Brand new 1735M broke after ~3hrs of use. Is this a freak occurrence?

[JWR]

That nice sharp, stepped shoulder machined into the hole doesn't help either.

MF list the front axle as cast steel, haven't found any info on rear axle material.

I'm not so sure. I have mixed feelings about the ribbed post. That design allows one to tighten the post while maintaining solid contact in the hole without depending on washers or external landings on the post. If it were threaded all the way thru the hole you lose solid contact internal with the casting. No matter, there are larger issues. The OP just has to let the dealer either repair the tractor or replace the whole darn tractor which I think is the right thing to do with 3hrs on it (!)

While there are MANY tractors & brands with the single end supported pin/anchor for the lift arm, the others I have seen (incl. my own 'Botas) have a much thicker, heavier pin AND the support material is mild steel rather than cast. Bends instead of breaks. I think MF made a mistake in that design. The casting looks plenty heavy but experience proves that wrong. We will never know how many units have failed but it is NOT rare. As a practical matter, I'd like to see AGCO/Massey come out with a retrofit kit that bolts on to provide two sided support for a heavier pin.

 

[TMGT]

I'm not so sure. I have mixed feelings about the ribbed post. That design allows one to tighten the post while maintaining solid contact in the hole without depending on washers or external landings on the post. If it were threaded all the way thru the hole you lose solid contact internal with the casting.

Main issue I was referring too was the sharp edge of the step which will create a stress riser, just not something I'd want to do on a more brittle cast peice.
I'd prefer to see more radius in that step.

 

[JWR]

Main issue I was referring too was the sharp edge of the step which will create a stress riser, just not something I'd want to do on a more brittle cast peice.
I'd prefer to see more radius in that step.

Wow, I really disagree with you there TMGT! Any radius or slope ( instead of a land or machined flat ledge in the post ) means that the more you tighten the nut on the post the more the outward expansion force on the cast material. Exactly what you want to avoid.

 

[TMGT]

Wow, I really disagree with you there TMGT! Any radius or slope ( instead of a land or machined flat ledge in the post ) means that the more you tighten the nut on the post the more the outward expansion force on the cast material. Exactly what you want to avoid.

There shouldn't be contact at the step, you want the compression load spread across the full tab, not just the smaller OD where the threads pass through.

 

[JWR]

There shouldn't be contact at the step, you want the compression load spread across the full tab, not just the smaller OD where the threads pass through.

No, the compression load from the stud/post should be rather small compared to the seriously larger load borne by the pin/post 90 degrees from that force inward/outward from the tractor. But small as the compression load is on the post, you do not want it to contribute by inclined plane or other angular transmission to the spreading of the hole. A slope (rather than a flat go/no-go machined rib) has the potential for multiplying the "nut tightening force" into bad news outward expansion force in the hole.

 

[TMGT]

No, the compression load from the stud/post should be rather small compared to the seriously larger load borne by the pin/post 90 degrees from that force inward/outward from the tractor. But small as the compression load is on the post, you do not want it to contribute by inclined plane or other angular transmission to the spreading of the hole. A slope (rather than a flat go/no-go machined rib) has the potential for multiplying the "nut tightening force" into bad news outward expansion force in the hole.

If your using the the step to as a stop then yes you wouldn't want a radius, however ideally it should be clamped through the entire tab and if there is a step there should be a radius without contact between the stud and tab at the step.

If they are using a slip fit pin with the step to create clamping load then that's an even worse design then I thought.

I'm guessing that's more of a cost/manufacturing decision then a engineering one since it reduces material loss and machining requirements.

 

[JWR]

I'm sorry TMGT. You lost me. I do not understand. English fails us in trying explain/describe without pictures and without face-to-face time. My understanding would not solve the 1735 owner's problems anyway.

Will be interesting to see the outcome.

 

[TMGT]

I'm sorry TMGT. You lost me. I do not understand. English fails us in trying explain/describe without pictures and without face-to-face time. My understanding would not solve the 1735 owner's problems anyway.

Will be interesting to see the outcome.

I agree, it's hard to explain things via text for me a lot of times.
I use to do some failure analysis and studied material science for a bit both in college and on my own. It is a subject I really enjoy, but outside of a full on technical report (which I'll spare you from here!) it's hard to explain.

Also everything is conjecture here without the parts in hand and doing some testing.

 

[JWR]

I don't think anyone is saying all single shear designs are bad, however in this application it is.

Topic being 3pt lower arm mounting designs: I mentioned earlier that my 'Bota B2150s use a single end supported pin but the pin is much thicker and mounted in mild steel rather than cast metal. Had ocassion to look at a few Deere models yesterday. The 3039R is roughly the same weight and HP as the Massey 1735. The 3039 uses a pin supported on both ends and looks to me like you could dangle the tractor on it with no damage. Very strong. View attachment 661259



Meanwhile I looked art a much smaller Deere, the 1025R which is half the weight and 23HP. The 1025 has a custom oddball pin , not very heavy, that hosts the lower lift link on one side and the sway bar on the other side of fairly heavy mild steel (not cast) material.

If the competition matters, the MF 1735 lower lift arm anchor seems light and under designed. Tends to make a case for a retrofit kit of some kind to beef up the support.

 

[Motorboatin]

Topic being 3pt lower arm mounting designs: I mentioned earlier that my 'Bota B2150s use a single end supported pin but the pin is much thicker and mounted in mild steel rather than cast metal. Had ocassion to look at a few Deere models yesterday. The 3039R is roughly the same weight and HP as the Massey 1735. The 3039 uses a pin supported on both ends and looks to me like you could dangle the tractor on it with no damage. Very strong. View attachment 661259

View attachment 661263

The Deere 3039 has an aluminum rear housing

It looks strong but no wheel spacers are offered because it can not take the stress