753 hydrostatic drive, help needed

[No-Lard]

I have been repairing & servicing this machine since new. It has almost no drive F or R on right side. What happened is the night shift serviced it and topped-off the hydraulic tank with diesel fuel (new employee) but was properly trained. The next morning I saw a very long oil trail leading up to it. Upon inspection I noticed the source was the breather cap on the hydraulic tank. I drained the tank where it sat and refilled with hy-guard tractor oil, ran it re-drained and refilled it three times to flush out system. It was too late, the damage was already done. The left side works normally, the right is very very weak F. and R. I tore-down the drive pump unit and all parts look good to me. No wear on pistons or end plates What should I look for? Should I have tore down the drive motor first, and is it more prone to damage from diluted oil?

 

[Tazza]

The drive pump, was there wear on the swash plates? the bronze plate with slots cut in it, this is where the rotating group runs. Even small marks in here will cause drive issues. If you use a sheet of wet and dry and a sheet of glass and flat plate them, you may have some success. Look at http://www.skidsteerforum.com/DesktopDefault.aspx?tabid=54&frmView=ShowPost&PostID=13406
This is essentially the same pump as yours, look down the bottom where it shows the pump.
Do that then you can look at pulling the drive motor down, you can even swap them and see if the problem goes to the other side or not.
Good luck!

 

[thetool]

Too late for this job, but for future reference, a way to isolate the pump or motor:
Lift the cab, disconnect the drive motor hoses at of the offending side, at the pump, and install steel caps. Yours will be #12 I believe, JIC or ORFS depending on serial number.
Of course you will have it topped off with clean oil, and start the engine, disengage the brake and gently stroke your drive lever. The pump is dead-headed, so if the pump is okay, it will want to stall and kill the engine. Don't do it long or continuously, just enough to check for stall. The pump does not enjoy this. On jack stands if there is any doubt abut the machine moving on its own, of course.
If the pump doesn't stall, the problem is in the pump. It does not exclude the motor, but you know the pump has a problem.

 

[No-Lard]

Too late for this job, but for future reference, a way to isolate the pump or motor:
Lift the cab, disconnect the drive motor hoses at of the offending side, at the pump, and install steel caps. Yours will be #12 I believe, JIC or ORFS depending on serial number.
Of course you will have it topped off with clean oil, and start the engine, disengage the brake and gently stroke your drive lever. The pump is dead-headed, so if the pump is okay, it will want to stall and kill the engine. Don't do it long or continuously, just enough to check for stall. The pump does not enjoy this. On jack stands if there is any doubt abut the machine moving on its own, of course.
If the pump doesn't stall, the problem is in the pump. It does not exclude the motor, but you know the pump has a problem.

Thanks both of you guys for the reply Now that I think about it, I guess I just naturally assumed the pump was bad, and didn't really think it out very well. I should have known better. I used the dead-head test on other axial piston pumps before, for example our Michigan L320's on the brake charging pumps. Well tomorrow I will pull the wheel motor down and inspect it. Now I have to figure out how to not have to eat this job. Also I fumbled and mixed the piston positions on one pump cartridge, can I get away with reusing it if all else is in good shape?

 

[Tazza]

Thanks both of you guys for the reply Now that I think about it, I guess I just naturally assumed the pump was bad, and didn't really think it out very well. I should have known better. I used the dead-head test on other axial piston pumps before, for example our Michigan L320's on the brake charging pumps. Well tomorrow I will pull the wheel motor down and inspect it. Now I have to figure out how to not have to eat this job. Also I fumbled and mixed the piston positions on one pump cartridge, can I get away with reusing it if all else is in good shape?

Thats a good idea for testing. The pump does have in-built relief valves so you won't cause damage at least.
Its best not to mix the pistons up, but its done now. The case they run in is SUPER hard stuff, so i would doubt there was any wear.
With the motor make sure you don't mix up the rollers! keep them the same way up and the same locations.
Good lick with getting it working.