Brush hog gear box ratio 1.69 vs 1.47

dieselcrawler · May 30, 2018

I'm replacing my brush hog gear box, old box is 1:1.69, New one is 1:1.47... Will the difference be very noticeable? The blades will be going faster, but would take more power (from my already underpowered lil tractor, 24 PTO hp) to keep them at that speed. I couldn't find the 1:1.69 ratio gearbox, and the price was right for the one I bought. Gear box, stumpjumper pan, shipping, $256.

Thoughts?

majorwager · May 30, 2018

diesel,
Did you buy parts from Agri Supply? And actually new gear box will turn blades a little slower? Unless I am missing something.

dieselcrawler · May 30, 2018

You're right, will be slower, geared to speed up faster than PTO by 1.47, not slower. My mistake. Might actually help power thru thick stuff better.

dieselcrawler · Jun 2, 2018

Wrench in the works...

Double checked pan measurements, one I ordered was smaller than the one I need, so I called to see if they had the correct one... no dice. Earlier in the day, I had checked a small brush hog (40" cut) that I've never used, it came with our BX when we bought it, and the gearbox is compatible, and the same ratio as what I was going to buy... so I canceled the order since it hadn't shipped yet, saved myself $256, and got to work.

I opened up the donor gearbox, it's clean, and hardly used, bearings tight, no signs of wear. I'll run it for now...

I started repair of the stumpjumper pan. The pan had separated from the main bar that has the center splined part and shoulder bolt holes, and was cracked and broken. I ground out the cracks, straightened the bar, and tack welded it all together. I've got it true within 1/16" or less, both centered and height. Started burning in all the welds, but ran out of MIG wire... bummer. Guess I'm gonna have to run to town in the morning.

dieselcrawler · Jun 3, 2018

Follow-up report: Repairs complete.

I got the pan welded, welded the main bar back into it, and smoothed up the welds that would interfere with the blades fitting properly. Got it all back together, gearbox oil filled, and took it for a test run about 11

m last night. Smooth as butter, at all speeds up to WOT. Hasn't been that smooth since it was new. Had to adjust tail wheel hight, due to the blades being closer to the ground again, maybe a little closer than originally due to how much I bent the main bar back down during the pan repair. Regardless I'm happy with the results.

Brumm · Apr 22, 2024

Did the 1:1.69 ratio gearbox work better?

CliffordK · Apr 22, 2024

My guess is that there are gearboxes for 640 RPM and 1000 RPM.

I hadn't thought much about whether they were speed reducers or speed increasing.

It may be that:
1:1.69 for 540 RPM PTO. (is this a speed increaser?)

1:1.47 for 1000 RPM PTO.

Nonetheless, I'm glad it seems to work with your tractor configuration.

Did you take the old gearbox apart?