft) making contact with the clutch retaining pin.

So what all my babling is say is, that click is not necessary for it to be in gear.

With the lower unit off it (slipping) out of reverse could just be due to a very strong clutch return spring.

Slipping out of reverse, if everything is back together and adjusted fine, could be due to one or both of those (springs) I mentioned being a little worn out.

Check the diagram below. Number 1 is the detent spring and 2 is the backing spring. Note the other circled item (which is the end of the horizontal shift shaft under the hood). It has little notches in it. The detent spring is supposed to (lock) into those notches to keep it in whatever gear you have selected. The backing spring also applies pressure to keep the detent engaged until you (shift) to a different gear.

If either of those is weak and your clutch return spring is particularly strong it can cause the detent to slip and force it back into neutral from reverse.

I hope I didn`t completely lose you here. Those could be a viable explaination for what is causing the slip...

Re: 40 Mercury slips in reverse at high rpm

Parts just came in. Going back together tomorrow. Wish me luck! Thanks for the help and diagrams. I will check that spring. I will let all know how it goes.
Jason