3 ph drifts down

   / 3 ph drifts down #1  

600rider

Gold Member
Joined
Jul 11, 2007
Messages
376
Location
union city pa
Tractor
2004 kubota b7510
Ok I have lived with this for a couple years so now is the time to fix it! I have a 2004 Kubota B7510 HST and the the 3ph drifts down all the time! It doesn't matter if I am driving the tractor or if it is sitting running while I am doing something else. doesn't matter if it is at idle or full throttle. I have even been going down the road and tried to lock it in the up position with the knob in front of the seat. I am thinking it might be a seal on the lift cylinder. Any thoughts?? Thanks, Ken.
 
   / 3 ph drifts down #2  
None of the 'B' series has position control. Without position control a SLOW drift down of the bottom links is normal.

The only palliative is check chains, such as Zerco, most commonly used with rotary cutters to assure down return to specific height. Zerco check chains work "fine".

In Photo #2 rotary cutter is UP, chains are slack.

In Photo #3 rotary cutter is DOWN, chains are taut. DOWN adjustment is repeatable and will hold as many years as the chains last.

MORE INFORMATION:

http://www.tractorbynet.com/forums/...271185-kubota-b3300su-zerco-check-chains.html
 

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   / 3 ph drifts down
  • Thread Starter
#4  
I dont remember it doing this when it was new. While I am going down the road with an implement or trailer on the 3 ph it will drop to the bottom quite fast. I dont believe this is what it is supposed to do. I think it should stay put for at least a reasonable amount of time.
 
   / 3 ph drifts down
  • Thread Starter
#5  
It wont even stay up with out anything on the 3 ph!!
 
   / 3 ph drifts down #6  
Post #4 + #5: You are correct, this is NOT normal.

When was the last time you changed your hydraulic fluid and hydraulic system filters?

If it is a leaking seal or lines your hydraulic fluid will be low.

How many engine hours on your B7510?

Has it been stored inside a structure or outside? With a tractor 8+ years old this can make a difference. Fittings can loosen in alternate freezing/thawing conditions leading to tiny leaks, hydraulic hoses deteriorate faster out in the weather.
 
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   / 3 ph drifts down #7  
Why not post this same enquiry, with all dis-function information consolidated, in the HYDRAULICS Forum?
 
   / 3 ph drifts down
  • Thread Starter
#8  
Jeff9366, The tractor is stored in a heated garage, has about 600hrs. on it, hasn't had the filter or fluid changed since what was recommended after the initial break-in period. None of the lines or seals leak fluid on the ground.
I was thinking it could be the seal on the lift cylinder so the oil would just bypass and would be internal so no leakage on the ground.
 
   / 3 ph drifts down #9  
Is there a knob on your tractor that controls the speed of your three point raising or lowering? If there is, and it is not adjusted correctly, that may be part of the problem.
 
   / 3 ph drifts down #10  
if it is like most tractors, the rockshaft seal if bad- results in your description, but the hydraulic control linkage would cause it to lift back up to the original position if the tractor had position control and the tractor was running..

When not running the quick lowering is the most common result with a failed rockshaft seal...one more thing a rockshaft seal failure will not affect fluid level, it will just end up in the sump..rockshaft seal replacement 001.JPG rockshaft seal replacement 002.JPGas can be seen in this picture the cylinder that the rockshaft piston slides in is open to the sump, this ones seal had completely disintegrated.
Replacing the seal and honing the cylinder restored the 3 point lift, to as new operation.
You can also check your work by using an air compressor and an inexpensive leak down tester as I did, this assures you that the seal is sealing correctly and that it didn't get damaged during installation rockshaft leakdown test 002.jpg besides those rockshaft covers aren't exactly light, and it's no fun taking it apart twice...
 
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