1984 35hp Mercury, won't go in reverse

[HTG]

This engine will go in reverse on land with the hose and works fine. For some reason, I can't get it to go in reverse when its in the water. I'm having some difficulty getting the throttle to go in reverse when its in water. When it does it just revs up but won't engage. Anyone know what I can check? Is this a major overhaul or something else?

 

[Texasmark]

Ask yourself what's different in the two instances besides sitting in the water which has nothing to do with it? Engine tilted up, cables kinked, would be a possible cause. One thing to watch is that if the engine ISN'T running you need to manually turn the flywheel or rotate the prop by hand AS you move the shifter from N to R. R has Cogs and slots, unlike the overrun sawtooth on the rear of F gear. Merc says you can damage your linkage if you force it without turning as stated.

 

[Swagonmaster]

Hey Texasmark, good to find you over here also.
As to the problem at hand, unfortunately I am familiar with this issue having recently needing to fix my 140 hp that wouldn't go in reverse in the water. Reason is that the shift clutch isn't being pushed back enough to fully engage reverse gear. There is enough pressure to turn the prop with no load but it just slips with the load of the water. The cause of this is either a VERY worn shift cam or more likely the shift shaft in the lower unit has been bent when the shifter was put in reverse without the prop shaft moving which would allow the dogs to align and engage properly. The lower unit has to be dropped but if like mine the shift shaft comes in from the top and so can be replaced without tearing the whole thing apart. Just make sure that the lu is level and the trans is in forward so the shift cam doesn't slide off to one side and make it really hard to put back together

 

[HTG]

Taking that lower unit off took me about a week to put back together the last time I took it off for a impeller. Any chance that it might be the spring behind the propeller that shifts the gear back and forth from forward to reverse? Thanks for the info.

 

[Texasmark]

There is a new kit out for Brunswick lower units of years back. Faztbullet brought it to the attention of a Force member. The kit contains a cam follower, 3 ball bearings and some other things but no spring.

I too thought the spring could weaken over age and Faztbullet assured me that since most engine functions are in F gear and seldom R is used, there seldom is any (to speak of) pressure on the spring....to paraphrase him from memory.

So, I guess the spring is out. I think you might remove your shifter cable on the water and shift by hand. Once you have the R selected and the engine responds properly. Shut it off and put your remote control lever in R with the cable still disconnected at the engine.

Once having done that, look at the alignment of the hole in the center conductor of the cable and the pin on your engine's shift lever. If the lever pin is beyond the cable, just adjust the barrel on the front of the cable to increase the length to the pin and a couple more flips of the barrel for a little "pre load" on the engines shift linkage.

On here and there, I usually boat here but with the @#$%^&**() going on I have a lot of free time so I went back to some old haunts, one of them being your reference.

 

[Swagonmaster]

Unfortunately the spring isn't the problem, it pushes the clutch toward forward it has to be pushed against the spring by the cam to engage reverse but other than having to drop the lower unit which is 2 bolts and 5 nuts to do it's really ot bad and the shift shaft is not expensive.

 

[Swagonmaster]

It is a bit of a chore but if you use a ratchet strap to help support the weight of the lower unit it's not bad. Put the shifter in forward to take it out, that takes the pressure off of the cam follower and put it in reverse to put it back in, that will make sure that it's all the way in gear. Please remember to turn the prop while moving the shift rod into reverse or you might cause the problem all over again. Pictures of the SECOND time I did this.

 

[HTG]

I'm not sure what I need to do after dropping the lower unit? Is there anywhere that I can find the steps that I would have to take to fix this?

 

[Swagonmaster]

A shop manual would make it easier boatinfo.no has the downloadable version for about $15. The tool to unscrew the top bushing is easily available, I found one on eBay for I think $16. I couldn't copy the link but here is the description
Mercury Mariner Mercruiser Shift Shaft Bushing Tool 91-31107T, Replaces 18-9817
item # 112813884004

The hardest part of replacing the shaft is keeping the cam from sliding off to the side where the shaft can't be reinstalled without a lot of hassle.

 

[HTG]

Thanks, I will have to try to find a video on youtube. I need to figure out if it could be anything else besides replacing the shaft. Anyone have a opinions on that?

 

[Swagonmaster]

Ok, I'm curious how did it turn out?