Go Bottomslip clutch brands and where to buy
 | gearnoise
Join Date: Jun 2010 Posts: 19 Davidson, NC 
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2011-06-30 179224
Background: I had a Howse 5' rotary cutter for over 20 years, its driveshaft was splined at both ends, no shear bolt, no slip clutch. It was attached to my old AC 5030, 2 cyl diesel, ~26 pto hp. I have rough ground (hilly, low stumps, etc). When I would hit something the cutter would either try to mash through it or the tractor would stall, no biggie. I finally got rid of it after I broke a blade (I had already warped the deck some years earlier when I tried to squeeze between 2 too close trees). I then bought a very used KK, same kind of driveshaft, which did not match up well with my tractor and which I didn't like for various other reasons.
Now: I have a newer more powerful tractor (MF 1533) and an almost new cutter (Befco RRD 160), which has the now typical 1-3/8" gearbox shaft and a 1/2" grade 2 shear bolt. I used the combo for the first time a couple days ago and in a couple hours went through 4 shear bolts (death count would have been higher if I had had more with me). So, I called up the manufacturer about what my alternatives could be (I do like this cutter a lot otherwise, nice design). The engineer I talked to strongly discouraged using a higher grade bolt, noting that they were a lot cheaper and easier to replace than gears. Of course I couldn't help wondering what the diff was vs the gears in my old Howse which were still in good shape when I dumped it (literally). But since my new tractor is definitely more powerful than the old one, I don't want to test it. He also mentioed that they sold a slip clutch for it through their dealers. But of course no dealer in my area has one in stock, all would have to order from Befco, which of course doesn't have one in stock either but could get one in a couple days from the actual slip clutch manufacturer.
Which leaves me to wonder, what companies actually make them, and is there a retail outlet? The one Befco has replaces the final yoke on the driveshaft (for ~$150), but an alternative would bolt on after the current driveshaft (for $???). Anybody know?
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 | greg_g
Join Date: Jan 2004 Posts: 1816 Western Kentucky 
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2011-06-30 179230
When the Howse guy mentioned "gears", I think he was talking about your tractor; the PTO gear train.
Eurocardan in Italy was at one time probably the world's largest producer of PTO drivelines, to include slip clutches. Maybe they still are, but I can't keep up with the Chinese invasion. I've had several of Eurocardan PTO shafts, and two of their clip clutches. Even if the Chinese have passed them up, I'd still buy Italian over Asian any day. Pretty sure AgriSupply hasn't contaminated their PTO line with Asian stuff yet, and I've been satisfied with everything I've ever bought from them. Click below
//greg// ....
Link: slip clutch stuff
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 | kthompson
Join Date: Oct 2005 Posts: 5275 South Carolina 
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2011-06-30 179236
If you are near a AgriSupply store they can be a great store to visit and get to know. Agree with Greg's thoughts there. ....
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| gearnoise
Join Date: Jun 2010 Posts: 19 Davidson, NC
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2011-07-01 179239
Well, the closest AgriSupply is about a 2 hour drive, but there are several Tractor Supply stores surrounding me, and one of them had the 1-3/8 smooth shaft bolt-on slip clutch in stock for $129, so I drove to Salisbury and bought it. One person recommended I still use grade 2 bolts, but I thought that would be stupid, they'll keep on shearing if the slip clutch is the least bit tighter (which I hope it is). Anyway, I put it on and I'll find out Saturday how well it works. ....
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| greg_g
Join Date: Jan 2004 Posts: 1816 Western Kentucky
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2011-07-01 179241
You're exactly right. I've learned not to ask agricultural questions in stores like TSC, Rural King, and the like. The employees typically have neither the training nor the background to answer competently. Your thoughts about using a GR2 on a smooth bore slipclutch were exactly right. What you'd end up with is an overpriced shear bolt driveline.
GR5 minimum, GR8 if you can find the right diameter. You might even have to go metric (class 8.8 or 10.9), because a tight fit is important. You do not want any slop in that particular bolt, it should fit tight from Day 1. Being harder than the material around the holes, a loosely fitting GR5 or GR8 will eventually egg out the bolt holes, and then your drive line will start flopping.
//greg// ....
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| gearnoise
Join Date: Jun 2010 Posts: 19 Davidson, NC
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2011-07-05 179277
Thanks Greg, and I let that &%$%@)*% clerk talk me out of the grade 8's, bought a couple grade 5's as a compromise. I didn't think about it at the time, but when one adds the slip clutch to the drive shaft, one has to remove the outer snap ring from the end of the gearbox shaft. That is what keeps the drive shaft connected to the cutter when a shear bolt shears, avoiding the end coming off and possibly becoming a deadly missile. So it is downright dangerous to use a slip clutch attached with grade 2 bolts. Glad I let my better sense at least prevail enough to get the grade 5's. In Befco's manual, with their slip clutch the bolt they designate is "HH M12-1.25x70 C8.8 Z P" I'll try to find a couple of those and replace my 1/2 inchers with them. At least the one at the gearbox end of the clutch. ....
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| greg_g
Join Date: Jan 2004 Posts: 1816 Western Kentucky
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2011-07-05 179279
I may be telling you something you already know, but the M12-1.25x70 means a 12mm bolt with thread count of 1.25/mm and a length of 70mm. The C8.8 is the class of bolt (metric equivalent to GR5). But thread count isn't very important here. 1/2" SAE is 12.5mm, so - if your 1/2" doesn't have to be forced through, the holes might already be worn. Loose fitting bolts only make the holes bigger over time. 70mm is almost exactly 2.75". So a 1/2"x2-3/4" SAE bolt should work just fine. Threads are also related to bolt hole wear. Ideally the bolt should be smooth where it passes through the holes, with less than 3/4" thread at the end - just enough so you can snug up the nut. A NyLok nut with a flat washer works best.
//greg// ....
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