48" Braber rotary mower cuts better on Bolens G174 than on Kubota B7510 HST

[Rod in Forfar]

I recently put a couple of tanks through the Kubota B7510 trimming around 15,000 tree seedlings with the 48" Braber rotary cutter. As long as the grass wasn't too long it did a good job. When I tackled a one-acre hay plot, however, it did a lousy job. The tractor's wide turf tires flattened about a quarter of the hay and the blades tore up the rest. At the time it didn't look too bad, but five days later I couldn't stand the mess any more and re-did the job with the 5' Rhino on the 35 hp TAFE.

Up until now I have blamed the crappy, off-brand 48" mower. The blades seem shaped improperly on it, pushing the grass down, rather than drawing it up.

With its ROPS the Kubota is too high for work under young walnut trees, so today was the turn of the Bolens. Normally I use 1st gear HI for mowing, but the hay was too heavy. We crawled around under the trees in 3rd LO with the PTO in 2nd gear. The "crummy" mower did a surprisingly good job.

If the increase in pto revolutions from 540 to 750 on the Bolens produces a major improvement in cut, could it be that 48" mowers turn too slowly with a standard, 540 rpm shaft such as the Kubota's? Simple geometry would suggest that the same gearbox used on a 4' will only deliver 80% of the tip speed it will on a 5' chassis.

 

[Rod in Forfar]

I've done some looking at parts diagrams. The 40" and 48" rotary mowers should have a steeper gear ratio than the 60" and 72" machines. The standard 40 hp rated gearbox runs at a 1:1.4 ratio. That's for the larger cutters. The correct one for a 48" is 1:1.9. The Braber I bought must have the 1:1.4 ratio and thus it works much better on the 750 rpm PTO of the Bolens than the 540 PTO of the Kubota.

 

[Capricious]

I've done some looking at parts diagrams. The 40" and 48" rotary mowers should have a steeper gear ratio than the 60" and 72" machines. The standard 40 hp rated gearbox runs at a 1:1.4 ratio. That's for the larger cutters. The correct one for a 48" is 1:1.9. The Braber I bought must have the 1:1.4 ratio and thus it works much better on the 750 rpm PTO of the Bolens than the 540 PTO of the Kubota.

I don't suppose the ratio is stamped on a tag on the gearbox?

Beyond that, one could turn the input shaft (1) complete turn while watching how far the blades rotate, and get the ratio that way, then you would know for sure.

My Mitsubishi has a (3) speed PTO: I will have to keep your experience in mind when I try weed cutting with it in a few weeks. I have a 42" cutter.