Cat D-4 Hydraulics and engine oil cooler

I have a Cat D-4 SERIAL#7U25926 w/dozer blade.I just purchased it recently and it is a very new experience for me to work on since most tractors I have restored didn't have Hydraulics.I found the drain plugs and filter on the Hydraulic tank and drained the oil and filter.The filter#7f7238 unavailable at local part stores,Does anyone know of another part# That would interchange? The oil (fluid) that came out of the hydraulic tank was milky and sludge was on the filter.Does the hydraulics on this D-4 get engine oil or Hydraulic fluid? Also the lift worked somewhat good considering the oil and filter that was in it and had enough power to push down and lift the front of the crawler off the ground but leaks down as soon as the lever is released.Are there any seals,O'rings in the hydraulic unit that could need replacing? There are no major leaks that I can see on the cylinders, hoses or hydraulic unit. The engine oil cooler has a major leak so I have decided to try and bypass it.There is a plunger and spring inside the bottom side of the engine oil filter housing.If it is removed can you just plug off the inlet and outlet on the oil filter housing? Is the engine oil cooler necessary to run? Any help will be very much appreciated,Thanks

CAT has that filter. Hold onto something when you ask how much. If you find another source or a work around to use another, Please post it!

It is likely that the water came in around the control shaft through the seal there. You may also want to open the thing up and clean the sludge out of the bottom of the tank while doing the seal.

If the lever is returning to the hold position properly, it is most likely you have a blown piston seal in one or both of the cylinders. If you can hold the tractor up without bottoming the pistons in the cylinders and keep it there for a while when you first start up and the oil and cylinders are cool, the leaking cylinder will normally get hotter than the good one due to the high pressure oil bypassing the piston. You may also feel the lines vibrating from the fluid passing through or hear it if you stop the engine and let it leak down. If you bottom the pistons in the cylinders, a piston relief valve will be forced open and the oil circulate through the good cylinder as well as the bad one.

Other than that, you can raise the blade and place it on a raised jack before isolating each cylinder in turn. Plug off the ports and then lower the jack and the control lever and see how well the isolated cylinder holds.

You can either loop the oil cooler lines back together in front if the filter base or plug them off. It is probably easier to loop it back together with copper pipe fittings or a hose and clamps than finding proper plugs and removing the bypass valve. The cooler is unnecessary with today's oil formulations being a lot more stable to heat. Many of the old tractors don't operate hot enough anyway if the radiator isn't stopped up. You need an operating thermostat in it to get it up to temperature and keep it there.

I assume you have the No. 44 hydraulic unit on your machine. It origionally took 10 weight crankase lubricating oil, but any good modern hydraulic oil should work. It will also work well with 10 weight non-detergent oil if you can find it. Heavier oils will not flow well in colder temperatures. The hydraulic reservoir is on the front of the machine and should fill on the left side. It does not share a reservoir with the diesel engine. I suggest that you refill the reservoir to the top of the filler opening and then cycle the hydraulics to get the air out of them and see if you have any leaks. The control lever will not stay engaged without applying force so it's normal for the hydraulics to bleed off if the lever is pushed forward and then released. It's more common for leaks to happen in hoses and cylinders then in the rest of the unit. Be careful not to touch the hoses with a bare hand as a crack can inject oil into your blood stream. Even an old D4 produces a 1000 pounds of hydraulic pressure. It sounds to me like your hydraulic system just needs a little oil and a new filter. CAT recommended changing the oil every 800 hours. Good luck.

Thanks D4 Doug and CC Jersey for the advise,I have decided to go ahead and change the Hyd hoses and clean out the hydraulic system as good as possible.I took the cover off the reservoir to clean it out the best I could.It looked good considering the watered down oil that came out of it but did have some sludge build up in the bottom.I called Yancey today and sure enough they do have the filter for the #44 unit for around $78 I guess it must be made of sterling silver because they are proud of the little jewel.The hydraulic hoses were a pain to remove at first but I finally use a high speed cut-off wheel to carefully cut into the steel braided lines long ways just enough to split them with a screwdriver and slip them off ridged steel line.If anybody tries this be very careful not to cut into the old hydraulic line too deep and ruin the steel ridged receiver line.I guess most of the d4's have this kind of hydraulic line connection because mine looks to be pretty much original I'm guessing.Well hopefully I will have it back running in a few weeks,Thanks again for the advise