Case 1845c tandem drive pump issues

[rico7467]

I put a pressure gauge on the pump and it starts out with 400 psi but as soon as you put it into a load it instantly falls to 100 psi. I inspected the charge relief valve and the orifices and everything seemed fine. It's a danfoss m91-46807r pump. Does this mean it needs rebuilt?

 

[lantraxco]

Speaking of hydrostat drives in general, somewhere in your pumps or the motors you have excessive internal leakage. Dis-assembly for inspection, rebuild as necessary would be my suggestion. Saner minds may chime in.

 

[alrman]

Does the pressure drop on both LHS & RHS?
Do you know if you have the Danfoss motors? If so, & pressure drops on one side only, there are some orings that can cause this issue in the valve chamber of the motor.
If the pump loses charge pressure on both left & right sides - the problem is likely the pump, possibly only the charge pump itself. It lives in between the tandem pumps & it will need to be removed to inspect it.
In saying this, I would still carry out a leakage test on both motors to eliminate them as a fault, before removing the pumps.
The problem with hydrostatic systems is, if there has been some type of damage to the rotating groups in the pumps - the damage is mirror reflected in the rotating group of the motors ....... = BIG $$$ repair

 

[rico7467]

I recently had both drive motors r er paced and the shop rebuilt the tsnd r m pump and I am still having an issue wit it not w as noting to go up an incline under a load. It doesn't breakout or lose rpm it just comes to a stop

 

[GaryHoff]

Its possible to install the charge pump improperly. If your problem has been since the rebuild, maybe that's all it is. Or maybe the pumps/motors were not primed upon installation.

 

[lantraxco]

Failure to fill the cases, especially on the pumps, will do that. Please don't ask me how I learned that in my early twenties... ointhead

 

[rico7467]

After doing more running of the machine I've noticed the power is there initially but after going and stopping about 5 times or so into a load is when it bypasses and it suprisingly will regain it's power only by lowering the rpms then rethrottleing. Then it has full power again

 

[GaryHoff]

okay.............. Lets get some facts straight first.

1. Both sides lack "power"?
2. The machine seems to run normal when the hydraulic oil is cold?
3. You had a shop rebuild your pumps and motors?
4. The pumps and motors were properly primed upon installation.
5. The hydraulic tank was properly cleaned.

Assuming all of the above is true, I would look at the charge check valve, in the relief block manifold.
Find your serial number break in the parts book, and inspect the check valves.

 

[rico7467]

Just curious...isn't that manifold just for the bucket functions? I know there is a charge relief valve in the charge pump on the tandem drive pump. Would That Be THE One I NEED To replace? It is a spring with a poppet.

 

[GaryHoff]

If you have the schematics, have a look at them. Basically, the charge pump is supplied with 5psi of head pressure, by the return oil of your equipment pump. If your charge pump is not getting enough oil on the suction side (possibly from bad check valve), it may loose pressure when you throttle your engine up, (more rpm = more flow = needs more oil)

Your charge relief in the pump seems to be working to me, as you are building your 400psi at idle.

Can you please advise on my questions on last post?

 

[rico7467]

You wouldn't happen to know the part number for that relief valve would you? And is that 9, 3or 13 in your pic?

 

[GaryHoff]

There is 2 options, depending on if you have a sterling or waterman valve. Before replacing, I would recommend doing some pressure tests first, T into the charge pump suction port, and you should have 15psi at all times. Check at low and high idle. At least remove the valve and inspect. Should be item 9.

 

[rico7467]

Is there a way to tell wetter I have a waterman or sterling manifold? I do not see a name on it just the number 98000094c