Alpha Drive SLAMS Into Gear

H2ONUT

H2ONUT

Well-Known Member
Nov 26, 2006
2,658
Savanna GA
Boat Info
2000 215EC
Engines
5.0 EFI Mercruiser Alpha
Getting ready to put the boat in this weekend. Was running it last night. Got the new prop on and wanted to shift it into forward and reverse to be sure everything was smooth. Going into forward it really bangs into gear. Going back to neutral it shifts fine. Going into reverse it chatters a bit then bangs into gear. Back to neutral is fine. Any ideas?? Didn't do this at all last year...
 
Lets start with the ‘easy’ stuff.

Turn the engine off, remove the key.

Now shift.

How easy (or hard) does the shift cable move?

Is the drive fluid full?
 
The First thing to suspect is the Shift cable

The Shift cable is the gear cable that runs from the alpha leg through the gimble housing and terminates on a shift interrupt switch bracket, usually mounted somewhere on the engine (rocker cover or exhaust riser).

To understand why the shift cable is usually the culprit you have to understand how the mercruiser alpha one gear shift mechanism works.

The forward and reverse gears are in the lower leg behind the propeller (in the torpedo shaped casing), they are both revolving all the time, one clockwise and one anticlockwise and the propeller shaft runs through the reverse gear and sits in the forward gear at the back of the casing.
Both gears are free to revolve independantly of the prop shaft and the shaft direction is only determined by the position of a sliding 'dog clutch' which slides along the shaft and engages with either the forward or reverse gear.

This 'Dog' is a cylindrical piece of hardened steel which has 'teeth' in either face and slides along splines in the prop shaft, mating up with similar 'teeth' in either the forward or reverse gear.

Now here's the thing
these teeth are slightly 'undercut' which means they are sloping backward and this is good in that there is much less chance of them ever jumping out of gear whilst under load, however when the engine is running and there is loading on the prop (ie it's in the water) These teeth do not want to disengage AT ALL, so heaving on the poor old gear lever would just stretch the cable and achieve nothing.

Mercruiser came up with an ingenious plan to overcome this

They split the gear cable into two separate parts, being the 'shift cable' (from the leg to the engine mounted bracket) and the 'gear cable' (from the control lever to the engine mounted bracket)

Mounted on the bracket is a mechanism which senses the tension between the two cables and when it reaches a certain level it operates a micro switch, this switch kills the ignition circuit and this in turn takes the pressure off the 'Dog clutch' allowing it to disengage with whichever gear it is in.

All this hapens in a split second and should be quick enough that the flywheel momentum allows the engine to continue running.

Imagine what happens when the 'shift cable' starts to get old and sticky, now you're getting the picture, it holds the microswitch over too long and stalls the engine, usually when you're just coming into a marina.

It Also causes problems when shifting INTO gear, as the 'stickiness' causes the mechanism to throw the microswitch over, however this mechanism should not actually flinch at all when shifting INTO gear.

IT IS NOT UNCOMMON TO SEE THESE MECHANISMS DISCONNECTED OR EVEN REMOVED WHEN FOLKS DID NOT REALISE WHAT IT DID.

Some people think that this is related to a 'start in gear protection' mechanism but this is not the case. If you are having shift p.roblems, check that the shift cable is not sticking first, it should slide very smoothly when removed from the bracket, but DO NOT TAMPER WITH THE ADJUSTMENT BARREL ON THE CABLE UNLESS YOU UNDERSTAND WHAT YOU ARE DOING, THIS SHOULD ONLY BE CARRIED OUT WITH MECHANICAL KNOWLEDGE AND A MAINTAINENCE MANUAL

Shift Problems can be caused by other factors which can only be assesed with the drive removed,

Sticky slider
Intermediate shift shaft sticking in its bushes
mud or debris around mechanism
Bent shift shaft
To name but a few, however, suspect the shift cable first.
 
Were it a new Alpha, I'd suggest a mere adjustment, but seeing as it is fairly older, I agree with the above post.... :wink:
 
OK, the shift cable was new last year. New fluid just added. Engine RPM's are around 850. With the motor off, everything shifts nice and smooth.

Now... with the prop off, it shifts nice, put the prop on, that when it bangs into gear... Also, in neutral the prop spins very slow but is not engaged...

Thanks for the above info... any other suggestions?
 
wish2fish said:
is this on land? From your description it sounds like you were preping you boat. I don't think you supposed to shift out of neutral when not in water?
Click to expand...


100% agree!

Going into gear out of the water would make a big clunk sould.

This is not on land, is it? :smt017
 
I have to proofread my responses. Looks like I have bad grammar!

After reading again about no problem without the prop tells me you are doing this on land!

If you did this out of the water, I would drain the outdrive and refill. check for metal particles. and refill.
 
Yup, on land... DOH!!!!! Didn't know you can't do that... Just wanted to make sure everything was working OK...
 
I have to drain the drive again anyway... I forgot to put the allen head bolt in the lower unit for the zinc before I put it back together... :smt021
 
Yes, had water running... This is my first Alpha drive, my other boats have had Volvo Penta drives...
 
H2ONUT said:
Yes, had water running... This is my first Alpha drive, my other boats have had Volvo Penta drives...
Click to expand...

Welcome to superior Mercruiser engineering!

We do a MUCH better job of preventing our repair people from being lonely. :smt038
 
Also, 850 rpm sounds a little high.
I think it should be 6-700 at idle...
 
I'll have to look into it, can't find my repair manual... Damn wife!

Drained the oil, looked fine, and nothing on the drain plug magnet.
 
OK, found the reapir manual... mixed in with the Avon catalog... :smt017

650 to 700 is the recommended rpm at idle in gear. So wouldn't it be a little higher with no load?
 
The slightly high idle speed may be contributing to the rough/loud shifting. When we took delivery of our boat it went into gear with a loud clunk and was obviously running fast -- I think it was also around 850 rpm. Made docking quite the challenge -- especially since I was a novice! Once the dealer adjusted the idle it shifted quite well.

Jeff
 
You must log in or register to reply here.

Forum statistics

Threads
113,172
Messages
1,427,835
Members
61,084
Latest member
AntonioJamm
Back
Top