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Ricco1

Loss of gearbox oil

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Rather stupidly I didn't check the gearbox (PRM hydraulic) oil for some time, maybe 200 engine hours. A snapped throttle cable today prompted me to have a look and when I did, it was virtually dry.

 

Obviously I've topped it up for now but I need to investigate the cause of this. Any thoughts on what might cause this loss of oil?

 

Thanks

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Probably the most common cause is if the o-ring on the shaft of the selector lever has perished a bit. It's quite easy to replace, and the o-ring costs less than 50p unless you get it from PRM's agents who charge about £15. If there's any oil around the shaft, or underneath it on the pump housing, that's your culprit. If not, suspect the washer on the drain plug - and note that if it is, tightening it doesn't help because it has a rubber insert and replacement is the only option.

 

Anything else is expensive and doesn't bear thinking about.

 

ETA I forgot to add, what about the oil cooler or the pipes to it?

Edited by Keeping Up

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If you'd lost your oil from your gearbox, would it not have appeared in either the engine bilge, or (depending upon your engine / gearbox, in your engine?)

 

Are you sure there had been oil in the gearbox? (I know - - it's a silly question!)

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If you lose oil you lose drive in a hydraulic gearbox. Well mine did! The oil seal leaked on the selector arm and dropped the oil in the bilge. it made it seem like the clutch was slipping and then gripping now and then.

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I suspect whatever has gone has gone recently. The engine tray was pretty well dry until 2 weeks ago. I changed the engine oil, some split when taking the filter out, haven't bothered clearing it out. I guess the gearbox oil has added to it without me noticing.


Probably the most common cause is if the o-ring on the shaft of the selector lever has perished a bit. It's quite easy to replace, and the o-ring costs less than 50p unless you get it from PRM's agents who charge about £15. If there's any oil around the shaft, or underneath it on the pump housing, that's your culprit. If not, suspect the washer on the drain plug - and note that if it is, tightening it doesn't help because it has a rubber insert and replacement is the only option.

Anything else is expensive and doesn't bear thinking about.

ETA I forgot to add, what about the oil cooler or the pipes to it?

 

Thanks, I'll check those things. Not sure about the oil cooler, that's beyond my very limited knowledge, is there something I could look out for?

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PRM hydraulic boxes have also been known to push their input shaft seal out. But as has been said, no oil on most hydraulic gearboxes mean no drive (Lister LH150 excepted - that give permanent ahead).

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PRM hydraulic boxes have also been known to push their input shaft seal out. But as has been said, no oil on most hydraulic gearboxes mean no drive (Lister LH150 excepted - that give permanent ahead).

 

There was still a little left in it! How might I identify if the problem you suggest is the culprit?

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If it's the front seal the oil usually drips from the bottom of the engine after running out of the bell housing. Have a good look/feel for any signs of oil underneath the engine and gearbox.

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Sometimes you have to give the engine a scrub then talc it, then run it. The talc shows up any leaks easily.

 

You shouldn't need to be that careful for a significant gearbox oil leak.

 

Richard

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I haven't resolved this yet. I gave the gearbox a good clean, can't see anything coming from the selector lever area. I guess the drain plug is the likely culprit but can't confirm this yet. I was thinking of putting a newspaper under this area, go on a long cruise, and see what's on the paper at the end. Is there any danger doing that, paper in a hot environment, fire?

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I had a similar issue on my share boat. Turned out the seal on the dipstick had perished and oil was coming out from there.

Disclaimer: this is only what I was told by a mechanic who looked at it and I lack the experience to fully agree or disagree. :)

 

Joe

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Update on this: The paper underneath reveals that it's not a significant oil leak, but I'd still like to fix it. It's definitely not leaking around the selector, all is dry there. When I feel underneath there is oil around the sump plug. Having said this, the oil seems to be dripping to the left of this (viewed from back of gearbox, selector lever on the right.) I'm wondering if the oil is coming out of the sump plug but because of the profile of the gearbox that it's dripping 2 or 3 inches away.

 

I think I'll start by replacing the washer on the drain plug although it's an absolute swine trying to get a spanner under there. Is this a standard washer, or do I need a specific PRM one?

 

Failing it being this is could be coming from where the 2 halves of the gearbox join together. Is this possible?

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It is possible the leak is from the joint of the case halves. IIRC Allan Jones had this on Keeping Up.

 

Also possible it is leaking from the input shaft seal into the bell housing and then down the back if the gearbox and underneath.

 

Regards

Ditchdabbler

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Its worth checking the hydraulic pump fixing bolts, situated beside the output half coupling. A couple of these bolts protrude through into the boxes inards and can leak badly if slack or the little copper washers under their heads are leaking by.

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