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TMS250b low hydraulic pressure

ECSMechanic

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Oct 12, 2023
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Ottawa
Anyone here that can help diagnose hydraulic pressure on a tms250b crane? I don’t have a lot of experience with crane hydraulics, but do have experience with hydraulic systems. Problem started out the operator needs to be at high rpm to get the swing to work. Checked pressures at the swing motor and found low pressure to the swing brake(less than 150psi). Checked pressure at the valve and also got low pressure. Less than 50psi. I checked pressure on the valve manifolds for the other functions, also reading low around 40psi. The weird part is all other functions work fine including the outriggers which I believe work off the same pump section. I checked gpm free flow of about 15 gpm. I also plumbed in a pressure gauge and was only getting 150psi. Would it lose that much pressure if there are bad seals in the swivel? I replace the seals in it about 7 years ago now and it worked fine until now. Owner bought a new pump but I would like more confirmation that’s the problem and not the swivel.
 

tractormech

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florida
I think the first thing you need is a different pressure gauge. The functions won't work at 40 psi. Nothing would work. The lock valves on the outriggers, boom and anything else won't open at that low of pressure. After you get a different gauge check pressure again. Mind you, making pressure but low flow will make it weak and sluggish. Does it do better cold and get slower as it gets warm? That's a classic worn pump symptom. That crane is pretty old and I'd be a lot closer to thinking a pump than a swivel. If you took the pump apart you'll see a lot of wear. And don't be surprised if the pump shaft isn't grown into the PTO. I bet it's got the real big heavy PTO and a 3 section pump?
 

CraneMechanic73

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hopefully you checked hydraulic filters at the start. Most cranes run outriggers and swing off the same pump or pump section. Assuming this machine is plumbed the same way. If the outriggers are good, then the pump is good as well.
 

ECSMechanic

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Yes, it is a three section pump. This is why I’m confused. I bought a brand new gauge from McMaster carr thinking it was the gauge also and used another new one I had. I assume checking pressure at the valves is a good place to check? All pressure lines have a port in them. I can clearly see tank labeled on the other side. I also thought nothing would work with that low of pressure knowing there are po check valves. Is the dump valve normally open or closed? As I said before, I don’t have a lot of experience with this system so I’m trying to figure out what it should normally be doing. I appreciate the help with this. I’m leaning towards a pump also, just didn’t want to throw on a 3k pump to find out something like a dump valve is stuck open.
 

ECSMechanic

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Oct 12, 2023
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Ottawa
hopefully you checked hydraulic filters at the start. Most cranes run outriggers and swing off the same pump or pump section. Assuming this machine is plumbed the same way. If the outriggers are good, then the pump is good as well.
I did check the the only one it has and it “looks” good but I did suggest getting a new one. I suppose something could be blocking the inlet to that pump section? And yes the pressure line goes to the outrigger valves and then to the swivel port for the swing.
 

crane operator

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I don't know what you mean by checking pressure at the swing brake. Swing brake is all mechanical and master and slave cylinder separate from the hydraulic systems in those cranes.

You also can't check pressure on the system without having resistance. Just putting your gauge with a t between valve and swing motor won't tell you anything. If you went to the motor, and put your gauge at the input hose to the motor and dead headed it, you would see what that sector of the pump is putting out/ if it hits relief pressure.

All that said, if the swing is the same as the outriggers sector: if it makes enough pressure at the outriggers to lift the crane off the ground, you have enough pressure to swing.

The brake system on those has what's essentially like a disc brake on the top of the swing motor and gearbox, with little puck brake pads. Typically what happens is either the manual swing, brake push pull cable gets frozen up, and is dragging. Or the master/ slave setup that comes off the foot pedal swing brake is dragging. Either one will make it really hard to swing.

Get the crane up on jacks, level. Get the boom in the air and pull the brake assembly/ calipers off. (its under the boom in the center of the turntable. See if it swings correctly then. Then fix your swing brakes. Because I bet they are just dragging.
 

tractormech

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florida
Something isn't sounding right. You say you got another gauge and got the same readings. You must be plumbed in wrong somehow because again, nothing will work on 40psi. You're dealing with around 2500 on boom, outriggers and so forth. Several years ago I did a swing brake on a 1982 TMS 275 and it was spring applied and oil released. If it goes bad there will be oil coming out of the swing gear planetary because it pushes past the brake piston. It was fiber and steel clutch discs inside a housing. Is yours like that? And 40 psi won't release the swing brake. There should be a line feeding the brake. Take it off and hook your gauge right to the hose end and check pressure there. I can't promise but I seem to remember a pressure reducing valve to the brake and it was like 600psi. How old is this crane? And you mentioned a possibly stuck relief valve. If it was stuck open you wouldn't have anything working so I don't think that's your problem. Did you determine if it does a lot better cold than hot? Does the boom slow down, extend/retract slow down? I assume each pump section goes to it's own control valve? Are the functions giving you trouble all on the same valve? Is it possible to swap lines and see if the problem stays put or follows the lines?
 
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crane operator

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A tms 250 shouldn't be a spring applied/ hyd release swing box. Should be the old style with the disc and pucks. But a few pictures would really help.
 

ECSMechanic

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I don't know what you mean by checking pressure at the swing brake. Swing brake is all mechanical and master and slave cylinder separate from the hydraulic systems in those cranes.

You also can't check pressure on the system without having resistance. Just putting your gauge with a t between valve and swing motor won't tell you anything. If you went to the motor, and put your gauge at the input hose to the motor and dead headed it, you would see what that sector of the pump is putting out/ if it hits relief pressure.

All that said, if the swing is the same as the outriggers sector: if it makes enough pressure at the outriggers to lift the crane off the ground, you have enough pressure to swing.

The brake system on those has what's essentially like a disc brake on the top of the swing motor and gearbox, with little puck brake pads. Typically what happens is either the manual swing, brake push pull cable gets frozen up, and is dragging. Or the master/ slave setup that comes off the foot pedal swing brake is dragging. Either one will make it really hard to swing.

Get the crane up on jacks, level. Get the boom in the air and pull the brake assembly/ calipers off. (its under the boom in the center of the turntable. See if it swings correctly then. Then fix your swing brakes. Because I bet they are just dragging.
There is the mechanical swing lock and the hydraulic brake between the swing motor and swing planetary gears. I put a gauge inline of both the service side and then the brake apply side. With either the brake pedal depressed or the engage/disengage knob in the cab the pressure is below 150psi. Apparently it takes 250-300 to fully disengage the brake. I used a portapower to disengage the brake and the swing would work without high rpm. Slow, but it worked. I’m not really sure how fast it should be. For all I know the pump has been weak for a long time. I may even have a combination of bad seals in the swivel and a bad pump. Either way the pump doesn’t seem to be making the flow or pressure it should. I’m surprised anything works with it reading only 40 psi.
 

crane operator

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The brake "supply" and "service" side pressure has absolutely nothing to do with the swing pump output pressure.

You've just got a mis adjusted brake pressure relief, or the seals are bad in the brake pack. That causes the swing brake to drag.

My tms500e has to be just right, on the swing pressure brake release setting, or the brake drags. And then it doesn't swing well.

If you want to check your swing pump pressure check it at the hyd. motor. The swing brake system is all stepped down.

You can adjust the pressure relief setting for brake release, should be able to follow the hoses back from the brake pack to find it. Book should tell you the setting psi.
 

ECSMechanic

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Here are some pics of what I’m working with. Another problem I have is I don’t have a dang manual for this thing. I’ve been trying to diagnose after work here and there. I should probably just get the manual but I wanted to try here first before spending 400 bucks. I can’t load the pics with the gauge but at idle about 50psi and at 2000rpm it’s at 260 psi. I was off on that one from before. 06EA2E85-2F6F-4F3E-ADD6-C8376B635C5B.jpegE5405388-0800-4AAA-8BF8-0173E078CBB8.jpeg03810632-0C9F-4C4A-AF9B-A7AB6BB646F9.jpeg801A304A-FA02-41FF-A3EA-58E97FAC7018.jpeg
 

ECSMechanic

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Something isn't sounding right. You say you got another gauge and got the same readings. You must be plumbed in wrong somehow because again, nothing will work on 40psi. You're dealing with around 2500 on boom, outriggers and so forth. Several years ago I did a swing brake on a 1982 TMS 275 and it was spring applied and oil released. If it goes bad there will be oil coming out of the swing gear planetary because it pushes past the brake piston. It was fiber and steel clutch discs inside a housing. Is yours like that? And 40 psi won't release the swing brake. There should be a line feeding the brake. Take it off and hook your gauge right to the hose end and check pressure there. I can't promise but I seem to remember a pressure reducing valve to the brake and it was like 600psi. How old is this crane? And you mentioned a possibly stuck relief valve. If it was stuck open you wouldn't have anything working so I don't think that's your problem. Did you determine if it does a lot better cold than hot? Does the boom slow down, extend/retract slow down? I assume each pump section goes to it's own control valve? Are the functions giving you trouble all on the same valve? Is it possible to swap lines and see if the problem stays put or follows the lines?
So the 40psi is what I’m getting at the valves. This why I’m confused also. I added some pics to the thread. I’m getting 260psi at the pump but only 40 at the valves. That’s why I feel like something is stuck open. The dump valve I assume since it has a coil only opens or closes with outrigger operation?
 

CraneMechanic73

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what you are calling a dump valve is the priority/blocking valve for the outrigger circuit. Kinda like early pump management. Since you’re not gonna be swinging while setting up your outriggers they plumbed both swing and outriggers to the same pump section. That valve will energize when you run outriggers to block the flow from going upstairs so the outrigger circuit can pressurize to run the beams and jacks. So when you’re not running outriggers the flow goes through the swivel to run swing.

So if you run the outriggers and see good movement and the machine comes up good then the pump/section is more than likely good and not the culprit
 
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ECSMechanic

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Oct 12, 2023
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what you are calling a dump valve is the priority/blocking valve for the outrigger circuit. Kinda like early pump management. Since you’re not gonna be swinging while setting up your outriggers they plumbed both swing and outriggers to the same pump section. That valve will energize when you run outriggers to block the flow from going upstairs so the outrigger circuit can pressurize to run the beams and jacks. So when you’re not running outriggers the flow goes through the swivel to run swing.

So if you run the outriggers and see good movement and the machine comes up good then the pump/section is more than likely good and not the culprit
The dump valve is mounted near the center of the machine and only tees off the pressure line to the swivel. I was going to check voltage and/or flow to see if it bleeds pressure. It’s only a 1/2” line so I wouldn’t think that much pressure could be lost through that, but maybe.
 

ECSMechanic

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It seems the best thing to do here is get a service manual. I found one for a tms250 series. The one I’m working on is a tms250b. Anyone know what the b stands for and I’m guessing that manual should cover everything?
 

ECSMechanic

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So after getting a service manual and going through everything, I realized I made a rookie mistake and missed that the plunger on the dump valve solenoid was stuck in. Grabbed some channel locks, popped it back out and sure enough the swing brake released and works just fine now. I appreciate everyone’s help!!9B050F9C-C541-4B46-9CFB-7C6ED39B4113.jpeg
 

CraneMechanic73

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A pair of pliers and a manual. Forget the pump replacement or swivel pack. That little valve was gonna cause a fair amount of unnecessary work. Good job
 
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