D4 hydraulic question

Since you are going to put new hoses on it, it would be relatively easy to completely drain the system. I would drain the tank then pull the front cover off to inspect and clean the interior, Cat still has the gasket, don't know about the filter, I would also pull off the hydraulic cylinders and position them so they can drain completely, it may take a couple days of tipping them back and forth and allowing them to drain, trying to flush out a partly filled contaminated system is nearly impossible to really get it clean.
That four hole plate on the bottom is where the filter lives.
The seal where the control lever shaft goes in to the top of the unit, is often where water gets in and may need to be replaced.
If you post the serial number of the hydraulic control unit, we may be able to tell you which filter it uses.

A couple other notes on the hydraulics, the filtering system is not a full flow system, it only filters a small portion of the flow, most of the oil just bypasses the filter and the system relies on crud settling out at the bottom of the tank and the two drain plugs on the bottom have magnets on them to collect metal.
These hydraulic units can last a long time, but it is critical to keep them full of clean dry oil.

Josh - This is very helpful information. I didn't want to start removing nuts & bolts without understanding the system a bit more. What is the capacity of the tank? I'm guessing i can expect a few gallons of drainage to be prepared for...?

Regarding the cylinders, do you see a problem with rinsing with diesel? I can't see an issue with the seals, but i've been wrong before.

Thanks for the education!

 

Rinsing with diesel should not be a problem, the tank holds 5 gallons, maybe another couple more in the cylinders and lines.
The only way water could get in is through that seal or if the fill cap is off.

Thanks! FYI - the serial number on the hydraulic unit is 7V-6900. Possible to find the seal part number along with filter based on the serial number?

Would the part numbers be in the D4 parts manual? I just purchased the parts, operator and service manual which should be in my possession in a week or so.

Thanks
 

That Hydraulic control unit uses the 2A5886 filter element, which is available and cheap, and the seal is a 5F1677.

Todd -
You need Form 31677-1, Operation and Maintenance Instruction - No. 44 Hydraulic Control:

  [attachment=69080]no 44 hydraulic control form 31677 1.jpg[/attachment]
 
You may also want Form 32856, No. 44 Hydraulic Control Parts Catalog:

 [attachment=69081]no 44 hydraulic control parts form 32856.jpg[/attachment]

The D-4 tractor book does not cover attachments like the # 44.

Will

Gasket is 4F4217, Parts catalog that covers 7V6900 on a D4, form 31264 and there are others.