863 - Cracked hydraulic pump; stuck relief valve?

[pblorworth]

I have a 1997 Bobcat 863 which cracked the hydraulic gear pump. I found that and have a new pump on order, arriving in a couple days. Now I'm trying to figure out what could have caused this issue in the first place. The crack goes directly through one of the bolt holes holding the pump onto the hydrostatic assembly, so my initial thought was that some water got in that bolt hole, froze, and broke the pump. But lately I'm wondering if the relief valve is bad. Then the previous pump could have seen far-too-high pressures, and cracked the housing. I don't want to repeat that story again, if this is the case. What's the best way to test that relief valve? I don't have any pressure or flow testers on hand. Can I just buy a 6k PSI pressure gauge and a hose, and attach it to one of the quick connect aux ports or tilt cylinder, then check whether the relief valve is working? I'm a bit afraid of that approach, since it seems like if the relief valve is set to high I'd effectively deadhead the machine into the valve and maybe blow up another pump. Grateful for any help ya'll can spare.

 

[flyerdan]

I doubt very much that a small amount of water would break the steel in a pump housing - it's not like the thin cast iron water jacketing that can break fairly easily.
The relief valve should pop off several times during normal operation if you roll the bucket back; by the time it hits the stops the relief should kick in before you can let up on the pedal.
I don't know of a way to test it without a lot of specialized equipment, according to the online parts catalog it could have either a fixed or adjustable relief valve, depending on s/n.
Hopefully someone will be along with a fairly easy and inexpensive way to test it.

 

[mikey]

I have the exact same issue on my 553 although i fitted my new pump and it did exact same thing did you ever get to the bottom of your problem dont want to keep buying new pumps at crazy money

 

[ZekeSkyree]

Looks like three of us have the same issue. I just posted for the same issue on another thread and am afraid to break another pump.

 

[mikey]

Looks like three of us have the same issue. I just posted for the same issue on another thread and am afraid to break another pump.

What model is your machine this is my pump x2

 

[ZekeSkyree]

I have a bobcat 642. Attached are a couple pictures of the failed pump

 

[ZekeSkyree]

OK, did a little more digging and pulled the relief valve. two things. One, there was no o-ring on the end and two, it looks like a part broke off (see close up).

Next step? From the relief valve, where do you guess the broken piece/O-ring would have gone? Hoping it stayed in the hydraulic system and did not go into the hydrostatic system, but not sure. Not looking forward to pulling every hydraulic part and inspecting it if i can figure out where it might have gone before it can damage anything else.... Thoughts?

 

[ZekeSkyree]

Another question. It would be nice to get the Bobcat into a shed, as it's getting cold in Illinois. Anyone have any experience with pulling one? Do not want to mess up any hydraulics by moving it, but getting tired of moving tools back and forth....

Thanks

 

[mikey]

Personally I wouldn't pull it id guess it would give your drive motors some grief if yours is like my 553 your oil will be filtered after the relief valve and before the hydrostatic so fingers crossed the filter will catch it

 

[brdgbldr]

Another question. It would be nice to get the Bobcat into a shed, as it's getting cold in Illinois. Anyone have any experience with pulling one? Do not want to mess up any hydraulics by moving it, but getting tired of moving tools back and forth....

Thanks

Not sure how much you have torn apart but there are a couple of ways to move the machine.

Make a sled for it. A large old hood from a truck or Cadillac put under the tires works well.

Clean the motors well. Remove the hoses from the motors. Cap or plug the hoses. Strap plastic bags over the motors, since the oil will come out when the motors turn. Make sure to keep any dirt away from the open motors and hoses.

There is also a way that requires removing a valve. Bobcat used to have a tow kit that replaced a valve so the motors could freewheel. I am not sure that this would be a good idea.

 

[ZekeSkyree]

Not sure how much you have torn apart but there are a couple of ways to move the machine.

Make a sled for it. A large old hood from a truck or Cadillac put under the tires works well.

Clean the motors well. Remove the hoses from the motors. Cap or plug the hoses. Strap plastic bags over the motors, since the oil will come out when the motors turn. Make sure to keep any dirt away from the open motors and hoses.

There is also a way that requires removing a valve. Bobcat used to have a tow kit that replaced a valve so the motors could freewheel. I am not sure that this would be a good idea.

I like the idea of pulling the hoses to move it. If I pull the hoses from the hydrostatic it would be a very easy. The bobcat is very clean, as I spent a ton of time cleaning it this year - Removed the motor and pulled a ton of crap from the inside, power washed it multiple times and actually found the drains. Thanks for the idea. Will see if I can move it today

 

[ZekeSkyree]

Personally I wouldn't pull it id guess it would give your drive motors some grief if yours is like my 553 your oil will be filtered after the relief valve and before the hydrostatic so fingers crossed the filter will catch it

Mikey, you get the gold star and virtual beer of your choice. You gave me the push in the right direction by saying "the oil is filtered after the relief valve". My mistake, i crossed two hoses when i put things together.

As you can see in the diagram, the middle port has the 40 micron filter and not the forward one. after buying a new pressure relief valve and swapping the hoses, the old girl is working perfectly. Also, after more closely reading the service manual, it said what you said, "the fluid flows from the control valve to the 40 micron filter".

Once again, my thanks...

 

[mikey]

Mikey, you get the gold star and virtual beer of your choice. You gave me the push in the right direction by saying "the oil is filtered after the relief valve". My mistake, i crossed two hoses when i put things together.

As you can see in the diagram, the middle port has the 40 micron filter and not the forward one. after buying a new pressure relief valve and swapping the hoses, the old girl is working perfectly. Also, after more closely reading the service manual, it said what you said, "the fluid flows from the control valve to the 40 micron filter".

Once again, my thanks...

Pleased yours is working just picked up my new pump and pressure relief valve tonight very scared about putting it back together

 

[ZekeSkyree]

Pleased yours is working just picked up my new pump and pressure relief valve tonight very scared about putting it back together

Mikey, best of luck on your bobcat. I find it odd it happened twice for you. Really hope it is the pressure relief valve. I found out there are two pressure relief valves on my Bobcat. One for the hydrostatic drive and one for the arms/bucket. Luckily the arms/bucket was real easy to swap, less than 10 minutes.

 

[ZekeSkyree]

Mik

Mikey, best of luck on your bobcat. I find it odd it happened twice for you. Really hope it is the pressure relief valve. I found out there are two pressure relief valves on my Bobcat. One for the hydrostatic drive and one for the arms/bucket. Luckily the arms/bucket was real easy to swap, less than 10 minutes.

Mikey, just another thought. After swapping the relief valve and pump, pull the coil wire and just crank the motor over. This is what I did before actually starting it. If it does not have any issues like slowing the engine due to hydrolocking you "should" be good.

 

[mikey]

Just got it up and running this morning it's obviously been the relief valve as all good now very very strange for a relief valve to fail that way id of thought it was more likely to fail the other way round and loose all pressure

 

[ZekeSkyree]

Just got it up and running this morning it's obviously been the relief valve as all good now very very strange for a relief valve to fail that way id of thought it was more likely to fail the other way round and loose all pressure

Excellent news. So glad it is back in service...