Gearbox problemo......HELP !

bettyswollocks · #1 (**permalink**) 06-23-2008

Starting a few months ago I noticed the pitch of my engine changing while underway, always within the first 5 minutes of operation. At first I took no notice as it only happened momentarily but the past two times I have gone out it has happened for longer periods and I realised that during these occasions the boat is no longer making forward motion. It's like the gearbox is slipping somehow. I checked the prop as I feared it may have shed its split pin and was slowly loosening but it is still intact and solid.

It seems the problem is either with the controls -which are of the type where you push a pin in to engage gear and then move a single lever forward for forward and back for reverse - or with something in the gearbox itself.

I have checked the gearbox oil and its topped up and clean.

When I bought the boat I was told it had recently had a replacement gearbox fitted and a visual inspection seemed to confirm this. It LOOKED new. It puzzles me why it only happens during the first 5 minutes of operation and what it could be. If the problem was with a car I would suspect the clutch but as boats don't have clutches it's not that........but I just can't see how a toothed gear could be slipping !

Has anyone had a similar problem with their gearbox or controls or can anyone enlighten me on the inner workings of a gearbox ?

The engine is a 30hp Perkins 3 cylinder and the gearbox a Hurth.

Rockter · #2 (**permalink**) 06-23-2008

Betty...

Shift the gearbox into gear and mark the position of the gearshift lever. Now, take off the shifter cable mount at the shifter lever, and see if you can move it further manually.

Send a man below to shift manually for you. Make sure that the shift lever is in its fully engaged position.
Now see if the symptoms repeat.
Is the shifter control a bit heavy? Does it feel unresponsive?

Can you send a picture of the shifter lever and gearbox?

It is possible that you are not quite getting the gearbox into gear.

bettyswollocks · #3 (**permalink**) 06-23-2008

There is no 'shift lever', as already stated it is a single lever system. There is a button below a single lever which engages the gearbox. Without the button pushed in the lever acts as just a throttle. Push in the button and a second cable is brought into play which goes to the gearbox.

I'm gonna take off the controls and have a look tomorrow before I start messing with the gearbox.

Rockter · #4 (**permalink**) 06-23-2008

Oh betty...

The shaft lever is on the gearbox end of the cable. The cable lever at the helm pulls on the gearshift lever (at the gearbox) to engage forward, neutral, or reverse. When you work the single lever at the helm, moving it does two things... it engages forward (or reverse) at the gearbox, then it opens the throttle (there is another lever on the engine for that).

Other owners (like mine) have two levers at the helm... gearshift, and throttle. Your single lever combines both of those functions in one lever but all engines can be operated with either system... but both systems have two operations that have to be covered... shifting and throttle.

Check the lever on the gearbox. The cable may not be going through its full travel. Disconnect it from the cable, and shift manually for a wee while (send a man below to answer your commands from the helm). If the gearbox does not slip, then cable movement is your problem. If that does not work, then you've got a gearbox problem, methinks, but I doubt it. gearboxes need very little care. If your has been treated reasonably, it will last a long time. Only absolute abuse, or running out of oil will kill them. A gearbox runs in an oil bath, typically splash lubricated, and they are absolutely ideal conditions for lubrication.

A picture would help.... of the gearbox, or even a gearbox model number.

bettyswollocks · #5 (**permalink**) 06-23-2008

Hahaha......well that clears things up.
Ok I'll give that a go. I'm hoping and praying that it is just a cable issue as I too cannot see how the gearbox itself could fail.

negrini · #6 (**permalink**) 06-23-2008

Betty, hope this is not the shaft sliping out of its flange, and eventually engage as it warms (stuffing box attrition) by increasing its diameter. I once was unluck .... way more complicated to replace flange, key, etc ...

Capnblu · #7 (**permalink**) 06-24-2008

I think your has gears, but it also will have mechanical clutch packs. I agree with the others who suggest checking the shifting linkage, also change the oil. I think the proper oil to use is Dextron II. There are many additives that can be used with Dextron II which may resolve your cold slppage problem.

bettyswollocks · #8 (**permalink**) 06-24-2008

I had a look today and the problem is that at partial revs (around1300rpm) the cable does not travel enough to properly engage the gear, so it's just going to be a matter of sorting the cable out to allow more travel.

While I was up close to the box engaging gear from the actual lever on the side I was astounded at the noise the gearbox makes. It sounds like it's being tortured. I know they probably contain straight cut gears but is this awful noise normal ??
The box is a ZF Hurth something 10 bye the way.
I'm also going to change the oil and see if it is full of scrap metal.

Rockter · #9 (**permalink**) 06-24-2008

Betty...

Going forward... forward!!.... it really should not make much noise at all.

Disconnect the gearshift cable from the lever, and engage manually, pushing the lever fully over to engage FORWARD.

Does it still make a lot of noise under load?

In reverse it will whine like a good 'un, but typically not forward. In reverse, the gears are typically straight cut, and they whine like crazy, but they don't graunch.

If it is making a lot of noise going forward, with the lever fully engaged, I fear that something has torn up.

Change the oil anyway, and check for debris. Run it a while first to stir it up.

A Hurth is not the most expensive gearbox in the world, at least compared to V**vo.

Hey, take a wee picture of the motor and gearbox and cables and post it on here for us.

Rockter.

bettyswollocks · #10 (**permalink**) 06-24-2008

oh thats not good then. This makes an awful racket when going forward. I suspected it would be breaking up as no manufacturer could seriously make a product that sounded so bad. I'm gonna look in the oil today but I'll be amazed if there is nothing in it.
Out of interest will the boat have to be slipped to change the gearbox ?
I guess at a push I can move the prop shaft about 4" back, will this give enough clearance ?