L39 Hydraulic Shudder When Hot

[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!!