JD300 Backhoe charge pump question

[ktoom]

1966 JD300. Only the reverser is working and no other hydraulic functions. Already changed the fluid 3 times, changed the filters and cleaned the screen in the tranny. Working on getting some test gauges made up.

Long story short, I wen't to do the procedure to see how much hydraulic fluid is being pumped out of the charge pump via the JD service manual. Nothing is coming out of the reservoir tank above the front hydraulic pump. I then disconnected the hydraulic line going to the front pump coming from the reverser and I'm getting about 1 gallon a minute. I also disconnected the lines going to the open center power steering as i know i have a leak in the steering valve. I need to test the reverser to make sure nothing is going on with that.

I was hoping that maybe something was wrong with the front pump and thats why no fluid was coming out of the reservoir tank to cooler... I have a hunch that the charge pump is just tired or something else is wrong in the rear of the tractor thats causing an internal leak. I already put new seals and disassembled the front pump and found nothing out of the ordinary.

What is a ball park number on how man gallons a min is okay for the charge pump to be pumping?Of coarse the wonderful JD manual doesn't mention it.

Thanks Chris

 

[Tx Jim]

Reverser operates from trans pump. IIRC trans pump flow should be around 5 GPM. You can check trans flow by removing hyd filter then crank engine for a set period and measure oil in bucket. It's possible stroke control valve in main hyd pump is faulty. Did the power steering not operate also?

 

[ktoom]

Ok so remove the side mounted hydraulic filter and not the vertical trans filter? Might you remember how long to crank it for?

I was thinking the stroke control valve might be faulty also, but want to rule out the trans pump first.

Power steering wont work at an idle, but when i try driving the tractor, the power steering seems to work cuz the tractor is at almost full rpm.

 

[Tx Jim]

I'm more familiar with JD ag tractors which only have one hyd(trans) filter so remove the vertical filter by turning over engine for 15 seconds one should have a little over 1 gallon in drain pan

 

[ktoom]

I removed the tranny filter and ran the tractor for 15 seconds. I got a little over a gallon of hydro fluid in my drain pan.

Im assuming the next order of business would be something with the reverser?

When i get the hydraulic tester gauge made up, I should be able to tell if something is going on with the reverser.

 

[Tx Jim]

I wouldn't do anything with reverser if it's working as you stated. I'd suggest looking for a high pressure internal leak

 

[ktoom]

Okay, here's an update. I made up a pressure gauge setup. Hooked it up to the reverser reverse port and had over 100 psi. The forward port is stripped and won't come out. I couldn't get to the one port on the back side of the reverser as I will need an elbow peace to do so.

I then tested the stand by pressure. My hydraulic pump only has one test port on the right side. Once I hooked it up the pressure steadily built up to 2300 psi. When I went to use a hydraulic function, sometimes the pressure would drop to zero and slowly build back up. Other times it would recover quick and return to 2300psi. After the tractor got warmer, the gauge would jump all over the place but would only reach as high as 1800psi. I capped off the high pressure line leaving the pump and still got the erratic standby pressure.

At this point, nothing is still coming out of hydraulic tank line that goes to the cooler. What I find is that even with the high pressure "out" line capped off, Im still not getting any flow out the hydraulic tank.

Yesterday I took out the stroke control valve and pressure control valve. I didn't find anything that looked bad. Is there anything in particular I should be looking for? I replaced all the seals in the pump 2 years ago.

 

[Tx Jim]

When you replaced seals in frt hyd pump did you check inlet/outlet valves for wear or broken springs?

 

[ktoom]

There were no broken springs. Valves seemed fine. Someone had already been in the pump once already. I only re-sealed the pump because the shaft seal started leaking bad.

If any of those valves were or are bad, would that be the reason why I'm not getting any flow out of the hydraulic tank?

Just not sure what direction to go in now.