JD 750 compact loader problem

[JoeJChin]

HI all .

I have done some searching about troubleshooting the loader hyd system , to find a specific problem I am having with my JD model 67 loader, on my 750 tractor .

I thought if I described it here , maybe someone could narrow it down for me.

I recently bought the tractor , and it had this problem when I bought it .

It seems as if the loader cylinders are leaking by , or the valve for the loader cylinders is leaking by .



The loader will not lift the front of the tractor off the ground , nor will it lift the back of the tractor off the ground (no counterweight, or loaded tires) .

IF I lower the loader , and lay the bucket flat on the ground , then try to "dump" the bucket , it will just start to lift the tractor slightly, then just push the loader arms up.

With the bucket in the "dump" position , resting on the ground , sometimes I can get the tractor to start raising , if I find just the right combo of valve position and high engine rpms.

The valve on this tractor is a two lever type .

If I run the bucket cylinders to the end of their stroke , either all the way extended or closed , I can hear , what I believe is the relief valve operating ( sounds like turning your steering wheel on your car too far and holding it there)

If I run the boom lift cylinders to their extremes you do NOT hear the relief valve much , if at all , making any noise .

I don't know if this is enough info to indicate either the valve . or cylinder leaking by , but I thought I would ask anyway .

Any info for further checks will be welcome

thanks

Joe

 

[kennyd]

Joe, the cylinders are easy to rebuild and it's quite common for a machine that age for them to be leaking by internally. Most valves can't be rebuilt since there are very precise tolerances involves.

 

[J_J]

Check out the relief pressure with a 3000 psi hyd gage and see how close to specs are the hyd pressure readings.

 

[Leejohn]

I would rebuild the cyls as kennyd said about the age of you machine.

 

[kennyd]

Here is the breakdown of the cylinders:



HYDRAULIC CYLINDER
(650 AND 750 TRACTORS)
Cart KEY PART NO. PART NAME QTY SERIAL NO. OR YEAR REMARKS
1 JD7826 FITTING 2
2 PT5249 HYDRAULIC CYLINDER BARREL 2 BOOM
PT5251 HYDRAULIC CYLINDER BARREL 2 BUCKET
3 14H863 NUT 1 3/4"
4 PT5246 PISTON 1
5 PT5247 SEAL 1
6 PT5248 ROD 2 BOOM
PT5250 ROD 2 BUCKET
7 AM118390 SEAL KIT 1 (SUB FOR PT5252)
8 PT5220 HYDRAULIC CYLINDER 2 BOOM
Cart KEY PART NO. PART NAME QTY SERIAL NO. OR YEAR REMARKS
PT5221 HYDRAULIC CYLINDER 2 BUCKET

 

[JoeJChin]

kennyd

To rebuild the cylinders I would need parts 4 , 5, and 7 ?????

Joe

 

[Leejohn]

I was waiting for kennyd to come back and help, but he must be offline. All you need is #7. You might want to wait until he gets back to you. That # 5 you might need.

 

[kennyd]

Generally the seal kit, #7 will take care of everything.

Here is a quick and easy test: use the loader for a while, then feel the cylinders. If they are extremely hot, then you can pretty much bet they are bypassing-or at least one is.

Cylinders, like windshield wipers, brakes, headlights and socks should be changed/rebuilt in pairs IMHO.

 

[JoeJChin]

I picked up a pressure gauge , just wondering where in the circuit would be the best place to check the relief pressure ?

thanks

Joe

 

[J_J]

The best place is in a tee in the IN port of the first valve in the series path.

The gage will read what any of the attachments hyd is doing.

If you only want to check each valve, just plug it into any work for that valve and work the lever to show the relief pressure.