Zf 5M Transmission failed, What is the replacement?

[ericseroijohnson]

Just pulled a failing 5M transmission off a Universal (Westerbeke) M20. Looks like $1250 to rebuild, but a 6M or 10M may cost not much more.

The 6M and 10M are a little longer (.95").

Have these been a satisfactory replacement for the 5M?

The first 5M failed after 50 hours. It was warranty replaced by Universal. That one failed after 100 hours. We determined that the prop was not properly engineered (lugging the engine). That failed 5M was rebuilt after re-propping. Now 600 hours later that rebuilt transmission is toast.

The re-propping allowed easy cruising at 2500-3000 rpm. At 3500 rpm the transom would get a little sooty.

Any recommendations?

Eric Johnson

[Pub911]

I replaced a Hurth 50 with a zf 6. The H50 was the same spec as the zf5, so i think my experience may be of interest.

As you mention, the zf 6 is about an inch longer, so I did have my shaft shortened and rekeyed to keep the prop right where it was. I had the good fortune of having enough room aft of the engine, so that the longer unit did not represent a major structural issue. I did have to redrill the cable-mount plate to adapt to a new bolt configuration - you may or may not have this issue if you're going from a zf 5.

Detailed design specs are available on the website for zf - don't have it handy, but if i find it I'll post it here. These were helpful in resting my concerns on fit.

I will also post a reference of the vendor that sold me the replacement (new) zf6 - it was surprisingly close in price to a rebuild I was considering - something like $1,200/usd. I was also able to get $150 back on my H50 from a local deisel mechanic in CT.

The unit has been in all season without an issue. I'm thrilled with it - and with the fact that I didn't botch anything in the process (e.g. shaft alignment).

Good luck.