New to me RD4, also my first Cat.

it appears to be a rd4 1936 year--check the blade valve linkage for binding--also the steering clutch linkage

Welcome, nice ole tractor.

Go easy on the that control linkage!!!!! What typically happens is the control shaft at the #44 unit drops down and binds the linkage inside the tank. Can cause some real damage to the linkage internally which has probably already occured.
  [attachment=62637]Float Linkage #1.jpg[/attachment][attachment=62638]Float Linkage #2.jpg[/attachment]
 

Probably needs the hyd oil and filter changed anyway. Service manuals can be found on ebay, check the serial #'s

Welcome and congratulations, that's a nice looking tractor, and a early production run one too, 1936 was the first year of production, looking at your photo's the track frames have been replaced with track frames from a later model D4, like a 7J or 2T/5T, the top carrier rollers are different to the early RD4. 

You might have later model track frames, or someone fabricated a mount for the newer rollers, or someone dropped a RD4 motor and radiator onto a later transmission, have a look at the back of the tractor, on the left side there should be a second brass serial number tag, if it is a different number to the motor, let us know.

Either way, keep that in mind if you need parts for your track frames at a later date, just double check what you have there, before buying anything, because there are often subtle changes over models with things like track frame dirt guards and recoil spring mounts.

The RD4 are a nice tractor to drive, I use mine to disc fields every year, they really bark with a straight through exhaust! Remember to turn the gas off on the pony motor to stop it, don't use the ignition switch.
Good luck
Mike

I pulled the cover off of the HCU. After disconnecting the rod that heads back to the operator station and disconnecting the spool from the vertical shaft that goes through the case. I found that the spool seems free and the linkage seems to be in place. That heavy vertical shaft seems to be froze up. 
As for the steering lever, I took the cover off at the base and found the hinge to be rusted. A little Weasel piss and working the lever, she's free!  
When the blade was installed, did they burn off the front carrier roller? The rollers do look like newer style. 

I pulled the cover off of the HCU. After disconnecting the rod that heads back to the operator station and disconnecting the spool from the vertical shaft that goes through the case. I found that the spool seems free and the linkage seems to be in place. That heavy vertical shaft seems to be froze up. 
As for the steering lever, I took the cover off at the base and found the hinge to be rusted. A little Weasel piss and working the lever, she's free!  
When the blade was installed, did they burn off the front carrier roller? The rollers do look like newer style. 

Track adjustment is on my list. It could use a set of rails. The bushings haven’t been turned, but quite a bit of internal wear.
I’ve changed the oil in both engines. The rest of the fluids are on my list too.