# Simplicity zero turn very jerky at low speeds



## Alex berte (6 mo ago)

I have a simplicity champion 2050 zero turn that’s been giving me some problems lately. At low speeds it is very jerky and makes A lot of noise. You almost have to push the levers all the way forward or back before the wheels do anything. It does fine at normal mowing speeds, only has problems turning and when loading onto the trailer. Are my hydros beginning to go bad? Is their air in the system? I need my mower functioning correctly as I run a mower business. I have a good amount of knowledge on small engines but I’m really stumped on this one 🤔


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## BigT (Sep 15, 2014)

Good Morning Alex, welcome to the forum. 

Your mower has a separate hydraulic pump and motor for each side. You don't mention a problem with one side or the other, so it seems to be something common to both sides? Correct me if I'm wrong. 

I'm thinking your pump drive belt may be slipping? Have you ever changed the pump drive belt, or replaced the tensioner spring? 









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## Alex berte (6 mo ago)

I know that the previous owner mentioned something about replacing some tensioners, so I’ll look into that. I’m not sure if it was for the deck or the transmission. One thing I did notice is that it seems like the hydros work fine when I am using both levers. It’s only when I’m turning or menuvering at low speeds that I notice a problem


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## sixbales (May 18, 2011)

Do you lose power going up a slope?


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## Bob Driver (Nov 1, 2017)

As BigT said, your machine is a full-blown hydraulic drive system. Jerky at low speeds is generally either a loose traction belt (yours is 1/2" x 72.5"), or a low flow problem with the hydraulic circuit. Yours runs two hydraulic pumps/wheel motors.... If it's jerky when turning in both directions, it's something common to both circuits (the filter/oil). They all jerk a little manuevering at low engine RPM. Might want to take a look at your idle speed setting to make sure you're getting enough pump flow at really low speeds/throttle setting to smoothly run the drive motors.

If it jerks more on one side, it's either the pump, or the motor, on that side. Jack the machine up and rotate the tires on each side by hand with the engine off. Listen carefully to the drive motors and see if you're getting any unusual noise, or binding, as you rotate them slowly. When you change the belt, rotate the pumps, and check for unusual noise/binding. The only way to really trouble-shoot to see if you've got a weak pump, or drive motor, is with a $500 flow gauge.....


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## Alex berte (6 mo ago)

Thanks bob! I’m going to take a look at the mower tonight, so I’ll keep you posted as to what I find. Also, if my belt is loose, I’d the tensioner adjustable in any way? Or do I just need to buy a new belt? Also what fluid should I use in this? It’s not low right now, but I assume it will be once I replace the hydrolic filter. I have some John Deere low viscosity hygaurd I Got for another machine, but I doubt that will work. The owners manual lists about 3 different types of oil and I’m not sure what is best. And to answer sixbales question, yes it does seem to lose power on hills, but only on steep inclines.


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## Alex berte (6 mo ago)

After looking into the problem I noticed a few things. First thing I noticed when I took the mower off the ground is how the wheels turn. They don’t make any strange noises or bind up, but they do cog over. Both wheels do this the exact same way. I’m not very familiar with zero turn transmissions, so I am not sure weather this is a problem or not. Another thing I noticed is with the belt system. The belt tension seems ok, but the pulley that is connected to the tension looks like it’s missing it’s upper lip. I’m not sure if this is how it should be or not, but thought it might be worth mentioning. I’ll include a picture. I have not yet got the chance to spin the hydro pumps, since I am waiting until I get a new belt to take the original one off. Only other thing I noticed is that one of the control handles seems to go back and forward Easier than the other one, but I assumed that’s just because the damper connected to it was weak.


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## Alex berte (6 mo ago)




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## BigT (Sep 15, 2014)

Alex berte said:


> The belt tension seems ok, but the pulley that is connected to the tension looks like it’s missing it’s upper lip. I’m not sure if this is how it should be or not, but thought it might be worth mentioning.


That is a single flanged pulley. See item #13 on attached parts diagram:









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## Bob Driver (Nov 1, 2017)

Most of the OEM's that run full blown hydraulic drive systems (Scag, Exmark, Ferris) suggest SL rated 20w50 motor oil as the fluid. I don't personally feel you gain anything by using synthetic, so I just go with Wally World Super Tech @ $18 for 5 quarts. Never had any problems using with any of my personal, or customer machines.

The hydraulic components on your machine are Hydro Gear. BDP Series pumps and HGM 12 series drive motors, both are as good as anything on the market today. Both components are very reliable, rebuild kits are readily available, and both units are fairly simple for the average DIY guy to rebuild.

Personally, I would change the fluid/filter, replace the drive belt, and make sure the idle is set at 1750 RPM. Another thing I would check is to make sure both by-pass valves are completely closed. They tend to get tough to turn as the machine ages and I've seen a lot of machines where the machine had been placed in by-pass to push and the valves closed again, but they actually weren't full seated again. Definitely influences the performance of the drive system. It also appears in the parts diagram BigT posted that there is an eyebolt that attaches the spring to the tensioner. Might want to give that a couple of turns and make sure the new belt is tight. While you're at the tensioner, make sure the two pivot bearings aren't worn out and causing the drive belt to "whip" at low RPM

Looking at a blown-up version of the belt shown in your picture, that belt definitely needs replaced. It's supposed to have a 1/16 inch "top margin" that rides above the pulley v-groove, yours is completely gone, and that's when a v-belt starts to slip in low RPM/High torque situations. Note the short sections of vertical straight edges at the very top of the belt cross-section below..... Those are the "top margins" of the belt, when they're gone, it's time for a new belt


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## Busted Tractor (May 22, 2018)

Check the suction lines between the pump inlet and the oil tank including the filter. They may not leak oil out but may leak air in. I have been told if you can twist the line on the fitting it will leak air into the line.


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## Bob Driver (Nov 1, 2017)

Busted Tractor said:


> Check the suction lines between the pump inlet and the oil tank including the filter. They may not leak oil out but may leak air in. I have been told if you can twist the line on the fitting it will leak air into the line.


Easy way to detect if air is being sucked into the hydraulic system is the fluid in the tank will be foamy.


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