rebuilding drive motor

[Wayne County Hose]

I rebuild cylinders here. I do not rebuild pumps or motors. I do not have the capabilities to test them before they go out so I don't do them. It's roughly $10,000 in equipment to do testing and then double that for tooling and parts stock.

I have insisted on fluid changes on some cylinders I do. I look at the fluid that comes out when I disassemble them. Sometimes, it is just so plain as day that the fluid is so old and contaminated that there is no way I can guarantee anything without a fluid change. I do explain it to the customer in a nice way. Most of the time, they really don't know they need to change their fluids on a regular basis so I explain the importance of it.

 

[EddieWalker]

Now that in itself would just pi** me off that they would not guarantee their work, especially if they actually tested the pump after a rebuild, or new, and maybe with you watching. And then want to rebuild the hydraulic motors associated with that pump. That would mean 4 hydraulic motors on my machine. No way. Sure I understand cross contamination, but if the fluid is going to tank from the hydraulic motors, and the pump is drawing from the tank through a filter, it should be ok. You could also have in-line high pressure filters installed.

JJ

I wasn't clear how my hydraulic system works. The tank is just an overflow and is not part of the circulating hydraulic fluid. My system operates in the 25,000 psi range and the smallest particle of metal can totally destroy it.

The engine runs three hydraulic pumps. One for the blade, and one for each track. The pump and drive motor are connected by four main hoses. Then there are the hoses that go to the forward and reverse control.

The hydraulic fluid pretty much stays within that loop. There is also a line for cooling and the filters. Each pump has it's own filter, which cost $80 each. While the filter will catch anything that goes through it, the fluid does not go through it all the time, or when just going form pump to drive motor.

I hope this makes sense, it doesn't to me except for the fact that I've worked on it and replaced those hoses.

The pumps are Sundstrand and it's Case used the same pumps used on the Deere 850.

Eddie

 

[J_J]

Eddie, Thanks, that sounds like a closed loop system, which is what we have in our Power-Trac. The fluid goes from the pump to the motors, and back to the input of the variable speed pump. It keeps using the same fluid until there is leakage through the motors into the motor case drains, and that fluid comes back to pump case drain and then to cooler and tank. A charge pump makes up for any lost fluid through the case drains. On my PT-1445. the one VSP pump supplies all four hydraulic motors, so you can see that would be a large expense to rebuild four hydraulic motors if that pump became disabled.

 

[slowzuki]

I can tell you when a pump comes apart on a common reservoir machine like a tractor, bits and pieces become strewn throughout the hydraulic systems which can mean big dollar repairs.

They get lodged into the 3 point hitch hydraulics and implement cylinders etc.

 

[EddieWalker]

...On my PT-1445. the one VSP pump supplies all four hydraulic motors, so you can see that would be a large expense to rebuild four hydraulic motors if that pump became disabled.

JJ,

One more clarification. My pump was the problem and what had to be rebuilt. For the warranty, they wanted to go through the drive motor to make sure it was clean, and that it wasn't going to send anything back into the pump. To do this, they charged me $1,000 to rebuild it. I don't think they actually replaced any parts, just new gaskets and to make sure everything was like it was supposed to be.

In your situation, I'd be very nervous if the pump went out and you didn't have them go through the rest of the system. What is worse, paying to rebuild the pump and then destroying it because you didn't make sure the rest of the system was clean, or paying the money up front and making sure it's all perfect? I got lucky and was able to get it done so cheaply.

Case wants $25,000 for a rebuilt pump for my dozer and they refuse to send the existing one out for rebuild. They will not guaranty the work that is done by an outside source, so they will only replace the existing pump with a new one.

This stuff gets expensive real fast.

Eddie

 

[J_J]

Eddie, What you said makes sense, but the only way you can keep a failed pump from jamming up the hydraulic motors, is to put a high pressure in-line filter on the output of each pump to motor, maybe there is, or is the filter on the intake only? You still have another problem if the motor fails, and maybe it will contaminate the pump. Same thing in my situation, if that pump fails, then all four motors are powered by the same pump, and are subject to contamination. I could probably put high pressure in-line filters in for around $150.00 each. You are right about this stuff being very expensive.

 

[kitsune]

I know this is an old thread but I'd like to add a little to the people looking for answers on hydrostatic pump/motor transmissions.

Oil filtration is paramount in keeping a unit like this running and getting the best life out of it.

Manufacturers always skimp on filtration.

25 micron might do for gear pumps, but 10 is where I'd be for piston products.

As far as the pump going bad and taking out the motor, this is true in most designs; unless a pressure filter is installed downstream of the pump.
In a hydrostatic system, the pump goes overcenter to reverse flow to provide the F-N-R to the motors for ground drive.
The system has to be plumbed and valved so that the flow always goes through the pressure filter regardless of direction.

This isn't hard to do, but it is expensive as a initial cost, which is why they are not on most general equipment.
Higher end equipment that uses electro-proportional valves or servo valves will most likely have a pressure filter after the pump due to the high filtration requirements of this type of valving, but probably not in the Swing Drive or Ground Drive circuits.

Since these filters are downstream of the pump they will catch most or all of the debris when a pump fails.

At that point it would be a good idea to find out the cause of the failure.
If the pumps been run to it's end of life, the motors are probably close as well.
If it's an early failure, then as discussed in the other threads you probably want to clean and repair the entire drive system.
If the oil reservoir is shared with any other functions, it be a good idea to look at those circuits as well.

To reduce costs, a gear pump is usually paired with the hydrostatic drive.
There can be more than one, depending on whether the design uses a dedicated charge pump.
Usually there is, as the hydrostatic pump needs a constant 200 to 400 PSI on the low side to keep the pistons firmly on the swash plate.
So the setup would be Hydrostatic pump/charge pump/gear pump for auxilary fuctions, Bucket, Load Hold and Dump for a tractor, power steering, PTO for auxiliary hydraulic accessories and so on. Depending on demand they will either split these flows with a priority valve or use an additional gear pump to keep the flows where they need to be when various functions are activated.


Many pumps and motors in this category have case drain lines and the flow coming form these lines is the leakage past the seals and clearances within.
This flow rate is sometimes published - sometimes in the pump manufacturers specification sheets.

If you don't know it or can't find it, and you've just purchased a new piece of equipment, it may be useful to buy or borrow a hydraulic flow meter and measure the case drain flow while new. As the equipment is used and ages you can check the flow against your original figures and get an idea on pump wear based on increased case drain flow due to component wear.