853 Down Tilt Problem

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roxrobin

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Aug 18, 2007
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6
I have an 853 with no power to the down tilt. All other elements are powered... up tilt, up lift, down lift, as well as hydrostatic drive. BICS is showing a solid four lights. This problem was present before I pulled the control valve and resealed it... and was present after. A local IR mechanic recommended replacing the pressure relief valve... No Joy. I read on this forum of instances of internal tilt cylinder leakage. Is it possible to have normally powered up tilt and no down tilt due to an internal leak?? Any thoughts on what other items could be the culprit would be appreciated. Thanks, Robin
 

jmatt20

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May 18, 2005
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126
yes it is possible ,the seal works one way and dosen't seat right in the other dirrection ..same seal for each direction . if you can remove and reseal your controll valve you should have no problem realsealing a cylinder. pul the cylinder out of the machine ,put it in a vice ,remove the head and pull the rod out. a big nut holds the piston on the end ,remove it and slide the head off and your ready to remove and replace the seals. the book shows a couple of special tools to install the seals but the job can be done without them. the fiber seal on the piston is the one to be most carefull with, soak it in oil for a while and then flex it in your hand for a while to take a little of the stiffness out of it ,then start one side of it in the groove and slowly work it around the piston. when it goes on it will seem lose ,like youv'e streched it out but the end of the tube is tapered and it compresses into the groove when reassembled. the rod seal is a bear also but it is rubber so as long as you don't cut it you can manhandle it all you want ,just make sure that when you're done it's seated like the one you took out. if you have time you can source the seals from a hydraulic shop for less than bobcat. you can also get the kit from bobcat and then take the old seals to the hydraulic shop and make up some kits for the next time you have to reseal.
 

roxrobin

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Aug 18, 2007
Messages
6
yes it is possible ,the seal works one way and dosen't seat right in the other dirrection ..same seal for each direction . if you can remove and reseal your controll valve you should have no problem realsealing a cylinder. pul the cylinder out of the machine ,put it in a vice ,remove the head and pull the rod out. a big nut holds the piston on the end ,remove it and slide the head off and your ready to remove and replace the seals. the book shows a couple of special tools to install the seals but the job can be done without them. the fiber seal on the piston is the one to be most carefull with, soak it in oil for a while and then flex it in your hand for a while to take a little of the stiffness out of it ,then start one side of it in the groove and slowly work it around the piston. when it goes on it will seem lose ,like youv'e streched it out but the end of the tube is tapered and it compresses into the groove when reassembled. the rod seal is a bear also but it is rubber so as long as you don't cut it you can manhandle it all you want ,just make sure that when you're done it's seated like the one you took out. if you have time you can source the seals from a hydraulic shop for less than bobcat. you can also get the kit from bobcat and then take the old seals to the hydraulic shop and make up some kits for the next time you have to reseal.
jmatt20... Thanks. Looks like I have my work cut out for me tomorrow.!!. This happened all of a sudden... one moment the tilt was working just fine... wagged the bucket vigorously to dislodge dirt... the next, no down tilt. Is there any idea what normally causes this sort of thing?? Or is it simply age and wear a tear??
 

jerry

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May 3, 2007
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jmatt20... Thanks. Looks like I have my work cut out for me tomorrow.!!. This happened all of a sudden... one moment the tilt was working just fine... wagged the bucket vigorously to dislodge dirt... the next, no down tilt. Is there any idea what normally causes this sort of thing?? Or is it simply age and wear a tear??
If the cylinder is bypassing internally it would only involve the piston seals, no real need to redo the gland seals unless you have leakage around the rod. It seems as though it would be a valve problem more than cylinder.
 

roxrobin

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Aug 18, 2007
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If the cylinder is bypassing internally it would only involve the piston seals, no real need to redo the gland seals unless you have leakage around the rod. It seems as though it would be a valve problem more than cylinder.
Jerry... which valve?? Thanks, Robin
 

jerry

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May 3, 2007
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Jerry... which valve?? Thanks, Robin
I think if you have no down tilt and it is in the cylinder it has to be the piston seal. disconnect the lines to the cylinder and plug the one which would admit oil to give you down tilt or put a gauge on it and operate the control. If you hear it bypass and the engine works a little or if pressure shows on the gauge it is the cylinder, if no oil is trying to come down the pipe the problem is further back. I don't know anything about your hydraulic circuitry, all of our stuff is old, so I can be of no help. Check the archives of this forum there is a lot of good info there and someone may have had a similar problem.
 

skidboy

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Jan 3, 2007
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I think if you have no down tilt and it is in the cylinder it has to be the piston seal. disconnect the lines to the cylinder and plug the one which would admit oil to give you down tilt or put a gauge on it and operate the control. If you hear it bypass and the engine works a little or if pressure shows on the gauge it is the cylinder, if no oil is trying to come down the pipe the problem is further back. I don't know anything about your hydraulic circuitry, all of our stuff is old, so I can be of no help. Check the archives of this forum there is a lot of good info there and someone may have had a similar problem.
I think that you have blown the end of a port relief valve or anti cav valve.It screws into the end of the control valve,beside the tilt spool.One end has a port relief and other has a anti cav. valve.It is quite common for the little HAT section to break off.I think that it would be this valve that the bc mechanic was talking about.
 

Tazza

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I think that you have blown the end of a port relief valve or anti cav valve.It screws into the end of the control valve,beside the tilt spool.One end has a port relief and other has a anti cav. valve.It is quite common for the little HAT section to break off.I think that it would be this valve that the bc mechanic was talking about.
From my experience the seals never seem to go THAT bad if its a piston seal. The internal clearance is pretty small and even without a seal it will still provide decent down pressure. With you pushing say 16GPM into that cylinder you simply will not be able to get that mush by-pass between the piston and the housing.
With that said, un-do the bobtach end of the cylinder, extend it as far as it will go. Remove the hose from the tube line that connects to the gland end of the cylinder. Plug the hose that you removed leaving the cylinder end open. Run the machine and try to push the ram forward, no oil should come out the ram, if it does you have a seal issue. If the seal does leak i still do doubt its the primary problem, it sounds like a stuck relief but i thought the lift arms were the only ones to have their own relief valves attached (other than the main one).
 

Fishfiles

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Feb 8, 2007
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1,698
Being you say up tilt is OK , I would say look on your tilt cylinder they may or may not have a fitting on the down side , between the fitting thats welded to the cylinder and the hydraulic hose that goes to the cylinder , this fitting is an orifice fitting and some machines had them installed to slow the bucket in the down mode so that if you have a heavy load and are lowering it with the tilt it doesn't go down too fast and bend the tilt rod , inside the fitting is a plastic disc with a hole in it , if you have this fitting which can be distinguished by a dole pin going thru the side of the fitting , take it off, if your hose is too short to reconnect with out the fitting , take the fitting apart , drive out the pin and throw the oriffice away then reassemble , it only restricts the flow on the down side of the tilt , which seems to be your problem
 

skidboy

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Jan 3, 2007
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94
Being you say up tilt is OK , I would say look on your tilt cylinder they may or may not have a fitting on the down side , between the fitting thats welded to the cylinder and the hydraulic hose that goes to the cylinder , this fitting is an orifice fitting and some machines had them installed to slow the bucket in the down mode so that if you have a heavy load and are lowering it with the tilt it doesn't go down too fast and bend the tilt rod , inside the fitting is a plastic disc with a hole in it , if you have this fitting which can be distinguished by a dole pin going thru the side of the fitting , take it off, if your hose is too short to reconnect with out the fitting , take the fitting apart , drive out the pin and throw the oriffice away then reassemble , it only restricts the flow on the down side of the tilt , which seems to be your problem
There is only one main relief valve in this control valve,if it was faulty all functions would be affected.Depending on serial nos.there are different combinations of anti cav,port relief and one that is a portrelief and anti cav.If the problem is normal flow but no power down it will be one of these valves
 

roxrobin

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Aug 18, 2007
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There is only one main relief valve in this control valve,if it was faulty all functions would be affected.Depending on serial nos.there are different combinations of anti cav,port relief and one that is a portrelief and anti cav.If the problem is normal flow but no power down it will be one of these valves
This model has the port relief (new) and a separate anti-cav valve. As you indicate, the main relief valve must be ok since the other functions are alive and well. I just tried opening the down port on the tilt ram and there is no significant flow with the pumps running and my toe through the floor board... so... must be one of the relief valves?? Is there anyway that the tilt lock valve can be affecting this?? Thanks again to all for the help, Robin.
 

skidboy

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Jan 3, 2007
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94
This model has the port relief (new) and a separate anti-cav valve. As you indicate, the main relief valve must be ok since the other functions are alive and well. I just tried opening the down port on the tilt ram and there is no significant flow with the pumps running and my toe through the floor board... so... must be one of the relief valves?? Is there anyway that the tilt lock valve can be affecting this?? Thanks again to all for the help, Robin.
When you extend the tilt ram out and hold down with your toe,do the hydraulics load up and pull the engine revs down ? (the same as it should do on the other functions )
 

roxrobin

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Aug 18, 2007
Messages
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When you extend the tilt ram out and hold down with your toe,do the hydraulics load up and pull the engine revs down ? (the same as it should do on the other functions )
No... doesn't give the impression of any loading at all. I've just looked at the hydraulic circuit diagrams again. There is a bucket position valve in the circuit that could be bypassing down power. Has anyone experienced such a situation before?? Or should I just go ahead and order the anti-cav valve (I've already replaced the port relief valve with a new one)?? Thanks again all... Robin
 

skidboy

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Jan 3, 2007
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No... doesn't give the impression of any loading at all. I've just looked at the hydraulic circuit diagrams again. There is a bucket position valve in the circuit that could be bypassing down power. Has anyone experienced such a situation before?? Or should I just go ahead and order the anti-cav valve (I've already replaced the port relief valve with a new one)?? Thanks again all... Robin
I would replace the anti cav valve.If you have a look at the circuit diagram i think you will find that the anti cav is on the base end circuit.If you pull the anti cav out ,have a really good look at it.You may not have noticed that the end is missing.
 

roxrobin

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Aug 18, 2007
Messages
6
I would replace the anti cav valve.If you have a look at the circuit diagram i think you will find that the anti cav is on the base end circuit.If you pull the anti cav out ,have a really good look at it.You may not have noticed that the end is missing.
Skidboy... THANKS.!!. You were spot-on.!!. It was the anti-cav valve on the back side of the control valve next to the port relief valve. As you suspected, the valve end and stem was gone (hmmm.... where to???). Probing didn't find anything. I hope it simply fell out un-noticed while I had it apart resealing it. I'll have to take a look in my parts washer this evening! Again, thank you very very much..!!.. Robin
 
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