Hi everyone: Recently picked up a D4D with CAT hydraulic system; one control lever for the blade and two short levers for auxiliary valves. Blade lifts and lowers with down pressure okay, but does not hold in position, in other words you raise the blade and it comes down on its own quickly. Safe to say I have a valve issue at the control or???
Have not tried hooking up the rear couplers to a disc or implement to test that portion yet.
Any pointers? I’m hoping it’s something simple.
TIA, JM

"juiceman" wrote:

Hi everyone: Recently picked up a D4D with CAT hydraulic system; one control lever for the blade and two short levers for auxiliary valves. Blade lifts and lowers with down pressure okay, but does not hold in position, in other words you raise the blade and it comes down on its own quickly. Safe to say I have a valve issue at the control or???
Have not tried hooking up the rear couplers to a disc or implement to test that portion yet.
Any pointers? I’m hoping it’s something simple.
TIA, JM

Sounds like a problem with the hydraulic relief, probably a little dirt or a piece of o ring stuck in it

Your problem could be in the valve or it could be in one or both of the cylinders. Cylinder piston seals or piston “end of travel relief “ valves if it has them.

You might be able to shut the engine off and listen for oil bypassing to locate the site of the problem. Or you may have to put a jack under the blade and then block off the cylinder ports before letting the jack down to test things. If you go that route, you have to isolate the cylinders since one leaking will allow oil to equalize and both will retract.

Cylinder piston packing would be my bet since they are sort of a wear item. Made to be replaced as they wear out. Control valves......not so much.

"b.sankey" wrote:

Sounds like a problem with the hydraulic relief, probably a little dirt or a piece of o ring stuck in it

Thanks Mr. Sankey. Time for me to find my book and start reading. Might have to drop it off at Rusty’s, so he can get away from the house!
The only other thing wrong is it has the small motor, but I decided it needed rescuing. JM

"ccjersey" wrote:

Your problem could be in the valve or it could be in one or both of the cylinders. Cylinder piston seals or piston “end of travel relief “ valves if it has them.

You might be able to shut the engine off and listen for oil bypassing to locate the site of the problem. Or you may have to put a jack under the blade and then block off the cylinder ports before letting the jack down to test things. If you go that route, you have to isolate the cylinders since one leaking will allow oil to equalize and both will retract.

Cylinder piston packing would be my bet since they are sort of a wear item. Made to be replaced as they wear out. Control valves......not so much.

Thanks CCJersey. I’ll let one of my wrench guys deal with it most likely, but I do have the service book, so I should read up and learn from it, and follow your advice as well. JM

A old time way of testing if it is the ram's packing leaking is when the ram is cold lift the blade and put you hand on the ram. If leaking by a lot of oil you should feel heat building very quickly.


Much easier to rebuild the ram packing than sealing most valve bodies.

Just a little update on the D4D. Steve sent the pump/tank to Holt, where they did find a broken spring for the relief valve. I got it out of there for a few hours worth and minimal parts.
The service order stated that that might not be the entire issue, as they did not have access to the hydraulic cylinders on from the machine (good mechanic I think). He was correct, as it turns out BOTH rams had very badly chewed up seals. I suppose I should have not gotten lazy on my end, and tested the rams first? Oh well, I have a nice working CAT now, so nothing to gripe about on this tractor. I can't wait to try this one out with the SD #40 scraper, which is in the process of sandblasting, primer and bling bling "old Cat yellow".
I want to thank all of you for your input, as it was all good!
Regards, JM