Transmission remote oil change project on ZF HBW 360

[jr_spyder]

Like most boats the oil drain plug on my transmission is extremely difficult to get to. I can suck the oil out of the dipstick/filler plug with a hand pump but that never feels sufficient and I imagine crud sitting at the bottom of the box. And it's a fairly awkward job to do itself.

Conversely the oil in my engine and genset is super easy to change with a remote pump system. I'd like to do something similar with the transmission. It should be a straight forward project with most parts easy to get. I've done work on car transmissions and lines and know to get the right rated fittings for pressure and compatible with transmission oil.

My challenge at the moment is the boat is 2,000 miles away so I can't pull the transmission drain plug to see what size/thread it is and then get the right adapter to put in it's place to attach a drain line. I'd like to have all the parts in hand when I return to the boat to do this project.

It's a ZF HBW 360 transmission, probably from around 1988. I've contacted ZF and they have tried to be helpful but have no conclusive answer. Does anyone here know?

This project, as well a project I'm doing with my fuel lines, has given me an education in the huge variety of fitting types and thread types out there. It isn't easy. SAE, NPT, JIC, UNF, -AN, BSPP, BSPT, and a bunch of others. Straight or tapered? Crush washer or o-ring or no? SAE or metric? And of course sizes, angles, adapters, etc. It's a quagmire, but I've enjoyed learning.

ZF's suggestion (guess?) is that the plug is either a 1/2" or 3/8" BSP. BSP is British Standard Pipe (I had never heard of this before), but there is BSPP (parallel) and BSPT (tapered). For a drain plug I'm quite sure it wouldn't be tapered, and would have a crush washer. I can certainly bring more than one size with me, but I don't want to multiply this by the various possible thread types.

Does anyone know for sure? Other advice on this project?

Thanks,

JR

[a64pilot]

In truth there is very little if any crud in a transmissions fluid, unlike an engine that has carbon and sludge a transmission is primarily just wear from the clutch packs, so if you change it at its correct intervals, even if you only getting 80% of the oil, that is fine.

If I really wanted to install a pump, as opposed to trying to find a fitting that will likely be hard to find, I’d remove the plug and drill and tap the plug and install a NPT fitting as they can be found anywhere.