Bucket tilt ok up/down not so much

where I should have checked first I checked last, I went to check the tension on the drive belt, (I did reach in in the past and it felt very taunt), after looking at it good the belt is toast. It’s been adjusted so many times over the years the adjuster was almost maxed and the cogs are no longer contacting the pulleys, only the ribs of the pulley are in contact the belt which has the belt worn down to the nylon. There’s no way that was gripping under load and wouldn’t squeal only contacting the nylon. Belt will be here in a few days. Stay tuned.

Well boys here’s where we are, replaced the belt which was trashed, seems a lil better not much, pretty sure I have my belt plenty tight, no squeaking and not over tight, replaced the packing on the leaking cylinder. Same thing. Will NOT PICK UP the bucket with any weight. Does anyone have any ideas before I order a pump ??

Anyone have the proper belt tension procedure ? I can’t find it in my manual anywhere for some reason

Is the belt a serpintine type belt, if so and it ran a long time in the condition as you described the pullys coulde be worn out, I saw this one time on an alternator and could not believe it, as such the belt needs to mate to the groves, and I would still plumb in to the hoses on the lift and bucket tilt and check pressures before ordering a pump. ie if the tilt has full pressure and lift dosent then it cant be the pump, as far as the aux it may be on a different pump some skidsteers are set up that way however normaly a high flow unit though.

Ward it’s a 4 section cog belt, belt is deff not slipping at this point.

At this point after sleeping on it over night. I can only see a few things left it could be.. now it does seem better than it was but still not usable or right.
Fluid comes from the pump, feeds the CV, goes from there to the interlock then to the cylinders. If the interlock was bad or not fully opening it would work but slow so I’m dismissing that. The pressure relief on this is a strange one not typical with a set screw, being a high flow a line comes off the tip if the pressure relief and goes to hi flow section I’m going to have to look deeper as to where. My thoughts on that are why over a few cycles would it eventually open and bleed off enough pressure to not be able to perform functions. It wouldn’t make sense to fail in that way.
It’s been mentioned activated aux hyd could control this, I know the std flow are not putting out unless called for. On the HF side I don’t have a connection big enough to check but will say this. This machines wiring was completely redone for the aux controls. I will in the next few days go over all of that and compare to the schematic to make sure it’s all correct. Other than those few things the last thing would be the pump. Fluid flow is from pump to CV, through interlock, through filters and back to tank not a lot of places for pressure to bleed off. Relief valve or pump at this point is how I see it and I’m not feeling the relief would start to pop early after a few cycles

Did you inspect the cylinders before repacking them?
Cylinders can have deep scratches, bent rods, worn areas on the cylinder wall etc.

I had a tilt cylinder on a Bobcat I was working on that had the wrong piston installed with a one way seal form a hydraulic jack. Actually worked ok just bled down constantly.

brdgbldr said:

Did you inspect the cylinders before repacking them?
Cylinders can have deep scratches, bent rods, worn areas on the cylinder wall etc.

I had a tilt cylinder on a Bobcat I was working on that had the wrong piston installed with a one way seal form a hydraulic jack. Actually worked ok just bled down constantly.

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Only one cly failed the internal leak test that’s the one I did, the barrel and glad were in really good condition showed no signs of scuffing at all, seals were simply hard and worn out.

I'm starting to wonder if you have a broken shaft or worn coupling going to your hydraulic pump. Only way to tell is by taking the pump off. I've never been inside an 853 pump setup but if it's the same as a 40 series your hydraulic pump will be farthest from the drive input to your hydrostatic pumps, thus if the shaft/coupling between your hydrostatic pumps and hydraulic pump fails your drive will still work fine but your hydraulic power for the lift, tilt and auxiliaries stops working... so what I'm thinking is when things are cooled off the coupling between the hydrostatic and hydraulic pumps has enough grip to spin the pump and build pressure enough to get you your 3000psi of pressure but once things get a little warm it starts to disengage and slip leading to your loss of pressure and flow... My suggestion is to remove the hydraulic pump and see what sort of shape the drive couplings are...

spitzair said:

I'm starting to wonder if you have a broken shaft or worn coupling going to your hydraulic pump. Only way to tell is by taking the pump off. I've never been inside an 853 pump setup but if it's the same as a 40 series your hydraulic pump will be farthest from the drive input to your hydrostatic pumps, thus if the shaft/coupling between your hydrostatic pumps and hydraulic pump fails your drive will still work fine but your hydraulic power for the lift, tilt and auxiliaries stops working... so what I'm thinking is when things are cooled off the coupling between the hydrostatic and hydraulic pumps has enough grip to spin the pump and build pressure enough to get you your 3000psi of pressure but once things get a little warm it starts to disengage and slip leading to your loss of pressure and flow... My suggestion is to remove the hydraulic pump and see what sort of shape the drive couplings are...

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That would make sense, however this is a splined shaft connection, I’m not expecting to find anything exciting in there
I may go down later and put a gauge on the aux and run it till it gets weak and see what my pressure looks like at that point.
If I do end up taking the pump off it’s not going back on. I’ve replaced everything from cylinder packing on back to the pump there nothing left….. unlesssssssss the wiring to the aux isn’t correct and something is being energized somewhere it shouldn’t be. That I could prob check by unplugging the aux controller and trying it. I did locate a pump for it today. That’s prob going to be next weeks headache. Biggest thing I’m not looking forward to is the sloppy mess it’s going to make

I went back and re-read the original post and have a question.

Originally the bucket curl was very strong, but the lift was weak. When you are having the issue with lift, do you still have a strong curl? Can it still lift the front tires up?

Just from personal experience... many moons ago the input shaft to the hydraulic pump on one of my 732s broke, machine stopped dead in its tracks and nothing worked... buddy loaded it up onto his flatbed truck with his excavator and hauled it home for us. Next day everything worked perfect again and kept working until months later it stopped dead again. Turns out the shaft was broken for quite some time as evidenced by the rust on the fracture surfaces but there was still enough friction for it to keep working for months. I've also seen splines worn to oblivion but still there's enough friction to keep things going...

ZekeSkyree said:

I went back and re-read the original post and have a question.

Originally the bucket curl was very strong, but the lift was weak. When you are having the issue with lift, do you still have a strong curl? Can it still lift the front tires up?

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Yes it will but it seems to get weaker but is still considerably strong. When the bucket won’t go up I can tilt it in to give it a nudge and help it and it’ll go up with the assistance

mike11 said:

Yes it will but it seems to get weaker but is still considerably strong. When the bucket won’t go up I can tilt it in to give it a nudge and help it and it’ll go up with the assistance

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In my 642, the bucket/arm pump is separate from the wheel drive pump. Not sure if that is the same with your model. But if so, I would think that the pump is fine if when you are having a lift issue the curl still has good strength..... Just my thoughts...

Curl eventually gets weak too if cycled enough but it takes longer. I’m going to rip into it deeper tomorrow. I’m going to drain the system, pull the pump and inspect the internals. If it’s best up it’s getting replaced, if the seals are hard I’ll reseal it

Don't forget that when you tilt the bucket to dump you are supplying oil to the largest surface of the piston, when you curl the bucket back you lose the area of the rod to act upon the piston, so a low psi will always out push the cylinder rod out while pulling it back in will always require more psi at the same load. which is why we always dead head a cylinder to get pressure readings.

Ok pump is now off and all apart, it’s spotless inside, no scoring not even much sign of wear, seals are stiff, I did order a seal kit I’ll be here Tuesday. Only other thing I see it could possibly be now would be one of the 2 PR valves, the one on my control valve is strange it’s double stacked with a line going over to the HI flow valve which also has one. When looking on bobcats website using my serial # I don’t see the correct valve it’s simply a PR valve with a screw not one like this. I know it’s been mentioned before aux hydraulics could be causing a bleed off somewhere. While I’m poking n digging, if anyone has any suggestions I’m all ears. I’m hoping this pump was leaking internally.
When I’m done with this machine I’ll be an expert on 853s. Hahaha
Thanks guys

After giving the pump a good looking over and cleaning before I opened the seal pack, I noticed there is a lot of wear in the main housings, more in the main section than the hi flow, it’s not scored but in the oil path worn down on the output side enough to visibly see and catch a nail on. Intake side is smooth going through, output side has a ditch where the gears run. That’s enough for me to say this pump is toast.

Update !!!

New pump came today, installed it with bobcat fluid. Machine is doing the same thing. No real lifting strength, after 6-7 cycles it won’t lift the bucket at all till I let it sit a few min.

Here’s what’s been done so far

Load check valve checked
Lift PR valve replaced
Manual lift lock valve replaced
Belt replaced
All suction lines replaced
Filters replaced
Pump replaced
All leaks repaired
Cylinders repacked

I’m about at my wits end with this thing. Looking at the schematic I can only see a in few areas id loose pressure (I’ve said that 1000x already)

Main PR valve
Or something in the select valve bleeding off.

Could a wiring issue in the aux controls cause this ???

What’s strange is it gets weaker with more cycles and never has full lifting strength:

This machine is a high flow and has a dual main pres relief valve which bc no longer makes. Which could be an issue.
Here’s the hyd schematic for my machine any help is MUCH appreciated

From other discussions, I saw of people having the same issue with this particular model a newer, modern pressure relief was put in however it does not have the tap on it going to the high flow so with that being said, the machine will run and function properly, except there will be no high flow hydraulics because they are no longer protected so they cannot be activated My question is that line that comes off that original valve what do I do with that? Do I simply cap it or can I somewhere down the road plumb another pressure relief valve to that protecting the high flow so I can run them ?
This is the original valve, which is no longer available