MX7 poor design

[pjbci]

The broken bolt came from the hole directly below where the new bolt is installed. It is behind the center mast in the sliding joint. A mx7 is way too heavy to have its entire weight supported by a 5/8”/16mm bolt. The cutter was new last october and has cut maybe 30 acres of pretty smooth pasture. This is the 3rd time it has broken. Have any of you all thrown away JD’s sliding joint and redisigned something else? I can think of a few better ways off the top of my head but want to see if others have already done it successfully. I might just simply replace 1/2”x2 straps (they are bending anyway) that bolt goes through with 1/2x3 and put 1” bolt in it as the sliding bushing groove is 1” wide.

 

[Hay Dude]

Isn’t it also supported by the lower 2 points of the 3 point hitch?
And when it’s mowing, isn’t it also supported by running gear on the ground?
My Deere mowers are tough as nails

 

[K5lwq]

Maybe just replace the straps with chains cut to proper length.

 

[ruffdog]

Bending straps and breaking bolts on a flat pasture? Something isn't set up right. Heck, I mowed for years without even hooking up the top link. Are you bouncing the rear tire on the ground or allowing it to ride on the ground?

 

[pjbci]

Maybe just replace the straps with chains cut to proper length.

That was my first thought. It would certainly be the quickest fix.


Tail wheels always on the ground when cutting, half to three quarters inch freeplay in sliding joint to allow it to follow countour. The guys at parts counter say, we sure do sell a lot of these, referring to the bushing that usually gets lost when bolt breaks. And yes the lower links do support the cutter acting as a fulcrum which puts all shearing stress on this bolt.

 

[KWentling]

If you have more than one top link mounting hole on the tractor, it needs to be in the lowest hole. That position will let the mower follow the ground better and not transfer the tractor weight to the mower when crossing low points.
That may be the cause of your problems.

 

[CalG]

That is a metric bolt by the "8.8" designation.

Go up to 10.8 or even 12 series and I would bet your issues would be resolved

8.8 is equal to a grade 5 SAE designation.

I notice the larger bolt below the broken one is an SAE grade 8.

Might be a hint there.

 

[pjbci]

It is a grade 8 that is broken and replaced with. The 8.8 is the same size with a larger head. Thanks though. I cannot find the 12.9 in 16mm locally.

 

[Zebrafive]

I see the bolt broke in the threads. Try a bolt with a longer shoulder, so not loading the threaded area?

 

[JCoastie]

maybe try a hardened hitch pin?