I have a 1999 Bobcat 773G with about 2400 hours on it. It runs very well but there are a couple of issues that I would like to figure out. The machine clunks in the driveline somewhere almost like a chain is binding. It feels almost as if a chain is trying to jump off of a sprocket?? Most of my work with it had been in sandy areas. It only clunks when in motion and it feels like you just bottomed out on a log. This clunking has me more concerned than my next problem, but I'd like to mention both. The second issue I have been having is that the bucket lift and tilt slowly lowers by itself after raising or tilting. I have only put about 25 hours on the machine since I purchased it second hand and it was not drooping like this when I purchased it. I know that all of the fluids were changed at the time I purchased it. I was told by another Bobcat owner that it was possibly my hydraulic pump getting weak. Would this problem come on that quickly? I don't think the cylinders need rebuilding because there are no visible hydraulic leaks and the lift/tilt both drop off at about the same rate. If this sounds like a hydraulic pump, can a mechanically inclined user rebuild it and how costly is it to rebuild yourself?
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For the clunking I think I would jack all four wheels off the ground and check the bearings on all the wheels , also at the same time you can rotate the wheels forward and reverse by hand and you may be able to locate the clunking ----------I have never seen where a bad hydrulic pump will let the boom and tilt leak down , the pressure is past the pump and held by the valve , if there is no external oil leaking then it has to be in the valve since both funtions are affected , I ave seen this before and seem I remember it being a little valve ( which I think is called an anti cavatation valve ) on the controll valve
skidsteer.ca
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It could be a internal leak in the cylinders too.
Does the boom leak down a foot over night or over 15 minutes. Also for the bucket, just how fast or slow is it. If its over a few hours I`d just leave it for now. If its over 5 minutes, it`s time to unhook your cylinders and test them for internal leakage (past the piston from one hose to the other) with compressed air.
The clunking, likely a bad bearing.
Ken
Thanks Fishfiles, I will look into that further
If I raise the bucket all the way up when warm it would probably take about 4-5 minutes for it to be on the ground. Like I said earlier, the 773 didn't do this just 25 use hours ago (when I purchased it). It came on fairly quickly. I just have a hard to time believing that the cylinders could go from working perfectly to leaking down (both the bucket and the lift) that quickly. I have no experience in this area, but I would expect the cylinders to leak down gradually over time....I have no idea. The valve that FishFiles mentioned sounds a little more in line with my thinking because it is happening to all hydraulic cylinders. I will look for a bad bearing but that must be one huge bearing with the clunk I'm feeling. Is there no rear end-tranny or chain-sprockets on these 773's? Sorry for the ignorant questions...I really need to get a good manual.
The clunking could even be a drive chain or sprocket. Test the slack and bearings first.
As for he leaking down, it could be your load checks in your control block too. That seems a bit excessive to drop that fast with only internal leakage, but its not un-reasonable.one way i found that seemed to tell me if its rams or load checks is to sit in the machine, raise the arms. Turn the machine off and watch the ram sicks be drawn back as the arms drop, push your heel down on the pedal and see if it slows or stops moving. If it does stop or slow its a tell tale sign your load checks are not functioning properly. This worked on my old 731 so i'm not sure if it will tell you a lo on your newer machine but essentially the load checks work the same.
On the clunk issue , picture two rear sprockets and two front sprockets , all four are independent and mounted on axles with inner and outer cone bearings and races , four chains go to the middle of the machine where a left and right carrier bearing setup supports the shafts which holds a double sprocket , the rear and front of the left get tied together on the double sprocket , and the same on the right , the hydraulic drive motors tie into each carrier bearing ------------I just thought of something , does your emergency brake work or not , as the brake assembly may be your clunk
I don't think my emergency brake works. I have never really tried to use it because it has only been used and stored in fairly level areas. I did once try to step down on it but it didn't seem to work. I will look at that also. Thanks for the advice guys.
My 773 has all hand controls (no pedals beside emergency brake) and I believe they are completely non-operational when the machine is turned off. I agree that it seems too quick too be internal leakage and doesn't make sense that internal leakage would come on so quickly on all hydraulic cylinders. Like I mentioned earlier there is no external leakage.
Rams don't need to have external leaks for them to still leak down. The inside of a hydraulic ram consists of a piston which is attached to the rod that comes out of the ram and a piston seal to seal against the inner wall of the ram. If this seal is damaged it can allow oil to move from one side of the ram to the other (from high pressure to low) allowing the ram to slowly fall. Its all internal and you won't see any signs of it from the outside.
Could it be as simple as alignment of the cables for the hand controls? I'm assuming the hand controls are linked to the spools with cables.
skidsteer.ca
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G series hand controls are fly by wire.
Cylinder packing can leak interally and go down hill farely fast. They can even have temporary bypass problems and act normal again for a short period, but will continue to get worse.
The part that does not seem to apply to this case is that both the lift and tilt started at the same time. But I can't understand how the valve, which has a separate section for each circuit could cause it to have a leak in both separate sections at the same time.
Testing the cylinders for internal bypass is relatively easy to do, compared to working on the valve imo.
Ken
If your brake doesn't work I think it's a good chance the bracket that holds the brake in place sheered off bolts or they fell out , possiblly the bolts that holds the wedge to the solinoid shaft may have broke , you can look where the brake solinoid is mounted and see if the bolts which surround it are in place or loose , those bolts hold the brake assembly to the bottom side of the case , you could unbolt the solinoid and then unbolt the base plate which holds the solinoid , then you can lift the brake wedge out the machine , you will be able to see down in there and see if anything came loose , you can also run the machine around with the brake removed to see if the clunk is stll there , I might also put a long magnetic retrival tool down the brake hole and work the bottom of the chain case to see if you get any pieces of torn up metal from the bottom which could be carrier bearings or such , good luck on that part --------
I know you guys are going to laugh at this one but the wheel lugs were not completely tightened on one rear wheel creating the thunking noise. They were snugged up close to the rim making it hard to see. Close but no cigar. Whoever took the wheel off last did a shoddy job putting it back on...they should cleaned the lugs with a wire brush and some WD40 or antiseeze. It was one of the first things I checked, but the rust on the lugs made it seem as though they were torqued on there well. It did this clunking since the time I purchased it and really sounded like something alot worse. I apoligize for not replying earlier with a follow up. I guess this is one of those "keep it simple stupid" moments that we all have once in a while.
I can't laugh, i had a problem like this once too. I was testing a machine i just pulled down and painted, i was testing it with just 2 nuts installed. It would every so often make an odd noise, it turned out when i put the wheel on i had the jack stand too far up the axle tube and when i thought the nuts were tight, they actually weren't so the wheel was floping around! It didn't cause any damage thankfully, but we all can get caught.....
Yes i know i should have had all 8 nuts installed, but when testing its easier to remove 2 than it is to remove all 8 if there is a problem.
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