M925A2 Front Winch Broke under load

[acolesurf]

This past weekend we were up playing in the snow with the M925A2, and I got stuck pretty bad in a snow drift. We ended up having to winch out, and after several hours of winching and shoveling, we were finally able to drive out and home.

The next day, I noticed a pool of hydraulic fluid under the winch, and upon further investigation noticed that the receiving pump(?) that attaches the the front drum had separated, and the bolts had stripped out of the case. That receiving pump(?) now rotates back and forth and it seems like the hydraulic lines are the only thing keeping it from going around full circle.

My question is, Has anybody else seen this failure before? Should I just helicoil the threads and reinstall it? I saw on a picture with one of Simp's trucks, he had what looked like an electric winch up front. This winch doesn't seem to have too much pulling power on a single line, so to get the truck unstuck, we had to use a snatch block and do a 2-1 back to the bumper of the truck. Would I be better off installing an electric winch instead of the hydraulic one?

Thanks for all the help everybody!

 

[tobyS]

It's a hydraulic motor, not pump.

It's not obvious where it's failed in the photo's. Is the flange shown on the last picture pulled away from the winch case? If so, it's hanging on, on the inner shaft and will probably be better to remove the motor and flange adapter. Is there only about 3/8" of length on the bolt that went into the case (seen sticking through the flange). See how far you can get a bolt to go into the case (before enlarging or doing anything). It should be grade 8 bolt... length is critical and you need 1" or so thread in the case. You may have to drill and tap to the next larger size bolt.

If that is where it came apart, it shouldn't be hydraulic oil, it would be gear oil.

 

[acolesurf]

Yes, the flange on the output of the hydraulic motor is separated from the winch case. Not sure why there was only 3/8" or so going into the winch case, maybe this was an after-military install? What is the purpose of that flange between the motor and the winch case? Just a spacer to align the output shaft to the winch gear?

 

[Scar59]

That's not right... appears the wrong lenght adapter bolts were used when assembled.

 

[74M35A2]

I know of a complete stock replacement winch in FL for $500.

Sounds like yours was weak anyway. Mine pulled me out of mud to the top of the tires, no problem, single line.

 

[M543A2]

I agree there was not enough engagement for the bolt threads into the aluminum case, and I agree with Toby's comments. Normal engineering practice is to have 1 1/2 to 2 x the bolt diameter engagement, up toward 2x best for aluminum. Someone used bolts that were too short. I would think with proper length bolts helicoils would hold it if there is not enough thread left as Toby says to just put in longer bolts as it is now. I would sure check that first, then if not good then go to helicoils with Loctite. If it does not hold you are not out much cost, but I don't think it will fail. The failure mode is probably that because the bolts were too short they easily loosened and allowed some rotational motion of the motor to the case interface to happen, ultimately causing the threads to fail.

 

[acolesurf]

I know of a complete stock replacement winch in FL for $500.

Sounds like yours was weak anyway. Mine pulled me out of mud to the top of the tires, no problem, single line.

I was researching a bit to try and see what to expect out of this winch in terms of pulling power. I agree, it doesn’t seem like I’m getting my full money’s worth with it right now. Before we went to 2-1 with the snatch block, it seemed like it was pulling until it reached the pressure bypass, and then wouldn’t pull anymore.

So to get more power out of it, it seems like I would have to increase the pressure bypass so the hydraulic pump can put more pressure into the motor. Not sure why it is limited to the 1,500psi out of the 3,500psi the pump creates, or what is the weak link in the system. The .5” cable should be able to handle a lot more.

Can the actual motor and drum be a loss of power to the winch assembly and be ‘weak’?


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[acolesurf]

Actually it looks like the breaking strength of the 0.5” steel cable is around 21,500lbs, so I guess bumping up the pressure bypass isn’t a good idea unless I know that it is bypassing at a lower psi than desired, which I don’t know how I would test that out for sure unless I hooked up some pressure gauges to the system...


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[porkysplace]

I was researching a bit to try and see what to expect out of this winch in terms of pulling power. I agree, it doesn’t seem like I’m getting my full money’s worth with it right now. Before we went to 2-1 with the snatch block, it seemed like it was pulling until it reached the pressure bypass, and then wouldn’t pull anymore.

So to get more power out of it, it seems like I would have to increase the pressure bypass so the hydraulic pump can put more pressure into the motor. Not sure why it is limited to the 1,500psi out of the 3,500psi the pump creates, or what is the weak link in the system. The .5” cable should be able to handle a lot more.

Can the actual motor and drum be a loss of power to the winch assembly and be ‘weak’?


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A weak hydraulic motor will limit the pulling power .

 

[acolesurf]

I guess the only real way to tell if this thing is actually pulling 20,000lbs is to hook it up to a scale and try pulling on it. I wonder how hard that would be to do?


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[porkysplace]

Was your truck a Red River Rebuild ?

 

[acolesurf]

Ya, it was


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[porkysplace]

That probably explains the bolts , they didn't really rebuild them.
Read post #8 of this thread RED River Army Depot
It is wsucougarx's post.

 

[Lukes_deuce]

I thought the cable was 9/16 or 5/8? It should have a higher working load than 21000. Usually winch cable is atleast 1.5 times working load (20,000 * 1.5) and then the cable's ultimate strength of 3X working load. Thats atleast how it should be rated. I have some 9/16 laying around that has a minimum breaking strength of 27000.

 

[porkysplace]

Actually it looks like the breaking strength of the 0.5” steel cable is around 21,500lbs, so I guess bumping up the pressure bypass isn’t a good idea unless I know that it is bypassing at a lower psi than desired, which I don’t know how I would test that out for sure unless I hooked up some pressure gauges to the system...


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The cable should be 5/8" x 200ft.
[h=1]5 Ton Winch cable size???[/h]

 

[tobyS]

Yes, the flange on the output of the hydraulic motor is separated from the winch case. Not sure why there was only 3/8" or so going into the winch case, maybe this was an after-military install? What is the purpose of that flange between the motor and the winch case? Just a spacer to align the output shaft to the winch gear?

They probably had a spline adapter that needed more length and put the extra flange in as a spacer, but they clearly failed to use long enough bolts. If they only pulled about 3/8 of an inch out, there is probably enough thread depth left to get at least 1/2" of thread engagement at the bottom of the hole. Run a tap into them and see if they clean up to start a bolt. You will need to custom fit the bolt so it doesn't quite bottom out when it's tight on the parts, but gets all the length of threads available. Socket head cap screws in that size are mostly grade 5, but you may need that head style.

There is a lot of torque to shear these bolts and push them sideways in the flange, especially with the extra spacer. I doubt that inserts would hold up.

Be careful that they are not through holes and you get a bolt into a bearing or some such interference.

 

[Jbulach]

Relief pressure is supposed to be 1750+-100, if I remember correctly. It would be easy to throw a gauge on one of the lines, while you have the motor off cleaning the threads up in the holes. Don’t forget to clean and reseal the flange as well, so you dont leak gear oil. If you need to adjust the pressure check out my dump bed install tread. Don’t go above the max pressure per the TM though, I believe the winch typically self destructs before the cable breaks.

However these winches are no different than any others, they are typically very unimpressive on the outer layers. I can stall mine without dragging the truck, with all six wheels locked, tires aired down, on soft dry ground. The beauty of using a block is not only do you double your pull, but you pull more cable off the drum as well, a pain you just have to get used to if your serious about winching. I have a 10k strain gauge, so I could put if on a two part line and get some numbers if they don’t exceed 20k, but I think that is all broke down in pull force per layer in the TM as well? I will try to pull a bolt out of mine and report back with length and grade. I don’t think the winch side housing is aluminum, but I could be wrong.

 

[tobyS]

The only problem with putting a gauge on is that it's open center and the pressure doesn't rise until there is a load that it can't move...stalled out...putting max torque on already failed bolts. I'm all for knowing the relief pressure but don't know how to make it go there without stalling the winch motor.

 

[Scar59]

My M925 is a'09 RRAD rebuild, I think I'll check my bolts too.

 

[74M35A2]

Winch is 200’ of 5/8” cable, unless it came with a level wind, then it has 250’ on it. Relief pressure is 1,800psi, built into the control valve.

Exterior gauge is risk of breaking off, unless just for testing and then plug the port.