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bobcat 853 travel issues

Dwallace

Well-Known Member
Joined
Jan 6, 2020
Messages
54
Location
32060
I have a bobcat 853c just put new engine in machine. it will move forward and backwards but will not steer. are there some screens in hydraulic system that could be pluged?
 

Dwallace

Well-Known Member
Joined
Jan 6, 2020
Messages
54
Location
32060
bought the machine with bad engine. so i'm not sure. it's purdy clean with only 5,000 hr. looks to be all there. all the lock outs seem to be bypassed. machine will move forward and backward if you move both levers same time. with little power available. will not steer. get it moving let off either side that side stops. looking for leaky hoses and clean case drains. change spin on filter. wasn't sure if it has a charge line that activates drive pump.
 

Arny L

Senior Member
Joined
Sep 23, 2020
Messages
277
Location
canada
Do the bucket and lift controls work. Is hydraulic fluid topped off. Check filter or replace. Check drive control lever linkages for wear and adjustment
 

Dwallace

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Joined
Jan 6, 2020
Messages
54
Location
32060
yes bucket works as it should. fluid is full. linkages all seems good. acts like the main pump is not going into full swash.
 

Vetech63

Senior Member
Joined
Aug 10, 2016
Messages
6,362
Location
Oklahoma
The left and right wheel drive should work independently with each lever. If you push the left stick forward......only the left side should move forward and so forth. So knowing this I have some questions.

1. Were any of the hydraulic hoses removed or replaced during the Engine rebuild?
2. Was any of the hand lever linkage removed?
3. Does the machine make noise when you attempt to turn?
4. When the machine moves forward or reverse, does it seem to have wheel power?
5. Does the hydraulic system make any noises when you are NOT trying to move or steer?
 

Arny L

Senior Member
Joined
Sep 23, 2020
Messages
277
Location
canada
Not sure if a 853 has similar hydraulics to a 743, but theres a good video on utube by DannysCam, how to fix Bobcat that doesnt move. Theres an internal filter in one of valve bodys under cab, that clogs up with junk and limits drive. Might be worth a look if you've run out of ideas. The only down side to that is if its clogged with filings, you've got bigger problems.
 

Dwallace

Well-Known Member
Joined
Jan 6, 2020
Messages
54
Location
32060
the machine did have a few rotten hoses.oil cooler lines. and 1 case drain line was leaking.
no linkages were removed
it doesn't make that normal wining sound when trying to steer.
forward and reverse is very weak.
no noise when sitting still.

case drain filters had a small amount of metal debris.
main spin on filters had some sludge.
someone has tryed to bypass lockouts. with jumper wire from a relay.
i'm wondering if there's another 12v function that activates the main pump.

also where to check charge pressure
 

Vetech63

Senior Member
Joined
Aug 10, 2016
Messages
6,362
Location
Oklahoma
I’ll bet your charge pressure is low. I know for sure on earlier machines there was a stone type inline filter in the system that could be removed and cleaned. You need to invest in a repair manual or get pressure specs and locations from your local dealer.
 

Dwallace

Well-Known Member
Joined
Jan 6, 2020
Messages
54
Location
32060
charge pressure is 310 at the test port on filter housing. got the machine up off the ground. with engine off you can roll the tires by hand. I don't think that is right? both sides are the same.
 

Vetech63

Senior Member
Joined
Aug 10, 2016
Messages
6,362
Location
Oklahoma
Check the charge pressure when you stroke the levers to travel, then report that pressure back here. You shouldn't be able to roll the tires by hand at all. Is sounding like your drive motors are crap.
 

Dwallace

Well-Known Member
Joined
Jan 6, 2020
Messages
54
Location
32060
charge pressure maintains 300-310 while levers are being stroked. both sides. was thinking about capping off hoses going to motor. then stroke the lever see if pump is puttin out. should bog engine. just can't see both motors being completely wore to this point.
I think this machine has sit for quite some time.
the guy had fuel problems with the machine so he added 12 volt pump. it made injector pump push fuel out front seal. caused engine bearing damage. makes me think it was functioning until engine failure.
trying to locate pressure reliefs on main pumps/valves.
 

Vetech63

Senior Member
Joined
Aug 10, 2016
Messages
6,362
Location
Oklahoma
The wheels turning by hand is a good clue.that shouldn't happen as the ratio in the drive motors full of oil would never allow that. The drive gears could be slipping in the motor shafts but u have only seen a single motor do that.
 

Dwallace

Well-Known Member
Joined
Jan 6, 2020
Messages
54
Location
32060
did a pump test by plugging the lines at motor. stroke the drive lever. at idle it barely bogs engine just briefly.
found page 3-4 of the service manual TOW VALVE says there are two valves on front of pump that can be opened to allow the machine to be towed? I have found one. and it was opened 1 turn like the book says. but can not locate another one. didn't change anything about machine function.
 
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