Tazza, i lapped the brass plates in the pumps and reassembled it and the machine is almost as noisy as ever. It is quiet going forward and backward, goes fast or slow with no trouble, it seems more hoppy when turning on hard dry surfaces than before. When I reassembled it I had it blocked up and drained all the oil from the motors then filled it up turned the wheels till they had oil in them again started it and set neutral. I did not take apart the replenishing valves or anything other than the pumps and port block. Could there be debris in these valves causing the noise? I have been running it just a few minutes a day for a couple of days now to give any air in the oil tank a chance to escape. The noise seemed to increase after using the backhoe I got this spring so before I use it again I will put a return filter on it just in case. Noise is worse under heavy load. How quiet were your machines after redoing the pumps? thanks, jerry
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Jerry - when i did my last pump like that, it did take a while for the air to bleed out. What happens if you block the machine, with the park brake off try and turn a tyre. If it can still be spun around you have air in there still, if it doesn't move it sounds like the system is pretty well air free. Does the noise get better with more throttle at all? I did find my 743 was always a bit noisy at low RPM.
How do the sticks feel? do they vibrate and try and fight you? they will always want to push back to centre but it should be a constant tug, not like bouncing of it trying to pull away. You did mention the port block, so i assume you cleaned or replaced that rotten filter. If it was plugged it would make more noise but it would also have low power. As you said it has heaps of power on hard "sticky" surfaces i doubt it's the problem.
I hope its just air still in there, how long have you run it since you pulled the pump?
How do the sticks feel? do they vibrate and try and fight you? they will always want to push back to centre but it should be a constant tug, not like bouncing of it trying to pull away. You did mention the port block, so i assume you cleaned or replaced that rotten filter. If it was plugged it would make more noise but it would also have low power. As you said it has heaps of power on hard "sticky" surfaces i doubt it's the problem.
I hope its just air still in there, how long have you run it since you pulled the pump?
Tazza, I replaced the bronze filter last year so I just cleaned it this time, there was a couple of small black flecks on it but that was all. Noise is less at higher rpm. I have run it about 1/2 hour total. I put a hose on the upper aux coupler and ran out a couple of quarts of oil and it did have fine bubbles in it. I also bought a 3000 psi gauge today and connected it dead head on the upper aux fitting and held the stick over to detent. The relief valve opened and the engine labored but the gauge did not move. I assume the gauge is no good. The I connected a return line filter in the line from the backhoe to the lower aux fitting and ran out a quart of oil to clean the line, connected it up and oil was circulating fine through the backhoe till I tried to raise the boom and blew the seal on the filter. How come? I still have not figured that out.
the gauge works it was the operator that was faulty. connected to the lower aux fitting I have 1700 lbs, will try the filter again on the other hose.
I don't know why the filter seal went....
1,700 PSI is quite low, it should be around 2,500
I wonder if its low charge pressure or something, it would make your drive loud and not as responsive.
sterlclan
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you could hook the gauge to the port block where the charge pressure light goes and see what you have....when I did mine the noise went away pretty quick... if it moves ok try to run it a little longer.. if the sticks aren't centered right it'll make some mean noises does it creep at all sitting with the revs up? how bad were the plates?mine continues to get better the more I run it as the plates "may" not have been totally flat and true as they wear a little it improves. I have had to adjust neutral several times since I did the plates did you clean the port block if so how did the poppetts in there look a worn poppett could be the problem....
I,ll check that charge pressure today, the filter seal went because the lower fitting on mine when the lever is in detent is the pressure line to the hoe. The book calls for 1900 so I may have to adjust that up. After switching the filter to the other line it is fine. the neutral on the sticks is good, the rear pump plate cleaned up good and the front one was scratched deeper, probably 10-15 thousandths. It cleaned up almost all, everything in the port block looked in good order. when running the aux to the backhoe I can hear a occasional blip of air going through so I will run it more and see how it goes after a hour or two. thanks for all the help on this.
gauge I bought from northern tool was 200 lb off, I borrowed a older gauge and it showed about 70-80 psi on the port block and 1900 at the aux although if it is run over the relief steady it drops to about 1800. the book says the pressure should be 1950 and the bypass valve will limit the charge pressure to 133. I wonder if I shouldn't replace the parts in the bypass valve, the spring may have weakened a little and poppet and seat may have worn.
You can install shims to increase the pressure too, that does seem a little low, especially if you aren't driving around. It will usually fall when you the wheels are moving but should be pretty steady when just idling.
Tazza , when you shim in increase the pressure do you do this in the neutral bypass valve to increase spring pressure? sounds like a good idea to me, if that is where you shim it I will try it. Thanks for the help.
I was talking about the charge pressure relief valve/poppet. You don't want too many shims or washers behind the main centre spring on the pump. The more pressure the more your arms need to work to move the levers.
I think we are talking about the same thing, it is just that it is called the neutral bypass valve on the flow diagram in my book. It is actually the charge pressure relief and is under the first fitting in the port block.
sterlclan
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I replaced the poppetts and springs in the port valve they werent much from bobcat the neutral one had a little groove and I think leaked by. I lapped plates after replacing them as changing them really didnt help with the issue I had.now my charge pressure runs about 150 sitting still and varies quite a bit when moving around lowest about 70
sterlclan
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oooops I meant port BLOCK damn hunt and peck typists.................Jeff
I did replace that spring, poppet and fitting today and it should be right now. The old spring had worn into the bottom of the old fitting and the new spring and poppet were .020 longer than the old. It doesn't seem to have made much difference in noise although I do think it is getting quieter the more it is used. it goes forward and backward quiet even with a bucket full of gravel or the backhoe on it, you do hear the chain noise though. it just complains when turning or digging into the hard packed gravel pile. I think I will just get used to it , if the replenishing poppets are worn could that cause noise also? Thanks for the help on this.
sterlclan
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possibly......I think that with use the noise "should"get less.........how did the seat for the poppet look? run it man........Jeff
Jeff, he bobcat parts guy said the seat is not replaceable and I did not look at it. Were you able to replace yours? Right now "run it " is the plan I am going with.
I wonder if its like my 753's cold weather by-pass relief valve. It lets out a constant hum when its running, it had the same problem, the poppet seat had been worn egg shape. Its a shame they don't harden the seat but they harden the poppet!
I hope yours settles down.
sterlclan
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no replacement but I did lap it a little with valve grinding compound and a new poppet (I bought a handful those buggers sure can fly) most likely it didn't need it but what the heck.... the prior owner of mine had installed it backwards and the seat wasn't too bad the drive on mine keeps getting better with use keep us posted..........Jeff