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Hydraulic problems on M817 Dump

Ed033177

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Hey guys I’m new here and looking for any help I can get. We have a m817 dump truck that the drive shaft for the pto came off of the transmission side and stuck into the ground while drive and it broke the input shaft of the hydraulic pump. Truck is loaded. Get a new pump put on and it will not do nothing. It will barely try if you rev to about 2 grand and pump got hot well I thought I just got a bad pump. So this time I replaced everything pump, pump bracket, and valve housing Problem solved it dumped the load with no problem, so I thought. After using truck the hydraulics have been slowly getting weaker and weaker now it’s back to where it will not lift a load without reviving it to 2 grand and if you let off the fuel it falls right back down. Before all this happened it would lift whatever you put in it at an idle with no problem. All linkages are adjusted correctly to my knowledge. The valve is being pushed as far as it will go with the lever so I don’t think that is the problem. The oil that was in it seemed to be thicker than hydraulic fluid. Do I need to put thicker oil in it. I am at a loss so any help would be greatly appreciated. Thanks
If I don’t respond back to any of your answers I sorry because I’m on the slow side of technology and how all this post stuff works. So thank you in advance and hopefully I can follow all this and be able to see all of your comments.
 
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Mullaney

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Hey guys I’m new here and looking for any help I can get. We have a m817 dump truck that the drive shaft for the pto came off of the transmission side and stuck into the ground while drive and it broke the input shaft of the hydraulic pump. Truck is loaded. Get a new pump put on and it will not do nothing. It will barely try if you rev to about 2 grand and pump got hot well I thought I just got a bad pump. So this time I replaced everything pump, pump bracket, and valve housing Problem solved it dumped the load with no problem, so I thought. After using truck the hydraulics have been slowly getting weaker and weaker now it’s back to where it will not lift a load without reviving it to 2 grand and if you let off the fuel it falls right back down. Before all this happened it would lift whatever you put in it at an idle with no problem. All linkages are adjusted correctly to my knowledge. The valve is being pushed as far as it will go with the lever so I don’t think that is the problem. The oil that was in it seemed to be thicker than hydraulic fluid. Do I need to put thicker oil in it. I am at a loss so any help would be greatly appreciated. Thanks
.
Well, I can say that the oil in the hydraulic system should be a 10wt oil. It definitely shouldn't be "thick" at all.

Possibly disconnect the PTO linkage, then operate the PTO from under the truck.
Does it work that way?
 

msgjd

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in the process of everything, did you lose a woodruff key(s) in the pto driveshaft? If so, the shaft might appear to spin but be slipping the second you move the hoist lever .. That would also explain the gradual worsening of the situation.. It's one of the possibilities, look at the easiest solution first.. Did you have a Soldier-B watch from below?
 

Ed033177

Member
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Location
Tuscaloosa
in the process of everything, did you lose a woodruff key(s) in the pto driveshaft? If so, the shaft might appear to spin but be slipping the second you move the hoist lever .. That would also explain the gradual worsening of the situation.. It's one of the possibilities, look at the easiest solution first.. Did you have a Soldier-B watch from below?
Both keys were put back in and set screws tightened but that doesn’t mean something hasn’t sheared so I will definitely check that. And no I have not physically watched while trying to dump a load but I have while raising and lowering with it empty. Thanks for the info on something else to look for.
 

Ed033177

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Tuscaloosa
Update. Truck was sent to shop and they informed me that we are overloading the truck hauling 10 to 12 tons and we should only be hauling 5 tons. Truck was dumping 12 tons with absolutely no problem until the drive shaft came off and busted the pump. Does anybody have any ideas. We are at a loss please anybody help with any ideas.
Thanks
Eddie
 

BEASTMASTER

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ya the truck is designed for 5 ton overland but can haul 10 ton on paved roads, I used to haul 10 ton + loads alot up north, nothing phased that hyd system, did the mechanics put a pressure gauge on the pump to see what it was putting out ?? they should have??
 

Ed033177

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Location
Tuscaloosa
Yes we were hauling 10 to 12 ton loads with no problems before. The mechanics just put 5 tons in it and said it dumped fine but I know good and dang well they had to give it fuel to make it dump even the 5 tons. I thought they were going to put a gauge on it but nope just told us we are over loading the truck. I am starting to think that they can’t figure it out and just want to throw the over loaded card at us.
 

msgjd

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ON-road, i have carried/dumped 12-14T of material using about 1/3rd throttle to dump, with no issues other than we have to keep an eye on the sheet welds and condition of the metal (if any rot) along the bedsheet above the hinges... The beds themselves are the weak point on these 6x6 trucks, a lot of leverage is put on the welded joints above the hinge area, more if the load is peaked higher at the front of the bed than mid-to-rear... I always try to stay away from the temptation to stuff the front higher than the rest or make use of the headache rack area .. I had welds break loose at the rear once long ago on a rusty M51.. it's not a good sign when you see the rear of the bed lifting in the mirror and not the front :(

The other concern is to not load them 12-14T every trip all day/every day.. It raises heck with the suspension (dogbone rubber bushings) , especially on tight turns on blacktop, intersections, or rudimentary (uneven) roads
 
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Ed033177

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Location
Tuscaloosa
Yessir thats what I was thinking. I am hoping that our problem is the rebuilt pumps. Hopefully we can get them to put a new one on it and that will solve our problem. But I’m starting to think that they are gonna keep throwing excuses until our 60 day warranty is up. 🤷🏻‍♂️
 

Jbulach

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Sounds like you need a different hydraulic repair shop. They need to check the pressure before throwing anything at it. Probably just a broken spring or stuck spool in the pressure relief.
 

Ed033177

Member
17
25
13
Location
Tuscaloosa
Well I would agree with you on that but the problem is is that everything has been replaced with bran new parts except for the pump they have all then rebuilt ones. The first rebuilt pump we put on it would not even lift the bed the second one worked fine for about 2 dumps and them got weaker and weaker so that’s why i think it’s the junk rebuilt pumps. And no they did not pressure check the pump like I thought they were going to do because we discussed doing that. When I asked them what they found on the hydraulics they just said we put 10,000 lbs in it and it dumped fine and that is the load limit. Like I said earlier even with 5 tons and the oil cold I know that they had to give it fuel to make it dump. Once you dump a couple times throughout the day and the oil starts getting hotter it about want raise the bed. I guess tomorrow I’m gonna have to start being a total jack butt to get them to actually try to figure out the problem. Anybody got any good suggestions on a good shop that actually knows how to work on these things cuz apparently I have been mislead on what all this place actually does and is capable of doing because on another note I asked them to adjust the valves and check the injectors because to seams to be raw fuel coming out of the exhaust. They just said the injectors are not leaking fuel anywhere 🤦🏻‍♂️
 
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