Brush hog help

[riverbottom88]

Hello all, new here. Was hoping to get some insight on troubleshooting a brush hog I just acquired.

Looks like it's a Tartar 4 footer if I'm reading the faded labels right. I got it for next to nothing from the owner and was hoping I could fix it up. Here's the issue.

When I engage the pto, the shaft spins freely as it should. But the blades start slowly and build up speed until they are spinning in sync with the pto. I verified this by standing back and watching as my wife engaged the pto. As soon as you get into any kind of brush or thick grass the blades slow, if not stop, and of course it will not cut. The tractor pto and shaft never slow or bog down.

My first thought would be a loose slip clutch, but the shaft does not have one. I believe it is a shear pin, but through the gear box intake shaft? The pin is not sheared. So rule both of those out. Could it be the gears are ground in the box, only catching enough to build speed but then slipping when any resistance is met to the blades? Any help is appreciated. I can grab an identical gear box for reasonable if need be.

 

[Slowpoke Slim]

Sounds like the gearbox is shot.

Curious if someone got tired of replacing shear pins, and did something "smart" like put in a grade 8 bolt (NOT SMART), and as they say, "the rest is history".

 

[mcfarmall]

Yep, gearbox is toast.

 

[John0829]

Is there a keyway for the blade carrier? Could be a sheared key.

 

[riverbottom88]

I'll have to double check what grade bolt is in there. A grade 2 would be about right, correct? Or maybe a 5?

 

[riverbottom88]

Is there a keyway for the blade carrier? Could be a sheared key.

I'm going to get it up on it's side and see if I can wrestle the castle nut off and take a look. I wondered about the blade carrier also.

 

[mcfarmall]

Is there a keyway for the blade carrier? Could be a sheared key.

Output shaft is typically a tapered spline.

 

[John0829]

And tapered splines are known to also use keys.

 

[riverbottom88]

Looks to me like the splines on both the output shaft and stump jumper are in good shape, and they were fully seated together when I took them apart. Don't think there could have been any slipping issues there. Also no keyway. At this point I think we're getting it narrowed down to that gearbox.

 

[riverbottom88]

Nevermind, I was wrong. Being a bit of a newbie to this i didn't realize how badly the splining in the stump jumper was actually chewed up. Only that little bit on the end is left and it wasn't making full contact with the spline on the output shaft. Seems it starts spinning more or less based on friction but then there is nothing to hold it tightly once the blades meet resistance. Gear box might be ok, might be in the market for a stump jumper.