L39 Hydraulic Shudder When Hot

[Jim Miller]

Well, south Texas is getting HOT. This weekend, after about 4 hours in 90+ temp (but the engine temp guage was normal) I noticed my L39 hydraulics started to shudder on the backhoe and FEL when I was making small - slow movements on the FEL or hoe. Normally, everything is smooth as silk. I noticed it last weekend too - but I thought it was just my imagination and being hot and tired after 4 to 5 hours seat time. But, this weekend after 4 hours of almost constant operation - the shudder was definately there.

My L39 has almost 900 hrs and I've put the last 125 hrs on it. I bought it used from Kubota dealer and he changed all filters a fluids at 775 hrs. I checked fluild level and it is at the top mark where it has been. No leaks on concrete floor at all. However, when I did check the fluid level later Saturday evening, I noticed a few very small (tiny) bubbles in the fluid - not foam - just several tiny bubbles on the dipstick. I didn't remember seeing them ever before??????

Any ideas??

 

[gwdixon]

My L48 does exactly the same thing. After the hydraulic fluid gets hot the boom gets jumpy.

I figured that it was because cheap hydraulic fluid was used at the last change (Traveler Premium from Tractor Supply). My thought that it thinned out too much when hot compared to UDT or true premium oil.

There is 15 gallon store of New Holland Ambra in my shed just waiting until the opportunity comes for a change-out. Only 125 hours on the cheap oil.

I'll be happy if someone comes up with a better answer.

 

[chim]

Don't blame it on your choice of hydraulic oil. I used UDT and Super UDT in a tractor that did something like you're discussing.

On the B7500 I had the steering would get a very noticeable "jerky" feel. It only happened while pushing it on the hotter days when using the 5' RFM in heavier grass. I blamed it on two things - The large heavy Landpride RFM and a smaller than ideal hydraulic cooler. I could make everything feel like normal by swinging by the garden hose and running cool water over the hydraulic cooler fins with the tractor idling for a few minutes.

 

[mike69440]

Well, south Texas is getting HOT. This weekend, after about 4 hours in 90+ temp (but the engine temp guage was normal) I noticed my L39 hydraulics started to shudder on the backhoe and FEL when I was making small - slow movements on the FEL or hoe. Normally, everything is smooth as silk. I noticed it last weekend too - but I thought it was just my imagination and being hot and tired after 4 to 5 hours seat time. But, this weekend after 4 hours of almost constant operation - the shudder was definately there.

My L39 has almost 900 hrs and I've put the last 125 hrs on it. I bought it used from Kubota dealer and he changed all filters a fluids at 775 hrs. I checked fluild level and it is at the top mark where it has been. No leaks on concrete floor at all. However, when I did check the fluid level later Saturday evening, I noticed a few very small (tiny) bubbles in the fluid - not foam - just several tiny bubbles on the dipstick. I didn't remember seeing them ever before??????

Any ideas??

Air or a sticky relef valve maybe?

 

[Jim Miller]

OK - The next time I use the L39, before I get going, I'm going to be very careful to look for any noticable bubbles in the fluid on the dip stick. Then I'm going to do my work until I feed the shudder come back. When it does (and I believe it will) I'll check the fluid for bubbles again and then try the garden hose cool-down on the hydraulic cooler fins trick for a few minutes.

I'll let you all know what I find.

 

[Jim Miller]

I'm the OP and my last post about this was in June 2012. My L39 still has the "jerky" feel after running about an hour or more. The FEL, backhoe and clutch all feel jerky after an hour of operation. When I push in the clutch my foot feels a small roughness that wasn't there before. When I operate the FEL or hoe, all the operating motions just get jerky. This is hard to exactly describe but if you've been using the tractor and everything has been smooth and then you notice all the movements are not smooth anymore it gets your attention. When I'm trying to be very careful where I'm putting the hoe or trying to gently ease the FEL down to dump something it really gets more tricky than usual.

I still have the tiny bubbles in the fluid and the fluid level is still at the full mark. When I first begin working, the tractor is very smooth and then it begins to have that studder or jerkyness.

I don't think it's a sticking valve - but - it is definately heat related. No leaks at all.

I'm open to any suggestions - including changing the hydro and filters. I just wanted to bring this back up to the forum to see if anyone might be able to help me.

Thanks!

 

[gwdixon]

I'm the OP and my last post about this was in June 2012. My L39 still has the "jerky" feel after running about an hour or more. The FEL, backhoe and clutch all feel jerky after an hour of operation. When I push in the clutch my foot feels a small roughness that wasn't there before. When I operate the FEL or hoe, all the operating motions just get jerky. This is hard to exactly describe but if you've been using the tractor and everything has been smooth and then you notice all the movements are not smooth anymore it gets your attention. When I'm trying to be very careful where I'm putting the hoe or trying to gently ease the FEL down to dump something it really gets more tricky than usual.

I still have the tiny bubbles in the fluid and the fluid level is still at the full mark. When I first begin working, the tractor is very smooth and then it begins to have that studder or jerkyness.

I don't think it's a sticking valve - but - it is definately heat related. No leaks at all.

I'm open to any suggestions - including changing the hydro and filters. I just wanted to bring this back up to the forum to see if anyone might be able to help me.

Thanks!

Since you have diagnosed the problem to be heat related (correctly I believe) then the only solution would be to make modifications to lower the heat of the hydraulic fluid. Did you diagnosis include manually feeling the cylinders to verify that they are hot? Harbor Freight and others sell non-contact thermometers that can help determine at what cylinder temperature functions start to fail.

I have not heard of using a transmission fluid type of cooler on tractor hydraulics but one could make a fortune if something of that sort could be developed. I know that I'd buy one for my L48.

The other option is to deal with the hydraulic oil itself. Using an oil that has a higher viscosity may help as well as using some synthetics (Amsoil).

This link is to an explanation of many of the aspects of hydraulic oil. It may help you in looking for a solution:

Characteristics of a Good Hydraulic Fluid - Hydraulics 101 - HydraulicFacts

Here is a quote (post #54 in this tread http://www.tractorbynet.com/forums/kubota-owning-operating/270613-where-buy-oil-hydraulic-filters-6.html )

So I just compared the specs of SUDT2 to AMSOIL. Because I believe my power steering problem is somehow related to the hydraulic fluid over-heating, the spec in which I'm most interested is the Viscosity @ 100 degees C, cSt. The SUDT2 is rated at 8.1. The AMSOIL is 9.8. Higher is better.

 

[Jim Miller]

Does the L39 have a transmission cooler? I know I don't have a transmission temp guage. I've been thinking about borrowing my meat themometer to dip into the fluid fill port. Or would one of those temp guns be better. Once I find the temp that the hydro gets jerky - then what should I do. I'm just trying to think ahead after I find that the jerky movement starts at 157 degrees. I don't know what to do with that information.

If the L39 has a cooler - then maybe its plugged up and not working correctly.

 

[gwdixon]

The information from the heat gun could verify and isolate the problem. If the boom repeatedly becomes jerky at around 157+ degrees measured at a consistent point on the boom cylinder, then the diagnosis would be more certain. No concern about a sticking valve or the like.

The air bubbles in the oil situation is an indicator that the hydraulic fluid you are using does not have adequate foam inhibitors to break up the bubbles (foam). Those bubbles can create problems.

Foam results from air or other gases becoming entrained in the hydraulic fluid. Air enters a hydraulic system through the reservoir or through air leaks within the system.

A hydraulic fluid under high pressure can contain a large volume of dissolved or dispersed air bubbles. When this fluid is depressurized, the air bubbles expand and produce foam. Because of its compressibility and poor lubricating properties, foam can seriously affect the operation and lubrication of machinery.

Proper foam inhibitors modify the surface tension on air bubbles so they more easily break up.

While the dealer may have changed the hydraulic fluid you can't be sure what he used or even that it was done. Hydraulic fluid stays quite clear over time. It does lose some of its additives and lubrication when old. The link I posted about the "Qualities of a Good Hydraulic Fluid" details many factors that may have lead to the problems you are experiencing.

Now you have to decide if it is worth $400, or so, to change the hydraulic fluid to Amsoil and replace the hydraulic and transmission filters. Right now, you are trying to evaluate a problem without full knowledge of the parameters.

As far as I know, none of the smaller Kubota backhoes have a transmission cooler. That would indicate to me that Kubota engineers expect the quality of the fluid should adequately dissipate the heat build-up. In addition, quality fluid would be less likely to get hot and reduced viscosity resulting in lack of lubrication and functioning.

In summary, change the oil and filters and don't go cheap.

 

[avc8130]

My L39 had a hydraulic cooler on the front in front of the radiator. I found out the hard way when a little rubber hose broke and spewed fluid everywhere.

ac

 

[gwdixon]

My L39 had a hydraulic cooler on the front in front of the radiator. I found out the hard way when a little rubber hose broke and spewed fluid everywhere.

ac

Did you every experience the problem the OP detailed?

 

[Jim Miller]

I'm the OP. After asking the question about the OIL COOLER last night, I looked at the Parts Diagrams I have and as avc8130 posted, yep it sure does - right behind the front black plastic grill on the tractor. It's mounted at the very front. Now I can't wait to get home tonight and see if there is anything blocking the cooler or if any of the lines have been hit or of I can see anything that would keep it from working properly.

I'll let you all know what I find. I'll also see where I can get a thermal gun. I really hope I'm on the right track!!!!

 

[avc8130]

Did you every experience the problem the OP detailed?

Honestly, I never really used my backhoe for too many hours in a row. The one time I tried to use it for more than 3-4 hours the hard hydraulic line for the swing pump blew. LOL

ac

 

[Jim Miller]

I just want to make sure that the TBN members that are following this thread know that the studder or jerky movement is with the FEL, backhoe and when I push the clutch in or let it out. The jerky movement is with all three not just one system. When I first start working the tractor all three have very smooth operations. All three get jerky after about an hour of operation. This past weekend I used the FEL almost 99% of the time - only used the backhoe just to raise or lower the hoe when I was stopping to take a load of fill dirt.

Can't wait to get home to look at that cooler!!

 

[Jim Miller]

I examined the Cooler very closely and didn't see anything wrong. All hydro pipes and connections look fine. I was hoping to find something. I did buy a infared thermometer to take readings on the heat and at what point the jerky movement begins. I'll keep you posted.

 

[mike69440]

With near 1,800 hard hours on my poor old L39, I never had problems with the hydraulics other than a blown oil pump seal when new. I use RP hydraulic fluid, same fluid for +1300 hours. Just a guess but I newvr had a clyinder over 150-160 Deg F working flat out.

 

[Jim Miller]

This past weekend I was on the tractor for 5 hrs on Sat. and 4 hrs on Sun. The morning outside temp was about 40 degrees. Here's what I noticed:
Before I started on Sat. or Sun., the hydro had small (tiny - about the size of a grain of salt) bubbles on the dipstick. The clutch, FEL and backhoe operations were smooth as silk! I was not using the backhoe at all.
After about an hour, the clutch started to be a little grabby and the FEL was jerky. I felt evey hydro cyl and connection and they were only sightly warm to the touch - only warm. After about 3 hours, the clutch was much more grabby and the FEL was more jerky. The hydro was warmer - but not hot at all.

Then I pulled the dipstick and when it came out there was a noticable pressure release noise (whoosh) AND the bubbles were much larger (about the size of BBs) but not foamy. I felt the dipstick and it was warm - but not hot.

After Sunday afternoon the job was finished and I loaded the tractor on the trailer and came home. Monday morning I unloaded the tractor and all hydros were again very smooth.

It seems I don't have a heat problem.
First hour of operation all hydro functions are smooth with tiny bubles in hydro fluid.
After about two or more hours of operation all hydro operations are jerky with larger bubbles and pressure in hydro resevoir.

Am I getting air in system? Is the air in the fluid what's making the jerky movement? I don't see any signs of fluid leaks.

 

[gwdixon]

I'll try once again. The bubbles can be considered foam. Since you don't know the quality of the oil and whether or not it has "foam inhibitors" then you will never know the answer. And bubbles are, or create foam, even though it may not be shown on a dipstick as froth.

Foam Resistance

Foam results from air or other gases becoming entrained in the hydraulic fluid. Air enters a hydraulic system through the reservoir or through air leaks within the system.

A hydraulic fluid under high pressure can contain a large volume of dissolved or dispersed air bubbles. When this fluid is depressurized, the air bubbles expand and produce foam. Because of its compressibility and poor lubricating properties, foam can seriously affect the operation and lubrication of machinery.

Proper foam inhibitors modify the surface tension on air bubbles so they more easily break up.

Here is another quote, it is regarding motor oil but applies to hydraulic oil:

Air is whipped into the oil by rapidly moving engine parts. Air is also trapped in the oil during high-pressure or when the pump sucks air in with the oil. The result is a mass of oily froth called foam. The presence of small amounts of water increases this engine oil problem. The basic cure is an engine design that prevents air from being whipped into the oil and excludes water. Even the best design, however, will not eliminate foaming completely.

A mixure of oil and air is not a good lubricant, cannot support bearing loads, and does not provide good cooling. Because it contains air, oil foam is compressible. This impairs its ability to prevent wear, and the result can be the collapse of hydraulic valve lifters and subsequent poor engine operation.

High-quality motor oils contain foam inhibitor additives that weaken the tiny air bubbles and cause them to collapse almost as soon as they are formed in the oil. These chemical compounds, composed principally of hydrogen and silicon, are called silicones. Only a few parts per million are required to make most oil adequately foam-resistant.

The Motor Oil Guide, The American Petroleum Institute.

 

[avc8130]

Is your breather clogged?

ac

 

[Jim Miller]

gwdixon I sense your frustration with my limited understanding about the bubbles/foam in my hydro oil. I will have to wait a little while to get enough to change out the oil and filters. At this point I don't know if I'm going with the Amsoil or the SUDT2. If you know the correct Amsoil number I would appreciate it. I'll be using Kubota filters.

avc8130, I have opened my air filter canister and checked both filters (neither appeared to be dirty) and I've washed the screen, radiator and the oil cooler fins.

Thanks!!