Hi, I have a Cat 924G loader with intermittent lift problems. Occasionally, when filling the bucket, this machine abruptly loses all lifting power to the loader arms. The bucket does not seem to be affected. This loss of lift will not occur with an empty bucket. It almost feels as if a valve is opening somewhere in the lift circuit and bypassing oil from the lift circuit. Returning the joystick to neutral and trying again will often result in it lifting normally again. I have also noticed that when it refuses to lift, if I hold the stick in the full rollback position, it will then lift the arms. Hyd oil is full and appears clean. Machine is in otherwise good condition and works flawlessly. No warning lights or strange noises. Thanks, Marv
Is the hydraulic system load sensing? I would think that on a "G" model they would be. I suggest that you check the o-rings in the resolvers (inside the caps at the bottom of each valve).
Thanks DGODGR. It sounds like you are on the right track. Yes it is load sensing. I'll wash everything off tomorrow and see what I can find. Are you talking about the four small allen plugs on the valve body on the opposite side of the cylinder ports or the larger hex caps beside the cyl ports? The valve on this machine is mounted on its "side" I guess you might say, so I'm a little unclear of the location. Thanks!
On my backhoe (416C) the resolvers are at the bottom. The hydraulic lines are plummed into the sides. The spool moves up and down when the levers are manipulated. The spools stick out of the top. The resolvers are at the bottom under a cap (appears to look like a float bowl on a motorcycle carburator). I can not comment on your machine. I have a Deere 544J and its valve body is on its side too. I am not sure if my machine has load sensing but the real difference is due to it being pilot control instead of mechanical operation. I'm sure yours is pilot control too. My spools are manipulated by hydraulic actuators, one on each end of each spool. I'm not sure where the resolvers would be, if they are on there at all, on my machine. If yours is the same I wouldn't know where to direct you to look. I would talk to the dealer myself. Maybe you could post a picture of the valve body.
Ok, thanks. That gives me a much better idea of where to look. It is pilot controlled. I have tried contacting two dealers already and can't even get anyone to call me back. I'll let you know what I find out. Thanks!
It certainly sounds like a resolver issue. Probably the one in the tilt section of the bank valve. I haven't personally had a hands on with this model, but it looks like the resolvers are internal and you have to dismantle the valve to get access to them. Item 6 on the View attachment valve.pdf
Thanks Cmark. Is #6 the primary resolver? Where is the secondary resolver located? I guess I should ask if that cutaway is the correct one for the 924G. Thanks, Marv
IME many things can be serial number specific. Sometimes Cat will make changes based on component availability, product up grades, cost, etc, etc. A 924G that is either sourced from different locations (Japan is the only one I'm aware of for that model) or is targeted for different locations (ie: Asia, Austrailia, America, Europe et al) may have different components. Even if that is the correct valve breakdown for a 924G it does't mean it matches your machine. Parts manuals and schematics are labeled with a serial number range. Be sure to use one that matches your unit.
The graphic is for an early 924G. DGODGR is right, a serial number is needed for an accurate parts ID. Systems operation tends to cover a range of serial numbers. I kind of assumed from your description that yours was an earlier machine. The later ones have a different system. There is no secondary resolver on this system. If the cutaway looks like yours, it should be OK for diagnosis. Post your full serial# if you're not sure. Good luck.
I didn't have much time to devote to this yet, but I did drain the oil and pulled the end blocks off both spool sections.The part that is located in position #6 does not appear to be removable from either end. I am wondering if there is a locking screw or plug that is holding the resolver in place that is installed from "outside" the control section? To sum it up, do I need to split the tilt and boom sections of the valve to get the resolver out? The graphic looks correct as far as I can tell. Ser# is 924GA9SW019xx Thanks, Marv
You don't say how many functions the loader has. I'm assuming you have the basic 2-function controls (Lift & Tilt). If so here are the Parts Listings for a 9SW series machine. View attachment Valve Gp - 2 Bank.pdf View attachment 142-2899 Valve Gp.pdf View attachment 142-2898 Valve Gp.pdf View attachment 160-0309 Valve Gp - Pilot.pdf I also have the Adobe pdf files for Disassembly & Assembly of the valve. I can't upload them because they are too large under the site rules for attachments. PM me with an e-mail address if you want them.
Its been a while since I had one apart but, you can remove the end cap, remove the poppet(10) and then the resolver(5). This pic (how the valve works in the raise position) is a bit clearer. In order to raise the work tool, pilot oil is sent to the left end of the main control spool (11). The spool shifts to the right. This connects the pressure passage (B) to poppet (14) and this connects the return passage to poppet (10). The pressure oil flows past the spool and the pressure oil encounters the resolver (5). The resolver senses the oil pressure and the resolver sends the appropriate signal to the pump. If necessary, the pump upstrokes. Pressure oil opens poppet (14). The oil flows to the head end of the cylinder. As pressure oil flows to the cylinder, the pressure of the return oil increases. The return oil pushes on the front of the poppet (10). The poppet opens. Pilot oil flows through an external line to the bottom of the area control spool (6). This causes the spool to shift upward. The oil flows from the back of the poppet (10) to the drain for the area control spool and the oil flows to the tank. The area control spool drains to the tank. The force that is exerted by the pressure on the front side of the poppet is greater than the force that is produced by the pressure and by the spring on the back side of the poppet (10). Return oil flows from the rod end of the cylinder to the tank. Supply oil continues to flow past poppet (14). The oil continues to flow to the head end of the cylinder. Return oil flows past poppet (10). The cylinder extends and the boom raises.
Many thanks to everyone so far. I managed to get the resolvers out of the valve body. That 1/2" hex in the end of them is pretty much invisible, hence my earlier comment about not being sure about getting them out. Replaced the o-rings on them both, and the balls and seats *look* OK, and no bits were trapped in either one. All the other poppets and spools seem to be moving freely and nothing looks scored or worn. Put everything back together, and it's still doing it. If I roll gently into the stockpile and gently get a half bucket or so, all is fine. As soon as I push into the pile like you normally would and start to lift and rollback, the lift circuit just quits completely. Holding full rollback while lifting will result in it lifting, but not fast or to full height, becoming worse with more weight in the bucket. Also, while it's sitting there refusing to lift, if I set the bucket on the ground and lower the arms to lift the machine instead, it will pick the front wheels up normally, and then the boom circuit will return to lifting a loaded bucket again. Basically, if I cross a certain threshold of lift pressure, it quits lifting until I "reset" things by pushing down instead. The other thing I should mention is that the arms will continue to drop about 4" after the stick has returned to neutral after lowering the arms. It's a gradual drop with a smooth stop, and you can hear oil moving quite noticeably through the pilot control in the cab when it does this. This drop only lasts about a second or so. It has done this ever since I first climbed into it, and it did it even before these lift problems. I apologize for the lengthy description; just trying to give as much info as possible. Since there is no easy way to test those resolvers for leakage past the balls under pressure, should I just order new ones? How sensitive are they to slight leakage? @Lee-online, ser# is posted already @Nige, yes, 2 functions and thanks for the email Thanks, Marv
Does your machine have ride control? If so, does it make any difference if you turn it off or on?
The check valves in the ride control manifold are known for failing on the early machines. This usually cased a drift problem. Removing and capping the hoses will eliminate the ride control circuit. The problems sound like a resolver issue. Are you sure you removed the resolver in the lift section and not the bucket section?
Hey Lee. I personally would be looking more at the bucket resolver than the lift resolver. If the lift circuit is operated and the bucket resolver is leaking, signal pressure is lost through the bucket resolver. On the other hand, if the bucket circuit is operated and we get a good upstroke on the pump, we can assume that the lift resolver is OK. Whaddya think???
If the bucket resolver was bad then wouldn't you expect one of the bucket functions to be slow and weak and the loader wouldn't lift the machine. What about the signal limiter, it could be faulty. Snapping a gauge on the signal tap will show what is going on, otherwise we are just guessing.
Hi guys, Yes, it does have ride control, and turning it on or off doesn't change anything. The drift isn't a big deal to me, I just thought it might help you diagnose the problem. I actually had the resolvers out of both lift and tilt sections. I ordered 2 new ones to remove any doubt about their condition. They are about 3 days away though. Even though operating the tilt causes it to lift, it still lifts weakly and not necessarily all the way to the top. When it decides to behave itself, it lifts at full speed right to the top. Maybe they are both faulty? Tell me about this signal limiter; where is it located and what does it look like? Where is the tap for a gauge and what kind of pressures should I be seeing? Is its purpose as the name implies, limiting the signal pressure that the stroke control on the pump sees? Is there a remote possibility that the oil to the lift cylinders could be bypassing in the ride control manifold? I would think that if this was the case the arms would not only not lift but would also drop right to the ground, but depending on the internals of the thing, maybe not? For the small effort to cap the lines I may as well do it to eliminate the possibility. Thanks, Marv
Lee. I'm certainly not saying that you're wrong, but my understanding is the signal limiter affects all valve sections?? Nige. You say that powering the bucket down makes a temporary cure. Are you pushing the lever all the way forward into float? Maybe there's a problem with the float control system. That's the solenoid on the valve bank.
@Cmark, Yes, powering the bucket down does effect a temporary cure. I'm not pushing it into float when I do this. I can't honestly say that the tilt circuit has full power when this happens either. It may be losing power as well, but may not be as pronounced as the loss of lift. Thanks, Marv
Okay. So if we suspect low power all round, the signal limiter could be a problem. It basicaly takes the resolved signal oil from either valve and limits it to a certain pressure. View attachment 9SW.pdf Item 11 on the graphic. Lee. What format are you using to upload attachments from SIS? .PDFs don't do a great job.
Use the "print format" in SIS and then print using a pdf printer like bullzip, it makes a pdf looking just like when you browse in SIS and scales nicely too. It would be intersting to see what the LS signal does when operating the lift and then lift and tilt combined.
The reason I was thinking SL was because if it was weak and dumping the signal then lifting with a full bucket would have the most load and would be the first noticed. Other functions may not be effected unless they go into a stall. Without checking pressures, it is just trial and error. That takes time and can get expensive. I save the pics, then use MS paint, resize and change to Jpeg.
Ok guys, where is the port for the SL so I can get some pressure readings for you? Many thanks, Marv
terms mobile vs heavy industrial I've been following this thread with a little interest, looking to learn from the mobile world of hydraulics-the terms "resolver" and "signal limiter" are foreign to me. Looking at the valve body and following the thread I think a resolver would be a "shuttle valve" and a signal limiter would be a "pressure compensator" that runs in parallel with a load sense control on a variable displacement pump. Can someone clarify? TIA Tom
I think that sometimes Caterpillar designers make their own names up for components, to suit the applicatin that they're in. Because these made up names then go in to the service literature which lots of people read and are trained by, they become part of everyday language for heavy equipment mechanics. In caterpillar land, a resolver will receive two different pressures and deliver the higher pressure, (a logical "OR", if you like). In this case it's the signal (load sensing pressure) to the pump compensator valve which controls the swashplate angle. The signal limiter is just a pressure relief valve in this signal line, but, "hey, boss, seeing as how it's job is to limit the pressure in the signal line, why not call it a "signal limiter"?" "Yup, looks good to me. go for it!" HOWEVER, Marv, it looks like your machine doesn't have a signal limiter. I gave you the wrong graphic in post #21. The schematic with a signal limiter starts at serial #2026. I think you'll find just one valve in the end manifold of the bank-valve. This is a flow control valve which allows the signal pressure to drain to tank when the controls are returned to neutral. This could potentially be causing your problem. The pressure tap for the signal line is on the pump compensator valve, which is bolted to the top of the pump. Attach a 5000psi gauge and compare what you get with bucket tilt and lift. The pressure tap on the bank-valve manifold is for pump pressure, if you want to take a look at that as well.
"Resolver" my ass ................... it's a double check valve ..............!!!!
mobile vs industrial I'll admit I'm not the most computer proficient but the adding attachments is a daunting task-anyway maybe I got it resized and attached. This is a typical industrial print of 2 circuits with load sense control for the pump. Items 23 and 24 are shuttle valves (your resolvers/double check valves)- shuttle valve 24 insures that the pump will see the highest pressure if the two circuits are operated at the same time. Variable dispalcement Parker piston pump, the load sense line feeds the load sense control with the pressure compensator (maybe your signal limiter)in parrallel. BTW items 23 are stacked under the DCV and 24 is threaded and tied into pilot lines. Tom
Figured I would give you an update on this machine. I installed two new resolvers and nothing has changed. I installed a pressure gauge into the tap for main pump pressure, and am seeing the pressure max out at about 1500 psi when activating only one function. When activating 2 functions at once, I'm seeing about 2200 psi. I guess there is no signal limiter, but there is that little valve at the top of the main bank to bleed off signal pressure when no function is activated. Is it more likely to be in the pump compensator itself? Is it possible that the margin spring in the compensator has weakened slightly and that the margin pressure is too low? I'm thinking if the margin is too low there will not be enough signal pressure to upstroke the pump??? Not sure why it's picking 1500 or 2200 to cut off though. Maybe there is enough internal leakage in that compensator spool to become an issue at those points. Ideas welcome! Thanks, Marv
If your pump/compensator is capable of making pressure with two functions, it should be able to make it with one. I would say it's unlikely to be your problem. You really need to check the signal pressure instead of the pump pressure. Now you've changed the resolvers, If you have low signal pressure then the flow control valve mentioned earlier is (as far as I can make out) is the only other component which can be at fault.
You're probably right Cmark. It might be easier if I had a gauge on both signal and main pressure at the same time, since it's kind of a chicken vs egg situation. If the main pressure is holding steady at 1500 with one function activated, then I think I couldn't see any more than 1500 signal pressure at that moment, according to the schematic. I can't quite grasp how just watching signal pressure alone can lead one to the problem. On a normally functioning system, if I dead-end a function, would one expect to see both signal and main pressure come up to the high pressure cut-off point of 3600 or so? With my current situation, what would you expect the signal pressure to be at when the main pressure is stalled at 1500? Thanks again, Marv
signal pressure + margin pressure (300psi) = pump pressure. Did you have the sectioned or one piece valve on it? apparantly there was a retrofit program to install new type of valve on older machines. I've had a similar issue on a 950H, couldn't lift for **** but just touch the tilt and the bucket went for the moon, the bore for the compensator spool in the tilt section was worn just enough to let signal pressure leak by, hard to spot with the valve installed in the machine but it was easy to see when it was pulled and looked at on the bench with good lighting.
hello everyone. I've read all through but i still can't get it. my 924G has a lifting failure , the controllers are acting void.
I know this post is 15 years old. My machine is having almost exact same symptoms . Any fixes ?