why is the axle weak?

Just out of my own curiosity, what makes the front axle weak on an N series? Is it the axle segments, the support or just the whole assembly? All of Ford's tractors used similar setups through the hundred series. What's the deal with that?

the kingpin, bolster,radius rod setup is weaker than say.. the front bolster and axle setup you see starting with the 65+ 4000+ ( non SU ) machines.

Though I do like the front axle on a ford rowcrop wide front frot end. I think it's a step bette rthan the ag axle setup..

Lightweight axle on a lightweight tractor.
Nimble, powerful for their size, reliable.
But put a loader on them and you will wear them out.
Compare them to the heavy axle on a late Hundred Series Industrial - first pic, or the later Ford front axles - second pic, and you will see why.

i love them hubs on the industrials..

So pretty much the stronger axles use a solid beam or heavier tube steel with larger hubs. Anything else I'm missing?

A simple material stress check of all the components of the front end on the N series shows the maximum stress occurs in the center axle part at about 2 1/2" from the vertical centerline.

Since the part is sand cast steel, the allowable material strength is reduced compared to cold or hot rolled steel or forged steel.

Doing the numbers based on the knee extension in the most narrow position, the front end is good for about only an extra 420# of static load.

With a front end loader the extra weight of the steel frame, bucket and payload is bouncing, which creates a dynamic applied load rather than just a static applied load.

Replacing the center axle with a 2" X 4" X 1/4" wall structural steel tube would increase the allowable dynamic working load to ~ 1475#.

The gap in the center support weldment is 2 5/8".
Believe the a 2 1/2" X 4" x 1/4" structual steel tube will fit.
Using this size of member, the allowable dynamic working load would increase to ~ #1840.

The center king pin has slightly more than 1" sq. in. of cross section. This part is far from the weak link, stress wise , but wear on this part causes undo stress on the radius rod, as witnessed from bent radius rods.

A typical front end loader scoup holds
~ 1/2 CU YD volume.
Some research indicates the weight of dry gravel is ~ 2835 #/ CU YD and maybe more depending on the water content.
So, 1/2 CU YD weighs ~ 1417 #

Based on the design of the front end loader, only some fraction of the loader weight and payload weight is taken by the front end axle.

If 100% of the extra weight is taken up by the front axle,

This would make the original N series tractor totally worthless to load gravel, maybe compost.

If reto fitted with a 2" x 4" x 1/4" steel tube, would be marginal to load gravel

If reto fitted with a 2-1/2" x 4" x 1/4" steel tube, might be acceptable to load gravel.

N series Fords were designed and built many years before front end loaders were invented.

Believe the N tractor was originally designed to pull a two bottom plow in soft dirt?

Bulldozer........great analysis........Dell

(quoted from post at 10:31:43 01/26/13)
Replacing the center axle with a 2" X 4" X 1/4" wall structural steel tube would increase the allowable dynamic working load to ~ 1475#.

The gap in the center support weldment is 2 5/8".
Believe the a 2 1/2" X 4" x 1/4" structual steel tube will fit.
Using this size of member, the allowable dynamic working load would increase to ~ #1840.

Click to expand...

If all you want to do is beef up the center axle why not use solid flat bar with approximately the same or even a slightly larger cross section as the cast axle? It can be easily bent to match the cast OEM axle and won't create a whole bunch of geometry problems.

Unfortunately I don't think that would help much. In practice most of the loader induced damage does not occur in the axle member itself. The failures we commonly see are cracked oil pans, hogged out, bent, or broken axle supports, badly worn axle pins, bent radius rods, and/or damaged wheel bearings/bent spindles. Fractured center axles are rare. Damage to them is usually a badly hogged out center hole at the pivot point which can often be repaired with a sleeve. Exceeding the design loads on the front end causes excessive wear and damage to all of the components - not just the "axle".

TOH

I might be bucking the tide here Wes, but I don't think they're weak.
I think they're abused, and they've held up to that abuse for 60+ years.
Guys throw a FEL loader on there and the next time they grease anything is
when the wheel falls off or the center pivot is so worn that the axle cracks a
distributor cap.
To fix that, they weld a nut on top of the axle so it can't move that far.
They are lighter duty than the newer models, no doubt there, but they've
been around far to long and held up to many uses they were not intended
for to be classified as "weak" in my book.
Good preventive maintenance will keep one in service for another 60 years.

Not true, there were front-end loaders available in the 1920s, including ones specifically designed for the early Fordsons. Did not have hydraulics though, it was cables and winches those days. For one example, look for Lessmann loaders in the Vintage Ads section on the left under Galleries.

Do not believe there is much wear to the axle.
The wear occurs on the king pin and king pin bushing causing bending of the radius rod.
The bushing and king pin should be on the maintenance list, since the load is applied as a single line load, which creates high contact stress on non hardened steel material and accelerates wear.

Do not believe the axle is weak for the loads it was originally designed to handle and has ample safety margin.

In my opinion the axle is under designed for front loader add on accessory.

Royse & everyone else,

I'm not agreeing or disagreeing on the suitability of these
tractors for various tasks. I've just never seen a collective
discussion/opinions as to why & what the flaws are for the
axle. It's better than getting not suitable, or to weak without
much of an explanation as to why. There's a vast amount of
knowledge/experience here, on this board. I'm an inquisitive
person that likes to know the reason behind things. And
sometimes my curiosity gets the better of me. So, thank you
everyone for your knowledge, I do greatly appreciate it.

Please read my previous post on the front axle strength.

The numbers will show that the front axle is not safe for extra vertical loads from add on implements applied at the center axle pin hole for load over 400#.

That is the basic reason.

Imagine the result ,if the front axle fractured from lifting a load of gravel with the bucket in the fully raised position.

In my opinion the front axle is not inherently weak for the original purpose of the tractor.