3 Point Hitch

[WVBill]

Newbie question:

How do the "innerds" of a 3ph work? What mechanism raises the lower link arms? Since there are no hydraulic cylinders visible outside, there must be the equivalent inside the tractor's gear case, right?

At first I thought that maybe the lifting mechanism was completely mechanical (e.g. eccentric cam and lever or something) but since there is clearly the sound of hydraulic relief valve operating at the top of the lift, it must be hydraulic. - meaning that there must be a hydraulic pump in there too.

Since my tractor is a gear type, I put gear oil into the transmission not hydraulic oil so I guess this 3ph hydraulic system uses gear oil not hydraulic oil.

I have no real reason to ask this other than I want to understand my tractor (Kubota B6100DT) better and there is nothing in my Kubota Operator's "Manual" about it at all.

Thanks

Bill

 

[Bird]

WVBill, I'm not very familiar with your tractor model, but yes, there is an internal hydraulic cylinder that raises and lowers the 3-point lift arms.

Bird

 

[gordon]

Here is a good page that goes into detail on the basics of the three point hydraulics http://members.aol.com/naa60512/hyd.htm
Hope this helps
Gordon

 

[TomG]

Most all tractors with hydraulics only have one pump (excluding the HST pump). The pump is usually on the side of the engine, and everything is powered through pipes, lines and valves--basically plumbing. Oil flows continuously in an open centred system, which you probably have. Oil is drawn from the reservoir to the pump, through a priority valve for power steering, through lines and open centred control valves and back to the reservoir. What happens when a loader or 3ph lever is operated is that the valve centre is closed, and oil is diverted to a cylinder. The pressure pushes the cylinder until the valve is released, or the cylinder reaches its limit and the relief valve opens.

Loader hydraulic cylinders ordinarily are double acting. They power in both directions. Double acting cylinders have two lines, one for each side of the cylinders. Pulling the control valve for a cylinder sends pressure to one line and opens the other to provide a return for oil on the other side of the cylinder. Pushing the lever reverses the pressure and return lines.

Almost all 3 point hitches are single acting and most have position control. They use hydraulics to lift, but gravity to lower. With position control, the hitch raises or lowers to a pre-determined level set by the 3ph control lever. A hitch where the control lever is set lower than ground level is said to be 'in float.' Most hitches have a flow control valve in the return line. The valve controls the speed of drop when the hitch is lowered. Other than the hydraulics, you might come to grips with hitch terminology like position control, draft control, float and several other terms. Getting a repair manual is good for understanding tractor workings.

 

[Bird]

TomG, very good description! Subject thoroughly covered in relatively few words; something I'm not so good at./w3tcompact/icons/frown.gif

Bird

 

[TomG]

Thanks. I think that' few words' is something you're usually much better at than I am. When I click back on some of my comments, I realize that I do run on a lot. In this case I was probably saved from too many words. I started mentioning 'power beyond,' and then realized that it's something I don't know much about, so I didn't comment.

 

[hayden]

Gear oil in the transmission? This could be a real problem. On tractor's that I'm familiar with the rear gearcase acts as the hydraulic oil resevoir, typically holding several gallons of the stuff.

Does your tractor have a separate gear box that takes gear lube in addition to the rear gearcase?

Be sure you are not putting gear oil in where there should be hydraulic oil. If you have, drain it all out and replace with the correct oil and replace the filter.

 

[scruffy]

Bill, on the L175, and several others of the geartype persuasion, the hydraulics and transmission share the same resavoir (sic), which is the transmission. It calls for (by the manuals)23 Quarts of SAE 80 weight gear OIL.

<P ID="edit"><FONT SIZE=-1>Edited by scruffy on 10/15/00 10:58 PM.</FONT></P>

 

[WVBill]

Thanks to everyone for your responses.

With your descriptions and references I was able to decipher the parts manual for by B6100D and figure out how the system works.

One of the things that made me think to ask the question is that everyone seems to be talking about Hydraulic fluid in their transmission - which is obviously the case if you have an HST.

In a B6100D gear transmission, the transmission/gear case takes SAE 80 gear Oil. Only other fluids that go in the tractor are Engine Oil and Water/antifreze. The only place on the tractor that uses Hydraulic oil is the FEL and it's system is completely separate from the tractor.

The piston that raises the 3ph must operate off of the gear oil. (only alternative would be the engine oil). I couldn't tell for sure from the parts manual, where the pump that supplies the pressure is attached to the engine.

I have the shop manual on order - maybe that will help clear things up.

Thanks again.

Bill

 

[W5FL]

MOST tractors manufactured in the last 25 years use a Universal Tractor Fluid (UDT in Kubota) that is both a gear oil for the mechanical transmission and a hydraulic fluid for the 3 point and loader. There were indeed a few tractors built with completely seperate transmission and hydraulic systems, but that was not the rule. Normally the same pump is used for the front end loader hydraulics and the hydraulic actuator for the three point (and for the power steering where a seperate pump is not provided). I have a Kubota M6800 and it uses only UDT for the mechanical transmission and hydraulic system as did my 20 year old Massey Ferguson as do all John Deere tractors that I have used.

p.s. How much hydraulic fluid does the seperate FEL hydraulic system hold?