ZF IRM220 gearbox on 63p

[asteven221]

Some time ago I posted seeking advice on a problem when engaging reverse. The symptoms are that the the propshaft doesn't start turning until about 4 or 5 seconds after going into reverse. Forward is fine. I get the feeling it's heat related as when cold I am sure it seems ok. It also seems to get better after the first atttempt to go into reverse i.e. try it once - slow to engage, back to neutral, try again and it's quicker to engage. It also seems to "bleed" into gear as opposed to a "clonk" if you see what I mean. It's definately worse after a blast at 20 knots. I have even seen delays up to about 10 seconds before it engages.

Some advice was offered which was appreciated and I have checked most of the suggestions, but the fault remains.

Thus far:-

Checked and Changed the oil. The old oil seemed fine to me.
There wasn't any obvious debris in the strainer nor metal filings on the magnet
Checked and made sure the levers and controls are adjusted correctly which they are.
Checked oil temperature with a digital thermometer after running and it's about 50 degrees on the faulty gearbox and 45 degrees on the good engine/gearbox.
Checked whilst running using a laser temperature gizmo, that reads surface tempereture and faulty gearbox always reads 5 degrees more than the good one.
The temperature does increase when running at 20 knots but I have forgotton how high it went. I think it got to around 60 / 65 degrees, but I maybe wrong as it was a few weeks ago. Suffice to say it's 5 degrees more than the good unit and it works fine. That's definate.

The test runs were not over a long time which may be significant. We came out the marina, throttled up to 20 to 22 knots and ran for about 10 mins. Stopped and took readings. Repeated the readings on the way back to the marina and everything seemed to remain consistant. We ran at idle for about 15 minutes testing by going in and out of reverse. It definately starts to get better, the more the lever is exercised. In saying that the gearbox would be cooling down when idling for a period of time.

There isn't any obvious mechanical stress when engaging reverse, although on the occassions the lever has engaged reverse and the propshaft has not started turning there is a slight grumble. It is very slight and not loud and doesn't sound too terminal - at least to my non expert ears. To hear the grumble you do need to be about 6 inches from the gearbox!

I would like to try and do as much as I can myself before introducing a Volvo/ZF expert as the nature of the fault means a trip out on the boat with the inherant hassle of arranging it, plus of course the expense! Fortunately I am still able to use the boat okay and the fault isn't changing - or more significantly gettting any worse. The only other thing I can think of to check is oil pressure which I am not sure how to do. I do have a oil pressure gauge kit I used to measure engine oil pressure some time ago.

If any experts out there can offer any suggestions as to what I should look for next I will be very gratefull.

Thanks a lot.

 

[spannerman]

What colour was the old oil, it should have been pretty clear, if black/brown its a sign that the clutch plates are worn, it sounds like the clutch is slipping anyway so you could be facing overhauling the gearbox although its strange that reverse has given up before forwards as it gets a lot less use.

 

[asteven221]

Thanks spannerman. I am pretty sure the old oil was fairly clear. Certainly it wasn't black like the oil that comes out the engine.

As I haev changed the oil to nice clean stuff, how long do you reckon it would take to start seeing a change in colour if as you suggest the clutch plates are worn? I know that a bit of a "lenght of string" question!

Someone previously mentioned the oil and the colour. Out of interest why would the oil change colour if the clutches are worn? I assume it's because the surfaces are breaking up in which case what are they made of?

Although I am comfy with engines and know how they work, I am clueless about gearboxes other than the obvious. In otherwords I can't visualise what's happening inside the box when I shift from neutral to reverse (or forward), which makes it difficult for me to troubleshoot especially when it comes to clutches. I've tried reading descriptions but it's confusing i.e. layshafts, input shafts, output shafts etc....... Drawings/diagrams are usually useless as well! I think I will need one of those cutaway models like they use to demonstrate how an engine works, so I can see what's happening.

Like you I thought it odd if reverse wears out before forward, but thinking about it maybe both are used almost the same. For instance both are used leaving and both are used at the destination. In between it's just forward that's engaged - for however long. Hours maybe?

Thanks again for your suggestions.

 

[spannerman]

As you said the discolouration is from the material breaking up, its similar to the stuff in your clutch in the car but this likes to have oil on it!
Its a series of plates in a stack with a steel plate between each one, the steel plates are splined to one shaft and the clutch plates are splined to another. They are in a pack with a hydraulic piston at one end which squeezes them all together so they all rotate together giving you drive.
If you have seen an automatic transmission or motorcycle clutch then you will have an idea of how it looks.
To disengage the hydraulic pressure is removed and they relax and slip allowing the engine (input shaft) to continue spinning without turning the output (prop) shaft, very simply put.
If they start to slip when engaged they get hot and burn causing the friction material to disintegrate and float around in the oil, then eventually you have metal to metal contact and absolutely no drive, then you have to replace the clutch pack and clean out the gearbox.
There are two clutch packs one for forward one for reverse, the lay shaft is a means of inserting an extra gear in the system to reverse the rotation of the prop shaft, in forwards the engine is literally coupled direct to the prop shaft so they run in the same direction, although there are usually a set of reduction gears to give the correct output speed for the propshaft.
If the oil was clean then there isn't clutch material present, but you could have a problem with gear cable adjustment not throwing enough to move the valve which controls pressure to the clutches, or an internal problem preventing the clutch getting enough oil pressure.
Hope this helps.

 

[volvopaul]

I dont suppose you have volvo EC controls fitted? if so then they may need setting up as you can alter the delay time into gear, if not then id disconnect the cable and sit in the engine room and move the lever by hand making sure your away from the shaft coupling, if its still the same then you will have either a clutch problem plates as said by S man, or broken slip rings at the end of the clutch drum, its an easy job to fit new ones, can be done with gearbox still on engine, ive seen this before.

I have also seen a case where the boxes have been swapped engine to engine when theforward clutch pack has worn, thus giving drive back to the bad side in forward, but leaving reverse poor.

The boxes are fairly cheap new, and sometimes hardly worth rebuilding when all the plates are melted and the drums are damaged/blue with heat.

 

[asteven221]

Thanks Volvopaul. I have already sat in the engine room with the lever of the gearbox being manually put into reverse and into neutral. The same symptoms persist. It's starting to look like a clutch issue I think.

Is it possible that the oil pressure could be causing the clutch issue? As I hve said, gearboxes are not my thing, but the description of how it all works in the manual suggest to me that oil is used to operate the shift. So i was thinking that maybe the oil pump (which is outside the gearbox) could be the cause. I am guessing really it has to be said!

I like your comments about fixing it without removing the gearbox - and even better - that gearboxes are fairly cheap. Music to my ears!

If the clutch for reverese was worn, would you expect the same symptoms with the engine/gearbox hot & cold? Or would it tend to be worse when hot? If it's the latter then it looks like the clutch is the cause, given that tthis problem seems worse when hot.

 

[spannerman]

The oil pump just creates pressure and the shift valve simply diverts oil to the forward or reverse clutch pack, the fact forwards works indicates there is no problem with oil pressure. So either its the shift valve not opening correctly (unlikely) or the reverse clutch pack has a leak bleeding off pressure and allowing the clutch to slip or the clutch is completely worn out, either way it would get worse when hot as the oil will be thinner.
I think you have to face up to overhauling both the clutches, its not economic sense just doing reverse.
You don't have to buy the parts from Volvo you can get them from ZF, I recently did a hydraulic box under warranty and the VP clutch plates cost £180 each x10 through Volvo, I checked the price with ZF and they were £20 each!