M936 wrecker boom leaking down

[ROCKWELL-C60]

Mine does same thing after lifting a heavy load following with great interest

 

[kendelrio]

Before you pull your cylinders apart, is there a counterbalance valve in the assembly they are hooked to? It would usually be a block that the lines have in common. If so it's possible your valve body is worn out or needs adjusting. Something to check before you start pulling stuff apart.

On our robots, we use hydraulic cylinders and CBVs to hold our arms in place.

 

[colesmotorsports]

Still haven't had time to do any thing with the cylinder yet , going to hook them to my skid steer and run and test them when I get some time, try to do next week.

 

[kendelrio]

This is what I'm talking about....

Counterbalance valves

 

[colesmotorsports]

I was wondering if there was a valve like that there , don't think there is ??? But would think there would be. Wish I could find a better picture of the whole hydraulic system , all valves , hoses , cylinder internals. I'll have to look harder I guess. Thank you!!!!

 

[Mullaney]

.
Just a quick read on the Counterbalance Valve link... Very Interesting.

As described, that system (valve) should require hydraulic pressure to lower the boom.
IE: Motor Running, Hydraulic Pump engaged and pumping fluid.

The M936 that I have with the boom up can be lowered with the engine off.
Since I work by myself, I have a rope that I throw around the boom handle and throw it off the back of the truck.
As I make my way to the front of the truck, I disengage the hydraulic pump and shut down the power plant.
I pull gently on the rope to lower the boom and pin it to the boom jacks.

I can't go up, but gently down works really well.

If the M936 had a counterbalance valve (just guessing here) that the boom wouldn't lower without hydraulic pressure.
There is one check-valve in the M936 hydraulic system. It lives under the truck near the pump.
Catastrophic failure is the only way it gets engaged as I understand.

 

[Ferroequinologist]

I do the same rope trick lol.

Would be expensive, but have thought on many occasions to convert it to electronic valves so I could use a remote. Gets old climbing on and off constantly when loading a trailer or pulling a motor.

There are no counterbalancing valves on the wreckers. The newer ones yes, but m936 and older no. Blow a hose and they drop like a rock. And you can lower them without power as Mullaney said.

Now my hyrail boom truck has them, and I blew a line on it once with it up in the air while on the track... that was a fun walk back to town to have a hose made, when without one I could have still lowered it and driven the truck down the rails. Instead I would have just recreated the scene from Back to the Future when I got to a power line.

But they do have a benefit as the boom and load didn't come crashing to the ground.

 

[colesmotorsports]

Would be cool to do electric valves for control, thought about doing it that before I bought the NOS valve body, paid $1600 for that . Thanks for info , appreciate it .

 

[Mullaney]

Would be cool to do electric valves for control, thought about doing it that before I bought the NOS valve body, paid $1600 for that . Thanks for info , appreciate it .

.
There is a thread about remote control for the M936 by one of our guys. Has a list of parts and information for remote operation:

Wrecker wishlist of mods

How "in the name of Sam Hill" would you ever pull those anchor pins OUT of the ground, after driving them in?! Actually, since they are hexagonal in section, you put a spare pin through the eye or a crow bar etc., turn it around a couple of times and they should pull right out (they turn a...

www.steelsoldiers.com

One thing to consider is that the electrical powered valves are ON or OFF.
The fluid is flowing or it isn't...
There is no "sneaking up on it" when you make a lift.

 

[colesmotorsports]

Decided pull spool valve and relief valve out. Spool it nice not a scratch one on it. The relief valve came out nice . Top assembly ,2nd part from the right was stuck in the bore. Took a punch and pounded it out the backside of the bore , it was really stuck. It had bunch of rust on it. Cleaned it up like new , go to put it back in the bore and you have to tap it in with hammer and punch. Bore is real clean. Worked that piece back and forth with hammer and punch and it moves a little easier but far easy. Question is , is it supposed to float back and forth or just fit tight ?

 

[colesmotorsports]

Sorry for screwed up picture, I tried fixing . Where it says Boom Lift Cylinders, talks about check valve that holds it from lowering. There is a check valve in the hose of each cylinder on the bottom port . I thought they just cushioned the hydraulic pressure from spikes. Any idea on the check valves???

 

[kendelrio]

I do the same rope trick lol.

Would be expensive, but have thought on many occasions to convert it to electronic valves so I could use a remote. Gets old climbing on and off constantly when loading a trailer or pulling a motor.

There are no counterbalancing valves on the wreckers. The newer ones yes, but m936 and older no. Blow a hose and they drop like a rock. And you can lower them without power as Mullaney said.

Now my hyrail boom truck has them, and I blew a line on it once with it up in the air while on the track... that was a fun walk back to town to have a hose made, when without one I could have still lowered it and driven the truck down the rails. Instead I would have just recreated the scene from Back to the Future when I got to a power line.

But they do have a benefit as the boom and load didn't come crashing to the ground.

Good info.

And based on what's been posted, it sounds like a 3 way open center valve with a pilot operated check inline. I would be very interested to see the hydraulic schematics of the system in question.

And you are correct about no power=no relief. We have 7 function arms and every function BUT the jaw (hand) function is counterbalanced. The reason for that is if we are grabbed onto a subsea structure and for whatever reason lose power, for all intents and purposes, the robot is now a part of that structure.

We use a 3 way-open center valve in that situation to allow the jaw to open in case of loss of power.

Following this thread with interest as hydraulics/electrically controlled hydraulics are an interest of mine as I use them every day at work.

That said, if anyone has interest in how we control ours, I know the types of cards, valves and power needed to build a system. It may be expensive depending on sourcing it.

Feel free to PM me so this thread isn't jacked...

 

[simp5782]

View attachment 832242


Sorry for screwed up picture, I tried fixing . Where it says Boom Lift Cylinders, talks about check valve that holds it from lowering. There is a check valve in the hose of each cylinder on the bottom port . I thought they just cushioned the hydraulic pressure from spikes. Any idea on the check valves???

It's called a plunger valve NSN 2590011311940

Figure 482 # 10

 

[charlesmann]

I just had a leak down issue today. I moved miller 225 bobcat welder, and after it was released from the hook, with the last function being boom raise, i started to crowd in and the boom started to lower. I stoped, pulled on the crowd lever and the boom didnt lower. I raised the boom again and immediately hit the crowd lever, and the boom lowered again. This time, i stayed on the crowd lever, and the boom bottomed out.

Any ideas? Possibly stuck check valve?

 

[colesmotorsports]

The spool valve and relief valve are easy to pull out and check if something got in them , really strange thou.

Mine I pulled hydraulic filter out and changed it, the old one was bad, had a little bit of everything in it .

 

[colesmotorsports]

Part #147
Well unhooked press side off control valve that runs boom cylinders hooked up hose to skid steer . Left return line hooked up from cylinders to tank. Pressured up cylinders went up slow and right back down , lost 12 gals of hydraulic oil out of skid steer and it ended up in truck tank . As I'm typing this I'm thinking something is wrong with how I tested cylinders this way, I don't know think I'm losing my mind lol think it's the cylinder like you say, I need to just accept it

 

[Ferroequinologist]

My boom will stay up for weeks lol. I did blow a lower hose (lifting side) once and it came crashing down, with a great full body hydraulic fluid shower lol. I think if it had pilot operated checks it wouldn't have dropped like that.

My money (even though technically it is your money) is still on an internal bypass in a cylinder.

 

[colesmotorsports]

Yes sir going to get other set of cylinders rebuilt , thanks

 

[colesmotorsports]

Cylinders are at hydraulic shop getting rebuilt, hope that fixes it , then start making a bunch of new hoses , how much pressure should the hydraulic system put out??? Going to hook gauges on and test when I get a chance.

 

[colesmotorsports]

Just got call from hydraulic shop on cylinders, all seals where coming apart ,chunks missing , rod and pistons are good, Cylinders need to be honed out some rust, going to cost about $600. Really glad to at least know what was causing cylinders to go down.