Breaking shear pins on my mower

[clemsonfor]

Like california said the overrun feature on a ym240 is in the threepoint gearing itself, unlike a ym2000 where this feature is left out and we ahve to get external devices.

 

[robsym240]

The mower is a JD 261 Grooming Mower, not a finish mower like I stated earlier, my bad. The shear pin breaks occur when I'm mowing and engage the clutch at normal cutting speed and release it without throttling down first and slowly re-engaging the clutch. It most often happens when I try to maintain my position on a hill by using the clutch rather than the brakes or when cutting in tight areas when I use the clutch rather than the throttle to slow down when turning. This is the first time I've used a tractor with a manual clutch and standard transmission so it may be user error, it may be that I'm releasing the clutch too fast and also that I shouldn't use the clutch for either of these circumstances. The mower belt and blades move freely and the belt does not appear to be too tight. I use the 540 rpm pto setting for mowing. The shear pin bolt is small, it's 1/4''x 2.5''. Thanks for all the great suggestion, it's not a huge deal and it is happening less often as I get more familiar with using it.

 

[clemsonfor]

you dont want to use your clutch to slow your progression or to do anything other than stop. That putting way to much wear on it and will cause it to fail earlier.

What you should do is use the foot throttle. WHen i am changing speed frequently or turning and want to vary my speed i will set the hand throttle at the slowest that i want to go, say in the turns, i will set it that speed. Then i will use the foot throttle to speed up inbetween the points i want to slow, once i take my foot off the throttle it will slow to the perfect speed for the turn or just my predetermined slow speed. I only clutch a few times a session. TO start out and to change gears then each time i get off, in bwtween i just vary my speed with the throttle which is what you want to do.

 

[Car Doc]

My YM240 came with a John Deere 260 5ft. Finish Mower that does a great job but every time I press on the clutch while the mower is running I have to throttle down and restart, slowly letting out the clutch or it snaps the shear pin (a nut, lock washer n bolt) and I have to shut it down and put another one in. It's getting better as I get used to using the tractor, last cut I only went through 3 and I'm getting pretty fast at installing them, but it's still a pain, any suggestions? I saw this over running clutch that Hoye offers could that help? Yanmar over running clutches

Is there any possibility there is a bind in the mowers right angle drive or the driveshaft u-joints are out of phase? I can see shearing bolts getting to quick on the clutch or trying to start the mower stuffed into tall grass but stalling the engine would be more what I would expect in that instance. I also wonder if the built in overrun clutch is working properly?

I am surprised they call for such a hard bolt as a sheer bolt? I have gone from grade 2 (no mark) to grade 5 (3 marks) on my mower and my post hole digger but that still doesn't make me feel like I did the "right" thing even though it has worked but a hard bolt I would never do it. my .002

 

[clemsonfor]

Cardoc that mower in the pic looks very similar to the one my friend had that he just traded away. He told me i could ahve it but i did not want to weld on it and he really called it junk. He said every time that it got the silightest amount of tall grass it would break #2, and 5's. He finially put 8s in it and it would work. I cringed when he told me that but its his stuff. I dont think he had used it in like 5 years he now mows with a BH rear discharge 720. He uses whatever is factory in it and no problem, i think JD has a design flaw in that thing?

 

[kenmac]

In using a high grade bolt, 1 would hope that you break something on the mower instead of the PTO gears,etc. I think I would try using a slip clutch instead of running rist of breaking something on the tractor using a high grade bolt

 

[Car Doc]

The comment I made about the drive shaft out of phase is worth a look I hope he takes me serious on it. I agree it may be a shot in the dark but on rwd cars and trucks it happens on a regular basis not kidding a bit.

Some shafts are indexed where you cant put them together wrong but a 90 degree out of phase square shaft w/o an index will tear things up in a hurry due to the force that's being applied to the flange every time the u-joint is forced to "give" it will push back against the sheer bolt.

And it would have a significant vibration also. I have seen shafts repaired and re-welded flanges put on out of phase on indexed shafts so anything is possible fwtw.

I am like you guys I know other guys that put hard bolts in and if it says to do so then by all means it would be prudent and called for. Its my logical common sense side that tells me to be careful haha. :thumbsup:

(kind of defeats the sheer bolt purpose if the bolt is harder than the shaft or flange but I am not a certified enginer jmho) edit: I see now where the sheer bolt is 1/4" that is awful small imho and may be the design fault Clemson mentions? fwtw I think my 45hp gear boxes all had 3/8" #2 soft bolts as spec pretty sure that is it?

My phd is a bolt eating monster pita to run or it was at one time.

 

[robsym240]

In using a high grade bolt, 1 would hope that you break something on the mower instead of the PTO gears,etc. I think I would try using a slip clutch instead of running rist of breaking something on the tractor using a high grade bolt

Thanks kenmac, The JD dealer says it calls for grade 9 bolt. I agree, I'd rather bust a shear pin than my tractor! I found plenty of choices in slip clutches, there are ones that fit on the pto at the tractor, some that are built into the drive shaft and ones that go right on the shear pin shaft at the mower gearbox, that one is about $70 (usd) plus shipping. I figure I'm just going to keep it as it is for now, this mower does a fantastic job other than that, it's a grooming mower maybe it's geared higher for more rpm's, who knows, but the only time it ever breaks the shear pin is when I'm doing something wrong with the clutch so it's a cheap but valuable way for my newbie self to learn to use it the right way. Thanks to everyone for the helpful posts, I will never use my clutch like I'm driving a car again!

 

[careyo63]

Come to think about it try this. When I Esp. have the Rpm's up on my 2000 and begin to let the Clutch Out. From a obsticle sharp turn etc. I Slowly at first Let the Clutch Out until I can feel when the Pto and FM Engage. Then the Transmission goes into gear. Once you feel the mower and pto Lockup then you can freely let the Clutch out or finish Engaging the Trans.

 

[clemsonfor]

I do just as cary said. If i have the tractor at 1500rpm and just dump the clutch it creates a heck of a jerk on the PTo driveline.

I mean, you can use your clutch when you want to stop but you have to remember tractors are meant to pick a gear to work in and stay in that gear till you change your range for speed you need or that your required speed exceedes what you can do with the throttle and still accomplish the task your doing, may it be plowing disking mowing or driving. So in a car you are clutching in normal conditions to get up to speed. A tractor has an unsycronized gear box, shifting on the fly is possible but you have to have practice and let it "fall into gear" or else you hear a good bit of grinding.

But for normal operation you wont clutch till you want to stop fro what ever reason, or say your going up a long hill with super tall grass your mowing and you have to drop a gear to still maintain power to mow up it.