ZF 25 M - Can I Swop it Out for a Different / Better Gearbox ?

[Simes]

Our very old Hurth gearbox has failed. It needs to be replaced but upon reading a few of the posts here I am beginning to wonder if the ZF is any good at all?

Does any company make a direct replacement for the ZF range? The ZF 25 M is the current replacement for our gearbox and old M 250 ( I am told).

Thank you,

Simes

[Sailmonkey]

Twin disc makes gearboxes that bolt up in place of ZF gears. Check the dimensions of the mg-360.

[TeddyDiver]

Think the real question is if the new fits also directly to the old shaft too?

[Sailmonkey]

The ZF and Twin disc both use the same shaft couplings. The only problem is the overall length. I think the twin disc is a hair longer than the ZF. For me it was not a problem to move the shaft aft by a 1/4 inch.

[Simes]

Sail monkey and Teddydiver,

Thanks for your fast response. The twindisc sounds like it could be the answer to my problem. Are these good boxes? Reliable, well made etc?

I will search their web site for a British supplier.

Thanks again.

Simessail

[Sailmonkey]

I'm impressed by the build quality, it seems to shift better than any of my ZF gears ever did.

[Jim Cate]

G'Day Simes,

Your post begs the question: if indeed your ZF tranny is "very old", why do you think that they are of inadequate quality/design? Over the many years, abuse or lack of maintenance could have shortened its life expectancy... one can imagine lots of scenarios of this sort.

I'm not a particular fan of ZF/Hurth trannies, having had to replace ours after 12 years of use, but I believe that in our case it was due to a marginal specification: the builder should have used the next larger size for this installation. Further, internet research revealed that for these transmissions it is important to regularly change the ATF fluid, and to use the particular grade specified, and in our case this may well not have happened. One wonders if that could have been true for your boat as well?

I've no experience with Twin Disk boxes, so can't comment on relative quality.

Cheers,

Jim

[Dennis.G]

Although I am having problems with my Hurth transmission, it has worked for 26 years on the boat, so I would not be one to call it unreliable.

The ZF 25M replaces the Hurth HBW 250. I don't know that anything changed other than the nameplate.

[Simes]

Hi Jim,

I recognise that my Hurth is very old. It is not the quality of my gearbox that I am commenting on. There are however many comments about the difficulties of gear change, hard clunks when engaging gear, rough running, seemingly constant oil topups and frequent oil changes.
These are the comments that make me wonder if there is not a better gearbox for my vessel?

For what it is worth I am probably going to rebuild the old box as the cost of a new one is close to £2,000. I think that I will keep my eyes open for a secondhand ZF / Hurth to keep as a service spare.

The Twindisc boxes do look to be nicely made with a lot of time and effort spent upon the gear bevels.

Thanks for all of your help and advise, you have helped me to arrive at what I believe is the right decision for our vessel.

Simes