Confused regarding serial number on my "new" RD4 tractor

Hello Folks,

I recently bought an old RD4 tractor on a chance it would run. Old Gal sat in the field for many, many years because the owner refused to sell it and he had planned on restoring it. Unfortunately the owner suffered some serious health issues and decided to sell the Cat to me. It took me 3 days just to get the machine running. Years old fuel had gummed the fuel systems. The Diesel filters were caked with brown bubblegum type goo. Pony gas tank had flakes of rust in the bottom. Fortunately I live in high desert country with very little humidity and little rain so rust is not a problem. I invested in a gallon jug of Seafoam and went to work.
Drained all the old fuel, took apart the pony motor carb, cleaned it, and got the little rascal to fire up. Oh boy did she smoke, but it ran surprisingly well and settled into a nice idle. Turned over the 4 cylinder diesel with no problem at all.
Oh, surprisingly enough the diesel engine oil was very clean, like it had just been changed, so I left it in the crankcase for the time being

Got all the air purged out of the diesel unit and it eventually fired up, but it sounded like a very unhappy motor. Eventually I got the unit up to my property and put 20 gallons of fresh fuel and half a gallon of Seafoam in the tank. Changed out the diesel filters and took the Cat up a very long steep sagebrush covered mountain in 2nd gear to really load up the engine. Wanted to give the Seafoam a chance to work. Half way up the mountain the motor began to lose RPM and I had to shift into first gear. At this point the motor was smoking a moderate amount from the exhaust stack. I barely made it to the top of the mountain in first gear. Drove it back down and repeated the scenario again. Started up the mountain in second gear, full throttle, and then something happened. The motor grumbled a bit, coughed a couple of times and then began to zoom up the hill in second gear. Smoke disappeared from the exhaust stack. Dang, it felt like I had a brand new motor in that old Cat. The engine sound became totally different, more relaxed so to speak and that all happened within a space of 10 or 15 seconds. Never seen anything like that before. Anyhow, at the end of 3 runs I could pull the hill in 3rd gear under full throttle. Cannot tell you how happy I am with the performance of this Cat.

Now for the dilemma. The front radiator guard has big RD4 cast into the steel frame. Also the tractor looks identical to a 1938 RD4 that a Gentleman had restored and shows off on YouTube. The main diesel however is a 5T5875. I cannot access the serial number on the left rear of the tractor because it has a huge D4N Hyster winch covering that serial number plate, and I ain't a big enough man to wrestle that winch off the tractor. Also in contrast to the nice running main diesel, the pony is a disaster. Leaks oil, burns oil etc. Some previous Dum-Dum took some or all of the pony apart and put it back together with blue Permatex sealer. Its getting a rebuild next spring with as many original Cat parts as possible.

So, Is it reasonable to believe that this old tractor does have this 5t serial number OR is the motor a newer transplant into the old tractor. Any help would be greatly appreciated. Sorry to be so long winded and tell you the life story of my new purchase.

Thank you Gentlemen for taking the time to read my post.
Kindest regards,
Chris

Does the tractor have the small or large final drive bearing hubs? Sounds like someone put a RD4 radiator on a 5T tractor.

Well Sir, the rear drive hub is a square looking affair about the size of a CD case (compact disk). It has 4 bolts holding it on and it has a standard automotive style grease nipple

It is MUCH smaller than the rear hub on my D6-4R which has the much larger specialized grease nipple. I hope this explaination helps.

Thank you Sir for your input.

Since I fairly new at this, how does the rear hub tell the story???

Chris

If it's the 4 bolt style then the motor must have been swapped. The T series had a circular hub like the size of a record.

Well, that is sort of disappointing. I thought perhaps the original equipment would be nicer to have. On the other hand, this little RD4 has lots of get up and go. Much more nimble and quicker than my D6-4R

Thank you, Gentlemen, for taking the time out of your life to answer my questions. I'm sure I'll have more as I get comfortable with this old tractor.

Wish I had something to contribute to the forum, but I have little Cat experience compared to most of you folks. I appreciate all your help.

Kindest regards,

Chris

Hi, Pulpdeth.
If my understanding is 'kee-wrecked', the 4G, 7J and 2T series all had the style of outer track frame bearing that you describe while the 5Ts had the larger round style of bearing. I would guess that your tractor may have had one or more transplants, certainly the diesel engine and maybe the radiator surround. I think the only real way to know what series the main frame is would be to 'wrassle' that 'huge' D4N winch off the back to expose the rear serial #.

Good to hear that another seems to have been saved and that at least the diesel is running well.

Just my 0.02.

Hub size changed part way through 2Txxxx production, the 5T's were all large hub. RD4's (4Gxxxx s/n's) had a different undercarriage that looked like the attached picture. Radiators could be swapped as well as undercarriage. Not very likely that 4G undercarriage would be swapped to later units so that might be a good indicator.

Hi pulpdeth,
When i put the 2T back together this to had a winch, i noticed that Serial Number tag had been moved from it normal place top LHS of the back to the bottom middle a place where the winch dose not cover so you may find it there as per the photo.

Yes Sir, my undercarriage looks identical to the one in your photo. Thank you kindly for posting the pic.
Chris