I have also heard that the 400 and later models had weak rear axles. I believe they are the same ones used in the H's and they say if you pull to much you can twist one off. I never wanted to find out, I doubt I would have much trouble for the amount of land that I'm working with.
My neighbor (good friend) has a old trip 2 bottom plow, it has been sitting in the weeds behind her shed for probably 10 years. Her husband used to use it on their garden until he passed away. It would be to small for the 400 but it would be quicker then the single bottom on the Kubota.
The 400 was a direct descendant of the M. The 300 was the descendant of the H.
The lineage went like this: H, Super H, 300, 350, 460. The bigger tractor was M, Super M, Super MTA, 400, 450, 560.
The transmission issues came in to play around the 450 era. The basic original "M" transmission was still being used in it and later in the 560. The M was originally around 36 horsepower and now by the 450 they were feeding 51 horsepower through the same drivetrain. By the 560 they were pushing 61 horsepower through it. Almost double what it was designed for.
It was a similar story for the H transmission. The H started life with 24 horsepower. By the 350 it was up to 39 horsepower and by the 460 it was up to 50. More than double it's original design.
When the 460 and 560 were put into service doing heavy tillage work failures started to become a big issue and IH responded with updates to the machines to change out some bearings in the transmission and differential to correct the issues. Once the bearing changes were made most tractors lived a reliable life after that. Machines that were early production that required the update had a triangle stamped into their serial number tag and were considered good. Machines from the factory after the updates were equipped from the factory with the revisions without the stamp on the serial number tag. The 660 was also included in this as well because it was still basically the M transmission however it used a planetary final drive to help bear the load going through the transmission. In this case they were feeding 80 horsepower through the transmission. Well over double it's original design.
From the beginning of M production through 560 production there were many tractors that experienced axle failures when used year in and year out with a mounted corn picker as it put a heavy load on the tractor. Mounted pickers are probably the roughest job that tractors had to endure.
Now our "M" had a Super M engine kit put in it back in the early 70's and the last it was dyno'ed it had around 54 horsepower. Back in the 90's we had a clunk develop in the rear end of it. Upon taking the top cover off we found that the ring and pinion case that holds the spider gears had every single bolt loose and the housing had cracked in several of the bolt holes and had put chunks in the bottom of the differential case. So many many years of prolonged heavy use are detrimental to them and should be avoided if possible. It's always a better practice to select a smaller implement and use a gear higher to get the same work done with less strain on the tractor.
Not knowing the past of your machine and how it was used I would take it easy on it to start. I would venture to guess it lived a life pulling heavy loads with those big weights on it.
Edited by IHCubGuy, October 10, 2016 - 10:48 AM.