Boom Will not float

[CharlesBrush]

Total newcomer here. Hope I'm in the right place.
Older Bobcat 843
Just had hydrolic block rebuilt because boom wouldn't float.
Press left pedal forward hard and motor boggs down and right pedal
loses all power. Boom doesn't float.
Is there an adjustment that I'm missing?
Any help would be greatly appreciated.

 

[oldnslo]

Charles,
If the loader is two feet off the ground and you try to engage float what happens? Does the loader stay in that position?

 

[CharlesBrush]

Yes, the loader will stay in that position.

 

[kthompson]

No idea on your control but some remote hyd on tractors do have float function and it is past the normal spot to raise (may be on the lower side) the cylinder. Sounds like it is not getting the full travel it needs or not linkage is not correct.

 

[Jabonee]

Total newcomer here. Hope I'm in the right place.
Older Bobcat 843
Just had hydrolic block rebuilt because boom wouldn't float.
Press left pedal forward hard and motor boggs down and right pedal
loses all power. Boom doesn't float.
Is there an adjustment that I'm missing?
Any help would be greatly appreciated.

Can you feel the detent when you step on the pedal? Was spool replacement part of the rebuild?:confused3:

 

[oldnslo]

Yes, the loader will stay in that position.

If the loader stays stationary while it is float can you operate the curl and dump functions on the bucket?

If there is weight in the bucket and you shift to float will the loader lower then?

Like Jabonee asks: Do you feel the valve moving into the detent mode for float?

 

[CharlesBrush]

kthompson, I agree with you. I have tried to adjust the linkage to increase travel but that didn't work.

 

[CharlesBrush]

Jabonee, I can feel the detent when I step on the pedal. The pedal will remain in forward position and the motor labors and I lose right pedal control of bucket. I specifically asked bobcat service to pay particular attention to the boom detent spool when I had it rebuilt, so I think they either replaced it or cleaned it up and re-sealed it.

 

[CharlesBrush]

Oldnslo, Cnt operte curl and dump functions on the bucket while in float. I do feel valve moving into detent mode, but again, motor boggs down when I put in to float mode. Should state that all other functions of machine operate properly until I attempt float mode.

 

[oldnslo]

Charles,
When you go into float and the engine labors can you tell if either or both of the hoses going to the lift cylinder stiffen or swell like they are under pressure?

Reason for asking this is to try and determine if the main directional valve is being shifted partially and pressurizing both ends of the cylinder or if there is a "safety" valve of some sort that is not being shifted or operating correctly while in float.

 

[CharlesBrush]

Oldnslo, will check and get you the result.

 

[CharlesBrush]

Oldnslo,
The hoses leading to boom hydro cylinders seem to jump ever so slightly when
I engage float position. It appears that the fluid in the hoses is being pressurized.
My facility maintenance guys have tried to adjust the threaded rod going in to the
hydraulic block to see of maybe the pedal wasnt pushing to rod far enough in to
the block, but the more you do that, you start losing UP control on the boom.
Hmm! Its a mystery.

 

[Xfaxman]

Just to eliminate any confusion, this is a Bobcat 843 like the OP is asking about:

Picture from an image search.

 

[CharlesBrush]

Xfaxman, Yes, 1980's something 843.

 

[oldnslo]

Charles,
Question:
If you fully raise or lower the boom and hold that function so still trying to move will the curl / dump functions operate?
With the engine off and you engage float the pedal stay in the detented float position? I believe you stated it feels like it does but just trying to understand all the conditions.

I have searched for a good detailed hydraulic schematic with no success. I did find a 108 page hydraulic service document that did not have a good schematic.

Since the loader works under normal lift lower mode The items that are confusing me are:
1) When going into float the engine bogs down which indicates pump is under pressure. Going into float the pump flow should be flowing freely for the other functions like tilt.
2) When in float no other functions work. Unless this is a series circuit the lift spool should not block flow to other functions. (see item 1)
3) If pressure is being built and the boom doesn't move, what spool position would allow this?

At this time I am at a loss what could cause this failure. Everything points towards the control valve but you had it checked out? Possibly dumb question but do you know if the repair shop tested all of the functions on a test bench to confirm operation?

 

[CharlesBrush]

Oldnslo, I cant tell you how much I appreciate your insight in to this problem. I will check with the Bobcat service on Monday and ask if they did indeed bench test this unit before returning it to me. I will also check to see if the pedal stays in float position when engine is off and report back. Thanks so much. Have a great weekend.

 

[100 td]

Float position generally just joins both sides of the cylinder together with tank, doesn't see any hydraulic flow. I'm guessing pump/tank (or PB) hoses are crossed etc., so when float is selected, the pump (or PB line) sees both sides of the cylinder instead of the tank (and goes into relief). Or a similar situation has been created because the valve has been set up with plugs in the wrong ports, or installed 180 degrees out etc..
So check hoses, check plugs/bungs in valve in correct position etc. Was there a plastic plug (assembly/dust/travel) left in the valve somewhere when it was installed, which is now blocking the tank port or redirecting flow within the valve?

 

[CharlesBrush]

100 td, I will run all that past my maintenance guys and Bobcat service on Monday and report back. Thanks so much for really delving in to this.

 

[SSdoxie]

Charles,
Question:
If you fully raise or lower the boom and hold that function so still trying to move will the curl / dump functions operate?
With the engine off and you engage float the pedal stay in the detented float position? I believe you stated it feels like it does but just trying to understand all the conditions.

I have searched for a good detailed hydraulic schematic with no success. I did find a 108 page hydraulic service document that did not have a good schematic.

Since the loader works under normal lift lower mode The items that are confusing me are:
1) When going into float the engine bogs down which indicates pump is under pressure. Going into float the pump flow should be flowing freely for the other functions like tilt.
2) When in float no other functions work. Unless this is a series circuit the lift spool should not block flow to other functions. (see item 1)
3) If pressure is being built and the boom doesn't move, what spool position would allow this?

At this time I am at a loss what could cause this failure. Everything points towards the control valve but you had it checked out? Possibly dumb question but do you know if the repair shop tested all of the functions on a test bench to confirm operation?

Bobcat does use a series valve, in that fluid returning from lift cylinders does go into the Open Center flow not back to tank like on most tractor valves.
It does sound like the lift spool is not traveling to fully engage float although the detent may be locking in place. The small float detent spool screws into a threaded end of the lift spool. If this detent is not threaded in fully and tight it could lock into detent before the lift spool travels far enough to connect both cylinder ends to return flow.

 

[oldnslo]

Bobcat does use a series valve, in that fluid returning from lift cylinders does go into the Open Center flow not back to tank like on most tractor valves.
It does sound like the lift spool is not traveling to fully engage float although the detent may be locking in place. The small float detent spool screws into a threaded end of the lift spool. If this detent is not threaded in fully and tight it could lock into detent before the lift spool travels far enough to connect both cylinder ends to return flow.

SS,
Thanks for confirming my thoughts on this. Nothing else really makes any sense other than the valve not shifting fully.