looking at tractordata
TractorData.com Kubota L3540 tractor information
what are you doing that requires taking the FEL off? the FEL itself is counter weight on the front.
seems like a lot of micro managing, trying to wiggle tractor into tightest spots possible. and guessing only for a couple spots. that one could reverse/forward a couple times and get done, due to dealing with FEL sticking out in front. vs jacking around taking FEL off and swapping in/out weights on the front.
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no FEL and extra weights + grill guard for weights = cheaper setup when buying unit used, and guessing tractor would only see things on 3pt hitch and/or pulling stuff.
vs
the FEL + grill guard for it = more expensive setup, when buying new. front weights + FEL on at same time = reduced weight FEL can lift up, without damaging the front axles and snaping/bending something.
i could see wanting to add some weight to the front, and reduce how much the FEL stuck out in front, when operating some 3pt hitch stuff. but... question is are you just wanting to spend money, due to it is burning a hole in your pocket or other? the only real thing i can think of, is if the tractor gets multi purposed, in spring/fall = field work. summer/winter multi task tractor. field work being the key issue, everything else i am kinda scratching my head about extra work pulling FELL off at all. maybe disconnect bucket from FEL. and create a custom weight that mounts to FEL? (instead of a 3pt hitch custom weight, a FEL custom weight). or strapping some weight into the FEL bucket.
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custom weight box, for FEL, remove general duty bucket, measure the brackets and hole locations, goto a local metal fab shop to get some brackets made up, and build a plywood box put in some rebar, and fill with concrete.
View attachment 402398
a reminder on grade school levers / fulcrums / a kids tetter totter... the further out the weight is in front, the more force it has to hold down the front wheels. 100lbs, 10 feet in front, vs 1000lbs 1 foot from front, type of thing.
the lower you can place the weight, the more you can lower the COG (center of gravity) of the tractor. other words weights at or above axles = more likely tractor tipping over, weight below axle's = less likely tractor to flip over.
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lower your tire pressure in your tires. no need to run at max PSI. 10 to 15psi, get that traction.
fill rear tires with a fluid, see if operators manual for tractor suggest filling front tires or not with a fluid. for additional weight.