help diagnosing 773 hydraulic issue

[shepherd]

Hi guys haven't been here for a while as my machine got a good bit of love last year and has been trouble free till we got hammered with these snow storms recently. The machine is 1998 773 with the single tilt cylinder and no hi-flow hydraulics. It has seen some hard use for the last two months pushing and stacking snow with a modified mulch bucket, most of the work is straight back and forth stuff, and the turning is usually on slick surfaces, so these problems were hard to notice at first. First, it is faster in reverse that forward. I know it used to be faster, but moving snow is kind of boring so I didn't notice it at first. Power is down at full forward, with an occasional whine, but not a belt slipping sound. The power is ok just under full forward, if I back off the control arms, I can push a heavier pile than at full. Second, I get a squeal/ while when I turn the machine on anything where I have traction and the tires have to "skid", and the motor bogs down a bit. Running in snow, I didn't notice it at first, plus I have a headset on for phone and radio, and I mostly watch the gauges. Third, and this might be related or not, when either tilt or lift gets to the end of the piston stroke, I can feel the hydraulic system load like it is struggling. If I am moving the wheels will slow at least by half speed. The lift arm power is good, I can lift enough to tip the machine forward and the lift speed seems to be normal. The drive belt is tight, the smaller belt to the fan box and alternator is loose but that shouldn't be related right? One thing that I am wondering is if I have the wrong fluid and maybe that is part of the problem. I popped a tilt cylinder hard line, and had a hose made to replace it. I had 20 gallons of hydraulic fluid for my boom lift, so after draining the bobcat we filled it with that. I hadn't considered it could cause an issue, in a system that can use motor oil but maybe? My thoughts are a stuck relief somewhere, or foaming fluid, am I on the right track? Aux hydraulics don't work, the computer board is shot as are the magnetic coils for the valves, (that'll be another post someday) so it can't be that. I'm hoping I can fix it before I have to pray while babying it through another storm. Thanks in advance to the knowledgable members here! Shepherdog

 

[OldMachinist]

I know you said the drive belt is tight but it sounds like the problem is in that area. Maybe the bearing in the belt idler is going bad or the belt is getting wet and slipping. I'd check the idler and then spray the belt with some belt dressing.

 

[frogfarmer]

Not knowing what fluid you were running compared to what it has now could be the issue causing all of the issues. If the fluid you installed has a working range in the temps you are working and you haven't noticed any foaming it might be something else but since the only change was the fluid it is most likely. It does sound like the belt might be slipping at times and just being tight doesn't mean its in good condition. When the belts wear they become thinner and no longer engage the side of the pulley as they should causing the belt to slip. I have run several machines that were faster in rev than fwd but it was always an adjustment. Only strange issue would be the loading of the system after the lift or tilt unless I misunderstood the explanation.

 

[shepherd]

Not knowing what fluid you were running compared to what it has now could be the issue causing all of the issues. If the fluid you installed has a working range in the temps you are working and you haven't noticed any foaming it might be something else but since the only change was the fluid it is most likely. It does sound like the belt might be slipping at times and just being tight doesn't mean its in good condition. When the belts wear they become thinner and no longer engage the side of the pulley as they should causing the belt to slip. I have run several machines that were faster in rev than fwd but it was always an adjustment. Only strange issue would be the loading of the system after the lift or tilt unless I misunderstood the explanation.

I went and looked the machine over this morning, as I have the front bobtach apart after shattering the pivot bushings. Here is some more info and observations. 1. The oil is a generic brand "service pro" AW-32, thy have a web page http://www.service-pro.com/documents/WarrenSpecs/WA-AWHydraulicOils.pdf it is a 10W oil, so pretty thin, but looks to be a decent hydraulic oil. I replaced the main hydraulic filter when I did the oil change and hose repair, is there another filter in the reservoir? There is a small silver can hanging from the bottom of the reservoir, what is that? 2. Drive belt, is maybe 2-3 years old, and is a bit loose. I checked it when I replaced the battery recently, and I thought it was tight, maybe I am getting too old.. What is the correct tension? I will tighten it when I go back this evening. 3. faster in reverse: I stared at the linkage with the cab tipped up. There looks to be some adjustment on the slotted section of the bar that goes from the handles back to what I think is called the pintle arms. I read that is one point of adjustment, but that there are also bushings in the pintle arms that wear. This thing is filthy with rust and grease, so I don't look forward to working back there. I'll see if I can get the squeal/ issue dealt with first and then on to the speed issue. Frogfarmer, to further describe the "loading" as I call it: If I am moving with the machine and operating the bucket or lift arms at the same time all is good, until the arms/ bucket get to the end of the cylinder travel. Extended or retracted makes no difference. At this point RPM drops, and travel speed drops. I first noticed it when I was using the bucket pointed straight down to break off some ice while moving, and then checked some other scenarios. NOT good when holding a load up high and speed drops unexpectedly! No more truck loading till this is solved.. When a cylinder hits full travel, isn't there a bypass that opens? It used to just stop but other functions would be unaffected. I'm stumped..

 

[Tazza]

I went and looked the machine over this morning, as I have the front bobtach apart after shattering the pivot bushings. Here is some more info and observations. 1. The oil is a generic brand "service pro" AW-32, thy have a web page http://www.service-pro.com/documents/WarrenSpecs/WA-AWHydraulicOils.pdf it is a 10W oil, so pretty thin, but looks to be a decent hydraulic oil. I replaced the main hydraulic filter when I did the oil change and hose repair, is there another filter in the reservoir? There is a small silver can hanging from the bottom of the reservoir, what is that? 2. Drive belt, is maybe 2-3 years old, and is a bit loose. I checked it when I replaced the battery recently, and I thought it was tight, maybe I am getting too old.. What is the correct tension? I will tighten it when I go back this evening. 3. faster in reverse: I stared at the linkage with the cab tipped up. There looks to be some adjustment on the slotted section of the bar that goes from the handles back to what I think is called the pintle arms. I read that is one point of adjustment, but that there are also bushings in the pintle arms that wear. This thing is filthy with rust and grease, so I don't look forward to working back there. I'll see if I can get the squeal/ issue dealt with first and then on to the speed issue. Frogfarmer, to further describe the "loading" as I call it: If I am moving with the machine and operating the bucket or lift arms at the same time all is good, until the arms/ bucket get to the end of the cylinder travel. Extended or retracted makes no difference. At this point RPM drops, and travel speed drops. I first noticed it when I was using the bucket pointed straight down to break off some ice while moving, and then checked some other scenarios. NOT good when holding a load up high and speed drops unexpectedly! No more truck loading till this is solved.. When a cylinder hits full travel, isn't there a bypass that opens? It used to just stop but other functions would be unaffected. I'm stumped..

Noise when turning on sticky surfaces like concrete or bitumen is normal, more so at low rpm.
As for the speed, check that the stering levers are not bottoming out on the frame the boots are mounted to. If so, you can adjust the travel with the slotted bits you mentioned that go to the pump. The pintle levers/stops on the pump are to set neutral, they wear over time, but if it doesn't creep, you can leave them alone.
Yes, there is a relief that allows oil to by-pass when you bottom a cylinder out

 

[frogfarmer]

I went and looked the machine over this morning, as I have the front bobtach apart after shattering the pivot bushings. Here is some more info and observations. 1. The oil is a generic brand "service pro" AW-32, thy have a web page http://www.service-pro.com/documents/WarrenSpecs/WA-AWHydraulicOils.pdf it is a 10W oil, so pretty thin, but looks to be a decent hydraulic oil. I replaced the main hydraulic filter when I did the oil change and hose repair, is there another filter in the reservoir? There is a small silver can hanging from the bottom of the reservoir, what is that? 2. Drive belt, is maybe 2-3 years old, and is a bit loose. I checked it when I replaced the battery recently, and I thought it was tight, maybe I am getting too old.. What is the correct tension? I will tighten it when I go back this evening. 3. faster in reverse: I stared at the linkage with the cab tipped up. There looks to be some adjustment on the slotted section of the bar that goes from the handles back to what I think is called the pintle arms. I read that is one point of adjustment, but that there are also bushings in the pintle arms that wear. This thing is filthy with rust and grease, so I don't look forward to working back there. I'll see if I can get the squeal/ issue dealt with first and then on to the speed issue. Frogfarmer, to further describe the "loading" as I call it: If I am moving with the machine and operating the bucket or lift arms at the same time all is good, until the arms/ bucket get to the end of the cylinder travel. Extended or retracted makes no difference. At this point RPM drops, and travel speed drops. I first noticed it when I was using the bucket pointed straight down to break off some ice while moving, and then checked some other scenarios. NOT good when holding a load up high and speed drops unexpectedly! No more truck loading till this is solved.. When a cylinder hits full travel, isn't there a bypass that opens? It used to just stop but other functions would be unaffected. I'm stumped..

I am still leaning toward the belt being the issue. When the cylinders reach the limit of their stroke the pressure spikes and will put more stress on the belt. When the belt slips the drive pumps and lift pump both lose power from the engine and the machine would act just as you explain. I don't remember the procedure to tighten the belt but I have always run them on what I would call the tight side. I know some of the machines had gauges for deflection built into the adjusters. If the belt has been run loose it may need replacement as they don't take much slippage before they are shot.

 

[shepherd]

I am still leaning toward the belt being the issue. When the cylinders reach the limit of their stroke the pressure spikes and will put more stress on the belt. When the belt slips the drive pumps and lift pump both lose power from the engine and the machine would act just as you explain. I don't remember the procedure to tighten the belt but I have always run them on what I would call the tight side. I know some of the machines had gauges for deflection built into the adjusters. If the belt has been run loose it may need replacement as they don't take much slippage before they are shot.

You may be right after all, I got in there today and found some weirdness happening with the tensioner. It is holding tension, but the spring is slow to return tension. I loosened the lock bolt and tightened it up, but when I let it go for a minute I noticed that the spring was slow to unwind the tension I had put onto the belt. Removed it, cleaned the back out of it, soaked it in some oil for a while and reinstalled. We'll see if it does the trick. I still have my linkage to adjust and the bobtach in 20 pieces before I can get to test it out. Certainly seems like it could be the problem though. Thanks for the ideas

 

[shepherd]

You may be right after all, I got in there today and found some weirdness happening with the tensioner. It is holding tension, but the spring is slow to return tension. I loosened the lock bolt and tightened it up, but when I let it go for a minute I noticed that the spring was slow to unwind the tension I had put onto the belt. Removed it, cleaned the back out of it, soaked it in some oil for a while and reinstalled. We'll see if it does the trick. I still have my linkage to adjust and the bobtach in 20 pieces before I can get to test it out. Certainly seems like it could be the problem though. Thanks for the ideas

Turns out the problem is completely the fault of the tensioner. When the system put any strain on the drive belt, the tensioners action was slowed by the amount of crud that had accumulated around the spring, and it would allow the belt to slip. It would apply tension though, it just took a while. By the time I pulled the cover and looked at the belt, it always looked ok, and I only discovered it when I removed the tensioner entirely. Just posting this in case it helps another person.. Thanks for the suggestions, SD

 

[7LBSSMALLIE]

Turns out the problem is completely the fault of the tensioner. When the system put any strain on the drive belt, the tensioners action was slowed by the amount of crud that had accumulated around the spring, and it would allow the belt to slip. It would apply tension though, it just took a while. By the time I pulled the cover and looked at the belt, it always looked ok, and I only discovered it when I removed the tensioner entirely. Just posting this in case it helps another person.. Thanks for the suggestions, SD

the post back that issue fixed and this is what I found is HUGE, also note that you had looked at it. but until you held it youre hand you couldn't see it. a lesson to us all.l

 

[7LBSSMALLIE]

the post back that issue fixed and this is what I found is HUGE, also note that you had looked at it. but until you held it youre hand you couldn't see it. a lesson to us all.l

im guessing you found back side of tenisor moon curve had agreat big divot.

 

[shepherd]

im guessing you found back side of tenisor moon curve had agreat big divot.

No divot, just packed with thick sludge. Mostly a mixture of grease and what looks/ smells like a previously shredded belt. I always post results on every forum, if I have them to share. My work and hobbies have me searching dozens of specialty forums every day looking for answers and learning how things work. Thanks to the moderators that keep this going, it has saved me a few trips to the dealer for diagnostics. SD