Changing transmission fluid in my ZF Hurth HBW 50 transmission. How simple is it?

jviss · Jun 14, 2023

Muttondressedaslamb said:
crappy Hurth HBW 50 transmission

Why "crappy?" I find those to be bullet-proof. And yes, you can just suck and fill, no filters. Best to do it while warm.

BigEasy · Jun 14, 2023

Muttondressedaslamb said:
Can I just drain the fluid through the dipstick hole with an extraction pump, then replace with new lubricant

Yes, that is the method to use. Usually there are no filters on these small transmissions. There isn't much oil in the transmission; If you use a measuring cup, when extracting the old oil, it will give you a good estimate as to how much to add. Going to have to do some research in your engine manual to determine what type of oil to use. My Kanzaki uses 20-30 wt motor oil.

jviss · Jun 14, 2023

BigEasy said:
do some research in your engine manual to determine what type of oil to use.

Yes, typically non-detergent SAE 30.

Terry Cox · Jun 14, 2023

Our boat has the type of transmission oil needed stamped on the bell housing, which was ATF. User manual contradicted the service manual; one said engine oil the other said ATF. The PO used engine oil. I replaced it with ATF. Used a vacuum pump to extract the old oil.

Our dip stick has a small ring mark about one 1/8" above the stick bottom, which is the full mark. Correct amount is determined by placing the dip stick cap on the transmission housing, not screwed in. No filters involved with ours. Very easy to replace.

BigEasy · Jun 14, 2023

Terry Cox said:
Our boat has the type of transmission oil needed stamped on the bell housing, which was ATF. User manual contradicted the service manual;
Our dip stick has a small ring mark about one 1/8" above the stick bottom, which is the full mark. Correct amount is determined by placing the dip stick cap on the transmission housing, not screwed in.

Good stuff @Terry Cox!
The oil type is also stamped on my Kanzaki transmission. My dipstick has the small indented ring also; very difficult visualize if the oil is relatively clean. (I have excellent close vision!) A mechanic showed me a trick to simply roll the dipstick on a clean paper towel to visualize the oil level. And, that is an important distinction to not screw the dipstick back into the housing when checking the oil level; just place the dipstick in the housing without screwing it in. (I have read multi page threads about screwing in vs inserting stick on housing arguments for properly checking oil level!) One final word of caution, do not overtighten the dipstick if the top part is plastic; the Kanzaki sticks are notorious for breaking off in the threaded part of the transmission housing.

Stu Jackson · Jun 14, 2023

jviss said:
Yes, typically non-detergent SAE 30.

This is completely wrong for a Hurth transmission. Hurths use Dexron ATF.

jviss · Jun 14, 2023

Stu Jackson said:
This is completely wrong for a Hurth transmission. Hurths use Dexron ATF.

One or the other, ha, ha! The manual is the definitive spec, as always.

Hollyberry · Jun 14, 2023

Stu Jackson said:
This is completely wrong for a Hurth transmission. Hurths use Dexron ATF.

Correct and important!!
Hurth/ZF gears have been pretty good to me over the last 40 years or so..

sesmith · Jun 14, 2023

FWIW, the rebuilder of my ZF (Hurth) 15ma told me to use the older version of Dexron, not the new synthetic Dexrons (V or VI now). The only place I can seem to find it these days is in the NAPA stores, sold as "Dex /Merc". Also, you should be changing it more frequently. I change mine at every 100 hr oil change, but then, I spent a bit of money getting it rebuilt a couple of years ago.