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post #1 of 9 Old 04-24-2019, 01:41 PM Thread Starter
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What's a good level of draw bar pull force for a tractor like a Super GT or SCUT? I tested mine today with a force gauge and it was able to pull with about 2,000 pounds of force using a slow even pull before the hydro relief kicked in. Also tested the bucket lift using my welded clevis mounts, it was able to pull almost 1,700 pounds before the rear tires came off the ground. That's with a 300'ish pound box blade and around 200 pounds of fluid in the rear tires for ballast. Tractor is a JD x595. And yes before anyone asks the relief valve is shimmed.
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post #2 of 9 Old 04-24-2019, 02:33 PM
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I hope some folks respond to this. I was wondering the same thing. I am converting an old Craftsman into a SCUT. Plan to shorten a Ford 8.8 an convert tractor to hydrostat. Your post is the best info I have seen on SCUT drawbar pull. For reference I was looking at HydroGears biggest ZT transaxles to get an idea what a SCUT should pull. Think the max was around 500-600 ft/lbs. This had me leaning towards 1200 ft/lbs. Based on your test I was low.

Last edited by T.Cruit; 04-24-2019 at 02:42 PM.
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post #3 of 9 Old 04-24-2019, 05:09 PM
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Re: Draw bar pull force

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Originally Posted by eKretz View Post
What's a good level of draw bar pull force for a tractor like a Super GT or SCUT? I tested mine today with a force gauge and it was able to pull with about 2,000 pounds of force using a slow even pull before the hydro relief kicked in. Also tested the bucket lift using my welded clevis mounts, it was able to pull almost 1,700 pounds before the rear tires came off the ground. That's with a 300'ish pound box blade and around 200 pounds of fluid in the rear tires for ballast. Tractor is a JD x595. And yes before anyone asks the relief valve is shimmed.
I'd love to see the video of the testing setup and procedure.

Maximum drawbar pull occurs just before wheelspin and requires mucho traction. The X595 weighs 1080 lb. With the 500 lb of ballast, and the countering weight of a loader on the other end, that puts about 1300 lb on the rear tires. The math says that you can't exert 2000 lb of horizontal pulling force with only 1300 lb of traction, but strange things happen in the world of GTs. (I've done lots of "it can't be done" things with mine.)

The other thing is that Tuff Tork rates the K92 at 650 lb-ft of maximum rated axle torque. With 26x12-12 tires, that translates to about 650 lb of line pull. But, as with most manufacturers, the printed specs are usually well under the reality that can be achieved.

A lift of 1700 lb is indeed impressive for a GT loader, and the math agrees that that is about the point where the rear wheels will lift off of the ground placing about 3600 lb on the front tires. Keeping the rear wheels on the ground with only 500 lb of rear end ballast does make it even more impressive. The lift cylinders on my GT FEL are 2x18 and the system maxes out at 1500 psi. With a (scaled) 1250 lb load strapped over the back of the 210 lb bucket and 600 lb of rear end ballast, my GT could still move, but if I got off, the rear wheels would have lifted off the ground. In addition, the lift cylinders on my SCUT FEL are 1.5x13 with a relief pressure of 2000 psi. It won't lift off the ground a weight that my GT can lift to full height.

Bob

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Last edited by TUDOR; 04-24-2019 at 05:23 PM.
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post #4 of 9 Old 04-24-2019, 06:40 PM Thread Starter
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I didn't take any video but this is what I used to measure the force - there's a needle (the red one) that measures the maximum force but I was watching the regular needle to see steady state. I just strapped the force gauge to a big old tree stump and pulled against it. Same stump for the lift test. The drawbar pull the tires were digging/ sinking in a bit so that might have helped with getting a little more traction. Was in 4wd with the rear diff lock on. Without the THRV I think it would have pulled harder - or more likely just spun the tires. The engine didn't even bog down, it just bypassed the pressure with the relief. I also pulled behind the bucket for the lift test, so that would be maximum lift power with the shackles back near the pin area but not with the bucket itself. I didn't want to test with the actual bucket as I was afraid it would bend. And I add a considerable amount more ballast myself at 220 pounds.


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post #5 of 9 Old 04-24-2019, 07:19 PM
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Re: Draw bar pull force

Nifty little gadget!! I want one!

Bob

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post #6 of 9 Old 04-25-2019, 12:09 AM
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Re: Draw bar pull force

My Sunstrand does not understand pressure relief.
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post #7 of 9 Old 04-25-2019, 12:06 PM Thread Starter
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Yeah it's a handy little gadget. Good for force measurement or even weighing stuff hanging from the bucket. I could probably make a short video of a pull test if anyone really wanted to see it.
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post #8 of 9 Old 04-25-2019, 04:02 PM
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Re: Draw bar pull force

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Originally Posted by Ariens93GT20 View Post
My Sunstrand does not understand pressure relief.
Actually, it does, depending on the configuration. The inline version has acceleration valves that limit high pressure shock loads caused by rapid movement of the drive control.

Bottom line for pressures in a Sundstrand is that the rear wheels of a tractor will break traction well before the pressure is high enough to cause even mild concern. The continuous duty pressure rating is 2500 psi. That's above the peak pressure rating for many of the other hydros and somewhat more than the maximum pressure that will be required for most GT tasks, including loader work with a ballast load of 1000 lb, which BTW, is within manufacturer's specs when applied correctly. A full ballast load can be as much as 1520 lb, if you can figure out a way to make the rear wheels weigh 600 lb each.

A GT engine will run out of horsepower before it can hurt a Sundstrand.

Bob

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Last edited by TUDOR; 04-25-2019 at 04:17 PM.
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post #9 of 9 Old 04-25-2019, 08:34 PM Thread Starter
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I caught a couple big roots today with the scarifier and THAT got me bogged down. Hit the hydro relief and tried lifting the box blade at the same time. Took the front wheels off the ground. That dragged the RPM down a bit. Think I may have bent the box blade a bit. Doh! Nothing a pull on the other side shouldn't fix.
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