How to recover from low oil in Hydro transmission ?

[westcliffe01]

Hi folks

I think I did something really dumb... I recently purchased a 2003 Bobcat B200 TLB. It has a diesel Tank on the left hand side of the chassis and the hydraulic tank on the right.

The machine has some small hydraulic leaks which I have not yet tracked down. I think it is primarily related to the power steering and transmission since the leak is worst when at full lock on the steering. Anyway, the sightglass on the hydraulic oil tank is very hard to read and what I thought was the level now appears to be a stain on the level indicator.

This past weekend I put about 50 hours on the machine and right at the end it started jerking (very subtle)a little when going forward or in reverse. All of the other hydraulics work fine (loader or backhoe).

I came to use it Monday and I had the impression it would not move at all. Then I found that if I just kept the hydro pedal down, it would start creeping and finally would build up to normal speed. But as soon as you stop, its the same routine every time.

Thinking that maybe the fluid level was lower than I had initially thought, I bought 4 gal of type 46 Hydraulic fluid and added it to the tank. All of it went in the tank, and there is no change to the sightglass. Since the diesel tank holds about 10 gal, I am assuming that the hydraulic tank has the same capacity and could take at least another 2-4 gal.

So in my mind, the finding appears to confirm the fact that the fluid level became low. The fact that after a delay the machine will operate and build to the same speed as original seems to indicate that I possibly have some air in the system that is causing the problem.

Those of you with some experience, please let me know if I am all wet and something else is going on. In general, does the hydro trans share the same oil reservoir on this machine or does it have its own ? How does one recover from a low fluid situation (does the air have to be bled out ?). And finally, why is it that the hydraulics on the loader and backhoe work perfectly, when the hydro does not ?

Many thanks
Keith

 

[Hooked_on_HP]

Stop now before you destroy a good tractor. First of all you need to know what type of oil it uses.Most don't use hydraulic oil. The wrong oil can ruin it. If you have put the wrong oil in it has to be drained completly and the filter changed. You need a operators manual so you will know where to check which fluids and what type to use. You invested a lot of money in a tractor that should last for a lot of years if maintained properly. There are no cheap repairs on a tractor.
Bill

 

[alchemysa]

I know nothing about Bobcats. You might be better to ask this in the Construction Equipment forum.
But anyway I can tell you this about my Kubota. It (like all Kubotas I guess) has a single reservoir for the HST tranny and implements. (This reservoir is in the transmission housing, its not a separate oil tank.). Theres a metal mesh filter between the reservoir and the tranny. This screen can clog and cause symptoms similar to those you describe even though the implements work fine.

I'm sure a Bobcat is built totally differently but you will still have various filters or screens you need to check and replace. If the oil has gotten really low its even more important to replace or clean the various filters. You might need a manual or professional help to explain where all the filters are located. Hopefully clean filters and more oil is all you need.

 

[LBrown59]

Stop now before you destroy a good tractor. First of all you need to know what type of oil it uses.Most don't use hydraulic oil. The wrong oil can ruin it. If you have put the wrong oil in it has to be drained completly and the filter changed. You need a operators manual so you will know where to check which fluids and what type to use. You invested a lot of money in a tractor that should last for a lot of years if maintained properly. There are no cheap repairs on a tractor.
Bill

There was just very recently a thread about a guy ruining a nearly new tractor buy doing just that.

 

[Coyote machine]

I too suggest you post this in the BOBCAT forum which is further down the page that list all the tractor Mfg.'s It has a Bobcat specific forum under the heading of Tractor specific forums.
More people with knowledge of Bobcats are likely to reply.

I do agree- until you know exactly what you are doing do NOT assume anything. Make SURE you are using the correct fluid in the correct amount and putting it in the correct hole. Otherwise all damage done will be because of guesswork, and that can be very costly.
DO NOT use the machine anymore until the problem is solved.

Maybe you could give some more history too. Where did you buy it- dealer or individual? Any warranty come with it? How was it used prior to your ownership?

Good luck.
Post back on progress and results....

 

[westcliffe01]

Before I bought the TLB, I read every shred of info on these machines, which have essentially been abandoned by IR. Since they closed down the European operation, they cut all owners off from the people who designed and built these vehicles.

From the info posted here, all of the hydraulic systems are supplied by Bosch Rexroth. The question of what comprises Bobcat Hydro oil has been discussed too and comparing both sets of info the type 46G oil meets the Rexroth specification. They have a chart for every pump and motor that shows which grade of oil would operate at an appropriate viscosity depending on operating temperatures. Just for understanding, I am about 70 miles from the nearest Bobcat Dealer. I don't refuse to purchase their oil out of principle, it just seems stupid driving 140 miles to get 5 gal of oil and they refuse (officially) to tell customers what it is.

So I am really not too concerned regarding the grade of oil, since I think I have that part of it straight. What I cannot figure out is why the Hydro Trans should run out/low on of oil when the impliments work fine without a hitch at all. Perhaps it has to do with the fact that the main hydro pump is far larger than the secondary pump that operates the loader and backhoe, therefore the flow rate is much higher and it may suck air first if the fluid level gets low.

At this point I know that the fluid level was low, but do not know if it got so low that any damage was done to the main pump. The unit at no time made any unusual noises or anything that would indicate mechanical damage. The machine was not working hard immediately prior to the problem starting. From what I have heard, failure of variable displacement pumps is typically not pretty. The only scenario that would typically have a benign failure is the pump being worn out (excess clearance) from too many hours or contaminated oil. My B200 just hit 1500 hours.

Even though I have done a lot of work with hydraulic systems, I simply don't have any experience with hydrostatic transmissions. From what I can gather, one has a pump, a motor and a flow/pressure control valve in between. The Earthforce system has a variable displacement pump with a governer and possibly a variable displacement motor, all of which complicates the system. I don't yet have a manual, but have tracked down a guy on ebay that has them. So I apparently have some heavy bedtime reading coming up soon...

For the last poster: Honestly I don't know the machines history. I bought it from a trucking company, who appear to have either bought it speculatively or took it in trade for a piece of trucking equipment. The machine had 1400 hours on it. Looking at the unit, the only thing that appeared to have done much work was the backhoe. It has by far the most wear. The loader bucket appears to hardly have been used. The bucket had never been removed from the quick change coupling on the loader arms, and the locking pins were frozen in place. This was one issue that was fixed before I took posession. It has obviously sat outside all its life and this has taken its toll on the instrument panel with most of the annunciator lamps lenses missing and bulbs blown. Otherwise, everything worked, the tires were almost brand new.

I will follow the recommendation and post in the construction forum, but others who are having issues with these machines seem to get little or no response - thus the reason I posted in this forum.

 

[RickB]

Actually, you have it backwards. The auxiliary hydraulic pump most likely flows substantially more oil than the hydrostatic charge pump. Therefore the hydraulic functions can seem normal (or nearly so) while the hydro is starved for charge flow if both use a common suction circuit. While it is true hydrostatic pumps and motors can flow quite a bit of oil, they are generally a semi-closed loop within the whole system, so charge pump flow is not all that great. The best you can do is install new filter(s), clean any suction screens, supply adequate quantities of the proper oil and hope for the best.

 

[westcliffe01]

I pulled the screen in the filler to the hydraulic fluid tank to verify total fluid volume. It turns out that the fluid level is just below the bottom of the filler neck. That means that there is about 9 gal in the tank, meaning that when I added 4 gal there was still 5 gal in there. So that rules out the "no oil or low oil" scenario.

I guess I had better wait for that manual and follow the troubleshooting procedure, because this seems to be unrelated to what I thought the original cause was.