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Kubota L2800 3pt hitch bumps after warming up

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orangemule
Join Date: Sep 2010
Posts: 5 Marbury, AL
TractorPoint Premium Member -- 5 Tractors = Very Frequent Poster

2010-09-30          174263


I'm new here and there is a wealth of knowledge here. Thank you, kind gents.

My problem: Recently purchased a 5 ft bushhog (used a 4ft no problem and this 5ft for about 10 hours before bumping started) and since then, but not immediately I noticed at full 3pt hitch height the hog would slightly dip and the hyd pressure would have to quickly pump (i think this is the 'bump') up the hitch again. Once warm, this becomes recurring nearly every 5 seconds or so, especially at higher rpms..in other words, the higher the rpm..the more frequent and pronounced the bumping becomes.

The FEL seems to have no effect on the rear misbehaving.
Also, I serviced the tractor last week hoping new oil/filter would help but it's the same.

Also, I tried adjusting the control position level rod per manual, to no avail tonight. There was some dust debris under adjusting rod, but cleaning did not affect bumping behavior.

One last note and I'll wait for advice:
I noticed the hyd fluid get a little low before all this started so I added some oil that I thought was Super UDT, but turned out to be regular UDT. Following that I changed oil and filter and used Regular Kubota UDT to replace. The manual states use either UDT or Super UDT. The view glass shows correct oil level.

What advice for next step?


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Kubota L2800 3pt hitch bumps after warming up

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auerbach
Join Date: Sep 2007
Posts: 2168 West of Toronto
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2010-09-30          174266


Correct if wrong. You mow with the deck resting on its own wheels, not with its weight borne by the hitch. But when you drive with it fully raised, it lowers a bit and then jerks up to full height.

I don't know the Kubota line but wonder if that deck is nearing the hitch's weight limit, especially going over bumps. There's likely a hitch lock valve on the tractor. Close it and the hitch stays where you left it. That's what it's for. ....

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Kubota L2800 3pt hitch bumps after warming up

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orangemule
Join Date: Sep 2010
Posts: 5 Marbury, AL
TractorPoint Premium Member -- 5 Tractors = Very Frequent Poster

2010-09-30          174270


Quote:
Originally Posted by auerbach | view 174266
Correct if wrong. You mow with the deck resting on its own wheels, not with its weight borne by the hitch. But when you drive with it fully raised, it lowers a bit and then jerks up to full height.I don't know the Kubota line but wonder if that deck is nearing the hitch's weight limit, especially going over bumps. There's likely a hitch lock valve on the tractor. Close it and the hitch stays where you left it. That's what it's for.


I do have a hitch lock valve adjusting knob just under the front of the seat, but honestly don't want to have to turn this knob every time I lift my hitch up.
The problem could just be the weight of the implement, and I'll return it and trade in if I have to. But, for now, I'm going to keep looking for advice on other potential hydraulic problems associated with the described behavior.
I'll try another implement this afternoon to see about the weight difference.

I'll check the spec sheet(s) for implement weight limits and call the bushhog dealer and get the implement weight just to make sure I'm within limits.

Thanks for your reply, it may be just too heavy.

Any other ideas out there? ....

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Kubota L2800 3pt hitch bumps after warming up

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orangemule
Join Date: Sep 2010
Posts: 5 Marbury, AL
TractorPoint Premium Member -- 5 Tractors = Very Frequent Poster

2010-09-30          174271


I checked the specs.
L2800DT
Hydraulic Lift capacity at lift point -- 1998 lbs
At 24 Inches behind Lift point --- 1435 lbs

Weight of 5ft King Kutter rotary cutter with flex hitch --- 535 lbs.

I'm beginning to think control valve?
Does anyone have insight before I go to tearing the top off the control valve housing? (never done before)

....

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Kubota L2800 3pt hitch bumps after warming up

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kthompson
Join Date: Oct 2005
Posts: 5242 South Carolina
TractorPoint Premium Member -- 5 Tractors = Very Frequent Poster  View my Photos  Pics

2010-09-30          174278


First totally agree with you Orangemule, some great people here. They have helped me often and greatly.

Now if this were an old Ford (601 model range) would agree you have what they called hiccups in their lift. Let me suggestion you look outside of the lift it self. Run the unit and then raise the lift not 100% but say 90% of max lift. Let the tractor just sit still for a minute or two and see if it still bumps. If not I suspect your PTO shaft is being jammed due to being two long when the lift is fully raised. To be sure you raise the lift, cut off tractor and try to disconnect PTO shaft, if you can slide it off then that is not the issue.

Second thought is your PTO shaft might be at such a sharp angle it is jamming or there is a bad bearing in one end and at that angle allowing it to slap.

If you still have not found the issue pull the PTO shaft and play with it to be sure it is sliding in fully and easy and there is no slackness in the universal joints. That is one thing I don't like about the safety shields, makes it hard to inspect. Look carefully to be sure the shaft has not twisted either causing it not to slide easy.

Third thought is there is an issue in the mower it self that shows up when the deck comes clear of cutting load. Be sure the blades and their mount are all secure.

....

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Kubota L2800 3pt hitch bumps after warming up

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Murf
Join Date: Dec 1999
Posts: 7199 Toronto Area, Ontario, Canada
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2010-09-30          174281


OrangeMule, it's been my experience that it's rarely the valve that goes, it's far more often the seals on the lift cylinder piston itself that let go.

The design of a valve is such that it's inherently far stronger than the piston seals, and any shock-loading or attempts at hyper-extending hits the piston seals the hardest.

The bumping you describe is the fluid bleeding down out of the cylinder while it's under load, and then when the valve senses that the cylinder is down it feeds it fluid to raise it back up to where it should be according to the control lever position. At lower RPM's it isn't as noticeable because the pump has a much lower output and the raise back up is likely very subtle.

I hope I'm wrong though, the lift cylinders are down inside the rear end are usually a real PITA to get to and change.


Best of luck. ....

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Kubota L2800 3pt hitch bumps after warming up

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kthompson
Join Date: Oct 2005
Posts: 5242 South Carolina
TractorPoint Premium Member -- 5 Tractors = Very Frequent Poster  View my Photos  Pics

2010-09-30          174289


Murf you probably are correct in your diagonis but for his shake sure rather it be the pto shaft...ugh.

The old Fords lifts had such a hiccup problem and were used a lot for tobacco cultivation which was a problem as the cultivators always jumping. A local company came up with a design for a slide to bolt onto the cultivator to support the weight of the culitvator taking it totally off the lift so you got level plowing. My in laws had such a tractor and with the right load on it running at the right rpm sitting still the tractor would almost get itself bouncing. ....

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Kubota L2800 3pt hitch bumps after warming up

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orangemule
Join Date: Sep 2010
Posts: 5 Marbury, AL
TractorPoint Premium Member -- 5 Tractors = Very Frequent Poster

2011-03-31          177721


for those interested, I've found a potential fix for this.
This L2800 is equipped with a hydraulic pressure relief valve located under the deck on the right side, basically just under my right foot.
In the manual it states that there are shims for this valve that can be added to (I assume) put more pressure on the valve to stay closed and only relieve pressure when there's overloading pressure. If the spring on this valve isn't strong enough to keep valve closed, it'll let a little hydraulic fluid through(?)..allowing 3pt hitch to dip, then the pump 'tops it off' to return to previous level. This is why my tractor hitch is bumping, I believe.

I'm going to either shim this valve or replace (and keep old one) and buy the shims in case it happens again.

I'll come back after and let y'all know how this turns out. ....

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