Hurth / ZF M15A Transmission Failures

[tomj]

Now for the Final SAGA!!!

After my last trans failure back in December 2009 at Green Turtle Cay in the Abacos, I replaced the trans with my 'spare' trans. To make a long story short, I had my failed 'spare' rebuilt while in Man O War Cay in the Abacos by a knowledgeable trans mechanic there. Same old story - the forward clutches and forward thrust washer failed - badly worn - causing slippage in 'forward' gear. I then had a 'rebuilt spare' to carry with me just in case.

In late April (2010) we successfully crossed over to Ft. Pierce, FL from Great Sale Cay in the Abacos. Spent a few days in Vero Beach, FL, and then proceeded up to Ponce Inlet (near New Smyrna Beach, FL) for a 2 day offshore run up to Georgetown, SC. When just south of the Charleston, SC inlet, we experienced our 5th transmission failure while motor-sailing offshore (there wasn't much wind). Like all of the previous failures, we had little or now warning of the impending failure - we simply began to slow down!!!! Checked a few things (like checking if we had lost the prop - but reverse worked fine)!!! Oh, by the way, we only got about 120 hours out of this last transmission!!!!!

Anyway, the failure occurred at about 2230 in the evening (we were planning on reaching the Georgetown inlet at slack tide the next morning at about 0700 to catch the flood current into Georgetown), about 25 miles south of the Charlestone inlet. Not wanting to enter Charleston Harbour at night, and as the weather was great, but only a very light wind, we decided to sail (at about 2.5 kts) toward Charleston, and have Tow Boat US (we had just upgraded to the 'Gold' towing service vice the regular 'Unlimited' Towing package) meet us at the inlet at dawn. Consequently we had a tow into Charleston to the City Marina. We had originally planned to replace the recently failed trans with the rebuilt spare which we carried, but after considering our luck(??) with this transmission, decided to call our friends, Kip and Linda (who run 'Boat Lovers Transport' of Coles Point, VA - only a few miles from our home in Kinsale, VA) and have them transport SHEARWATER back home to Kinsale, VA. We got towed again by Towboat US to a nearby boatyard, where a few days later we were loaded and heading north on I-95 to VA (amazing how the old boat beats to windward at 65-70 MPH - and with no masts or sails up!).

Anyway, we are back home from the Bahamas (great trip except for the transmission breakdowns) and trying to decide how to re-engineer our power plant with a different type/brand of transmission. Still leaning toward a Twin Disc...........

Tom and Kaye back home in Kinsale, VA

[Stillraining]

Dang sorry to hear this again...I have the same tranny...don't know if its an "a" designation though.

Im hoping not to put 120 hours on it in 10 years though. we will see how that works out.

[tomj]

The "A" in the 15 MA model designation means that it's an 8 degree down angle trans - they look about like the 15 M trans, except that the output flange is 8 deg down from the input shaft - makes for a more level engine - in my case the engine sits at about 10 deg from horizontal vice about 18 deg.

Good luck on your trans -

[NCboatrx]

Technodrive have info on their new TMC60A transmission on their website but we have been told that it wont be available until the end of this year.
Stanley

[Steve Pope]

I am just in the process of replacing my 2nd ZF10 transmission with a PRM150 hydraulic box, after the 2nd failure I felt I could no longer trust the ZF. As I have to reposition the motor to accept the PRM I am also fitting a python drive CV type coupling at the same time. I was able to import the box, coupling and heat exchanger from the UK including freight for less (just) than the replacement cost of a new ZF10 which had a delivery time of app 6 weeks against 1 & 1/2 weeks from England.

[tomj]

Originally Posted by NCboatrx

Technodrive have info on their new TMC60A transmission on their website but we have been told that it wont be available until the end of this year.
Stanley

Stanley,

Thanks for your input - I just looked at the TMC 60 A specs on the Technodrive web site. I will be looking into this trans (spec wise) as a possible replacement - will have to look whether it will mate up with my original bell housing. Hopefully, their specs are not as inflated as the Hurth!

PHASOR is now using the Twin Disc MG340 & MG360 gears which will mate with my bell housing, however they are straight drive vice down angle. The TMC 60 A is a 7 deg down angle vice the 15MA is an 8 deg down angle, but that would not require much change to the eng beds/mounts.

Tom in Kinsale

[Blue Stocking]

I have over 2000 hrs on my HBW150, which I think is the old designation for the ZF 15, with no problems. Clunks into gear , clunks coming out, rattles in between, but performs great.

[NCboatrx]

Technodrive of Italy was purchased by Twin Disc some years ago. The TMC 60 is marketed in this country as the MG360.

The bolt up and the input spline of the TMC60A will be exactly the same as the standard TMC60. This should be the same as your ZF. The output coupling is also the same.

Regards, Stanley

[tomj]

For your information, the thrust washers (on the 'forward' side) have been considerably worn - at least on the two which I've rebuilt (photos of these 2 washers are shown below) - the rest were replaced under warrantee and I never received info on their 'post mortems'.... Seems that the thrust washer is a poor substitute for a proper thrust bearing (either roller or ball bearing thrust bearing), as it is a steel washer (approximately 2.1" Diameter; .2" thick; with an 1.25" hole in the center) with a thin 'sintered bronze' layer on the wear side. One thrust washer has worn completely through the bronze layer and has considerable wear into the steel. The other washer shows considerable wear on the bronze layer, but is not completely worn through the bronze layer. The bronze clutch plates show some wear (approximately 0.012" on each of the 4 bronze clutch plates).

Tom in Kinsale, VA

[Stillraining]

Thanks for that info Tom...That is unbelievable with 200 hours on it.

We had my tranny apart but didn't see anywhere near that amount of ware...There was some pitting on the gears though...Time will tell how it holds up. ...FWIW mine is also the older HBW150, with an undisclosed amount of hours on it.

[tomj]

Have heard from several unrelated sources (mechanics) that the 'old' Hurth/ZF 150's had long lifes, and were good boxes - something happened around 2000 (perhaps some re-design??) and the failure rate went 'way up'. Today I ordered a Twin Disc/Technodrive TMC60A, which is a 7 deg down-angle (vice 8 deg. down angle with the Hurth/ZF 150A). The new trans will be a direct bolt-on to my existing adapter/bell housing, and is basically the same length with the same output shaft bolt pattern, so looks like I can use the existing prop shaft. As I ordered the trans with the 2.45-1 reduction gear ratio, I will need to go to a slightly larger pitched prop.

Tom in Kinsale, VA

[Jetexas]

I just finished rebuilding a Hurth ZF5 transmission for my 2 cylinder Phasor project.

When I bought it, it had reverse but no forward. Upon disassembly I found very little wear on the clutches and the shifter was properly click the output shaft into forward and reverse. However, the gears on the input shaft were not connecting with the output shaft.

There are ring shims that are fitted on the ends of the shafts under the caps to properly align the input and output gears, so that they engage. The exploded diagram shows four shims on each shaft, but when I disassembled mine, I found three shims on the input shaft and two on the output shaft.

When I reassembled it with the same amount of shims, I had reverse, but it totally locked up in forward due to poor gear alignment. By trial and error I found that proper shifting and engagement actually precluded the use of any shims.

I get the feeling that the gears in these Hurst ZF boxes shift slightly on the output shaft over time and the alignment of the gears is actually a bigger cause of failure than clutch plates and bearings.

But then again, who knows what my box actually went through in its previous life, and I'm just a random guy with a workshop manual and a wrench.

Phasor does put weird looking damper plates on their motors.

[Boracay]

My experience with pitch calculations suggests that the accepted methods give a little too much pitch on heavier cruising type boats.

Is it too difficult to check how the existing prop performs before repitching?

[tomj]

Hope this is the last post I make on this LONG thread. We had our 5th trans failure while offshore from Ponce Inlet, FL to Southport, SC back in May, on our way back from the Abacos. We were motorsailing (about 5 kts wind) and just south of Charleston, when we started going slower - no adverse trans noise, etc. - I said "Oh Fudge"! as I knew we had another trans failure. To make a long story short, we sailed in to the breakwaters off Charleston, called Towboat US (Gold by this time), and got towed to the City Marina (nice place by the way). We had a spare trans with us, but with our 'success' with these trans (about 120 hours on the last trans rebuild), we decided to call our friends and neighbors near Kinsale, Kip and Linda who own 'Boat Lovers Transport' and have them truck us back to the Chesapeake. By this time we have -0 confidence in this trans. Amazing how well an Alberg 37 goes to windward at 55kts and even without the masts / sails up.

Anyway, after a lot of research/measuring/pondering AND time and effort, we now have a brand new Twin Disc 60A transmission. We just returned from a short shakedown cruise, and have about 18 hours on the unit. Seems very quiet/smooth, etc. Hopefully, it will be a keeper. The installation was fairly straightforward, but did require a bit of 're-engineering,.

Our thanks to Twin Disc folks, to 'Stanley' and others on this forum for their suggestions and recommendations.

Tom and Kaye

[Maine Sail]

Originally Posted by tomj

For your information, the thrust washers (on the 'forward' side) have been considerably worn - at least on the two which I've rebuilt (photos of these 2 washers are shown below) - the rest were replaced under warrantee and I never received info on their 'post mortems'.... Seems that the thrust washer is a poor substitute for a proper thrust bearing (either roller or ball bearing thrust bearing), as it is a steel washer (approximately 2.1" Diameter; .2" thick; with an 1.25" hole in the center) with a thin 'sintered bronze' layer on the wear side. One thrust washer has worn completely through the bronze layer and has considerable wear into the steel. The other washer shows considerable wear on the bronze layer, but is not completely worn through the bronze layer. The bronze clutch plates show some wear (approximately 0.012" on each of the 4 bronze clutch plates).

Tom in Kinsale, VA

Tom,

This is VERY common on the Hurth/ZF boxes, except for the v-drives. This is especially true if the gear is accidentally left in forward while sailing. Leaving in in the direction of sail & spinning allows metal particles from wear into the transmission fluid. When the gear box runs these metallic particles are "splashed" up into and make it to the thrust washer and go to town wearing it away.

Changing the fluid in the Hurth/ZF boxes MORE than the recommended intervals can increase the life. I change mine once per season or every time I accidentally kill the engine with it still in forward, even for just a few minutes. If you have inadvertently left it in forward while under sail and spinning the fluid should be changed asap. I always "flush" it too with a sacrificial quart or two which is far less money than a new box.. I also ALWAYS drain it off the bottom and never use the "suck it out" method, which always seems to leave behind the metallic bits.

Here's another toasted thrust washer..


And some toasted clutch plates from leaving it in forward while sailing.