Hi there, I've just finished doing a bunch of work on my old backhoe including rebuilding my stabilizer and swing rams. Now I have an issue with the swing go figure. Yes the cam and bolt and pivot are all good and I have installed a new cam pivot bearing as well. Great! no more leaks but... now the swing drifts radically with any lean at all on the machine. I does function well and slows as expected and the end limits. With the machine running ,hands off controls, any lean and it drifts..quite badly and quite annoying. Now, also when the machine is parked say overnight and I push on the bucket (hoe in travel position) with my hands the hoe just swings over like it's completely disconnected from the swing cylinders..free floats like there's no fluid in the cylinders. It was fine before the repack. Having said this, the rod to the sequence valve moves freely and moves the valve freely. I have not messed with the sequence valve at all. Has some thing happened in that pesky valve to cause this? Should I be removing it and attempting a rebuild? Seems odd to me that this is occurring now.. Kinda like it has to be bled or something...Any Ideas?? I apologize for the long post...
Sequencing valves are very trouble free on those hoes, my first thought considring the work done would be to recheck the rod packings in the cylinders, if not installed properly they are very easy to cut and your description indicates a very extreme leak and the fact that the problem did not occur till after the cylinder rebuild is suspicious
Hi Melben, thanks for taking the time...Respectfully, I have quite a number of cylinder rebuilds under my belt. I did search out and buy what I thought to be quality kits as I don't want to be redoing because of crappy bits. I did inspect the pistons and the bores closely while performing the work. Also I was very careful to exercise the rams slowly at idle after completion.. I'm not opposed to pulling them down again if I have to. I'm just wondering if there could be something other that could cause this. The sequence valve is indeed dry and not weeping. Some sort of air lock is not likely? very strange.
or a stuck relief somewhere.... I'm not too sure who posted it but I did read on here that someone had a number of problems with these sequence valves...but no detail
so as I wander around pruning...in order for this "neutral" scenario to occur wouldn't both cylinders have to have a problem? as they both work in unison .. one pulls while the other retracts. I can't possibly have made a boo boo on both...
As Melben has suggested in numerous previous posts cycle your swing functions multiple times and check for heat in one or both of the cylinders which will indicate fluid blowing by a seal. No matter how many cylinders you have built before if you got a faulty kit there's no shame in a redo, it just sucks...The worst part about faulty parts is second guessing your work when you know for a fact that your efforts were spot on but unfortunately it happens..
Thanks for your remarks. Everything I know I've learned the hard way . 60 yrs old now with two red seal trades and 44 years of tying up boots. Perhaps you'll be kind enough to put some links here regarding melben's numerous posts ?
please correct me if I have it wrong, but as I see it, a cut in one packing would do it as both cylinders are acted on on opposite sides. One leak would do the trick and the heating thing sounds like an easy check. you could even shoot it with one of those infrared laser thermometers.
Did you remove the swing cylinders when you resealed them ? If the boom swings as freely as you describe it seems to me it isn't a bad packing. A lot of oil has to move for a boom to swing that fast.
Could still be air in the system. I'm not sure but doesn't the swing have less flow than the other cylinders to slow it down? If so might take more back and forth to bleed all the air. My hoe uses a rotary cylinder but the lines to it are 1/2 the size of the other lines. Another thing you could check is how much swing power you have. Low swing power might point to leaking cylinder packing.
Is the cushioning at the end of the cycle EXACTLY the same on each side. It only takes a very small amount of adjustment for those valves to play up.
Sorry Jake but I'm not that computer smart, I can fix the hydraulics but not the computer
Thanks a lot to all you guys taking time to jibber about my issue. I always tell guys at work I don't have answers, .I only have ideas. I can't fix my computer either lol. So,yes I do agree that one cylinder could cause a drift in theory but I have to agree with tinkerer here.. a lot of oil has to move to create a free swing condition like this. No , I did not in fact remove the swing cylinders. Should I have ? Seemed like unnecessary work to me. It's almost like one or both are slowly draining after sitting. alrman, I have not played with the adjustment of the valve rod yet and I couldn't swear that the damping is totally equal at either end of the stroke.... seems close from the seat. It seems to me that the function of the cam and rod is just to dump oil as the cam bearing and rod activate the plunger in the valve. I don't think this is all the valve does though. I've looked at the exploded view in my parts manual and a "drain" tube is listed...3 of them depending on your valve bank configuration. Now , there is the swing valve in the bank and the sequence valve and the cam and pivot for travel dampening and the drain tube connection. Can someone try and explain exacting how this set up works? It's a bit of a head scratcher for me! Thanks a lot for any and all replies.
I asked about removing the cylinders so that we would know if the hoses were reconnected wrong. No there is hardly ever a need to remove swing cylinders to reseal them. Do you have or need the service manual for your SK ?
many years ago I had to learn how the double tilt cylinder set up worked on a Cat D6C from the early 70's. There were flow directing one way check valves that had been chucked out during a replumb on the blade. Nobody realized how the set up worked. I didn't know what these check valves were at the time and neither did the 2! ...yes 2.. mechanics that hucked em out. I needed that old Cat years later up on a road building job and I needed that tilt working! It took a lot of reading and routing around on the web to figure it out ( in the old days you went to the library or the old guy down the road) Lots of single tilt systems... not so many dual cylinder set ups. This kind of reminds of that...reciprocating cylinders.. tube end vs rod end volumes and stuff.....
Thanks Tinkerer for that clarification. I do have a service manual on my computer. Is this info in it? Have I completely lost it?? lol
Ok ,so I went back to my service manual to the sequence valve section and I have been in there before and now realize again that the short coming here is a lack of theory of operation. I did look for a kit and I read on the forum of a connection to find one. I could definitely do a rebuild on the valve using the manual but cannot seem to figure of the operation of the system it's a part of...
figure out .... that should read
You said all was well until you resealed the cylinders. I wouldn't disturb the swing sequence valve.
Yes this is a true statement, although I did Pull the top boom pin and weld and resurface it for wear, install a fresh alignment bolt, pull and repack the pivot and install a new cam bearing. I did not loosen the jam nuts nor adjust the link from the pivot to the valve at all. As it wasn't damp at all I thought why go there. Also I did check the rod and valve to make sure all was free. So yes, confounding. When I discovered this issue I was just wiggling the boom looking over wear. It swings over freely and then comes up hard part way over...like the piston coming up against fluid...and then it goes tight like one would expect until it sits for a while and then same thing. Hence my comment above regarding relief.
I go away and think for a while ,then come back...lol. So it seems like something's wrong with my cylinder rebuild(s) or.. As alrman has repeated...the valve rod needs adjusting in small increments to find the happy spot. Maybe my cam and pin work has thrown it out of whack. If the plunger in the valve is not right on , some port is exposed allowing a bleed down..? I will try adjusting it and see what happens. Any thoughts....
Try that. Hopefully Alrman, melben or ggraham will revisit your thread and give you more guidance.
Jake, as others have stated, warm the oil in the machine using another circuit, when the oil is very warm, then swing and hold it it in one direction for a minute then feel the cylinders where the piston would be and see if the barrel heats in that area. Heat would indicate the passage of warm oil through a leak. When I repack those cylinders I wrap 5 or 6 turns of electrical tape around the packing and put a stainless steel clamp on and compress the packing for a few minutes, it will slide right in much easier. I have many years experience with those machines , what you are describing still sounds like cylinder problems. I reserve the right to be wrong but if the problem did not exist before the cylinder repair I would not tear into anything else till I had eliminated the cylinders as a problem, as I stated before, sequencing valves are extremely trouble free.
Hi melben, thanks again for taking the time here. I most certainly will follow your advice on checking for a bypass situation and have no doubt or your experience and vast knowledge on the subject. You are a well respected member here from what I can see! I would like to put this to you though.. when my digger is running and warm the swing "appears" to be working as normal indicating to me that both cylinders are filled.. both rod ends and both tube ends. It seems like fluid is slowly bleeding out of one or both at one or both ends via the valve thusly creating an air void in one or both cylinders . There are no visible leaks.. This creates the "neutral"compression space I'm pushing against when I lean on it. If were just oil bleeding by the piston seals, wouldn't both ends of the cylinder(s) be full of oil still?. Where would the oil go? I'm leaning towards a rod adjustment to center the valve. Do you know how this reciprocating swing set up works exactly? What does that drain tube do? I certainly respect and appreciate your input. I will get to the bottom of it and post here the end result.
The test to check if one side of a cylinder is hotter is about the simplest test there is. There doesn't have to be an external leak for the internal seals to leak. If oil is bypassing the internal seals it would/could cause the oil level to be lower on one side of the piston. You seem to be questioning all the suggestions for troubleshooting your problem. Questioning everything instead of listening and trying what has been suggested leads to pages long threads that people get annoyed with and eventually stop trying to help leaving you on your own. God forbid you have another problem you need help with. People won't want to be involved in another pages long thread where everything suggested is questioned. If everything worked fine before the cylinder rebuilds, a problem with the seals would be the 1st thing to suspect is the problem. Checking for temperature differences is an easy way to confirm or deny this.
I didn't see where Jake answered Alrman's first question. ---->"Is the cushioning at the end of the cycle EXACTLY the same on each side. It only takes a very small amount of adjustment for those valves to play up."
If the swing is working normally as far as swinging with the engine running then it should be easy to see if the cushioning is equal. Even if it is not exactly equal to the 1nch is not problematic, that is were you touch up cushioning with a rod adjustment There are some dynamics that happen when there is packing leaking because of the unequal volume between the rod end and piston end, A cylinder with leaky packing can be extended as there is room for the oil on the piston side for the rod side oil due to rod diameter and a void can be drawn behind the piston. However, if the rod is tried to be pushed in the oil volume is greater on the piston side and as the oil tries to go to the rod end with the rod end valve closed the rod end cannot accept the oil so the cylinder becomes for all practical purposes a simple displacement cylinder of whatever the rod diameter is. If a gauge were inserted into either end of the cylinder it would read well above the pressure that would normally be there with a good piston packing if it were holding up a load, This is what makes diagnosing hydraulic problems challenging, add the fact of two cylinders in the mix and it really gets fun!
Wow...Dave. what's with the arrogance buddy! I did respond above Tinkerer. What's up with you guys? Hey? I work full time doing 10 hour shifts running a cat 336 with an sm 45 hammer hanging off it .Plus 5 acres to maintain plus my mechanical junk Maybe you're all retired and bored or something. Tell me what is wrong with diagnostics? That's what's going on here .If nobody knows or is willing to participate in meaningful discussion and only wants to lord their arrogance on others wanting to learn they shouldn't be here saying anything! IMO. melben, thank you once again for your intelligent input and time!
Nuthin up with me. No arrogance here. I'm just trying to help you in a small way. Suggestions have been offered to help you. I may be missing something, but it seems to me that you don't answer or try to do the diagnostic suggestions that were posted. Alarman graciously asked about the way it swings from side to side and you didn't respond. Warming the hydraulic oil so that the cylinders could be checked for leakage was another suggestion that you seemed to have ignored. You said it swung okay before you sealed the cylinders. Now it swings goofy. Common sense for me would be to verify that the cylinders are in fact sealed properly. Then I would be looking at the sequence valve adjustment. If there is a problem with the cylinders and you get the sequence valve way out of adjustment by messing with it you will compound your problem in a bad way. I'm sorry you are working long hours. I spent a lifetime working stupid long hours running construction equipment also.
I certainly wasn't trying to be arrogant just telling it like it is. Instead of trying simple things that have been suggested you question them and try to come up with your own theories on what is or could be causing the problem. Members on here have an incredible amount of knowledge and experience. Questioning everything suggested tends to irritate them. You're fairly new to this forum so likely aren't familiar with some of the threads that have gone on and on needlessly because people with a problem appear to not accept the advice given. Very knowledgeable members have even left the forum altogether because their expertise has been questioned and they're tired of going over the same thing over and over. Instead of just thanking Melbin for his experience maybe you should be thanking everyone who is trying to help you. I agree with Tinkerer.
Computer acting up, deleted a double post.
Ok gentlemen, I have to respond to this. Firstly, I may be new to posting here but I am in no way new to reading here. I'm also not new to life nor machinery. I've done my homework and read vast amounts of material on all manners of things before I ever consider posting. Where exactly do you get the idea.. any of you.. that I don't listen or take in what's being said? That presumption is imo tantamount to arrogance. Perhaps some "senior" members would be well advised to go back and look up the word forum... "A place for the discussion of ideas." Senior member syndrome I'll call it. I've seen it many times on many forums , although never directed at me. If members are just too tired to bother any more.. get lost then. So. Dave, is this forum on some kind of time clock like a professional chess match? I'm not looking at or working on anything at someone else's behest! I'll look into my situation using any knowledge from others that know more than me gleaned from various sources, when I see fit. I may never fix it. That ,my friend , is my prerogative. Once again, if someone sees my thread and doesn't want to respond...that's their prerogative. I have been friendly and mindful of peoples responses and I learned young to appreciate people's time and say thanks! Tinkerer , back a ways I said that the swing appears even. If I measured EXACTLY I would report that. OK? I've read everything I can find especially alrman's posts. No one as of yet has posted knowledge of haw EXACTLY this reciprocating cylinder set up works. Perhaps that's my fault for not narrowing my thread down to just that! Hey? That old 6 had bypass ports built right into the cylinders.. how bout that? So , Dave, if you're trying to get rid of me you're doing a good job . Is that too long winded for ya????????????
Wow ! Like I posted before, you seemed to have ignored alrman's first question. And the rest of the members questions. Did you warm the hyd. oil and check the cylinder temperatures as suggested ? Until you verify to us that hydraulic cylinders are functioning like they are supposed to, I don't think anyone will offer any more help. I didn't think your thread was about the theory of operation. That is usually covered in the hydraulic flow charts in the service manual. I don't know of any arrogant senior members have ever tried to "get rid of someone" I never doubted your ability's to repair anything. Your D6 repair was impressive actually. If you don't want to check the cylinders with an infrared temp gun you could dead end the cylinders and then remove hose on that end and apply more hydraulic pressure to the cylinder and it will either gush oil out of the port or it won't.
Wow is right!!! Yeah your response is too long winded and I'm sure others would agree with my assessment. It is very clear you were looking for someone to agree with your line of thinking and in complete denial that you may have botched something when doing the cylinder seals. A large portion of the members on here work a full time job and/or have their own things to do. They come on here to offer their expertise and experience to try and help others out. They don't have the time nor the patience to go back and forth with someone who is trying to get approval for their misguided theories. You've been friendly and mindful of peoples responses???? Not so much. Yelling at Tinkerer is somehow mindful and thanking him? I was trying to help keep your thread from getting lost among all the other threads where members are seeking advice. Many of the same members trying to help you are also trying to help others. I was never trying to get rid of you just offering what I thought was friendly advice to help you get your machine fixed. You took it the wrong way, instead of considering it, and went off the deep end. That's on you! Good Luck fixing your backhoe
Jake; I forgot to ask if you have or need the service manual ? I have it in .pdf form.
Hey give the guy a break, he's been tying his own boots for 44 years.