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Case 1840 Hydrostatic Drive Issue Please HELP

alrman

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If it doesn't move, it can't vary the swash plate.

There is an internal spring inside the piston, which centralises the piston in the housing to give the neutral position.
I'm not sure how much tension it has on it, but it has to move.
 
Last edited:

Justice1840

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Dec 20, 2018
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Maryland
I figured, just want to make sure before I try to pull apart. Not sure how both are stuck like that. Just my luck.

Ok so I will try to free up servos, get new end plates, replace all seals, polish swash plates and slippers. Any other suggestions?
 

alrman

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A new charge pump for sure.

And pull the drive motors & strip, inspect, clean & repair them.
Plus, thoroughly clean those high pressure loop hoses.

If you don't, any contamination/worn items in them will continue to wear after you refit your rebuilt pumps & undo all the time & money spent - within a few hours of operation.
 

Justice1840

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Understood. Will attempt the motors after getting this thing back together.

What did you see wrong with the charge pump?
 

Justice1840

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True true. Glad you mentioned it, that would have went back in.

Thanks for all of your input. Again, this is my first time so if you see anything else please let me know. Going to try to order parts tomorrow. I will keep you posted.
 

alrman

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Get the Sunstrand numbers off the pump & call a Sauer Danfoss agent to compare prices with CNH.
Consider service exchange prices on the M91 pumps if you can find them also.

Those drive motors are made for Case so there isn't an after market option on parts for them.
The output shaft is Case OE.
You may find seal kits over there, but I've always had to use CNH genuine seal kits for them here in Australia.
 

rondig

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fort macleod alberta
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excavation
That is issue....cavitation for sure...sorry about your luck....they can be rebuilt. If case is good....you can talk to jack at evco in tuttle ok...he is very good at rebuilding...also very fair....i can get pilot controlled rexroth tandem hydros at a very good price...i have an OEM deal with them.
20131105_083418.jpg these are the drills we build from scratch...it has a tandem rexroth A22vg series
 

Justice1840

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Waiting on parts for tandem pump so I decided to pull motors. I pulled one apart so far and it looks like new inside. No scoring at all.

All that I can figure is I must have contaminated the pump with something when I had it out for cleaning and painting. Can’t be sure. Your thoughts??? Being a closed loop system you would think that whatever went through pumps also went through motors. I was never getting pressure to motors even at initial start up as far as I know, so maybe it stayed contained in pumps??? I don’t know just guessing.This leads me to believe I could have another issue, but again I’m guessing.

I did think of something that I meant to mention at the beginning. With all 4 tires off the ground, I can turn the tires on either side with almost no restriction. Very little restriction, none, very little, none, and so on. I feel like it should have a lot of restriction and be hard to turn???
 

phil314

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Otsego, Mn
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The wheels should not turn freely when in the air.
Is it at all possible the bypasses were not fully seated?

Nevermind, I see you did check the bypass valve.
 

alrman

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It is all very unusual....

The wheels should be very hard to turn - if at all.

......The towing valves weren't open were they????
 

rondig

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Looks to me like like not enough charge pressure...oil starvation...did you start the machine without filling the case first from the case drain
 

Justice1840

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Bypassed/tow valves were removed and inspected. Looked good from what I could tell. Replaced them to book tourque specs. So I believe they were seated, but can’t be sure

I definitely had oil in the system. I did not do anything with case drain when I installed though. Can you explain?

If tandem pumps were low on oil or no oil, would it do this damage? I’m just curious if it is running low on oil somehow. Every time that I have pulled a plug, gauge, or hose there has been oil there. One thing that I had posted earlier though is that after running for a couple of minutes charge pressure is dropping to 5-10psi. Does that mean I’m not getting enough oil supply?
 

rondig

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If you dont fill the case the pump runs dry till it does. If the wheels turn with the counter balance valves released and the motors are good then there was not enough oil in the loop. Anyways i have been a hydraulic tech and an authorized hydraulic system designer for danfoss and rexroth for years...closed looped systems are a lot more complicated then u think...the fact that you, what i assume is ordered the barrels and pistons and maybe the slippers , and did not know that ALL piston pumps must start with pre filled cases tells me that you are out of your element...send it out to someone...there is very special tools to set these things....especially a tandem pump...
 

Justice1840

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I appreciate your concern.
But the fact is that it did have oil in it. My thought is the oil is going somewhere and not returning fast enough. Like i said I have insufficient charge pressure, but still 200-300psi through the start up process. After running for a few minutes I only have 5-10psi. Sounds to me that there was not enough oil there. Why? I’m no hydraulic tech or designer by any stretch of the imagination, but I think very logically and this makes no since to me unless something is restricting the oil from returning or something similar. Maybe a valve open that shouldn’t be. I don’t know that’s why I’m asking.

Sending it out is not an option. If I can’t fix it than I don’t need to own it. So can we get past the sending out or buying new. It’s a challenge now and I’m going to fix it if I have to rebuild it 10 times. I will most likely never be a hydraulic tech or a designer or whatever you would like to call yourself, but by the time this is done, by myself, and with the help of the very knowledgeable people on here, that have already been a great help, I will be able to trouble shoot my machine and have ample knowledge about it if another problem ever shows itself.

I did not order a new barrel or pistons. I am having those parts lapped. I’m waiting on seal kit and charge pump
 

rondig

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Good luck.....and learn....that pump was not contaminated it was cavitated. The "rebuilt" pump will do the same. However i do agree there are some very knowledgable people here, but they are totally guessing at the problem as am i...your slipper is very scored and non rebuildable ....it will cause your swashplate to stick as soon as you come off charge pressure...anyways as i said at the start good luck with your project...
 

Justice1840

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I agree, I am leaning more toward cavitation vs contamination also.

But why am I not getting ample oil back to the pumps?
 
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