Hello all......... New to the site and can say I really find the forum very informative........great discussions and information. My issue is related to the lift arms drifting down slowly; the problem seems more noticeable without a load in the bucket. I lift the arms/bucket and go to neutral on the pedal and the bucket lowers at a rate of approximately 1" per 3 seconds. I checked my manual and the trouble shooting section indicates that there is a seal leak in one of the valves. Other than the drift, the lift arms work great with plenty of lifting force and no visible fluid leaks anywhere. This makes me believe that I do have a valve leak issue internal to the valve body. So......my question(s), has anyone else dealt with this lift arm drift issue and can I rely on the simple seal fix to resolve the problem? Thanks in advance for the input. Albert
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This is something i was actually going to cover when i found time.
I read an article that dealt with cylider creap, most people believed that when a double acting cylinder creaps it is a problem with the piston seal but its not. If there are no external leaks out of the cylinder it is a valve leakage problem, just like you have.
What model machine do you have? do you know what control block you have, as in brand wise?
I have a 731 that had a gresson control block, i had the same problem. I would lift my arms and they would slowly fall on their own. I pulled the control block out and replaced the seals in the load checks, the seals were all shredded, this is most likley where your problem is. Some of the later machinkes use a bobct brand control block, their load checks are different, basically a spring and poppet that is easaier to replace.
Gaining access is your biggest problem, removig the block is equally hard.
Someone else may have an idea.
Also, welcome to the forum!
I read an article that dealt with cylider creap, most people believed that when a double acting cylinder creaps it is a problem with the piston seal but its not. If there are no external leaks out of the cylinder it is a valve leakage problem, just like you have.
What model machine do you have? do you know what control block you have, as in brand wise?
I have a 731 that had a gresson control block, i had the same problem. I would lift my arms and they would slowly fall on their own. I pulled the control block out and replaced the seals in the load checks, the seals were all shredded, this is most likley where your problem is. Some of the later machinkes use a bobct brand control block, their load checks are different, basically a spring and poppet that is easaier to replace.
Gaining access is your biggest problem, removig the block is equally hard.
Someone else may have an idea.
Also, welcome to the forum!
Tazza, Thanks for the input. It is a model 743 with the newer control block (1989 model year). I think I may be able to get to the valve cap on the block under the cab seat without removing the block itself. Al
You can indeed get access under the ROPS and through the engine bay, but its not easy! Its even harder to remove the block.
Here is a scan of what the block looks like with all its internals:
If its just 1 section your having problems with, make sure you change all the seals in that section.
You will loose a fair amount of oil, but you can't help that. Give the block a good de-grease before you start to help prevent geting dirt in your system.
I have replaced all my seals on my 743, but it was all done out of the machine which made it ALOT easier.
Just a little trick, use a dolip of grease on the spring when re-installing your poppets. This will help hold the poppet to the spring so it won't fall off. Grease ALL O rings before assembly, this will prevent them pinching and causing leaks.
Good luck with it, i'm sure you will do fine. Any problems just give us a yell.
Thanks for the info!
Al
Hi Gents, I recently bought a well-used 743. It had a hydraulic leak, crept forward, and the lift arms come down on their own. The dealer nearest me is fairly new, and doesn't have alot of Bobcat knowledge. They are very nice, though. The leak happened to be the one hose you have to take the engine out to replace. (They didn't know you had to remove the engine, nor did I!) It used to creep straight forward, after they adjusted it it creeps in a backward circle! They thought the lift arms dropping was caused by the leaking hose, but it appears to be the same as the above post. I'm looking for more specifics on fixing this myself. What pieces need to be replaced? Are the pieces universal or Bobcat specific? Does hydraulic fluid come pouring out in the process? The dealer had it for 4 1/2 weeks. I brought it home on a Sunday night and took it in on Monday morning, and just picked it up this morning. Mine sounds like the arms are coming down alot faster than yours, probably 10 or 12" a second. Also, I got a service manual, but the dealer could only get the 743B manual. Does anyone know the difference? On a side note, The dealer told me the hydraulic pump had gone bad, but I learned on this forum about the aux hydraulics being on would make it groan and not lift right. They were embarassed when I told them the problem. Thanks to all the knowledgable posters on here sharing. This is what makes the net a great thing. Also, when I turn the key backward to try to preheat the glowplugs, the engine turns over. I've gotta find this wiring mixup. Does anyone know where to get a cheap replacement seat? Thanks for any input. Curtis
Hey there, the seat i bought was from a place called TVH international. They do all sorts of stuff, mine cost just under $200 aussie dollars. Thats for a semi-suspension seat, complete with runners and a seat belt. My dealer wanted $500 odd for a bare seat!!! no runners or lap belt.
Ok, your lift arm problem, it sounds like it will too be a problem with your load checks in your control block. The main problem is they are a total cow to get access to. Yes, oil will pour out absolutley everywhere.... Your only option is to drain as much oil as you can before you attack the control block. Getting back to the load checks, to do it rite, i believe you will need to remove the whole block and get the seats machined flat and replace the poppets. It sounds like there is a bit too much wear on the poppets and seats causing oil to by-pass.
As you did mention it drops pretty fast, have you tried with the machine off, pushing your heal down a tad and see if they stop moving? if it does, it could be your centring spring on the back of the spool has lost a bit of tension causing it to not centre correctly.
As for your glow problem, i have seen other people wire them up like that, they wired the glow plugs to the starter so when you crank it glows. Have a look in the back where the start and glow solenoids are and remove the extra wire that has been put from the starter to the glow solenoid.
There isn't alot of difference between the 743 and 743B model, there are a few small things but you can work around that.
If you need any other info just give me a yell!
Hi Tazza, I did notice a cross over wire going from the back solenoid to the front one. The parts manual doesn't show one, but I didn't want to mess with it until I got some info. Man, I was hoping to get a seat for less. The dealer replaced a bunch of hyd hoses, including removing the engine, so I just put a little over $600 into her. I didn't want to drop so much on a seat. I'll look around a bit more. They charge $75 an hour (US)! But only charged me for 3 hours. I'm not complaining...they could have soaked me. That sounds like alot of work for the control block. That can't be done on the machine? I'm fairly mechanically inclined, but haven't messed with hydraulics much. The arms drop pretty darn fast....reallly annoying. I can't quite figure out all the parts in the diagram. Would it be the spool side or the relief valve side, or both? I'm gonna tackle the steering adjustment tomorrow. I probably should have pushed the dealer a little, but I didn't want them to add any to the price. The backward circle is annoying, too. It needs a bunch of other little things, too. the fuel guage doesn't seem to work, the lights don't work, the hourmeter is nonfunctional. Does yours have lift assist rams for the cab? I checked out all your pictures. That looked like a fun project. Very impressive. Thanks for all your help. (I can't get paragraph splits to work on my posts)
Yeah, mine has those pesky gas struts. They are magic to lift the ROPS but they are nasty to get back in after removing the ROPS.
Yeah, my *baby* has taken alot of work indeed, i'm just not sure about the engine, i hope its just air still caught in the cooling system but it seems to gurgle out a bit of air. I'm just hoping its not exhaust gas, i just need to work out how to test for it.
As for working on the spool, on the machine really is difficult, especially with the engine still in it. You should be able to gain access to the load checks without removing anything but you will need to modify a few cheap spanners to get to the plugs holding the load checks in place. Do check your centring first, you don't want to do a job like that if its not needed.
Now to fix your paragraphs..... Login, click up the top where it says profile, rite down the bottom check the box that says "use HTML editor (free text box)" the click apply. Then presto!
Getting the steering just rite is a real pain in the A$$, trust me! mine still isn't rite and i just gave up.
If you are mechanically minded you will be fine, just remember with hydraulics you need to keep it clean clean clean. When you replace O rings ALWAYS oil them up before re-installing them and if you repair anything with moving parts use alot of oil with re-assembly to prevent it running dry before it fills with oil, especially with pumps! they will quickly fail if you don't.
That wire you speak of fron the front to the back may just be an earth, mine used to have that before i changed solenoids.
If its the load checks, they are on both sides, they are the caps on the side facing the hydro pump, the same side as your tube lines. There are 2 per section.
Hopefully that answers all your questions so far
Man, that cab is heavy. I don't have struts. I got the steering adjusted pretty well. At least it doesn't back in a circle by itself!Yeah, mine has those pesky gas struts. They are magic to lift the ROPS but they are nasty to get back in after removing the ROPS.
Yeah, my *baby* has taken alot of work indeed, i'm just not sure about the engine, i hope its just air still caught in the cooling system but it seems to gurgle out a bit of air. I'm just hoping its not exhaust gas, i just need to work out how to test for it.
As for working on the spool, on the machine really is difficult, especially with the engine still in it. You should be able to gain access to the load checks without removing anything but you will need to modify a few cheap spanners to get to the plugs holding the load checks in place. Do check your centring first, you don't want to do a job like that if its not needed.
Now to fix your paragraphs..... Login, click up the top where it says profile, rite down the bottom check the box that says "use HTML editor (free text box)" the click apply. Then presto!
Getting the steering just rite is a real pain in the A$$, trust me! mine still isn't rite and i just gave up.
If you are mechanically minded you will be fine, just remember with hydraulics you need to keep it clean clean clean. When you replace O rings ALWAYS oil them up before re-installing them and if you repair anything with moving parts use alot of oil with re-assembly to prevent it running dry before it fills with oil, especially with pumps! they will quickly fail if you don't.
That wire you speak of fron the front to the back may just be an earth, mine used to have that before i changed solenoids.
If its the load checks, they are on both sides, they are the caps on the side facing the hydro pump, the same side as your tube lines. There are 2 per section.
Hopefully that answers all your questions so far
I clipped that crossover wire and now I hear the click for the glowplugs. I don't understand the reason to only have the glowplugs come on with the starter
If I take the control block off, I'd like to go right through it. Any idea about how much the parts would be? I was a little off on the amount it drops....it might be only about 3 inches a second...it just seems fast. I don't think it's the centering, that sucker drops until the pedal is pushed far enough to raise.
I think I need pins and/or bushings in the quicktach. That seems a bit sloppy.
The hourmeter was unplugged, there are a couple of wires it could be. I'll try the closest one first. Is the black multiposition rotating switch on the right dash the light switch? It doesn't do anything. My light isn't connected to anything.
Thanks for the help on the message stuff, too. I like the faces! I'd bet there will be lots more questions.....lots. Thank you for everything so far. I wouldn't have dared clip that wire otherwise. Every little thing I fix, I like the machine more.
bobbie-g
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Seat Forklift Backhoe Bobcat Case Skid Steer Tractor jd Item number: 190023037166 Roadkill, try this ebay item. Just ran across it after I read your post. I have no info on the seat. Good luck. ---Bob
skidsteer.ca
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I sorry but I feel you guys are getting ahead of yourselfs with the control valve thing.
Tazza I would be vary interested inn reading the article you have though.
In my expierience I have seen re packing a piston on a hyd cylinder fix the dreaded creep more then once. With poly pack cylinder seals you can even have a creep that comes and goes thogh this is not nearly as common as a creep that is constant and noticably getting worse.
I'd be unhooking and capping the hoses to one cylinder, then the other. Lift the boom with just one cylinder conected to the system and see if you creep is still there. If it gone try switching cylinders, see if the other side creeps.
If it goes away with once of the cylinders disconnected then it is likely a piston seal. If you think this is the case remove the suspect cylinder. CAP (seal off) the port farthest away from the chrome shaft. Hook your air compressor to the port that world retract the ram, and put the air to it. If the cylinder is good the ram will re tract and stay retracted. If the piston seal is leaking it will retract , then begin to extend. This is a definite indication of a internal piston seal leaking.
If un hooking one cylinder then the other makes no difference then I would go after the control valve if I cannot find any lines or hoses leaking.
With the valve I'd start by unhooking the hoses to both cylinders and capping the hoses on one side.
I'd connect my trusty 3000 psi guages , one to each of the lines that was connected to the second cylinder. Start the engine and step on the lift pedal.. The guage on the lift side should come up to what ever your relieve valve pressure setting is. say 2500 psi, when you release the pedal it should stay there if there are no leaks or valve problems.
In my expierence with load checks, they don't creep when the valve spool (control pedal) is in the center (neutral) position. I have a problem with the one on the tilt circuit of my 553. It hold fine until I move the pedal slightly from center, then the bucket starts to slowly dump even though I'm pushing with my heel, (curl bucket) until I push the pedal enough that the hyd pump starts putting oil in the cylinder, then the bucket comes up. It stays put fine as long as I don't move the pedal slightly off center.
So do a little trouble shooting and start with whats easy, not with whats hard.
Of course oil leaks can cause the problems you mention , but I'm assuming your not having to add hyd oil and there is not a puddle under the loader.
Regards
Ken
As for the load checks not having an effect, my old 731 would creep down constantly, i re-sealed both cylinders and made no difference. I pulled the vavle bank out as the spools were leaking, i replaced all the seals, including the load checks and theat fixed the problems. The seals were shredded, most were hard and brittle and others were in 2 pieces. These were not the bobcat branded valves though, they were a gresson valve bank.
Ken, here is the article about cylinder creep:
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[FONT=Arial, Helvetica, sans-serif]One of our readers wrote to me recently about the following problem:
" I am having problems with the boom on my crane creeping down. How do I determine if it's the valve or cylinder that's leaking?"
A popular misconception about hydraulic cylinders is that if the piston seal is leaking, the cylinder can creep down. Fact is, if the piston seal is completely removed from a double-acting cylinder, the cylinder is completely filled with oil and the ports are plugged, the cylinder will hold its load indefinitely - unless the rod-seal leaks. What happens under these conditions - due to the unequal volume either side of the piston, is fluid pressure equalizes and the cylinder becomes hydraulically locked. Once this occurs, the only way the cylinder can move is if fluid escapes from the cylinder via the rod seal or its ports.[/FONT]
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From what you say, that it stops moving when you push the pedal far enough to get it to raise that sounds exactly like what mine used to do with bad load checks. If you push it rite down and the rams stop moving that confirms its not your rams leaking.
As for seals for the control block, i paid about $15 from a hydraulic seal shop for mine, but i do recommend buying toe correct ones from Bobcat. You will need genuine rubber boots to cover the spool rods. They are only cheap and keep the dirt out.
The spools don't have seals as such, they use 1 quad ring either end of the rod. I think this area is only low pressure too, as there really isn't alot holding them in place.
As for the big switch, its for lights, i'm not too sure what they all do, but how i wired mine up was one click wwould turn the back lighting ont he gauges, 2 would turn the front lights on and 3 would turn on front and rear lights.
I don't have any gauges (or caps, I know the caps would be cheap) to test the pressure and I don't see any leaks. It sounds like the control block seals would be the most difficult but the least expensive and most probable culprits. As long as I can catch and reuse the hyd fluid. (I hate making messes). The "dealer" said around $50 for 5 gals. And they're about 40 miles away. And $75 an hour is a bit much. Ken, I appreciate the info on diagnosing, unfortunately I don't have the tools.
It's really not that usable the way it is, so I'm gonna have to jump into it.
I may try to rewire the lights. Someone rewired them separately, but I guess that's another thread. There are actually a few empty holes in the dash. This old 743 could spawn a whole mess of threads. She's 19 years old, after all.
hehe, the smiley face is always needed.
Ok, the caps really aren't cheap unfortuatly, i unded up making a few plugs out of old hydraulic hose fittings. The hoses were replaced so i chopped the fittings off and welded them up. The plastic ones you use just to keep dirt out are a few cents each.
No matter what you do you will loose alot of oil, have pleanty of old rags on hand. Drain as much fluid as you can before you start. When you finish, give it a really good degrease. Give it a good clean before you start too, just to prevent getting any crud in your system.
skidsteer.ca
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Tazza
I agree with what the article mentions, however often when a loader boom is lowered, gavity pulls it down faster then the pump fills the down side of the cylinder. This leaves a vaccum that oil leaking by the piston from the up side can go to.
However at some point the cylinder should hydro lock.
Even without cap, the cylinder can be removed and taken to a air compresor. Just put pressure in the extend side then and listen for it leaking out the opposite port. Still cheap and easy imho.
Ken
This is true, its really hard to test these things without special test gear. I like your idea of attaching a pressure gauge to the hose of the ram to check the pressure drop, that may be yet another device for me to make...... I better add it to the list of things to do before death, unfortunatly that list is becoming ohh so long...
I hope in my earlier posts i didn't seem too rude, that really wasn't my intention, after i read what i said when it was posted i was thinking ooh, that sounds a bit harsh.
I agree with starting with re-kitting your rams, do the full set, even if your pressure and wiper seals seem ok, replace them anyway. Seals are cheap, do the job rite first time, they cost me all of $25 AUD per ram, i think thats cheap enough, you don't want to be removing the rams multiple times, trust me its NOT fun.
skidsteer.ca
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A 3000 psi guage can be had for $25, plus a few fittings, most people have access to an air compressor, even hyd caps are farely cheap compared to shop labour or randomly guessing at the problem. If you can get a portable compessor you can pressure test the piston seal right on the machine just by hooking air to one port and listening for the leak in the other. And if a guage would help me test the valve b4 I went to the trouble and wasted oil to pull it out, I think that is money well spent.
My apologies if I sounded rude also, I just know what my experience tells me. I like testing to narrow down the problem area when ever possible. I have pulled to many things apart, rebuit them and then found out that was not the problem. Any honest mechanic will tell you they have been there, It just a place I try not to visit often.
Ken
I personally didn't take anyone for rude. I wholeheartedly agree that diagnosing is the smart thing to do. That being said....I ordered the seal kit for the control valve (there must be some percentage of being right!) . I noticed that the diagram doesn't show any detent balls. I'm thinking the lift and aux spools should both have them, though. The kit is $65. I kind of wish I had the component repair manual. Oh well, what's the worst that could happen?
