Gearbox problems

[Ryeland]

I've got a PRM120 on a Beta 38 engine, the gearbox has done probably 1300-1400 hrs.

 

Recently, it has started to become more and more difficult to get the box to engage in 'ahead' first thing in the morning (astern is OK). To start with the propshaft does rotate but very slowly, maybe just drag from the lube oil? Then after some engine revs, and a few ahead/astern changes, there is sometimes a 'clunk', and the drive engages. This morning I had to do this several times to get going. Once things are warm (?) the box behaves as normal and full drive is available.

 

This has got MUCH worse since I changed to ATF from engine oil about 40hrs ago. I did change the ATF after a few hours so what is in there now should be virtually 100% ATF. Maybe coincidence, maybe not.

 

The gearbox control lever is moving to it's end stops alright. There is no sign of oil leaking from anywhere, and the level is OK.

 

Any ideas please?

 

Thanks

 

Richard

[Martin Megson]

Not sure if it the reason but he gearbox is designed to use engine oil. The specs are in the manual, link below.

 

PRM Manual

[nbfiresprite]

Engine oil should be used in a PRM 120 gearbox and changed every 500 hours. .

[Ryeland]

The manufacturers current recommendation is ATF. I checked this by phoning them before doing it.

 

Richard

[Tony Brooks]

The manufacturers current recommendation is ATF. I checked this by phoning them before doing it.

 

Richard

 

 

 

Correct

 

Even though I pointed this change of specification out in a thread within the last week too many people

are still trotting out the old PRM advice.

 

I think the engine oil was having some sort of effect on the cones so they changed to ATF like Hurth.

 

Can't think what is going on in the OPs box unless something is jambing when cold or a thrust bearing has worn.

[bizzard]

It might be worth a try flushing it by mixing 50/50 Paraffin and ATF go for a a gentle trip for half hour then drain and install fresh ATF. This should clean out any muck or possibly metal swarf that might be making it stick.

[boots]

Engine oil can cause the clutch plates to slip and give symptoms similar to the OP. we had similar problems (was using engine oil at that point) and when we contacted PRM they suggested this might be the cause.

 

Found them very helpful, might be worth giving them another call.

 

Sadly for us, the issue was more serious caused by physical damage before we bought the boat.

[steelaway]

I've got a PRM120 on a Beta 38 engine, the gearbox has done probably 1300-1400 hrs.

 

Recently, it has started to become more and more difficult to get the box to engage in 'ahead' first thing in the morning (astern is OK). To start with the propshaft does rotate but very slowly, maybe just drag from the lube oil? Then after some engine revs, and a few ahead/astern changes, there is sometimes a 'clunk', and the drive engages. This morning I had to do this several times to get going. Once things are warm (?) the box behaves as normal and full drive is available.

 

This has got MUCH worse since I changed to ATF from engine oil about 40hrs ago. I did change the ATF after a few hours so what is in there now should be virtually 100% ATF. Maybe coincidence, maybe not.

 

The gearbox control lever is moving to it's end stops alright. There is no sign of oil leaking from anywhere, and the level is OK.

 

Any ideas please?

 

Thanks

 

Richard

 

 

 

Hi

 

I repaired one these once.

The only problem was that the cables were wrongly adjusted so that it went hard into reverse but the cables set up would not allow the lever to go into forward.

There are various holes in the levers at the control and at the gear box and adjustments on the cables to balance up the lever movement, forward and reverse.

 

 

Alex

[canals are us?]

I have also had gearbox troubles (no oil) and PRM emailed me to say the Mechanical PRM120 should use ATF and 0.8 of a litre. Thanks For the Advice

 

 

James.

Edited April 5, 2013 by canals are us?

[RobinJ]

It might be worth a try flushing it by mixing 50/50 Paraffin and ATF go for a a gentle trip for half hour then drain and install fresh ATF. This should clean out any muck or possibly metal swarf that might be making it stick.

It is worth trying this, as we found a problem with a box that had been left standing and something had been depositied on the shaft from the oil (this case ATF) and was jamming the dogs! (took about 3 or 4 rinses to get rid of the black deposits)

 

Also when was the oil last changed or level checked, it could be getting low or thick and taking time to work in cold weather?

[Ryeland]

Thanks to everyone who replied.

 

After talking to PRM engineer yesterday, we have a probable explanation.

 

The cone clutch faces have grooves in them to remove the oil from the mating surfaces as drive is engaged. As the clutch material wears, the grooves disappear, making it more difficult for the oil to be removed, and so the clutch slips.

 

With a bit of slip the oil heats and thins and eventually flows from between the surfaces.

 

This is borne out by drive being very difficult to engage on Thurs morning when it was really cold. Yesterday afternoon was much warmer and it only took about 10seconds to engage, on first attempt.

 

PRM say that ATF is usually better than oil, so the problem getting worse since the change is probably coincidence.

 

So new cones needed ie box rebuild.

 

I don't really know whether it is reasonable to need this after less than 1500 hours? But we have done over 2100 locks and 3000 miles.

 

Richard

[n.b.Goldie]

Thanks to everyone who replied.

 

After talking to PRM engineer yesterday, we have a probable explanation.

 

The cone clutch faces have grooves in them to remove the oil from the mating surfaces as drive is engaged. As the clutch material wears, the grooves disappear, making it more difficult for the oil to be removed, and so the clutch slips.

 

With a bit of slip the oil heats and thins and eventually flows from between the surfaces.

 

This is borne out by drive being very difficult to engage on Thurs morning when it was really cold. Yesterday afternoon was much warmer and it only took about 10seconds to engage, on first attempt.

 

PRM say that ATF is usually better than oil, so the problem getting worse since the change is probably coincidence.

 

So new cones needed ie box rebuild.

 

I don't really know whether it is reasonable to need this after less than 1500 hours? But we have done over 2100 locks and 3000 miles.

 

Richard

 

 

 

1500 hours seems a bit low to me. 3 or 4 thousand maybe. Could just be unlucky or there could be an underlying reason for the apparently premature failure. Perhaps folk such as Tony Brookes or Bizzard or RWLP might have some ideas

 

Have a look at the PRM 150, a more robust box used by many hire fleet operators. If the cost of a 120 rebuild is near the cost of converting to a 150 it might be worth it.

 

Regards

Ditchdabbler

[bizzard]

Make sure its not struggling with a partially seized up or overtightened stern tube gland bearing or misaligned prop shaft.

The flushing is worth a go 'I've cured a similar mechanical Tecnodrive box and a couple of LH150 Lister boxes which were neglected and full of sludgy muck.