Bobcat 453 hydrostatic leak

[Lachlant54]

Hi guys. I have a bobcat 453 I bought as a project. I've replaced a lot of the hydraulic hoses and some of the hoses from the hydrostatic pumps. And now I'm currently having an issue with the hydrostatic pumps leaking. The first time I found it must have built up too much pressure and had bent the cover plates underneath that cover the bearing for the steering shafts, and the sealed plugs were cocked to the side and were leaking. I replaced the o-rings and the plates and tried it and it happened again. I pulled out both relief valves and and both of them were hard to push the pins in but then they loosened up and felt easier to push in. Reinstalled them. I checked them again the next day when I fixed the plugs again and they were the same. I soaked them in hydraulic oil and gave it another go. The bottom plates aren't leaking now but the top plates were the shafts go into the pumps are leaking.
Sorry for the long post but I was hoping to get a few more opinions on what is causing these new leaks to pop up. Could it be that the relief valves are bad
Thanks guys

 

[Lachlant54]

Another thing it does is it'll run for a bit before it starts leaking then when it starts to leak the bucket tilt ram will tilt the bucket all the way down. Any advise on that would be appreciated also

 

[River Fluid Power]

Another thing it does is it'll run for a bit before it starts leaking then when it starts to leak the bucket tilt ram will tilt the bucket all the way down. Any advise on that would be appreciated also

I would guess that you may have something hosed incorrectly. You should double check all of your hoses to make certain they are all hooked up to the correct ports. The bearing cover plates getting bent out and allowing the seals to leak is indicative of high case pressure. If your hosing is correct, it's time to pull the pump out for inspection.

 

[Lachlant54]

I would guess that you may have something hosed incorrectly. You should double check all of your hoses to make certain they are all hooked up to the correct ports. The bearing cover plates getting bent out and allowing the seals to leak is indicative of high case pressure. If your hosing is correct, it's time to pull the pump out for inspection.

The relief valve says 3400psi. Should cast pressure not be that high. What would be causing high case pressure, what would should I be looking for when pulling the pump down

 

[River Fluid Power]

The relief valve says 3400psi. Should cast pressure not be that high. What would be causing high case pressure, what would should I be looking for when pulling the pump down

The relief valve that says 3400 psi is a high pressure relief for the loop between the pump and motor. The case pressure should only be around 20 psi or thereabouts. If you have internal damage on any part that seals in system pressure, it can leak out into the case. This would cause external leaks at the pintle covers. The pintle covers are the small, thin plates held on by torque screws. Internal damage to any flat surfaces that run against each other, or damage or stretching out of the piston bores is what you are looking for inside of the pump.

 

[Lachlant54]

The relief valve that says 3400 psi is a high pressure relief for the loop between the pump and motor. The case pressure should only be around 20 psi or thereabouts. If you have internal damage on any part that seals in system pressure, it can leak out into the case. This would cause external leaks at the pintle covers. The pintle covers are the small, thin plates held on by torque screws. Internal damage to any flat surfaces that run against each other, or damage or stretching out of the piston bores is what you are looking for inside of the pump.

Awesome. Thankyou very much for the info. I got around to pulling the pumps out. Sure enough I for some scoring on the west plates and rotating housing, I could feel the west with my finger nail. I know it may sound a bit rough, but I polished them over some 1200 and 2000 grit wet and dry with some wd40. Cleaned everything perfectly with solvent and compressed air. Got it back together. But I have another question. Before I start the bobcat, should I be pre-filled the case of the pump before I start the bobcat so it doesn't score it until it fills with oil. I did install all parts with a layer of new clean hydraulic oil. Thanks again

 

[River Fluid Power]

Awesome. Thankyou very much for the info. I got around to pulling the pumps out. Sure enough I for some scoring on the west plates and rotating housing, I could feel the west with my finger nail. I know it may sound a bit rough, but I polished them over some 1200 and 2000 grit wet and dry with some wd40. Cleaned everything perfectly with solvent and compressed air. Got it back together. But I have another question. Before I start the bobcat, should I be pre-filled the case of the pump before I start the bobcat so it doesn't score it until it fills with oil. I did install all parts with a layer of new clean hydraulic oil. Thanks again

You're welcome. If it's not too much trouble, you should also polish the bottom of each barrel where they ride on the valve (wear) plates. And yes, you should definitely fill the case of each pump with as much oil as you can.

 

[Lachlant54]

You're welcome. If it's not too much trouble, you should also polish the bottom of each barrel where they ride on the valve (wear) plates. And yes, you should definitely fill the case of each pump with as much oil as you can.

Yep did that and got them perfect. Also did the shoes on each piston slightly and they came up really nice, the cam that the shoes rude on were already really good. Hoping that it solves my problems.
Also, if my 3400psi relief valves were sticking, we're would the pressure in the high pressure side go? Would it want to force its way back into the case? Only asking cause I'm a bit paranoid of it happening again. Is there anything you can do with the pin in the relief valve to stop it sticking?

 

[Wayne440]

...if my 3400psi relief valves were sticking, we're would the pressure in the high pressure side go?...

If the engine doesn't stall first, whatever part is the weakest link will fail- hose, pump case gasket or (insert expensive part name here)

 

[River Fluid Power]

Yep did that and got them perfect. Also did the shoes on each piston slightly and they came up really nice, the cam that the shoes rude on were already really good. Hoping that it solves my problems.
Also, if my 3400psi relief valves were sticking, we're would the pressure in the high pressure side go? Would it want to force its way back into the case? Only asking cause I'm a bit paranoid of it happening again. Is there anything you can do with the pin in the relief valve to stop it sticking?

The relief valves relieve system pressure from one side of the loop yo the other. System pressure that can't escape would build until you had internal separation, also known as lift off. As soon as the pressure escaped into the case, the components would reseal and start building again. The cycle would repeat, and you would likely feel or hear a rapid pulse. Did you verify that your hoses are routed correctly?

 

[Lachlant54]

The relief valves relieve system pressure from one side of the loop yo the other. System pressure that can't escape would build until you had internal separation, also known as lift off. As soon as the pressure escaped into the case, the components would reseal and start building again. The cycle would repeat, and you would likely feel or hear a rapid pulse. Did you verify that your hoses are routed correctly?

Yes I'm 100% sure hosing is correct, but I have just sent through photos of it to a local hydraulic fella for him to check. I installed the pump again after polishing the wear plate and rotating group and still doing the exact same thing. Might sound dumb but what if I was to drill and tap in case drains that drain directly to the tank, as the cases don't drain to there

 

[River Fluid Power]

Yes I'm 100% sure hosing is correct, but I have just sent through photos of it to a local hydraulic fella for him to check. I installed the pump again after polishing the wear plate and rotating group and still doing the exact same thing. Might sound dumb but what if I was to drill and tap in case drains that drain directly to the tank, as the cases don't drain to there

No case drains on your pumps…….I assume that the gear pump on the back of the piston pumps has been changed?

 

[Lachlant54]

No case drains on your pumps…….I assume that the gear pump on the back of the piston pumps has been changed?

It's could have been. Each piston pump has an internal drain back to that gear pump. Just wondering if a drain directly to the tank would help