slipping slip clutch

[yanmars]

I have a heavy duty Bush Hog brand 6 foot brush hog. This Spring I mowed down quite a few saplings and thorn trees etc. Most under an 1 inch in diameter, some up to 3 inches or so. It worked well. Today when I took it out it would barely cut 6 or 8 inch high grass. When it got into the thicker grass the PTO shaft was rotating slowly. I think the slip clutch is slipping, either that or could the main nut holding the blades on underneath be loose? I have had it to the dealer twice in the last 2 years because the nut came off and the blades came off. I told them to torque it high enough or use loctite or spot weld it. Hopefully it is not loose a third time.

If that is not it and the slip clutch is slipping. Can I just tighten the nuts slowly, say a half turn each and see if the puts more tension on the unit so that it cuts the thicker grass? Keep doing so slowly until the unit functions and does not slip excessively. Thoughts or ideas. Thanks

 

[Sawyer Rob]

I'd check the nut under first...

IF, that is tight, then I'd make sure the clutch plate isn't wore too thin or broken and if good, I'd adjust the clutch for the HP of your tractor...

SR

 

[3Ts]

I have a heavy duty Bush Hog brand 6 foot brush hog. This Spring I mowed down quite a few saplings and thorn trees etc. Most under an 1 inch in diameter, some up to 3 inches or so. It worked well. Today when I took it out it would barely cut 6 or 8 inch high grass. When it got into the thicker grass the PTO shaft was rotating slowly. I think the slip clutch is slipping, either that or could the main nut holding the blades on underneath be loose? I have had it to the dealer twice in the last 2 years because the nut came off and the blades came off. I told them to torque it high enough or use loctite or spot weld it. Hopefully it is not loose a third time.

If that is not it and the slip clutch is slipping. Can I just tighten the nuts slowly, say a half turn each and see if the puts more tension on the unit so that it cuts the thicker grass? Keep doing so slowly until the unit functions and does not slip excessively. Thoughts or ideas. Thanks

The PTO shaft should be rotating at 540 rpm. There should be an indication on your tachometer as to what engine speed that is, usually a little over 2000rpm. Assuming you have an "open" slip clutch, you can mark it so you can see if it's slipping. Just take a white marker and draw a line across the friction disks and metal plates, run it a little, recheck if they are still in alignment.

However, from the rest of your post, I'm inclined to believe that the nut on the gear box underneath the mower is loose - again. There should be a castle nut on there with a cotter pin to keep it from loosening up. It does not appear that your dealer can fix it, I've not had to tighten mine, ever! Do not expect to be able to tighten it by hand with a wrench even with a pipe on the wrench. You really need a big impact wrench to get it tight enough. It may be possible to get an independent car mechanic or maybe a machine shop to tighten it properly. Or, you can also use this as an opportunity for a new impact wrench. HF has some big ones for not much money. Even small compressors will run them, you'll just have to wait while the tank refills between trigger squeezes.

 

[DK35vince]

If that is not it and the slip clutch is slipping. Can I just tighten the nuts slowly, say a half turn each and see if the puts more tension on the unit so that it cuts the thicker grass? Keep doing so slowly until the unit functions and does not slip excessively. Thoughts or ideas. Thanks

That is how I set my slip clutchs.

 

[yanmars]

Often questions are asked for advice and then no report back on success, or not. I tried to tighten the large nut under the mower, even my 2 inch nut was not large enough. Put a pipe wrench and cheater bar on, still could not tighten it and it did not seem loose and was not proud of the shaft. Probably would not have enough strength to tighten it what would be needed, I think over 350 foot pounds.
Went to the slip clutch bolts/nuts. I did tighten them all about 1/2 turn. They actually seemed to me to be too loose. Did some light mowing, not in real heavy stuff but it worked well with no slippage. Will try tougher jobs in the future and see what happened. Hoping I am good to go.

 

[3Ts]

Thanks for the report back. And it does sound like you're good to go. Remember that once a year, to loosen the nuts and let it slip and re-tighten the nuts to keep the plates from corroding.

 

[Rebeldad1]

"When it got into the thicker grass the PTO shaft was rotating slowly. I think the slip clutch is slipping,"

If you are running the pto at 540rpm the pto shaft should be rotating at the same speed. They are mechanically locked together with the splines. The nut under the gearbox would have nothing to do with that or the slip clutch as they are past the pto.

 

[ruffdog]

"When it got into the thicker grass the PTO shaft was rotating slowly. I think the slip clutch is slipping,"

If you are running the pto at 540rpm the pto shaft should be rotating at the same speed. They are mechanically locked together with the splines. The nut under the gearbox would have nothing to do with that or the slip clutch as they are past the pto.

That is what I was thinking.....what does the nut or anything else on the cutter have to do with the tractor maintaining the correct PTO speed? It sounds like an issue with the tractor.

 

[ptsg]

That is what I was thinking.....what does the nut or anything else on the cutter have to do with the tractor maintaining the correct PTO speed? It sounds like an issue with the tractor.

Or as simple as the OP using the PTO shaft with the clutch on the tractor side. If the clutch spins, the shaft spins slower.

 

[crashz]

I have a slip clutch on my John Deere 506 mower that I regularly have to play with. I keep it a bit loose to absorb shock, but too loose and you never see it slip, but you'll smell it! Then can get wicked hot very quickly.

But thank for reminding me: its time to loosen mine too.

 

[yanmars]

Just to check the nut I put a line of white out across part of the same to see if their would be misalignment after use. The good news the PTO ran at full speed and did not slow down in heavy grass/mowing conditions. Just mowed 10 minutes. When I went to check the white line it did not help as they were all rubbed off from the friction of the grass etc. Will keep watching, thinking the slip clutch was too loose to function properly.

 

[ruffdog]

Is the clutch on the tractor end of the pto shaft?

 

[yanmars]

Here is a photo of the unit.

 

[ruffdog]

Well, that's interesting......

 

[OzKioti]

I have an 8" clutch with two wearable discs on my 6' slasher (rotary cutter). Slasher has a 90hp gearbox, and it's driven by the 76hp Kioti, so maybe, I dunno, 68 or thereabouts PTO hp.

I've been running with the same clutch plates for 16 years behind a 47hp tractor.

Recently, I re-sowed some pasture after roto-tilling, and man, did that new grass get up and going! Very tall and very thick. When I went to slash it, the clutch started slipping, and it released it's smoke. Clutch plates were pretty well toast, so I fitted a new pair.

Recommendation was to tighten the eight bolts all the way to fully compress the springs, then back off three turns. The bolts are 12.5mm bolts, with 1.25mm thread pitch, so that's a backoff of 3.75mm, a bit over 9/64" (Metric is SOOO much easier!!!)

Well, the thick grass again caused slippage, so back in the shed I tightened up another half turn. On the way back to the long patch, the slasher bottomed out on a high patch of ground, but was good on the shorter grass, however it started slipping and smoking again on the thick patch.

Back to the shed to find one of the two plates had shattered.

I'm thinking that by going down to two and a half turns, I tightened the eight springs too much, and the shock from bottoming the cutting disc/blades may have caused the plate to shatter.

I've just picked up a new pair of plates, and I'm thinking I may have been driving into the thick grass too fast, so maybe attack it slower and give the slasher a chance to "digest" the long grass? I'm pretty sure the previous 47hp tractor would not have been up to the task at all, so I think I over-drove the clutch. The hp rating for a twin plate 8" clutch is 60hp I believe.

Thoughts guys?

 

[OzKioti]

UPDATE - New clutch plates installed, and the eight springs were backed off three turns from fully compressed. I put the tractor in a lower gear, and attacked the grass at about 3 km/hr instead of 8 km/hr, and all good! (That's 1.9 & 5 mph approx)