Reverse Gear Losing Fluid MD7A - SailNet Community
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post #1 of 6 Old 12-23-2012 Thread Starter
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Reverse Gear Losing Fluid MD7A

I have a reduction gear attached to a Volvo/Penta MD7A. The reduction gearbox will stay full until you put it in reverse or forward with shaft spinning then it very slowly will loose fluid "talking even with it hardly holding a small ammount it takes probaly 20 hours of operation before it would not show on dipstick". Do I just need to replace the seal where shaft meets motor? I have the workshop manual but its shows nothing about this. Trying to find an article on how to do this.
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post #2 of 6 Old 12-23-2012
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Re: Reverse Gear Losing Fluid MD7A

Can you see where it drips into the engine pan/bilge?? That should give you an idea if it's the input or output shaft seal that's leaking.. although if you change one you may as well do both, I suppose.

Not familiar with that setup so can't speculate on what you might be able to do in place but most likley pulling the gear is the way to go.

In the meantime some good oil pickup mats in the bilge and paying attention should get you by..


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post #3 of 6 Old 12-23-2012
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Re: Reverse Gear Losing Fluid MD7A

You may find a wee line of rust pits just where the lip seal contacts the shaft, so causing the leak. They are not easy to see.
Your gearbox is very similar to my old Volvo MD17C gearbox.
I had a similar problem.
The old seal is a 120x100x12 mm if I remember... that is 120 mm OD, 100 mm ID, and thickness 12 mm. I think the thickness was 12 mm. The dimensions are written on the seal.

Disconnect the final drive coupling.
Pull the propshaft aft to give some room to work.
Drain the gearbox oil, or suck it out with a pump.
Now, be careful!!!! There are 4 (?) bolts that hold the box on to the motor. When you take off the gearbox, the gearbox shims are very likely to fall into the bilge so put a plastic bag under the gearbox to get ready to catch them. They are big thin shims about 3" across. You may have to thump the box with a rubber mallet. Do not lever it off.
Take the gearbox out, and catch the shims. Sometimes the box drops off unexpectedly... careful.
You will be able to pull the final drive shaft out of the gearbox now and examine it.
Clean it up and get out your magnification glass. You will probably see a wee line of pits. Clean them up a bit.
You can easily drift out the old seal.
BUT, drift the new one in a wee bit further, but make sure it is square on.
Re-assemble the 'box, put it back on the motor (with the shims), but do not reconnect the propshaft yet.
Now refill the 'box with oil and check for leaks.
Now start the motor, and put the box in gear both forward and aft, and check for leaks again (use a wee mirror to help you).
If the box leaks, it will drip and sling oil everywhere. Mine would sling a big line of oil up the engine room wall and roof.

Let me know how you get on.

If this does not work, then we can turn the shaft down by 2 mm on the diameter, and put the next smallest seal on there. Emery paper did not work when I tried it, even when used in a lathe. The next smaller ID seal is 120x98x12. The 98 mm ID seal was available in 1998. I trust it will be now.

Do not despair. We will get it to work and not leak.

You are welcome to PM me if you wish. I can talk you through it on the 'phone. It's not a problem if you prodeed systematically and it would please me no end if you did not have to go the whole way down the learning curve that I did. Some 15 years after I did, the gearbox does not leak, and on the same (Stifa) seal from 1998, and it cost 3.50, close to $5. Do not buy the seal from Volvo. It will cost you more than 14 times that (in 1998, 49) and it is the same seal. Paying $5 doesn't hurt, so buy two or three of them and keep them on board.

Oh, and never buy another engine from Volvo. The motor is affordable but the spare parts are not.


Last edited by Rockter; 12-24-2012 at 12:50 PM.
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post #4 of 6 Old 08-15-2013
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Re: Reverse Gear Losing Fluid MD7A

I have the same problem. Every time I go out I need to add oil to the reverse gear and the dripping oil is fouling my bilge.

I was in Napa Auto Supply recently and they have an oil additive that claims to stop oil leaks. Of course there is no guaranty it will work, but it might be worth taking a shot instead of going to the trouble of trying to replace the seal. Any comments on this? Is there a risk doing this?

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post #5 of 6 Old 08-17-2013
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Re: Reverse Gear Losing Fluid MD7A

The additives are the kind of thing that is so cheap to try that you have to do it. I have found that they work just about often enough to justify trying. They work by softening the seal so that it may reseal itself. That is if a hardened seal is the problem.
There are other problems that cause leaks also. So far I have had no problems related to the additive itself.

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post #6 of 6 Old 08-18-2013
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Re: Reverse Gear Losing Fluid MD7A

Thanks Mechsmith. A mechanic cautioned that if I put too much additive in it can gum up the transmission. It sounds like you have direct experience using additives. I'll give it a try.

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