Bobcat 853 Lift Problem - weak and slow

[jimbob99]

I recently purchased a bobcat 853 with over 5,000 hours on it. I pulled the isuzu motor and rebuilt it completely. It runs smooth & strong, drives strong and the tilt seams to be working fine, maybe a little weak, but it works. The lift cylinder, however, only goes up when at full rpms and then only slowly. If I try to do anything else; tilt, drive, etc. it stops completely. If I have a load on it, it won't go up at all unless I use the tilt to give it a boost. It does go up all the way given enough time. I checked for leaks, but no luck finding anything yet. It's a hydro-static drive, so I think the pump is ok, and the tilt works alright (not weak, but not strong either, way stronger than the lift...), so what could it be? Could the cylinder's be bad? I'm new to anything hydraulic, but I've got plenty of hours wrenching, just need to know where to start. Any help would be appreciated.

 

[Tazza]

I think if the cylinder was that bad, it would fall down quite fast, but it is possibe. My guess is the relief valve for the lift segment of the control block. Something may be stuck in it.
How strong is your tilt? can you hook the bucket under something or drive into dirt and tilt back, see if you have power to get the bucket lip up.

 

[mike_belben]

I think if the cylinder was that bad, it would fall down quite fast, but it is possibe. My guess is the relief valve for the lift segment of the control block. Something may be stuck in it.
How strong is your tilt? can you hook the bucket under something or drive into dirt and tilt back, see if you have power to get the bucket lip up.

If itll drive into a pile or tree and spin the wheels without a lot of screeching from the hydrostatic drive @ wot then we can assume charge pressure flow and pressure are fine. How fast will the bucket curl complete a cycle? Normal or sluggish? Next will the bucket curl down hard and fast enough to jolt the front tires in the air. If you mash the pedal at wot it should bounce you right up pretty quick. If yes, the main charge relief in the loader valve block is good, if not look there. If that isnt it the problem is likely to be in the loader section of the valve block. Either a cracked body, bad spool, bad seal or orings between sections, etc. Hopefully its just your relief cartridge.

 

[mike_belben]

If itll drive into a pile or tree and spin the wheels without a lot of screeching from the hydrostatic drive @ wot then we can assume charge pressure flow and pressure are fine. How fast will the bucket curl complete a cycle? Normal or sluggish? Next will the bucket curl down hard and fast enough to jolt the front tires in the air. If you mash the pedal at wot it should bounce you right up pretty quick. If yes, the main charge relief in the loader valve block is good, if not look there. If that isnt it the problem is likely to be in the loader section of the valve block. Either a cracked body, bad spool, bad seal or orings between sections, etc. Hopefully its just your relief cartridge.

.... Could be a load check valve in the loader section. You can probably remove the plugs without pulling everything. Does the loader drift down on its own?

 

[David larry]

Ever find the problem I'm having same issue

 

[imtools]

I recently purchased a bobcat 853 with over 5,000 hours on it. I pulled the isuzu motor and rebuilt it completely. It runs smooth & strong, drives strong and the tilt seams to be working fine, maybe a little weak, but it works. The lift cylinder, however, only goes up when at full rpms and then only slowly. If I try to do anything else; tilt, drive, etc. it stops completely. If I have a load on it, it won't go up at all unless I use the tilt to give it a boost. It does go up all the way given enough time. I checked for leaks, but no luck finding anything yet. It's a hydro-static drive, so I think the pump is ok, and the tilt works alright (not weak, but not strong either, way stronger than the lift...), so what could it be? Could the cylinder's be bad? I'm new to anything hydraulic, but I've got plenty of hours wrenching, just need to know where to start. Any help would be appreciated.

The fact that the hydrostatic drive works well probably doesn't mean a thing. On my 825, there are two pumps, one for each set of drive wheels and a third for the bucket operations, pointing to the fact that the pumps are separate.

 

[imtools]

I think if the cylinder was that bad, it would fall down quite fast, but it is possibe. My guess is the relief valve for the lift segment of the control block. Something may be stuck in it.
How strong is your tilt? can you hook the bucket under something or drive into dirt and tilt back, see if you have power to get the bucket lip up.

A falling bucket when the unit is not running is not indicative of a leak past the piston. Assuming the lift is enacted by hydraulic oil entering the side of the cylinder opposite the rod, consider this: every inch worth of oil on the non-rod side would occupy more than an inch on the rod side thereby locking the piston in place. The oil has to go somewhere, either leaking out the rod seal (obvious) or thru the return side of the valve. This is not to say that the problem here isn't a leaky piston, just saying that in a static mode, a psiton leak has to be along with another leak.

 

[David larry]

Okay so I tried the tilt method and it is in fact weak as well so that means the pump that controls that segment of hydralluics is bad? Cause there is 3 pumps?

 

[Rickey]

We just replaced the seals on our 743b. Easy to do , hard to get. Put all new lines on too

 

[River Fluid Power]

Okay so I tried the tilt method and it is in fact weak as well so that means the pump that controls that segment of hydralluics is bad? Cause there is 3 pumps?

Sounds like it could be a weak aux hydraulic pump.