JD 300B Hydraulic pressure problems

[cliffj59]

I have recently purchased a 1973 JD 300B loader without a backhoe and It has the 3 point lift, but when I have the 3 point lift raised and raise the loader bucket the 3 point lift drops a little. Everything runs fine until the oil heats up and then the loader gets slow on raising up no matter what the RPM's are. This weekend I will be checking the transmission screen, changing the two filters under the right foot board and putting in new fluid. I have ordered a hydraulic pressure test kit but would like to know where to start for the pressure test.
Thanks

 

[Tx Jim]

Welcome to TBN
Trans pressure should be 155-165 psi,main hyd 2250 psi. With machine at operating temp with engine running,3 pt raised look in hyd filler hole behind seat for spraying oil which indicates leaking 3 pt control valve seals. Can you post a close up photo of loader control valve? Do you understand that your tractor has closed-center hyd system?

 

[cliffj59]

Welcome to TBN
Trans pressure should be 155-165 psi,main hyd 2250 psi. With machine at operating temp with engine running,3 pt raised look in hyd filler hole behind seat for spraying oil which indicates leaking 3 pt control valve seals. Can you post a close up photo of loader control valve? Do you understand that your tractor has closed-center hyd system?

Yes I can get a pic shortly of the control valve. I do understand that it has the closed system and have been reading about the diffrence between the open and closed systems.
Another thing is that I can crank the tractor and raise both the loader and 3 point lift and cut the tractor off the 3 point lift starts droping slowly as soon as the engine quits, the loader barly creeps down but it will come all the way down after about 2 or 3 hours.

 

[Tx Jim]

3 pt lowering with engine off sounds as if 3 pt piston seal &/or 3 pt control valves are leaking. Have you looked in hyd filler hole with engine running,3 pt raised????

 

[cliffj59]

Not yet just saw your post this morning when I got to work I will run to the house shortly and check it out.
I do have 3 small leaks on cylinders, one on the top link at 3 point, one on the side draw bar cylinder and one on the loader cylinder. These are slow drips

 

[cliffj59]

3 pt lowering with engine off sounds as if 3 pt piston seal &/or 3 pt control valves are leaking. Have you looked in hyd filler hole with engine running,3 pt raised????

Tx Jim I just looked in the filler hole with tractor running and 3 point raised and yes there was oil coming down from the top of the housing. It wasn't a pressure spray but it was a steady dripping of oil.

Here are some pictures of the loader control valve

 

[Tx Jim]

On 3 pt lowering before raising when loader control lever is activated I suspect leaking 3 pt control valves &/or piston is the cause. i suggest to remove from tractor FEL control valve "return hose" then plug orifice on tractor,aim open return hose into hyd filler hole or 5 gallon bucket,start engine with FEL control lever in neutral & no oil should exit return hose. If oil exits return hose then I suggest to check for leaking internal seals on plug(key 19).

 

[cliffj59]

On 3 pt lowering before raising when loader control lever is activated I suspect leaking 3 pt control valves &/or piston is the cause. I also suggest to check for leaking internal seals on plug(key 19).

What part is this picture so I can look it up in my parts book?

 

[cliffj59]

On 3 pt lowering before raising when loader control lever is activated I suspect leaking 3 pt control valves &/or piston is the cause. I also suggest to check for leaking internal seals on plug(key 19).

What part is this picture so I can look it up in my parts book?

 

[cliffj59]

I see now this is the loader control valve thanks Tx Jim I recieved my high pressure test kit yesterday and will be getting into this over the weekend.

 

[cliffj59]

On 3 pt lowering before raising when loader control lever is activated I suspect leaking 3 pt control valves &/or piston is the cause. i suggest to remove from tractor FEL control valve "return hose" then plug orifice on tractor,aim open return hose into hyd filler hole or 5 gallon bucket,start engine with FEL control lever in neutral & no oil should exit return hose. If oil exits return hose then I suggest to check for leaking internal seals on plug(key 19).

This sounds easy enough I will be starting with this in the troubleshooting process

 

[Tx Jim]

A laser thermometer is a good tool to check temperature of hyd control valves on closed-center hyd system with problems. The valve with the highest temp is more than likely leaking internally.

 

[cliffj59]

I checked the Transmission pump and got 130psi when I would raise or lower the 3 point it would drop to 30 psi and then build back up to 130. it would do this when i raised or lowered the FEL also. as soon as the tractor was cut off it dropped to 0 and the 3 point dropped to the ground. I looked into the hyd fill hole again after the tractor heated up good and it is spraying more than I thought. Going to get parts to rebuild the rockshaft cylinder and see what that does.

 

[Tx Jim]

Check trans pump pressure with reverser in both fwd & rev. I think trans pump pressure can be shimmed up a little. I'll suggest to R&R RS piston seal & control valve seals. You'll need to replace the quad ring that sits in a recess on RH frt topside of trans case. T17882 RING,SEALING ADD 1.56 USD

 

[cliffj59]

Check trans pump pressure with reverser in both fwd & rev. I think trans pump pressure can be shimmed up a little. I'll suggest to R&R RS piston seal & control valve seals. You'll need to replace the quad ring that sits in a recess on RH frt topside of trans case. T17882 RING,SEALING ADD 1.56 USD

How do you shim up the pump pressure? What is R&R RS ? But I did find the T17882 washer and where its at.

 

[cliffj59]

Check trans pump pressure with reverser in both fwd & rev. I think trans pump pressure can be shimmed up a little. I'll suggest to R&R RS piston seal & control valve seals. You'll need to replace the quad ring that sits in a recess on RH frt topside of trans case. T17882 RING,SEALING ADD 1.56 USD



Tx Jim are the seals on here?

 

[Tx Jim]

Along with replacing keys 9 & 10 in your 2nd photo you should replace o-rings & backup washers on this photo. The piston housing is located under rockshaft housing.

 

[cliffj59]

Along with replacing keys 9 & 10 in your 2nd photo you should replace o-rings & backup washers on this photo. The piston housing is located under rockshaft housing.

Ok I'll get all the ones mentioned and replace them,

I did the pressure test while putting the reverser in both for and rev with no pressure drop a steady 125 psi. So I checked pressure when moving the rockshaft lift, Pressure would be 125 and when I pulled the lever to raise it would drop to 50 psi until it raised then back to 125 psi.
It would be 125 psi steady and I could raise or lower the FEL and the pressure drops to 50 PSI.

 

[cliffj59]

Along with replacing keys 9 & 10 in your 2nd photo you should replace o-rings & backup washers on this photo. The piston housing is located under rockshaft housing.

OK is there anything on the FEL control valve that needs replacing?

 

[Tx Jim]

I would recommend checking o-ring/back up washer(keys 17 & 18) on FEL control valve which I think has to do with keeping valve in closed-center mode.