Repairs Grasshopper 721DT

[NWGH]

I appreciate the response. Having to work on other stuff I put this on the back burner till today and will use your info to attempt to remedy. By the way, what is the small belt that is behind the hydro for then?

Have to admit I've no idea, not being able to look at your machine, but since you report a belt between the hydro and engine and mine doesn't have one, I'm guessing that there is a design difference between your 721DT and my 623T. What year is your mower? I purchased mine new this year, but it was built in 2017.

What I see (once a protective cowling is removed) is that the 623T Kohler Command Pro engine has both a front and rear shaft. The front shaft and the tandem hydraulic pump shaft are assembled parallel and directly in line with each other (i.e. end to end). Not sure how big the gap between the shafts is because there is a floating but rigid cylindrical coupler which pretty clearly serves as a limited universal to allow for any small shaft misalignment. By floating I mean that the coupling cylinder feels relatively loose, and can easily slide back and forth about 3/16". I haven't looked closer, but undoubtedly there is an interior key or splines on both shafts which "lock" rotation of both components. In any event, I have no "small belt behind the hydro" like you report, so your machine is certainly different in that regard. For completeness the rear engine shaft on my 623T powers the PTO, but that's likely incidental to this discussion.

I would suggest checking if your engine and pump shafts are offset and if the "small belt" you report connects pulleys that are in line between those two shafts. If so, that would just be a different approach to connecting power between the engine and your hydro pump, in which case that belt becomes the prime suspect for your problem. If it got thrown, broke, or started slipping, it would certainly cause both wheels to become inoperative at the same time.

cpurvis suggested the complete pump may have died. I'm not familiar enough with the tandem pump design to know if that is likely, but if the belt hypothesis above does not pan out, then from your reported problem I would still focus on components common to both pumps. That's because the separate left / right pump sections, while co-housed in the tandem pump chassis, would probably not both die at the same time (that is, that possibility would be the last thing to check on my list). The common components which would more readily explain simultaneous failure are limited to the shared drive shaft, a common fluid reservoir, and a common filter, so be sure to check that the shaft did not break (or freeze up), that the fluid level is not low, and if both of those are OK, that the filter is not plugged. Unfortunately, I don't think you can check the filter without draining the hydraulic fluid, which is expensive. If someone is aware of additional common components to check, please chime in.

The note by 173abn that the pump on the 721DT might be powered via the PTO puzzled me. There could certainly be unusual designs out there, but isn't the 721DT PTO switchable on/off like most mowers? If so, and the pump was also powered by the PTO shaft, then you wouldn't even be able to drive unless the PTO was enabled, which to me seems counterintuitive from a safety standpoint. Or am I missing something?

Good luck with your troubleshooting!

 

[Jjracoon]

Have to admit I've no idea, not being able to look at your machine, but since you report a belt between the hydro and engine and mine doesn't have one, I'm guessing that there is a design difference between your 721DT and my 623T. What year is your mower? I purchased mine new this year, but it was built in 2017.

What I see (once a protective cowling is removed) is that the 623T Kohler Command Pro engine has both a front and rear shaft. The front shaft and the tandem hydraulic pump shaft are assembled parallel and directly in line with each other (i.e. end to end). Not sure how big the gap between the shafts is because there is a floating but rigid cylindrical coupler which pretty clearly serves as a limited universal to allow for any small shaft misalignment. By floating I mean that the coupling cylinder feels relatively loose, and can easily slide back and forth about 3/16". I haven't looked closer, but undoubtedly there is an interior key or splines on both shafts which "lock" rotation of both components. In any event, I have no "small belt behind the hydro" like you report, so your machine is certainly different in that regard. For completeness the rear engine shaft on my 623T powers the PTO, but that's likely incidental to this discussion.

I would suggest checking if your engine and pump shafts are offset and if the "small belt" you report connects pulleys that are in line between those two shafts. If so, that would just be a different approach to connecting power between the engine and your hydro pump, in which case that belt becomes the prime suspect for your problem. If it got thrown, broke, or started slipping, it would certainly cause both wheels to become inoperative at the same time.

cpurvis suggested the complete pump may have died. I'm not familiar enough with the tandem pump design to know if that is likely, but if the belt hypothesis above does not pan out, then from your reported problem I would still focus on components common to both pumps. That's because the separate left / right pump sections, while co-housed in the tandem pump chassis, would probably not both die at the same time (that is, that possibility would be the last thing to check on my list). The common components which would more readily explain simultaneous failure are limited to the shared drive shaft, a common fluid reservoir, and a common filter, so be sure to check that the shaft did not break (or freeze up), that the fluid level is not low, and if both of those are OK, that the filter is not plugged. Unfortunately, I don't think you can check the filter without draining the hydraulic fluid, which is expensive. If someone is aware of additional common components to check, please chime in.

The note by 173abn that the pump on the 721DT might be powered via the PTO puzzled me. There could certainly be unusual designs out there, but isn't the 721DT PTO switchable on/off like most mowers? If so, and the pump was also powered by the PTO shaft, then you wouldn't even be able to drive unless the PTO was enabled, which to me seems counterintuitive from a safety standpoint. Or am I missing something?

Good luck with your troubleshooting!

Starting to figure out what is going on. The belt is for the optional hydraulic lift system that was equipped on my mower. It was functional until I added the Powerfold system. I am wondering if there is a conflict since one is battery operational and the lift system is hydraulic. I replaced the control arm pads and had to cut around the lift control button and now that system quit working. I thought I was fairly mechanical inclined but this system has got me wondering.

 

[NWGH]

Starting to figure out what is going on. The belt is for the optional hydraulic lift system that was equipped on my mower. It was functional until I added the Powerfold system. I am wondering if there is a conflict since one is battery operational and the lift system is hydraulic. I replaced the control arm pads and had to cut around the lift control button and now that system quit working. I thought I was fairly mechanical inclined but this system has got me wondering.

In the manual for my 623T, a Drive Assembly drawing shows the engine side coupler hub has a 1" bore and a .25" square keyway. Is it possible yours is similar and the .25" square key has sheared within the coupler hub?

I'd suggest directly observing that shaft while running. Are the pulleys for the hyd. lift turning? Is the cylindrical coupler to the transmission (the tandem hydraulic pumps) turning? Even better, is the fan at the forward end of the tandem pump housing turning?

Those questions are relatively easy to answer by observing from the side on my 623T, but I imagine observation might be more difficult on your 721DT with its engine cover and radiator. I don't advise anything, but a random thought - if interested *use at your own risk* and with all applicable safety concerns: small (<1" cube) and inexpensive (<$20) video cameras are readily available. These are made for automotive back up vision, but might be mounted under the seat appropriately to show what is happening in real time. Or perhaps just securely mount a smart phone in video record mode, to be retrieved and played back after a short run period?

 

[Grasshopperman101]

Jjracoon what year is your 721D? That particular model has been around for a long time and has about 3 or 4 different transmissions depending on the year. If your not sure of the year send me the serial number and I can tell you the year!

 

[Jjracoon]

Jjracoon what year is your 721D? That particular model has been around for a long time and has about 3 or 4 different transmissions depending on the year. If your not sure of the year send me the serial number and I can tell you the year!

Mower was built in 2010. I have not been able to work on it because my job has kept me away. Been 100 degrees in my shop too and I am lazy. I hear a cold front is on it's way so maybe I can start figuring out my problem.

 

[Jjracoon]

Mower was built in 2010. I have not been able to work on it because my job has kept me away. Been 100 degrees in my shop too and I am lazy. I hear a cold front is on it's way so maybe I can start figuring out my problem.

Now able to get back to my 721DT and as was stated there is a sleeve over the shaft and it does slide forward and back. When the engine is running the sleeve wants to slide back to the rear and the hydro isn't turning. If I place a shim to restrict the sleeve from sliding back the hydro works and the fan is turning. Any suggestions as to how to repair this problem would be greatly appreciated.

 

[Jjracoon]

Have to admit I've no idea, not being able to look at your machine, but since you report a belt between the hydro and engine and mine doesn't have one, I'm guessing that there is a design difference between your 721DT and my 623T. What year is your mower? I purchased mine new this year, but it was built in 2017.

What I see (once a protective cowling is removed) is that the 623T Kohler Command Pro engine has both a front and rear shaft. The front shaft and the tandem hydraulic pump shaft are assembled parallel and directly in line with each other (i.e. end to end). Not sure how big the gap between the shafts is because there is a floating but rigid cylindrical coupler which pretty clearly serves as a limited universal to allow for any small shaft misalignment. By floating I mean that the coupling cylinder feels relatively loose, and can easily slide back and forth about 3/16". I haven't looked closer, but undoubtedly there is an interior key or splines on both shafts which "lock" rotation of both components. In any event, I have no "small belt behind the hydro" like you report, so your machine is certainly different in that regard. For completeness the rear engine shaft on my 623T powers the PTO, but that's likely incidental to this discussion.

I would suggest checking if your engine and pump shafts are offset and if the "small belt" you report connects pulleys that are in line between those two shafts. If so, that would just be a different approach to connecting power between the engine and your hydro pump, in which case that belt becomes the prime suspect for your problem. If it got thrown, broke, or started slipping, it would certainly cause both wheels to become inoperative at the same time.

cpurvis suggested the complete pump may have died. I'm not familiar enough with the tandem pump design to know if that is likely, but if the belt hypothesis above does not pan out, then from your reported problem I would still focus on components common to both pumps. That's because the separate left / right pump sections, while co-housed in the tandem pump chassis, would probably not both die at the same time (that is, that possibility would be the last thing to check on my list). The common components which would more readily explain simultaneous failure are limited to the shared drive shaft, a common fluid reservoir, and a common filter, so be sure to check that the shaft did not break (or freeze up), that the fluid level is not low, and if both of those are OK, that the filter is not plugged. Unfortunately, I don't think you can check the filter without draining the hydraulic fluid, which is expensive. If someone is aware of additional common components to check, please chime in.

The note by 173abn that the pump on the 721DT might be powered via the PTO puzzled me. There could certainly be unusual designs out there, but isn't the 721DT PTO switchable on/off like most mowers? If so, and the pump was also powered by the PTO shaft, then you wouldn't even be able to drive unless the PTO was enabled, which to me seems counterintuitive from a safety standpoint. Or am I missing something?

Good luck with your troubleshooting!

Thanks for your help. Good news, I shimmed behind that sleeve and it forced the sleeve forward. The hydro works and I was able to test mow last evening with no problem. It seems that the sleeve over the year had worn off in the back to a point that there was too much play for it to engage. I am sure it will need to be replaced but need more research to see how.