Oil & Fuel Kubota B21 Foaming Transmission Fluid.

   / Kubota B21 Foaming Transmission Fluid. #1  

TomSeller

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I recently bought a used B21 for a very good price. When loading it I noticed the hydraulic fluid foaming and coming out the overflow tube in the rear. I thought I had it troubleshot to an intake tube on the hydraulic pump sucking air and tightened that. All was good and I filled it with about 1/2 gallon of SUDT after getting it home. Loader is strong, backhoe is strong, HST strong enough to stall the engine. Good power and starts well. 1600 hrs.

This afternoon when warming up the tractor for about 20 min, I found the foaming condition back. We just had a rain and wind storm but you can see the oil and foam on the ground. Much of the foam had dissipated by the time I took the pictures. Fluid appears to be clear when foam subsides. I have never had problems with foaming while simply warming up a machine, I had it in range with the brake on to warm up the fluid faster. I filled it up to the top mark on the dipstick.

Would a poor quality oil foam on warm up? ie engine or gear oil? I don't know what the owner put in the transmission tank. Any other reason the fluid would foam and spill on these B21s? I did not see anything in the owner's manual about doing anything special when filling the transmission so as to not overfill. It filled normally to the high mark. My knee-jerk reaction is to drain it, change filters and fill in with SUDT.
 

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   / Kubota B21 Foaming Transmission Fluid. #2  
That's interesting. BTW, congrats on finding the B21. I find the larger TLBs so useful around our place that I'm now looking to add a small one myself. This time the nod will go to the smallest one we can find that has HST and PS. Prefer Kubota or JD....but any brand is a possibility; manuverability and ability to work in tight places are what we're looking for in this tractor.

On the foaming, the only time I've seen foaming that looks like that is with some of the older flushing oils back when when HST first came out. I wonder if the DPO used flushing oil and didn't get it all out. Regardless of what is causing this, I agree that your first step is to drain and refill. Only problem with that is the cost - but I don't see you have much choice. My JD and Kubota HSTs don't seem to ever drain all the oil when changing. So it were me, I'd go so far as to drain/fill several times with inexpensive hydraulic oil and then finally fill with the preferred fluid.
Hmmm....during that process you could probably reuse the same filter by draining it separately and reinstalling. Maybe several times over the course of a week.
good luck,
rScotty
 
   / Kubota B21 Foaming Transmission Fluid. #3  
First thing I'd do is be sure that it has the right fluid in it.
 
   / Kubota B21 Foaming Transmission Fluid. #4  
Also consider that all the hydraulic cylindars are fed from the same oil as the HST. so the flush method described by rScotty will be necessary to get rid of what appears to be contaminated oil. The B21 HST capacity is something like 7 gallons, you may be able to get away with 5 gallons per flush actuating all hydraulic functions. 3 flushes plus a refill is a lot of $$$, mess and drain oil. I would consider a dealer consultation on this one.
 
   / Kubota B21 Foaming Transmission Fluid.
  • Thread Starter
#5  
Also consider that all the hydraulic cylindars are fed from the same oil as the HST. so the flush method described by rScotty will be necessary to get rid of what appears to be contaminated oil. The B21 HST capacity is something like 7 gallons, you may be able to get away with 5 gallons per flush actuating all hydraulic functions. 3 flushes plus a refill is a lot of $$$, mess and drain oil. I would consider a dealer consultation on this one.

Yeah flushing the fluid 3 times would be expensive. Here is a time when I wish had not been recycling my used hydraulic fluid and could just flush with old fluid. I am struggling to think of what type of oil would foam so much under warm up conditions just above idle. Maybe I can ask the dealer if I can have some old fluid to flush with. I have a JD and a Kubota Dealer in town. When I first saw it, there was much more foam and all the discolor goes away when the foam dissipates. I wiped a bit on my finger from the dipstick but before I could take a picture, it was straight fluid.
 
   / Kubota B21 Foaming Transmission Fluid. #6  
   / Kubota B21 Foaming Transmission Fluid.
  • Thread Starter
#7  
I'd be rechecking all the inlet hoses, and clean the strainer to the charge pump, if it is blocked it will cavitate I expect. Also make sure your 3PH is down and PTO valve is set correctly. Then there is some oil, relatively cheap, my get something else cheaper.
Super Tech Heavy Duty Tractor Hydraulic and Transmission Fluid - Walmart.com

I do plan on checking the strainer when I do the fluid change as well as both filters. I had not thought to check the PTO lever, it looks like up is off? I would have thought down was off since that is the position it will likely get eventually kicked to on a TLB with the backhoe on it more or less full time. I'll check out Walmart, thank you for that as well. I don't shop there much and don't think of it.
 
   / Kubota B21 Foaming Transmission Fluid. #8  
Yeah flushing the fluid 3 times would be expensive. Here is a time when I wish had not been recycling my used hydraulic fluid and could just flush with old fluid. I am struggling to think of what type of oil would foam so much under warm up conditions just above idle. Maybe I can ask the dealer if I can have some old fluid to flush with. I have a JD and a Kubota Dealer in town. When I first saw it, there was much more foam and all the discolor goes away when the foam dissipates. I wiped a bit on my finger from the dipstick but before I could take a picture, it was straight fluid.

The foaming sure is interesting....I haven't seen what you describe in 45 or 50 years, but mixing diesel fuel or kerosene into the transmission oil used to be a commonly done way to make up a cheap home-made flushing fluid. Lots of garages did it. And yes, that mix sure would foam. In fact, foaming was the aim as it was thought to clean out particles better that way. It could be that is what you are facing. If so, the problem is getting all the flushing oil out and good undiluted HST back in. I don't know of any way to do that except as we've already gone through. But do reuse the filter, and start with any cheap bulk hydraulic oil from the farm store. At least it would be cleaner than someone else's old oil. We used to use 10wt. motor oil for the first few hydraulic system changes after a flush. As Mikesee said, half of the oil in any HST/Hydraulic system is in things like the cylinders and hoses which don't gravity drain. IF that really is what happened, you are you are going to have to drain it many times - and also have to run it through all gears and all hydraulics in between changes.

The partly good news is that if the flushing oil we're decribing here really is the reason for the foaming, it that doesn't automatically mean that there was some problem that the DPO (Dread Previous Owner) was trying to fix. I had a mechanical repair shop in the 1960s, and we routinely did this type of flushing. It was simply considered to be good practice and good maintenance. In addition to routine maintenance, flushing was considered to be absolutely necessary if the hydraulic system had been contaminated by a failed component or with water. Normal wear on the internally wetted brakes are also a source of particles. I don't do that sort of flushing anymore; not even on my own machines. But I'm not ready to say it was wrong either. In fact, I just this fall I had to have the crowd cylinder on the JD310 rebuilt because it was squawking. The mechanic said the bores were all clean & smooth, but a buildup of sludge under O ring seals was pushing them too tightly against the sliding surfaces. Turns out that sludge buildup was the source of the squawk. So all it needed was an twenty dollar O-ring kit (and a thousand dollar bill for labor). Would periodic flushings have prevented that problem? Well, after half a century of turning wrenches I'd give that answer as a firm "maybe".....and even shade it slightly in the direction of "probably". .. ....

Since you have a JD and Kubota dealer nearby you might ask them what they do when a hydraulic system needs flushing. Or do they even still do that?
It's worth asking; and I'm kinda curious what they would say.
.... Luck, rScotty
 
   / Kubota B21 Foaming Transmission Fluid. #9  
I read somewhere that mixing dissimilar brands/types of oil can produce foaming. If it were me, I would just drain it, change any filter(s) involved then refill with Kubota hydraulic oil. Then see what happens.
 
   / Kubota B21 Foaming Transmission Fluid. #10  
If you can wait for the results before doing anything I recommend a used oil analysis. That would probably tell you if you had anything "bad" in the oil.
 
 
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