Drive Saver shaft coupling questions

[Barking Sands]

I have read previous threads on the topic. Some like them some dont. But has anyone had one and then had it fail? Either fail from the prop hitting something or just fail in general? I am interested in HOW they fail. Has there been any new thoughts on the matter.

https://propshopinc.com/drivesaver-5-quot-borg-warner-hurth-flexible-shaft-coupling-504/

Some claim that it will act as a "circuit breaker" in the driveline. Here is the verbiage from the website:

DriveSaver® absorbs extreme shock and torque usually caused by a hidden log, line, or rock. DriveSaver® is designed to break apart, leaving your transmission and engine intact. That's right. DriveSaver® gets destroyed, not your costly transmission and engine. That's the kind of total protection you can't afford to be without!

Seems like a suspect claim. With the bolting arrangement...if the flex portion comes apart there will still be an arrangement of bolts and nuts in the way of each other that would surely force the shaft to the side and make a terrible racket? Maybe even damaging other items such as shaft seal area or structure?

My boat came with one installed but its age is unknown. So I am thinking about replacing it...or just doing away with it. I think it has been in place for some time and I put new packing in the stuffing box a few years ago and its been perfect since that time only dripping a small amount while underway and not dripping at all while at rest. I really dont want to upset that apple cart by moving the shaft. Although I am a lifelong mechanic, in this area I dont have much experience. So I would appreciate the thoughts from the group. Currently I am leaning towards just replacing it with an identical new unit. Maybe keep this one as an emergency spare.

 

[RT Firefly]

Greetings,
Mr. BS. We had 2 on our previous boat. 18 years and no failures nor did I hit anything. I'm sort of in the "if it ain't broke, don't fix it" camp.

 

[Comodave]

They were installed in our last boat when we bought it. I had some vibration in the starboard side. I took them out and had spacers made by Spurs. Then we could do an engine alignment and the vibrations went away. The spacers were not cheap but they fit perfectly.

 

[Barking Sands]

Thanks RTF. 18 years x2 is a pretty good track record. That make me want to lean towards replacing it with a new one and keep this one as an emergency spare. One thing I forgot to mention is upon close inspection it seems like there may be internal separations. You may have seen when urethane gets week or compromised you can get what looks like internal "slices" or cracks that appear lighter in color emanating from the bolt holes. Its hard to tell. But its enough for me to either replace or eliminate this particular unit. in the short term.

 

[Barking Sands]

They were installed in our last boat when we bought it. I had some vibration in the starboard side. I took them out and had spacers made by Spurs. Then we could do an engine alignment and the vibrations went away. The spacers were not cheap but they fit perfectly.

I do have a very very slight vibration only at a few RPM ranges. I have not put a dial indicator on this shaft yet to see how true it is. To my naked eye it looks pretty good.

Why did you need spacers? Were you not able to just pull that shaft fwd 1 inch? Pretty sure I have room to do that. But as I said I cant see the surface condition of the shaft that would then ride on the stuffing box seals.
Do you remember the cost of the spacers?

 

[Comodave]

The shafts didn’t have enough room to pull forward in front of the props behind the struts. I don’t remember the cost but it wasn’t cheap, but what is with boats?

 

[Unclematt]

I have one on my boat and it failed going down the Illinois River. Had to get towed to Peoria where it was "repaired" Made it to Tarpon Springs just after crossing the Gulf when it failed again. Turns out I had broken engine mounts which should have been found by the mechanic in Peoria.

 

[Barking Sands]

I have one on my boat and it failed going down the Illinois River. Had to get towed to Peoria where it was "repaired" Made it to Tarpon Springs just after crossing the Gulf when it failed again. Turns out I had broken engine mounts which should have been found by the mechanic in Peoria.

When it failed did it spit the bolts out or did they just rattle together and make a racket? Any other damage except the shaft saver? Thanks for the reply.

 

[Barking Sands]

The shafts didn’t have enough room to pull forward in front of the props behind the struts. I don’t remember the cost but it wasn’t cheap, but what is with boats?

Thanks Dave. But if you had enough room you would have just pulled the shaft fwd and coupled it?

Anyone ever pull a shaft fwd or change the distance via other means and caused an issue? I wish I could see the condition of the shaft in the shaft log. If I knew it was smooth and in good shape I would probably just remove the shaft saver.

Again...as it stands right this second im leaning towards just replacing it old for new.

 

[bshanafelt]

Drivesaver makes two versions
One is ‘heavier duty and blue color instead of the orange

Mine has been in service for 20+ years and over 3000 hours with no trouble thus far

 

[Barking Sands]

Drivesaver makes two versions
One is ‘heavier duty and blue color instead of the orange

Mine has been in service for 20+ years and over 3000 hours with no trouble thus far

Thanks for the tip. Ill check it out.

 

[Slo-Mocean]

I used to run them on my commercial parasail boat and after a couple failures from light groundings decided i would much rather be able to save my vessel and have a possible bent prop than be stranded with no propulsion . I'm talking light sand low rpm groundings, it doesn't take much resistance to shear them.

 

[Cigatoo]

We have a drive saver or the like on our boat. Came with the boat so not sure of the exact manufacturer. We also have a steel spacer in the spare parts locker. It appears that if the drive saver gives one could install the spacer as a replacement. I have never done any of this (hopefully never will) so just an assumption on my part.
Single engine boat FWIW.

 

[Unclematt]

The first time I noticed a vibration that got bad very fast. That time it sheared the bolts. The mechanic only replaced the bolts and reused the drive saver. The second time it was destroyed and had to be replaced. The last repair was done correctly and has been problem free ever since.

 

[sunchaser]

A good thing to do every year or two is to retorque the coupling bolts whether equipped with a drive saver or not. Driver savers will not easily tolerate loose or mis-torqued bolts. My experts say bolt torque issues, mis-alignment or bad mounts create the preponderance of drive saver issues.

 

[Barking Sands]

All great info and much appreciated. I have decided on replacing with new. I will keep this one as emergency spare. I just need to get measurements so I get the same unit.

On the bolt tightness...great advice. Not long after acquiring the boat I put a wrench on each nut and some where loose. As a matter of fact some of the stack up of washers was not right. Another reason to replace this one as I suspect it had been run at times with moderatley loose hardware.

 

[SoWhat]

My DriveSaver buckled, in theory resulting in a 'slow' stop taking the shock away from the transmission. Not sure what would have happened to overdesigned Velvet Drive but I'm not sure I want to find out, I replaced it.

 

[Barking Sands]

My DriveSaver buckled, in theory resulting in a 'slow' stop taking the shock away from the transmission. Not sure what would have happened to overdesigned Velvet Drive but I'm not sure I want to find out, I replaced it.

View attachment 144652

Almost like a hard reverse situation. Odd though.

 

[High Wire]

Ours lasted 20+ years installed by one of the PO's. I removed it when installing a new shaft. To be clear, its more of a fuse than a circuit breaker. It fails once then replace. If you have one you need to carry a spare just like a fuse.

 

[Action]

A suggestion - use a thread locker on the fasteners when assembling.
Like the Drivesaver", thread locker keeps the fasteners together when the fasteners are being vibrated. You will not have the situation in post #16 with a thread locker.

Loctite makes two products. The blue is sufficient to keep things together and be able to remove at replacement time. There are other brands. A tube for under $10 will last a very long time. Not too many things that cheap for a boat.

 

[jleonard]

To be clear, its more of a fuse than a circuit breaker. It fails once then replace. If you have one you need to carry a spare just like a fuse.

When I repowered my old Mainship, the new setup was a little shorter than the oem. I had to move the shaft back approximately 1 inch.
When I discussed a drive saver with our marina,, they told me the same thing: if you go that way buy 2 because you'll need a spare.
I decided to have a 1 inch solid spacer machined and I installed that. I'm glad I went that route as it was no maintenance, no worries. With lock washers, it never loosened up and stayed in alignment.

 

[Brooksie]

I, perhaps, have the oldest Drivesaver here on my lobsterboat; 30+ years. One of the great, unsung, advantages of the Drivesaver is that it electrically isolates the driveline from the engine and thus the negative battery pole.
I do zinc my shaft, propeller, skeg bar, & rudder shaft but do not to connect to other metals, thruhulls and so on.

 

[Slider70]

Shortly after I purchased my last commercial salmon troller I installed a drive savor. I saved the old bolts removed to install the drive savor with the idea that if the drive savor was fractured I would just remove it and bolt up the coupling hard.

My throughs with the savor was it might save me some damage from getting one of my six steel trolling wires in my prop. The big tides in some areas I fished and emergency sharp turns could cause this?

Twice I got the wire in the prop but both times it just got sheared off instantly with no damage to the prop or the drive saver. I did finally have the drive savor fracture. This was the result of another vessel grounded in the harbour and trying to power loose. He blew ground line (very heavy line for longline fishing that some fool had junked on the bottom) up into my wheel as I was idling slowly forward. The line wrapped my prop until the driver fractured.

I don't know if it saved my twin disc gear or motor mounts? I suspect it did? But it didn't save my stuffing box as it was ripped completely out! A spectacular pulse raising result.

I didn't install a new savor. I simply went up on the ways, fixed the stuffing box and bolted the coupling back together with the bolts I had saved.

John

 

[Barking Sands]

Thanks for all the replies. Great info. 30+ years on a drive saver..wow. You might consider changing it though. That material does degrade with time.

 

[Steve DAntonio]

I've seen them break, I shared a photo of one that had failed in the earlier thread, however, I have never seen one save a drive. The proverbial solution in search of a problem.

If you install one, it can push the shaft far enough aft that it exceeds the recommended overhand distance of one shaft diameter.