Link Belt Swing Issues

[Ratmotorhead]

Hello gentlemen. I believe I've made some headway on my excavator. Upon pressure testing I have found that I had no unloader pressure (which would be my set pressure.) I believe that is why it would not let my swing brake release. This set pressure from my unloader valve had a line going directly to my left and right swing spool which may be giving me my non brake release problem.

I also disconnected the free swing valve and plate underneath the brake by plugging them. Has John C. ever disconnected the free swing feature on a 4300C Link Belt? Any comments from those of you with more experience than me?

In the past I have had good pilot pressure and relief pressure at the swing brake. 3900 pounds on left and right swing. But no set pressure since the unloader valve was not working. A rebuilt unloader valve now gives me 3900 PSI pressure to send back into the spool. Does that pressure operate my crossover relief valve? This could be the culprit.

 

[John C.]

I've only worked on one 4300C. All the others were C2 machines. I don't remember how the free swing on the Link-Belt works exactly. I remember something about two pilot hoses attached to where the adjusting screws were for the original swing relief valves. A photo of the top of the swing motor might jar a few brain cells to clear some of that smoke up in my head.

 

[Ratmotorhead]

 

[Ratmotorhead]

 

[Ratmotorhead]

Hey John C. Here's a couple of downloaded schematics which show my free swing lines which are attached to the small square block underneath the swing brake. I really don't want to use the swing brake feature until I get the swing brake working correctly. I am able to get the correct actuating pressure which is 2986 PSI. I had no relieving pressure from my number 3 pump (unloading valve), which is 2700 PSI. After repairing my unloader valve, unloading pressure is correct. I'm hoping that allows my swing brake to release. Any comments would be appreciated.

I believe the single line out of that block still needs to be attached, but the two lines going to the free swing solenoid can be plugged and the switch inactivated.

 

[John C.]

The single hose should be the swing brake release and that solenoid valve needs to work. You should be able to check voltage going to that solenoid and when you operate any function the computer will make the wire hot to open the solenoid valve and allow pilot pressure to release the swing brake. The swing brake is spring applied and pressure released.

The two hoses I believe just released back side swing pressure on the motor when you put the swing lever back to neutral. Basically the motor would just freely rotate then. Those can be capped. The free swing was a throw back control for the people who used to run friction machines. I don't recall anything about an unloader valve but that could be there to release that back side pressure.

 

[Ratmotorhead]

Thanks for the reply John. The single hose on the right side schematic goes to my pilot pressure valve marked t on the valve the double lines go to a solenoid then to tank. This is a 4300c model inside the brake it does not have any pads for release only the valving

 

[John C.]

As I recall the brake discs are mounted at the bottom of the motor and lock the shaft from turning when no oil is fed to the piston on top of them. I suspect that single hose going to the opposite side than the two hoses is the swing brake release.

 

[Ratmotorhead]

This machine being a 4300c is different than a c2 it has no discs in the swing motor I rebuilt it last year after a long dispute with a professional co Once I get the correct sequence of how the release functions I should be good to go

 

[John C.]

I'm guessing then that instead of swing brakes that you have a pin that is dropped in a set of holes between the house and the carbody.

 

[Ratmotorhead]

Sorry about the slow replies I've been dealing with the flu. Thats right John c. It has pin I am able to pin it for my set pressure verification test which is 2986psi the relieving pressure for my no 3 pump is 2702psi which I also get now that my unloader valve has been repaired. It seems that I can't get the back pressure to release and I wonder if that has to do with the plate with the three hoses under the brake valve on top of swing motor. The solenoid for those hoses has one hose to left swing one to right swing the other to tank If I go to swing left the right side hose should open up to tank via solenoid valve and vise versa Am I thinking right or am I missing another component

 

[John C.]

That would make sense but like I said, I haven't studied and worked on one of those machines.

 

[GregsHD]

It almost sounds as if the swing motor is pressuring up both sides, locking the motor. I'm thinking something to do with the crossover reliefs.

The swing lock pin is manually actuated?? You keep saying swing brake but then say it doesn't have any brake in the motor, I'm confused...

I see you've been working on this problem for a few years...

I'd pull that motor apart again and give it a thorough look over.

 

[Ratmotorhead]

Hey GregsHD thanks for the response. The machine is a linkbelt 4300c it does have a manual drop pin when over the front or rear tracks I have rebuilt the swingmotor myself and had new swashplates made since they were trashed it was a pretty straightforward repair. this swingmotor. Dowmax has no brake unit inside it only has the Kawasaki brake valve on top. No braking pads in it either only relief valves that are on left and right inlet lines. There is a plate under the brake .two hoses go to solenoid then tank. Another hose on opposite side of plate goes to pilot relief valve. I am able to adjust the actuating pressure at both inlets to 2986 psi like my books show and I also can adjust the set pressure to 3057psi since I have had my unloader valve repaired (scored seat) it just seems like both sides stay pressured up and cannot relieve pressure on the opposite side of the swing . Now here's the kicker. The computer has been removed years ago this machine had a magnet on it and the previous owner ran it for a long time as it is. Something has to let the opposite pressure bleed off when swinging left or right could have to do with plate under brake crossover valve , or would crossover take care of this itself. Hmmm

 

[GregsHD]

I have no experience with this particular machine, sounds like a half crane going backwards reinvent the wheel swing "brake" operation!

I assume you bought this machine the way it is (no swing)?

If a scrap yard used it until it no longer did the job it must have a ton of hours so any failure is possible.

What part are you referring to as swashplates? If the swash plate was trashed so would be the piston shoes. You can't just get a machine shop to whittle up parts for a piston motor, they are extremely precise. Especially if you have no factory dimensions etc..

I'm curious if the valve plate was installed in the correct orientation? In some motors you can install them in two positions, right and wrong!

Did you remove the motor from the swing drive and inspect? Perhaps the swing drive is trashed and locked up?

What is the purpose of the brake valve if it has no brake? It must have some sort of swing brake.

Since the computer was removed and it was in a scrap yard any kind of Jerry rigging is possible internal or otherwise.

From the picture above the pressure lines from the motor go directly to the main control valve, there should be no way for the "return line" to get blocked.

I've seen rags or cap plugs get left in lines causing cylinders to "lock", it can cause all manor of head scratching....

Did you get any story from the previous owner?

 

[Ratmotorhead]

Umm yea the machine was bought this way with swing issues I already knew about for less money than you could repack all of its cylinders for. I could scrap it or part it out and recoup the money three times over what I have in it. But I like to challenge my brain and it it's not costing me a dime to let it sit and if I fix it woohoo for me. The man I got it from gave up on it saying he can't stop it from dragging when swinging and with no computer nobody wanted to put time in it and he didn't have deep pockets. The swingmotor ate the lower bearing and sent the usual swarf thru the system. I spent the summer draining tanks cylinders and anything else I could remove to clean inspect and reassemble. Almost all parts are discontinued except a few so I sent the swingmotor to a rebuilder in Minnesota who said they could redo for 5500.00 after three months after no response I got it back with the swashplates exploded because they pressed it apart without removing a knock pin . But they didn't charge me for anything. Thanks. I got a spare wornout motor with the machine and used remaining parts to rebuild except swashplates which I had made at a machine shop in town not difficult just duplicate then I had it case hardened for longer wear. I am aware of how it goes together had to build my own jig for reassembly and is straightforward in my book I tested it in my shop with a hydraulic pump and motor ,it forwards and reverses fine. The lower gears are free because I spun the house with my backhoe 360 degrees.

 

[GregsHD]

Did you pull the swing spool to inspect for damage from the $hit that went through it? All that hard metal going through the system is a major key, and not good. I'd pull every bit.of the swing circuit apart to inspect. The bench testing of the motor is another good piece of information. Thumbs up on the good deal though!

 

[Ratmotorhead]

I have actually pulled both control valves and cleaned and inspected for scoring Good shape. Also disassembled and cleaned brake valve on top of swing motor , it looked nice. By the way I am very specific on my reassembly ,not only how it came apart but also using my schematics to make sure it wasn't put back together wrong previously . My pilot filter was cleaned ,new filters installed intake screen in tank replaced . I have removed and inspected my pilot pump, number 3 pump ,my pilot control valve ,my shuttle valve, and made sure I had pilot pressure out each side of shuttle when trying to swing left or right and that pressure was going to correct control at main valve and moving that valve also. I have all functions boom,bucket,dipper, tracking forward,reverse. Tracks pressure up from auto tension, main pumps sound good full of oil . Engine runs good. 60 lbs oil pressure. Did repair starter . It will swing left and right,but only a couple of feet for maybe 30 seconds but then you can feel it start to drag then it locks up. During my little bits of swing testing I keep it close to where I can drop the pin in and not have to fight it so I can check my relief pressures. Without a computer to tell the swing solnoid to open and relieve back pressure I would think that the crossover valves would take care of that. Hmmmm any suggestions

 

[Ratmotorhead]

Well guys after having this excavator in my yard for nearly three years , I have swing with no brake problems. It seems that it must have unloader pressure to send pressure back into control valve to relieve back pressure coming from swing motor. As soon as it worked I must have spent an hour swinging back and forth and in circles. So far so good,now off to other issues.

 

[Ratmotorhead]

Update on excavator. The swing is working perfectly what a relief my only problem now is since I have been swinging it in circles and left right,it loosened all the crud in the fuel tank. I was getting as putter after about 20 minutes , and my filter was half full. Traced injector lines and found inlet screen to feed pump totally plugged. Seemed someone removed sediment filter assembly and just had a hose from tank to feed pump. I installed a quart size sediment filter before feed pump and back in business. Now off to fab bucket ears. I have a 52 inch and a 48 and a 24in easco which will make a good stump remover, wish me luck