Repair of Hurth ZF gear

[Mickeyrouse]

I’m having shifting problems on my Hurth ZF 25M gear. Is there anything peculiar to these gearboxes? Or should I expect a qualified transmission shop that works on manual transmissions to sort this thing out? I’ll remove the gear and place it on their bench.

[SailingHarmonie]

I have the same transmission, mated to a Volvo TMD22 and after 8500 hours it developed a leak in the rear shaft seal. When I looked at the drawing, it was obvious that the entire kit needed to be disassembled to change that seal. Something I don't have the tools or setup for on a cruising boat.

I talked with a major marine transmission shop, and they refused to touch it. They said by the time they got the parts (bearing, seals, other wear parts) and spent the hours to disassemble and put it back together it would cast much more in shop time than a new unit. Which is what I did. I even offered them the old one--for free--to rebuild on their own time. They STILL didn't want it. Frustrating that a $5 seal cost me $1600, but that's the way of things sometimes.

Don't forget, while you have the transmission off, it would be a good time to replace the damper plate. Your local transmission dealer should be able to source that for you.

[roryboy]

There are small transmissions designed such that both the input and the output shaft seals can be replaced without cracking the case. ZF makes the output shafts in one piece to save money. But not your money.

[Mickeyrouse]

Originally Posted by roryboy

There are small transmissions designed such that both the input and the output shaft seals can be replaced without cracking the case. ZF makes the output shafts in one piece to save money. But not your money.

[skipperpete]

To know the specific shifting problem helps a lot regarding how deep the dive into the transmission needs to be. It could be as simple as a worn shift yoke and thats relatively easy to replace, no need to strip the main shaft at all, just need new gaskets for the cover plates and a new yoke. You can strip the ZF 25 with a heavy duty puller and a selection of hollow spacers but the sticking point is getting the circlips out to release the spring pairs, it requires a steady pressure to compress those springs. Some mechanics here in Australia call em dollar an hour gearboxes… when they get toward 2,500 hrs they usually have some sort of problem that requires opening up the case and often its easier to buy a complete replacement.

[SailingHarmonie]

Originally Posted by skipperpete

To know the specific shifting problem helps a lot regarding how deep the dive into the transmission needs to be. It could be as simple as a worn shift yoke and thats relatively easy to replace, no need to strip the main shaft at all, just need new gaskets for the cover plates and a new yoke. You can strip the ZF 25 with a heavy duty puller and a selection of hollow spacers but the sticking point is getting the circlips out to release the spring pairs, it requires a steady pressure to compress those springs. Some mechanics here in Australia call em dollar an hour gearboxes… when they get toward 2,500 hrs they usually have some sort of problem that requires opening up the case and often its easier to buy a complete replacement.

And ours lasted nearly 9000 hours, so seems a bargain to me. If they are well treated and cared for, they last a LONG time.

It's actually my fault it failed. I missed the failing engine mounts that caused a misalignment that was the proximate cause of the failure of the seal.