Cat 279C - Aux Hydraulics - Is this normal or is it broke?

[GaryBDavis]

I have a Cat 279C skid steer. I bought it used and it's been great. I thought nothing was wrong with it until I used a buddy's 289D to drilling post holes. When I put down pressure on the post hole auger with my 279C, it will stall the auger when I get down deep in the hole. But on my buddy's 289D, it never stalls the auger. It applies what seems to be full power to the auger when pushing down with the FEL whereas mine seems to run out of aux power.

So, my skid steer doesn't apply full power to the auxiliary circuit when applying down pressure with the FEL, but his does. So is there something wrong with my skid steer or is there a design difference between the two machines? Maybe I have a bad relief valve or something like that. Or maybe there's an updated hydraulic divider valve in his.

 

[Xfaxman]

First step is to check the pressure at the aux connector, then check the operating pressure when PHD is digging and when stalled.

This is what I put together. It can be turned around to plug into either connector:

Plugged into the aux connector, showing max pressure with relief valve open:

Plugged inline with the brush hog, showing operating pressure when blades are spinning:

 

[oldnslo]

What is the operating pressure of your 279 vs buddy’s 289. Cat may have updated the hydraulic pump and increased the operating pressure on the 289. I believe some newer skid steers run 4,000 to 4,500 PSI while older machines might not reach 3000 PSI

 

[Silvic]

I don't disagree with checking the pressure but the first thing I would consider is the flow rate.
i.e. what is the max gpm of the hydraulic pump on the units.
Does one have a high flow option and the other only low flow?
Even if both are low flow what is the low flow gpm difference if any (probably very close if both low flow).
I would suspect that the 289 has the high flow option and the 279 does not.
Checking the pressure though is a good idea.

 

[GaryBDavis]

They are both low flow machines and rated about the same with regards to hydraulic flow. When I used the 289D, it performs about the same as my 279C. I use the same implements with both - stump grinder, shredder/mulcher and post hole digger. I really don't notice any difference between the two when operating these tools except the aux flow when using down pressure.

I could test the aux pressure/flow but I already know it drops when I use down pressure. I need to know if this is a design difference between the two. I called the local CAT service guy said he would have to check with the engineers. I figured he should know off the top of his head if a 279C was supposed to loose pressure/flow when down pressure is applied.

 

[Xfaxman]

When you apply down pressure it makes the auger harder to turn, which increases the aux pressure.

With the auger not touching the ground, try blocking the down movement with a chain to a tree limb and apply down pressure to see if it stops spinning.

 

[Rustyiron]

The same auger drive? The better units are a planetary set up where the motor/chain & sprocket is more of a "basic" unit.