John Deere 300B Hydraulics Again

[72Cuda]

Hi, I am new here, at least as a member. Have been following this site for years and it has been very educational and there is a lot of knowledge base.

My issue again is with the hydraulics of a 300B with loader and backhoe. I have read the previous posts, followed the advice and learned a lot. I have a couple of conditions different from the previous forums however. First, I do not have a reverser. Secondly, I am having problems with air in the system. Initially I thought it was water. I have purged the system and replaced fluid 3 times. Within 1 minute of startup the oil looks like milk. (literally) New filters each change and checked the screen, never any debris discovered.

So I have done pressure testing. Ran the high pressure test on my 2440 and pressure reading was 2000 PSI while cranking, immediately went to 2250 on startup. On this unit I have zero pressure for about 6 or 7 seconds, then jumps to about 2100 PSI. Drops to about 1500 PSI during loader operation and loader speed is good for first cycle. Raising the loader a second time pressure drops to 1000 and operation is very slow. Backhoe is similar, fast at first but quickly slows down, eventually dropping pressure to 0. Suspected main pump supply issue.

Not sure however if any of this data is even pertinent. Will air in fluids reduce the pressure readings?

I have checked the filter relief and it is not stuck. Flow from transmission pump to main pump was slow and not a steady stream, more of a spurting action. Probably a couple of quarts a minute. Due to the air (bubbles) in fluid I was not sure how well this would pass through the filters, so I removed the filters, I then had close to the 5 GPM specification flowing from the transmission pump to the main pump.

I then tried isolating the systems. I first removed the hose from the tee in the line coming from the main pump and going to the accumulator, which then goes to power steering. Don't know why but I then had zero main pump pressure. At that point I quit trying to test one system at a time and will have to revisit that. I am also unsure of another issue. There is a Hydraulic Reservoir above the main pump. My shop manual shows the flow in this line going from this reservoir to the transmission reservoir. When I remove this hose however, I have flow coming from the transmission to the reservoir above the main pump. (reverse flow according to manual)

I am currently letting the fluids settle and relax. I then plan to destroke the main pump and see if I build up air with only the transmission pump active. I just obtained a low pressure gauge and will also check transmission to main pump pressure. I assume if I am getting air (cavitation) at the transmission pump the tractor will have to be split?

Any advice is greatly appreciated.

I bought this machine as a project and bucket list item. Have replaced the lift pump, injector pump, alternator, clutch pressure plate etc, rebuilt swing arm bushings, replaced hoses etc etc. Tires like new, runs great. At this point I have no intentions of quitting. This is going to be a nice machine when I am done.

"As I get older, I reserve the right to be less rational"

 

[DLTTrekkers]

Sounds to me that you never cleaned your screenefilter in the gearboxsump?

 

[Tx Jim]

Sounds to me that you never cleaned your screenefilter in the gearboxsump?

2nd paragraph 72Cuda stated he changed filter & checked screen with no debris found. I

 

[Tx Jim]

72Cuda
Welcome to TBN
I think aerated oil will have less pressure due to air replacing oil in same volume. I will guess there's a leak on suction side of trans pump.

 

[72Cuda]

Thanks for the welcome, good to be here. I was pretty much thinking the same thing regarding the suction side leak until today, now I am not as sure.

I went up and destroked the main pump. Ran the tractor for 10 minutes, had good flow from the tranny pump to the main pump, fluid stayed perfectly clear.

I then reengaged the main pump. Ran for 10 minutes again, but did not operate any hydraulics. Stand by pressure maintained at 2100 PSI under what I will describe as stable fluid conditions. Again, fluid stayed perfectly clear.

I then restarted the tractor and ran the loader through 1 cycle, second cycle slow and jerky, same thing with loader. After about 2 minutes I shut the unit down and fluid was milky.

Wondering now if main pump might be creating the foamy condition under flow conditions. Doesn't seem to be making any noise.

 

[72Cuda]

72Cuda
Welcome to TBN
I think aerated oil will have less pressure due to air replacing oil in same volume. I will guess there's a leak on suction side of trans pump.

I added info to thread rather than responding to your comments, not sure if this was the preferred option, still trying to figure out this site. Thanks for you comments.

 

[Tx Jim]

Although I've never witnessed it I suppose an inlet &/or outlet valve in frt pump could be malfunctioning creating the air. Not necessary in this case but problem is many pumps have been replaced only to determine that pump replaced was not the hyd problem. Where does loader control valve return the hyd oil to tractor?

 

[72Cuda]

Well, your original diagnosis may have been correct.

There is a small family owned John Deere Dealer near my farm, probably been in business for 80+ years. Has never modernized like many, and only works on older pre computer tractors. My dad started doing business with them in the 60's.

I stopped there to see what he would charge to flow and pressure test my unit. He stated he did not own a flow meter setup. Said he could never justify charging 3 - 4 hours doing testing when he could have been using that time to split the tractor and begin to fix it like he know he would have to do anyway. "Got to like that."

He explained my unit is notorious for developing cracks in the intake tubes for the transmission pump. When I detailed the symptoms he stated that the problem was likely caused by a drop in fluid level in the reservoir when I activate the hydraulics, likely dropping it below a crack in one of these tubes causing cavitation.

As a test for this theory he suggested I over fill the reservoir 3 to 4 gallons above the standard fill line to see if there was a change in symptoms. I did that and immediately had much stronger hydraulics. Though still some pauses after continued use, it was 100% better than before. After some time of operation I shut down and checked the fluid. Though there was still some foaming likely caused by captivation or leaking, the test was conclusive enough that my next step will be to have the unit split and the pump, o rings tubes etc. checked and or replaced.

I will respond when we have completed this work but that will likely be a month or more out. Shops by me right now are swamped trying to get equipment back to farmers to begin field work. Since my unit is more of a hobby I advised them to prioritize that work first.

Thx, will keep you posted.

 

[Tx Jim]

Thanks for update. I disagree with your local family owned JD dealer service tech about need for GPM flow tester for checking JD closed center hyd systems. Back when I was JD dealer service manager I had access to flow tester & found it very useful. Hyd flow on a JD tractor could be tested in a lot less than time than 3-4 hrs
Jim