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Old 09-21-2015, 06:17 AM   #1
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Twin disc MG 5111-A

Hi

Any one had experience with Twin disc gearboxes, we are experiencing low gear box pressure on the Starboard engine, at first I thought it was possibly a faulty gauge / wiring , however this does not appear to be the issue. The engine is going in and out of gear ok and we can cruise along at 8 knots no issue , but still low pressure.
Any idea's or previous experience with these transmissions and issues ?

Chris D Liberty
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Old 09-21-2015, 06:48 AM   #2
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To help better diagnose, how old and how many hours on the gear? It may be something simple like the oil pressure sensor going bad. The Twin Disc on my charter boat is 25 years old and have replaced that sender at least once already. When was the last time you changed the oil?

Ted
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Old 09-21-2015, 06:52 AM   #3
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I would definitely wait for more knowledgable replies than mine but I wonder if dirty oil or a clogged filter screen would cause this? Let's see what the more knowledgable crew says.... Is the low pressure in both forward and reverse? What does it read in gear? Suspect other knowledgabe crew would need to know that.
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Old 09-21-2015, 07:02 AM   #4
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Mechanic just serviced the engines and changed the oil in the gearboxes at the same time. We also had the same guys clean back , prime and repainted the engines, we felt this may have caused and issue somewhere ?,the twin disc guy is coming on Wednesday to inspect / review and see if he can rectify. He will place a gauge directly on the gearbox to see what the pressure is doing. The boxes are 25 years old, but talking to twin disc they said they have gotten up to 30,000 hours out of these boxes in the past. We don't believe it is the sender , but can't rule that out yet.
Hopefully will know more Wednesday afternoon.
Just thought I would put it out there and see if people have had experience with these boxes?

Chris D
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Old 09-21-2015, 07:08 AM   #5
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Let us know what you find out. I changed my oil and my presure went down about 50 PSI on both of them. Still within the range according to the manual though.
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Old 09-21-2015, 07:10 AM   #6
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Will do Rogerh

Thanks Chris D
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Old 09-22-2015, 07:21 PM   #7
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Hi Chris,
These are heavy-duty trannys and pretty much bulletproof, 35 years old and 21,000 hours.

The only issue I've ever had is can't get the screen filter out of the housing. It just won't budge with the recommended 10mm bolt inserted.

I am certainly interested in the TD guys findings but, if it's behaving normally, would suspect the gauge or sender.
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Old 09-22-2015, 08:26 PM   #8
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90% of gear pressure issues are related to electric senders and gauges. Getting a mech to put a test gauge on it is the best next step.
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Old 09-22-2015, 10:20 PM   #9
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Ask the TD mechanic if the oil should be non-detergent. Or does it matter?
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Old 09-23-2015, 02:22 AM   #10
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My book just says single weight. I had used 40 but I'm switching to 30 for this next period. It's getting harder to get.
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Old 09-24-2015, 02:37 AM   #11
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Twin Disc Guy yesterday and we thru the gauge on the port where the sender unit is normally, and the pressure was low around 30 psi. The boxes should run at 215 psi at 2/3 throttle under load, and should read about 205 when in gear at about 600 rpm.
So next test was to remove the port screws for both Reverse and Forward and attach a gauge to each. We did this and found we had correct pressure in reverse , but the low pressure in forward. Wht they determined from this was that there were no issues with the pump ( good news) however they removed the valve box and we believe there is a blockage or broken spring inside causing the low pressure. Just waiting on them to open that up and report back, hopefully this is a relatively easy fix.

fingers crossed

Cheers Chris D Liberty
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Old 09-24-2015, 05:52 AM   #12
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Interesting, this is where I thought I might have a slight blockage. Over a few runs now it is running about 190 to 200 at 1200 RPM. It started at about 160 but has improved over time. Let us know what he finaly determines. Thanks and good luck.
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Old 09-24-2015, 06:33 AM   #13
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If you can have a look at the plate on your gear box it will have the recommended PSI stamped on it . There will be lots of other numbers, serial, ratio etc. if you go to the twin disc site and down load the operators manual it will show you what information is where on the plate, that's if like mine it is fairly worn. Might be worth checking the pressure. The only true way to check it is have a gauge placed in the port were the sender is .

Cheers Chris D
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Old 10-01-2015, 07:43 AM   #14
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Thumbs up

Ok all,

We discovered today what our problem was with low pressure. Before I tell the issue, I have been on a bit of a journey over the last week. I had the twin disc agents out , and after testing with gauges on the box informed me we had correct operating pressure 210 psi in reverse, but in forward 40 psi ?
They believed the issue was in the selector valve, so they took that away, and after inspection said it was ok. They then said it must be pump, so off it came and again after inspection they found no issue. They then said it must be inside the box, which entailed basically removing it from the boat. It is quite a large unit and weighs 245 kg , so can't really be man handled.
I suggested that before we go any further we put the removed parts back together, drop the oil again , to possibly flush out any rubbish, refill and give it one more go to be sure that in the process that we still have an issue, as a blockage may have been resolved. They told me that they thought we would still have low pressure, but I insisted we do it.
Today they put it back together and we fired it up, we disconnected the gear selection cable and put the transmission into gear by hand at the valve , when we did this to everyone's surprise we had correct oil pressure in forward and reverse.
We then connected the gear lever cable and tested it from the controls at the helm, but this time low oil pressure ? What we discovered was that the cable was not pushing the lever over hard enough to fully engage the transmission. Once we fixed this issue by adjusting the cables our issue was solved.
It is amazing how such a simple adjustment matter caused such a worrying issue and Protential damage to machinery. A lesson that everyone needs to keep in the back of their mind in relation to transmissions.

At least I will be out this weekend giving her a run now!!

Cheers Chris D Liberty
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Old 10-01-2015, 08:09 AM   #15
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Great news and very good to know. I hope they did not gouge you to bad.
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Old 10-01-2015, 12:27 PM   #16
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I'm very glad this all ended well, but really? The Twin Disc guys didn't check the adjustment first? Really? I'm amazed at their lack of common sense.

How much did they charge you for this nonsense?
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Old 10-01-2015, 08:34 PM   #17
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Good for you sticking to your guns to try it again, in place. So sorry you had to go through all that frustration. Better days ahead. 😎
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