ATF change on hydraulic transmission: is there a better way?

[S/V Alchemy]

Having passed the "breaking in" period of my Beta 60, it was time to do the initial transmission fluid and filter change. It's a Hurth ZF25A hydraulic transmission which with I am quite pleased to date.

The problem arose when I needed to drain the "old" (still looked pristine to me) transmission fluid. The drain plug is an odd size for what I assume is a European design: it took a 7/8" socket, but it was a little loose so maybe it was actually a 23 or 24 mm metric socket...which I don't have that big of a metric socket....

I had to crack this above a deep (nearly three feet) bilge space, as it's a steel full-keeler and for the most part, by feel. The container I had was too small and I probably drained about half the 1.8 litres of ATF into this bilge. Oh, joy.

Two solutions suggest themselves: One is to someone hang a pan or bucket off the coupling or the transmission housing to capture the draining ATF so that I have a hand for the plug, which I do not wish to drop down the deep bilges, and a hand for the socket wrench. The other is to do what I did with my previous sailboat's Atomic 4 (which has a common sump for both block and transmission): I tapped and put in a brass elbow and a petcock at the lowest point of the oil pan and pumped out the oil at change times with zero spills directly into old antifreeze jugs.

The Beta actually drains its own sump this way. My question is this: has anyone actually replaced the drain plug of the transmission with a hose barb and petcock to facilitate ATF changes and has either pressure or heat caused problems? As a safety factor, I could secure any hose involved so that it is above the engine and could also make the petcock secured so that it could not open without intent. Thanks to all who answer.

[sailah]

I guess my first question would be to determine the thread size. Easy to do if you have the plug in your hand. Most metric threads are straight threads and would require an O ring or gasket of some type to seal.

Most US threads that seal like that are NPT threads and the thread is tapered, these seal with out a gasket or o ring.

Once you know the thread it's easy to get fittings etc to build a short hydraulic hose whip than you can secure out of the way to facilitate draining.

I'm doing a similar task to my engine in a thread here. Maybe I'll do transmission too now that you've got me thinking about it.

Based on the tools required per their service manual 7/8" is indeed one of their sizes but so is 22mm which would be a "small" 7/8" 0.875 (7/8") 0.866 (12mm)

http://www.bukh-bremen.de/files/346/...s%20ZF45-1.pdf

[a64pilot]

Silly question, but can't you suck it out?
If not it's real common on aircraft to have a quick release drain for their oil sumps, slip a hose on and simply push open the drain, then I know you could suck it out if a gravity drain method isn't possible
Have to know the thread of course
http://www.aircraftspruce.com/catalo...clickkey=20487

[Kokanee]

On my ZF25A, I just suck the old transmission fluid up the dipstick hole. I do it soon after I shut the engine down, before any sediment may drop out. From my calculations this method drains over 90% of the volume, so I'm happy with that.

[Lepke]

I have 2 mains and 2 generators. I plumbed in all plus the transmissions to use the bottom drain and have a flexible hose (to avoid vibration damage) and a ball valve that can be locked. I prefer to drain from the bottom drain so I get all the old oil. Unlike sucking out oil.
I have a centrifuge, so I also have plumbing and a pump to move the oil between the centrifuge and engines. Makes the equivalent of an oil change a couple minute job.

[bongo]

Our boat has a Westerbeke 40 with a Paragon Hydraulic Transmission. I could not believe how difficult it was to c/o the lubricants. And most of it would end up in the bilges. You had to be a contortionist with long arms. Sailah is correct on the European straight thread vs the NPT taper thread. I used Permatex #2 to seal/lock the threads. I put a hose barb in each drain with a high grade hose that was long enough to loop up over the transmission/V-drive. The other end of the hoses have barbs and pipe caps. Changes are now easy, and not one drop is spilled. Been this way 10 years.

[sailormon46]

I use a gallon freezer bag. Works really well when there is no room for other containers.

[S/V Alchemy]

Originally Posted by sailah

I guess my first question would be to determine the thread size. Easy to do if you have the plug in your hand. Most metric threads are straight threads and would require an O ring or gasket of some type to seal.

Most US threads that seal like that are NPT threads and the thread is tapered, these seal with out a gasket or o ring.

Once you know the thread it's easy to get fittings etc to build a short hydraulic hose whip than you can secure out of the way to facilitate draining.

I'm doing a similar task to my engine in a thread here. Maybe I'll do transmission too now that you've got me thinking about it.

Based on the tools required per their service manual 7/8" is indeed one of their sizes but so is 22mm which would be a "small" 7/8" 0.875 (7/8") 0.866 (12mm)

http://www.bukh-bremen.de/files/346/...s%20ZF45-1.pdf

Thanks for that link! It will come in handy. To answer your question, yes, it is likely a metric thread and does feature an O-ring. Of course I have a 21 mm socket but not a 22 mm!

[S/V Alchemy]

Originally Posted by a64pilot

Silly question, but can't you suck it out?
If not it's real common on aircraft to have a quick release drain for their oil sumps, slip a hose on and simply push open the drain, then I know you could suck it out if a gravity drain method isn't possible
Have to know the thread of course
SAF-AIR OIL DRAIN SUMP VALVES from Aircraft Spruce

The gravity drain is actually all too possible. Works really well and is clearly at the low point in the housing. The issue is that the hydraulic innards are pretty closely packed in there, and I would hesitate to push any kind of hose down into the workings as I would with, for instance, the oil sump on a diesel, where I know the workings are relatively large and predictable bearings, journals and cranks.

That's why I'm toying with the idea of a hose barb.

[S/V Alchemy]

Originally Posted by Kokanee

On my ZF25A, I just suck the old transmission fluid up the dipstick hole. I do it soon after I shut the engine down, before any sediment may drop out. From my calculations this method drains over 90% of the volume, so I'm happy with that.

That's possible (see above) but I'm reluctant to do that here. Prior to tapping the common transmission/block pump of my old Atomic 4, which sat at the maximum 15 degree angle, I used to drain the oil by taking off the gearbox top plate and pumping out one of the lowest corners...but with the plate off, I had a very good top-down view and could avoid touching the hose to any part of the (considerably more basic) planetary gears of the motor.

[S/V Alchemy]

Originally Posted by Lepke

I have 2 mains and 2 generators. I plumbed in all plus the transmissions to use the bottom drain and have a flexible hose (to avoid vibration damage) and a ball valve that can be locked. I prefer to drain from the bottom drain so I get all the old oil. Unlike sucking out oil.
I have a centrifuge, so I also have plumbing and a pump to move the oil between the centrifuge and engines. Makes the equivalent of an oil change a couple minute job.

You've clearly thought this through. I assume you have no leaks from any of the plumbing and have used the right thread sealer for oil and ATF?

Thanks to all for your thoughtful answers. I like to do a sanity check now and then. I have now 300 hours runtime to consider my next step.

[boeing1]

I also suck out the ATF via the dipstick, as much as it holds it is not a big problem.

[soerencarlsen]

7/8=22mm and don´t use an open end spanner

[sailah]

You could always take your drain plug, drill and tap it for something like a 1/4" NPT. A lot of hydraulic hoses are 1/4" NPT and cheap. Leave the hose attached and secured with a pipe cap on it. When ready to drain, remove cap and suction to your container.

The drilling and tapping of the drain plug I would do in a lathe to make sure it's concentric.

I'm going to do this on my ZF Transmission this fall when I install my remote oil change pump. Happy to do yours no charge if you want to go this route.

[S/V Alchemy]

Originally Posted by sailah

You could always take your drain plug, drill and tap it for something like a 1/4" NPT. A lot of hydraulic hoses are 1/4" NPT and cheap. Leave the hose attached and secured with a pipe cap on it. When ready to drain, remove cap and suction to your container.

The drilling and tapping of the drain plug I would do in a lathe to make sure it's concentric.

I'm going to do this on my ZF Transmission this fall when I install my remote oil change pump. Happy to do yours no charge if you want to go this route.

Thanks for the kind offer, but I believe I could manage that and I have the right lathe. It's an interesting idea and 1/4" NPT is quite doable. Gives me the best of both worlds, really, and leaves that big plug in place. I'd still want a small petcock, however, as a safety element, and I would have to consider the volume of the hose as part of the ATF quantity otherwise. I would also imagine that even with a short run time to warm up the ATF, flow would be improved.