ZF305A-1 MARINE GEARBOX

I suspect shaft end play which is normal and necessary and the "clunk" sound when changing direction of rotation would normally shift the shaft within the end play envelope from one extreme to the other causing the "clunk".

I have heard it before on my buddies tug and I believe it is normal. Go forward with no fear.

Further explanation would be that as you shift between fore & aft direction there is rotation of the prop due continued movement of craft in original direction causing the prop to be turned by the water. So as you shift and the gears align in a manner to facilitate a direction change there is a little movement from the driven end and that from the prop. When the gears then align "clunk" as the opposing rotations mesh in the gear box and power transmission resumes from the engine.

All is well mate.

I think that first of all, you must discard a mechanical fact as producing the "clunk", checking the correct clearance of push bearing and/or integrity of elastic suspension elements in the Vulkardan coupling.

Also an excess on a gear radial bearing could cause such occassional noisy running condition.

If clearance is excessive, probably the displacement of shaft can produce the noise that you identify as "clunk".

Surely "ZF claim there is nothing in their gearbox that can make this noise" when the gearbox is on perfect running conditions.

I don't agree to consider that "clunk" noise as normal and that "All is well"; surely something is wrong.

Technical data at http://zf-group.com

With my wish of be useful to you.

CARDON (ME)

I suspect your gearbox has helical gearing.

So there could be two causes:

* Increased backlash due to wear on gears

* Bearings not properly mounted (too little or no pretension, probably even play).

The first was already mentioned by some above, by reversing load, the opposite face will mesh, so on one or more gear meshes, this could be accompanied by some noise, but then I would recommend to check whether your gears are lubricated sufficiently.

Bearings could also be a factor. If your manufacturer did not install them properly, then the shaft with inner ring could shift when reversing load, creating the noise. A shifting distance of a few tenth's of a mm could be enough to create a big bang. If you reverse your load periodically, bearing life could be shortened considerably.

Thanks all for your comments. I fear I haven't properly explained the gearbox.

My understanding is that both forward & reverse gears are "Meshed" at all times. There are seperate hydraulic clutches for each gear (forward & reverse). When either forward or reverse is engaged, that respective hydraulic clutch becomes engaged.

Forward or reverse gear is engaged by a hydraulic control box mounted on the gearbox (with a cable to the helm position). The only way I can engage either gear WITHOUT the clunk is to engage the gear VERY slowly. I imagine this partly opens the hydraulic valve and only allows the clutch to engage very slowly. I have taken this up with ZF suggesting that the control valve needs a restrictor to reduce the hydraulic flow, but they are against this suggestion as it may reduce the life of the clutches.

The "clunk" noise occurs whenever I engage either gear and only once. This happens if I engage a gear from a stationary position, or if I an underway.

I hope this further info helps. Thanks for the comments so far.

Owen

Hello OwenSmart,

This information helps a great deal. In my experience hydraulic clutches often operate slightly different from the type clutch found on the average vehicle. They in effect incorporate a normal clutch function of disengaging plus what is termed a clutch brake. The clutch brake will stop the gear box elements rotation allowing an interference free engagement differing from the normal clutch operation of which the gear box elements are allowed to continue rotation though slowly.

I suspect that when you very slowly engage the gear you in effect are allowing the clutch brake time to stop the rotating members eliminating the "clunk".

Dear Mr Owen,

After sent my comment about an hour ago & evaluated your last comment, perhaps I can give you a humble suggestion (maybe it sounds shily), meet some pro's truck driver ask them when did they had the last U-Joint replaced, then asked them what was the most symptom occurred before that, If you found the same "clunky" thing regard to Your & their experienced then you are about to find your answer.

as you see, the propeller shaft (rear wheel drive & 4x4 automobile also applied this component) main body used a tubular steel design despite a solid rod in order to comply unnecessary power waste caused by over weighted component (especially in power train) either to reduce material cost, in some designed meant to accommodate telescopic design to allow part extension due to exessive angle changes. This tubular design also give us another very typical characteristic (allow me to used the phrase of acoustical signature) you can easily create an echoic funky clunky sound use a slight amount of your muscle power and a small wrench.

And now imagine that a clogged part directly connected to the tubular shaft, metal to metal, and a little help from the mighty brother john with a tremendous sudden twist...??????, clogged part would create a hammering effect in the process of engage or disengage that produced clunky noise.

You would have noisy rattling & dragging sound if the problem is on your clutch or gearbox, because it contained (mostly) solid state components, you can try by using a bigger tool and more muscle, you only have a louder noise and yet almost none of clunky sound when two or more solid state material collides. Sometimes clutch and gearbox problems could lead into performance de-rated, which is (in my understanding) not happening on your boat.

Well I think too much bla..bla...bla....from me, now it's your turn to decide.

Dear Guest,

If the trouble were a misaligned or damaged bearing yoke assy the clunk sound would precipitate a growling, raging vibration as shaft rpm increased causing everything aft to shake and rattle at a level which would be a distinct acoustic signature distinguishable from any other sound on board the vessel.

Dear Sir,

The "clunky" noise that bothering you might appear from the clogged universal joint / spider joint that connecting the vulkardan coupling and the gearbox or propeller shaft , You can easily recognized the problem by twisting The yoke & the transmission shaft that connected the vulkardan & the ZF, in normal way you can only have a smooth axials movement of the universal joint, but if you found any clogged movement (some people called it backlash) in certain arrangement even 3 degrees backlash is enough to creates those clunky sound, in some cases the backlash could come from defected Yoke or propeller shaft end. exam it carefully, see where the clogged is coming from? the spider bearing, or the U joint housing, either in the yoke or the prop shaft, if the problem came from U joint, the repair cost is affordable, but if it came from the last one, visit a metal workshop for a rebuilding is a wise idea despite replacing whole unit.

By the way, this "small" problems could be a catastrophic when it happens while the engine is running in full power. 375 ponies comes from happy "brother john" down there is awesome enough to produce centrifugal forces to disintegrated clogged or crack component and throw it all over the engine rooms, you'll be lucky if your engine room wall is strong enough to take the punch from the engine part wreckages.

Have a Nice Try & Happy Boating.

Thanks guys for the further comments.

I must apologise as yet again I have not provided sufficient information.

Firstly, there are no universal couplings or spiders in my setup. The Vulkardan coupling is attached directly to the engine flywheel. It is enclosed in a diecast bell housing that attaches directly to the rear flywheel housing on the engine. The rear flange of the Vulkardan coupling then couples to the gearbox input shaft via a spigot. The gearbox front flange is directly attached to the bell housing (that encloses the Vulkardan coupling). Thus the engine, coupling, & gearbox form one integral propulsion arrangement. I hope this picture (taken during construction) helps. Please note that the rear engine mountings have lowered since the picture was taken to put them as close as posible to being laterally in line with the propshaft axis.

The output from the gearbox is directly coupled to the 2¼" solid stainless steel (alloy) Propellor shaft. The Propellor is a 31" 3 blade prop with a 23½" pitch. The engine mountings are sound and correctly positioned in accordance with the instructions provide by John Deere. The propshaft has had its alignment checked and is correct. The propellor sizing has been checked using a program called "Propking" and is all within specs. The prop has been checked to be sure that it is tight on the propshaft and it also is in order. The propshaft bearings are rubber (a bit like an "inside out" water impellor). The Vulkardan coupling has "get home" stops in case the silicone material between the flanges lets go. The coupling has been removed and checked and is in sound condition. The coupling sizing has been checked (by ZF) and they claim it is within specs. A ZF reseller supplied the complete propulsion package and ZF have checked the sizing of the various components and claim all is OK. This agrees with what the "propking" program suggests.

Therefore, everything between the prop and the gearbox output flange is solid and tight, and there is only the Vulkardan coupling between the engine flywheel and the gearbox input shaft.

Listening carefully, the "Clunk" noise seems to be coming from the gearbox, but I am well aware that noises are transmitted within metal constructions, and may be coming from elsewhere.

I really appreciate the assistance you guys are providing and hope this further info will help narrow the problem down.

Best Regards

Owen

Thanks OwenSmart,

But I do think the explanation given in post #7 describes the condition. Also the "clunk" is a normal sound associated with directional changes in gear boxes when you don't allow the clutch brake to stop the components from rotating completely before shifting. I do operate equipment with this type gear arrangements and using hydraulic clutches.

Peruse the following as this may help you understand:

www.motioncontrols.globalspec.com/datasheets/808/MidwestBrake

Thanks all for your comments and assistance.

It seems that the problem is down to either the clutches (& brakes if fitted) not actuating in correct timing, or an end-play problem.

My understanding of the gearbox is that the gears are constantly meshed and which of the two clutches are activated determines which way the boat goes (forward or reverse). That may eliminate there being any brakes which will eliminate this as a source for this problem. I will check with ZF on this.

To me, posting #1 appears as a likely cause.

I will do a few other things first like change the spin-on filter and oil as well as clean the pump filter, and have the propshaft alignment re-checked, just to be sure every other possibility is eliminated. The boat is due to be slipped in a couple weeks so I will check the prop etc then.

I am not sure how long this thread is left here. Once I get to the bottom of this I will add another posting so that you all know the final outcome.

Thanks all for your comments. Believe me, they have all been helpful.

Best Regards, Owen

OwenSmart:

The thread will be open when you are ready.

You are welcome.

Fair winds and following seas