Volvo Penta MSB4 Gearbox Issue

[DonCarlos]

Hi, I am a long time daily reader and valuer of Cruisers Forum but this is my first post!

I have a gearbox issue that I hope someone can give some guidance on. I have a 1992 Volvo Penta TMB31B engine with a Volvo Penta MSB4 gearbox. Engine only has about 900 hours and I understand it was well maintained for by its previous owner (I own it for just 4 years). I was returning to my berth yesterday and had to hang around for some time (a boat was in my berth that had to be moved). It's an estuary and there was a tide flowing of about 1 knot, so I was in reverse stern to wind to keep me in position. I thought that it was strange I was not being held in position but my berth became free before I thought too much about it. On entering my finger berth at about 1 knot I put her into reverse and nothing happened - I revved her up more and still nothing. I got the boat stopped with a spring line – thankfully nobody was hurt and no damage was done to gelcoat. However when I looked at the gearbox there was a hole about 50mm wide in the top casing. I believe that the reverse problem occurred while I was outside the marina but that forward worked subsequently. There seems to have been adequate oil and no evidence of emulsification in that oil. I never changed the oil in the gearbox (I do not know when it was last changed) but I did check its level about 50 engine hours ago.

I am having a professional look at it tomorrow (I do routine maintenance but I know this is beyond me and so will not attempt it myself), but from talking to him he has never seen this before. I wonder if any of you could give me some insight or guidance on more general questions. Such as: Is this a known fault that arises with this gearbox? What might possibly have caused it? Am I right in having a sense of doom and that a replacement gearbox is a likely solution? If so and assuming that MSB4 gearboxes are not being made would it be likely that a new gearbox could be obtained that would fit the engine? Would considering a reconditioned gearbox (if such a thing was available) be a viable option? Even if the gearbox could be fixed should I be worried of the same issue recurring?

Sorry for all the questions. Regards, Mark

[DonCarlos]

Just to add to my original post. I (consistently) mistyped the gearbox model - it is MS4B. Also from looking at it again the centre spindle has raised up about 50 mm and from looking at a fragment of the casing it had worn it badly. So it looks like for whatever reason the centre spindle was forced up, wore away and weakened the casing before the casing broke and the spindle then raised up another 50mm. Mark

[Diesel Bill]

Hi Mark, Sorry to see trouble with the gear box. Although I'm not familiar with this particular gear my guess is some type of shock load caused the failure. is it possible that at one time in the past the transmission was shifted into reverse with the engine RPM well above idle speed. If so then the case could have cracked from the shock load and went unnoticed till the shaft and bearing assembly wore away the casing causing the loss of reverse gear. This is all just a guess and I'm not saying it's the cause. In any case I wish you luck in getting it sorted out.

[DougR]

Hello Mark,
Sorry to hear of your troubles. Two statements in the thread ring true.....your sense of impending doom and Diesel Bills comment about someone shifting into reverse at high revs...more likely someone performing such shifts many times over the years.

There is a vertical shaft which runs thru the center of the gear box and it carries the cone clutch and the shaft rides inside the forward and reverse gears and gear cups. This shaft is located vertically by a washer and two keepers on its bottom end (similar to valve keepers), and a large nut on its top end. The nut (seen thru the hole in the top cover) comes in different thicknesses and the whole mess is assembled with a certain amount of clearance.

Over the years as the gear box wears, the clearances start to expand and high RPM shifts into reverse begin to peen the brass washer on the bottom of the shaft. When you shift into reverse the shift cone moves down and engages the
lower gear and the reaction to that is to push the shaft in an upward direction. Finally there comes a time when a shift into reverse will either fracture the brass washer/ clip retainer on the lower end of the shaft, or the clips will come loose and drop out of of the retainer. At that time when the shift cone goes down, the center shaft goes up and right thru the top cover of the gearbox.

It is probably possible to rebuild your transmission, but it might not be cost effective. Or you might be able to find a rebuilt transmission to replace it with. This would be the easiest course of action relative to getting things back in service.

A second option would be to replace the transmission with a ZF 45A transmission of the same reduction ratio. This is the best way to go, but a bit more complicated. The ZF has the same down angle as the VP gear, but it has a slightly deeper drop center and it's slightly shorter fore and aft. This means that the engine will have to be lifted some and moved aft a bit to get the gearbox coupling and the propshaft couplings to match up. ( I don't recall the distances off the top of my head, but it isn't much) Also it's a good plan to update the spring damper plate on the engine flywheel with a more modern torsional damper. I think VP used to have a kit with all the bits and pieces to do this. All of this will leave you with a quiet shifting hydraulic transmission which will easily handle your TMD31 engine.

DougR

[DonCarlos]

Thank you both for your input - I really appreciate it. While I am always careful about leaving speed reduce to idle before changing gear, who knows its history over the years before I got her. I will update the thread when I hear back from the professional. Mark

[DonCarlos]

Following discussion with the professional we agreed on DougR's suggestion of trying to get a re-conditioned one. The next problem is where to locate one. All leads for re-conditioned VP gearboxes in the UK or Ireland I was able to find on the internet have proved unsuccessful. I know many people who recondition gearboxes and engines are smaller and may not have an internet presence. I would appreciate if you know someone who handles re-conditioned VP gearboxes in the British Isles to let me know (or PM me if you prefer). Thanks, Mark

[DonCarlos]

Just to close out on this - in case someone in the future is in the same situation. Second-hand and re-conditioned MS4Bs seem to be impossible to find. I did locate one in good condition in Portugal, but it was the wrong reduction ratio. I assumed that Sweden would have a good supply, but could not find any there either. But I did locate a company in Dover which re-builds Volvo gearboxes and shipped it to them and they re-built it. It is now back in my boat and all seems good. It was not cheap - was perhaps 2/3 the cost of a new ZF45A. Going the ZF route would probably have left me with a better and quieter overall solution but there was more disruption and uncertainy with that route than I was willing to face in the middle of the sailing season.