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jerry

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Hello, newcomer here and with a question. I have a friend with a 93 853 that has the boss system. If he starts it and lets it idle it can idle all day and he can use the bucket and drive systems as long as it does not exceed a fast idle everything is fine. If the throttle is advanced within a minute or less it will show a hydraulic pressure code, a buzzer will sound and shortly the machine will shut down. It can be restarted right away with no problem unless you advance the throttle. I believe it is either a sensor problem or else pressure is building in the system. He thinks it is electrical and has taken the boss box off, drilled it open and had it checked out. It was fine. I have gone thru the archives here and did not see anything similar. As far as I can see there are no hidden filters and the machine does not have the case drain filters that some have. I will have to say though, the archives do have a lot things that have been helpful with my own 632. Thanks in advance for any ideas. jerry
 

skidsteer.ca

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Jan 20, 2006
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On the old Boss system there is a number that follow the code that helps indicate the specific problem, Do you know what code (codes) it throws. Believe the ones with the lower #s are serious ones that cause shut down. It could be as simple as one of the hydraulic filters.
Has he put a guage on the charge pressure to see what it reads?
The sensors read the charge pressure going into and out of the filters. there need to be a minimum pressure and not to much difference between in and out.
Put a guage on each side and check at various rpm.
I cured a code on a 753 by just tightening the screws inside the boss holding the circuit board. But it was throwing jibberish codes as a result of a bad ground.
Worn sensors, bad grounds and coroded or broken wires will play havoc with the boss.
If the problem is constant and predictable (which it seems) it does sound like a sensor or a filter/ flow restriction problem
Ken
 

jerry

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May 3, 2007
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2,040
On the old Boss system there is a number that follow the code that helps indicate the specific problem, Do you know what code (codes) it throws. Believe the ones with the lower #s are serious ones that cause shut down. It could be as simple as one of the hydraulic filters.
Has he put a guage on the charge pressure to see what it reads?
The sensors read the charge pressure going into and out of the filters. there need to be a minimum pressure and not to much difference between in and out.
Put a guage on each side and check at various rpm.
I cured a code on a 753 by just tightening the screws inside the boss holding the circuit board. But it was throwing jibberish codes as a result of a bad ground.
Worn sensors, bad grounds and coroded or broken wires will play havoc with the boss.
If the problem is constant and predictable (which it seems) it does sound like a sensor or a filter/ flow restriction problem
Ken
Thanks ken I'll see him next week and take another look at that display. He did replace the pump on the machine and I did ask him if the pressure was checked after replacing it in case it had been set up as the pump began to fail and would thus be too high with a new pump. He said it had been checked by bobcat tech and was o.k. jerry
 

skidsteer.ca

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Thanks ken I'll see him next week and take another look at that display. He did replace the pump on the machine and I did ask him if the pressure was checked after replacing it in case it had been set up as the pump began to fail and would thus be too high with a new pump. He said it had been checked by bobcat tech and was o.k. jerry
there are 2 pressures though. the main hydraulic pressure which is @ 2800 to 3000 psi depending on the year (memory, please check book) and charge pressure which will be much lower 100 to 300 psi.
On many machines the hyd pump is the charge pump and the replentishing valve controls wether the oil goes to the high side or the low side.
But something makes me think the 853 has separate pumps. The big one on the end of the hydrostat is the hyd pump, think the charge pump is within the hydrostat
Ke
 

jerry

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May 3, 2007
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2,040
there are 2 pressures though. the main hydraulic pressure which is @ 2800 to 3000 psi depending on the year (memory, please check book) and charge pressure which will be much lower 100 to 300 psi.
On many machines the hyd pump is the charge pump and the replentishing valve controls wether the oil goes to the high side or the low side.
But something makes me think the 853 has separate pumps. The big one on the end of the hydrostat is the hyd pump, think the charge pump is within the hydrostat
Ke
Thanks Ken for the info, next week I will have to spend a day studying that 853 and the books so I know more about it. It seems to me that in one of your past posts you mentioned running a Serco loader which is coincidental because I just retired as a machinist from Serco. 41 years machining , 22 at Serco the last 10 on CNC. I have been reading the thread from Sterclan on the groany 630, my 632 I got last fall groans a lot on turns, less with high rpm tho. When I got it I changed the hydraulic filter and found it was collapsed inside, bobcat brand too. I then changed the bronze filter and found not much of the brassy particles but dirt and very fine wire bits which I hope were part of the filter. Is it the nature of these old ones to groan since they are driven directly from the motor to the chain or are there problems I should be looking at. The machine is just used around home a few hours a week. One thing tho when I am coming off the trailer with fairly steep ramps it does not gain speed on its own which I think it would if there were much wear in the drive motors. jerry
 

skidsteer.ca

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Jan 20, 2006
Messages
3,853
Thanks Ken for the info, next week I will have to spend a day studying that 853 and the books so I know more about it. It seems to me that in one of your past posts you mentioned running a Serco loader which is coincidental because I just retired as a machinist from Serco. 41 years machining , 22 at Serco the last 10 on CNC. I have been reading the thread from Sterclan on the groany 630, my 632 I got last fall groans a lot on turns, less with high rpm tho. When I got it I changed the hydraulic filter and found it was collapsed inside, bobcat brand too. I then changed the bronze filter and found not much of the brassy particles but dirt and very fine wire bits which I hope were part of the filter. Is it the nature of these old ones to groan since they are driven directly from the motor to the chain or are there problems I should be looking at. The machine is just used around home a few hours a week. One thing tho when I am coming off the trailer with fairly steep ramps it does not gain speed on its own which I think it would if there were much wear in the drive motors. jerry
They all moan and groan some, especially when pushing hard or if rpm is low. That pretty normal for any skid I have ever sat in. (bobcat, deere, new holland) However groaning gets worse if you have problems, so its tough to call it based on that alone.
When you say the filter colapsed , I'm wondering if the bypass is disabled and the pressure differential crushed the element??
Most of the time one side just gets lazy as the oil warms up if the motor is bad. Yours sounds more like a charge issue, or could just be a sender. You need to ge the pressure guage out to verify this. Perhaps change the filter and open the old one and see if there is any new trash.
We have had our old serco (around 86 vintage, model 200, 3208 Cat. for 8 years now.
We bought it as a fixer upper (at 7600 hours, motor was smoking some, needed injectors, center boom knuckle was worn bad, and the 1/2 serco bypass clam was busted though the cross member of the jaw on the prong side, lots of new steel and welding) and have used it 1000 to 1500 hours for loading tree lenght and slash and load 100”. Its a good basic design that is easy to service and repair and rugged as hell. Those twin 6” main lifts just won't give up.
It has handled 15000 or so cords for us now will vary little trouble. However I need to pull the center manifold out and re seal it now. It leaks when it feel like it while the unit is sitting and loose all its hyd oil. Thats a job I'm not looking forward to.
 

Fishfiles

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Feb 8, 2007
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1,698
I would suggest that your friend change the hydraulic oil as I would almost bet he has multi grade engine oil , like 10w30 or 15-40 in the tank as 10-30 was the recomended oil for years , but not any more , Bobcat changed to hyrdaulic oil in their hydrostatic and hydraulic applications , I have found that the heavier oil has played havic with the hydraulic oil warning and shutdowns , if the oil doesn't solve the problem I would look to the sensor then the wiring to the sensor as this has also been a common problem with the older 7 and 8 53's
 

jerry

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May 3, 2007
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2,040
I would suggest that your friend change the hydraulic oil as I would almost bet he has multi grade engine oil , like 10w30 or 15-40 in the tank as 10-30 was the recomended oil for years , but not any more , Bobcat changed to hyrdaulic oil in their hydrostatic and hydraulic applications , I have found that the heavier oil has played havic with the hydraulic oil warning and shutdowns , if the oil doesn't solve the problem I would look to the sensor then the wiring to the sensor as this has also been a common problem with the older 7 and 8 53's
Thanks for the help fellows. All of these suggestions sound good and we will try them. I'm guessing he has multi viscosity oil in because it is cheaper, when I put bobcat oil in mine it cost about $80 but I think in cold weather it is better. jerry
 
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