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M936a1 boom leaks down

NDT

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It's likely the boom cylinders bypassing internally. I would put a stethoscope on the control valve to attempt to hear if oil is flowing there which would tend to confirm the cylinder diagnosis.
 

Mullaney

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My m936a1 boom leaks down quickly after picking heavy load, where should I start looking?
I agree with NDT. Cylinder Packing (rubber o-rings and quad rings) get tired over time. My jib cylinder (extension) started out with the "leaking back" problem... Over time, it has finally started leaking around the "wiper ring" on the cylinder. Trouble is that in BOTH situations - without a pair of A-Frame hoists and chain falls - or another wrecker it is a little bit difficult to remove the affected cylinder to repair it.

There are two lift cylinders on the boom where your drifting down problem seems to be happening. It could be one or both. If you rebuild one, I would go ahead and rebuild the second one at the same time...

Be careful as you disassemble the cylinder. Keep track of what went where, then wipe it all down and go to a local hydraulic shop. They will have a pretty good chance of matching the ring sizes, backing rings and the wiper seal for you. You could also take it there and ask them to rebuild it - but obviously it will be cheaper to do it yourself. BE CAREFUL during disassembly. You don't want to let the cylinder internals fall out and bump the table. That is generally a pretty soft metal.

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FullSpecial

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If it leaks down a little ways then stops it's the cylinder packing, If it leaks down all the way its the valve. Remember the fluid HAS to go somewhere.
 

Mullaney

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Thanks hopefully its the valve think I'll try there first, any body got a diagram of valve
Valve diagram attached below with o-rings etc shown in the "Exploded View". TM 9-2320-272-24P-2 has the part numbers on PDF Page 1077 in my copy. If you need more details - I can rip a few pages out of the PDF and post it.

Crane Valve Body Elevating Cylinder Tubing.jpg Crane Valve Body Hoist Control Valve Assembly (Exploded).jpg Crane Valve Body Hoist Control Valve Assembly.jpg Crane Valve Body.jpg

While you are looking at valve bodies, Don't forget that the return pipe from the end of the gondola also supplies fluid to the rear winch valve body.
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Mullaney

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gotcha. Sorry, to far to drive my 936 to help you change your ext cylinder. Im sure it would make it from central tx, but damn the fuel and hotel bill.
No doubt about that! THANKS though for thinking about it. I made a deal for a M1089 and if my insurance guy will get motivated, I can drive north about an hour and drive it home. I think with the A-Frame I have and the knuckle boom on the truck I bought, I should be able to do the job. That was the main reason for buying the other truck - but I think I can find a way to have fun with it too :cool:

Seems that it has a few hoses that need attention. Guess I should tend to that before I count on that boom to hold the M936 boom in the air... Funny. Seems that every project has two or three other things to deal with before a goal can be reached...
 

charlesmann

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@Mullaney
how much the booms weigh? my tractor has 10' of height reach and 3000 lbs of capacity. if i ever have to do it, I'm thinking of how to do it too. plus its only the ext section that needs to get rmvd from the main boom right? the ext section can't weigh that much huh?
 

m715mike

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gotcha. Sorry, to far to drive my 936 to help you change your ext cylinder. Im sure it would make it from central tx, but damn the fuel and hotel bill.
Well, Sir, if you want to go on a road trip to help replace a cylinder in the boom of another M936, you are more than welcome to come to Montgomery, TX. Mine needs to be done as well.
 

Mullaney

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@Mullaney
how much the booms weigh? my tractor has 10' of height reach and 3000 lbs of capacity. if i ever have to do it, I'm thinking of how to do it too. plus its only the ext section that needs to get rmvd from the main boom right? the ext section can't weigh that much huh?
So, I wasn't sure about the height - so I ran out back with a tape measure. To the highest point on the boom where the roller is I am at 9 1/2 feet. That is with the boom transport jacks in their lowest position. I climbed up to the gondola and there is about 3 inches of "chrome cylinder showing" on the lift cylinders. I am guessing it might come down to 9 feet or a little less without the transport jacks in place.

Hate to say I have no idea what that extension and cylinder would weigh...
 

Mullaney

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Well, Sir, if you want to go on a road trip to help replace a cylinder in the boom of another M936, you are more than welcome to come to Montgomery, TX. Mine needs to be done as well.
Bummer. But at least you are a lot closer than I am!
 

charlesmann

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Well, Sir, if you want to go on a road trip to help replace a cylinder in the boom of another M936, you are more than welcome to come to Montgomery, TX. Mine needs to be done as well.
i haven't even got it registered yet. haven't decided which way to register, farm, former mil veh or normal tags. farm would be better, but only allows me a 150 mile radius, and my farm is 151 miles, but iv went to natchitoches, la with my farm trailer to recover a huge downed, pecan, weighing 12,600 lbs. so maybe i wouldn't get messed with. fav is way to restrictive and regular tags are around $350 a yr.
in addition, iv got a hole in my muffler, and not sure if straight piping it would pass dot inspection.
but yes, let get the kinks worked out, and i can come down there and help ya. you in a hurry? I'm doing 3 wk rotations in chili, south america and got 2.5 wks left
 

charlesmann

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@Mullaney
if its just the ext boom and cyl., i wouldn't think it would weigh over 2000 lbs. iv gotta figure a way to release the tension on my other 936 hoist cable. its sucked up tighter than navy pelosi's purse strings, to a bumperette and i need to start yarding the crane section apart. id hate to cut the chain just to release tension. if the truck ran, i would just crank it up, but the xmsn is burned up, fuel lines were cut, dirt dobers have built mud huts in the fuel hoses. and I'm sure the batteries are as dead as pelosi's sex life.
any idea how to release the tension? crack the hyd lines going to the hoist winch motor and pull the cable with the front winch on my other truck? iv got the truck on blocks so i could rob the tires/wheels and find the best rubber for dot inspection don't want to yank it off the blocks.
 

Mullaney

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i haven't even got it registered yet. haven't decided which way to register, farm, former mil veh or normal tags. farm would be better, but only allows me a 150 mile radius, and my farm is 151 miles, but iv went to natchitoches, la with my farm trailer to recover a huge downed, pecan, weighing 12,600 lbs. so maybe i wouldn't get messed with. fav is way to restrictive and regular tags are around $350 a yr.
in addition, iv got a hole in my muffler, and not sure if straight piping it would pass dot inspection.
but yes, let get the kinks worked out, and i can come down there and help ya. you in a hurry? I'm doing 3 wk rotations in chili, south america and got 2.5 wks left
Just a thought... I am not an insurance man - but the KEY to them (your insurance company) actually PAYING A CLAIM is that you are following the guidelines that are spelled out on the policy that you buy. They are looking for an excuse to not pay a claim - and you know and I know that 150 vs 151 miles is "BS" but it is the rule and the guys with the checkbook set the rules.

Not that I haven't ever broken a rule or two in my time, but if you ran over and flattened a Prius that was 151 miles from your farm - that is going to leave you hanging in the wind. :-(
 

charlesmann

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Just a thought... I am not an insurance man - but the KEY to them (your insurance company) actually PAYING A CLAIM is that you are following the guidelines that are spelled out on the policy that you buy. They are looking for an excuse to not pay a claim - and you know and I know that 150 vs 151 miles is "BS" but it is the rule and the guys with the checkbook set the rules.

Not that I haven't ever broken a rule or two in my time, but if you ran over and flattened a Prius that was 151 miles from your farm - that is going to leave you hanging in the wind. :-(
true. but i could claim my brakes failed and pushed the man-bun wearing punk that 1 mile, actually less, bc the last 2/3 of a mile is private road. which I'm sure i could find a place to hide the body. of the car that is.
 

Mullaney

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@Mullaney
if its just the ext boom and cyl., i wouldn't think it would weigh over 2000 lbs. iv gotta figure a way to release the tension on my other 936 hoist cable. its sucked up tighter than navy pelosi's purse strings, to a bumperette and i need to start yarding the crane section apart. id hate to cut the chain just to release tension. if the truck ran, i would just crank it up, but the xmsn is burned up, fuel lines were cut, dirt dobers have built mud huts in the fuel hoses. and I'm sure the batteries are as dead as pelosi's sex life.
any idea how to release the tension? crack the hyd lines going to the hoist winch motor and pull the cable with the front winch on my other truck? iv got the truck on blocks so i could rob the tires/wheels and find the best rubber for dot inspection don't want to yank it off the blocks.
You mentioned a tractor. Maybe with hydraulics on it? It might cost you a hundred bucks in hoses, but you could disconnect the "in" and "out" on the winch and with some adapters (small hydraulic hose would work) you should be able to power the winch. I wouldn't try to power the entire crane. Just the boom winch. Maybe? Seems like it would be a "controlled environment" that way...
 
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