Harsh Forward Engagement / Lack of Braking from HST
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Thread: Harsh Forward Engagement / Lack of Braking from HST

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    Harsh Forward Engagement / Lack of Braking from HST

    Hey guys, in advance I would like to preface that this is a Yanmar SC2450 (SC2400) which from my not-to-educated SCUT knowledge is very similar to the 1025R.

    I have searched high and low on the cub and Yannie sites with no luck, I have studied the technical manual for the machine and nothing really stands out, hence me asking hear. Plus I imagine many of these HST's operate similiarly anyhow. If not, or this is an unacceptable post, please move or delete, my apologies.

    Here's what I got going on. Since I bought the 2010 SC2450 with 30hrs on it, when I work it hard (e.g box scraper, heavy FEL work), the brake function would start to diminish. When releasing the forward (or rearward) pedal direction it would feel roll and not stop. Sometimes the brake would slowly engage, other times not at all. I never really cared to much since at that point I'd been pushing it to the limits for a while and it was time to quit anyway. The next day it was back to normal, forward/reverse/brake all HST working normal.

    Up until recently after a decent hard working, it did not resolve itself after the cold soak. Now when I let off the pedal (mainly going forward but sometimes reverse) there is no braking function. Not all the time but more often than not. Also, now with that happening, when changing directions (with the rocker-style pedal) it engages harshly into forward from reverse. E.g. If I back up rather quickly and let off, it normally slows down in reverse, but rocking the pedal to forward there will be a noticeable change in the resistance (lighter) felt in the pedal and while continuing to depress it will suddenly very harshly engage forward range. Sometime so harshly that it pops the high/low lever out of low into high range.

    From what I can see, all of the linkage is moving freely and the damper is returning it to neutral position every time. Even though the "arm" connected to the shaft into the HST returns to the neutral position and moves forward and rearward with the pedal movement, the above characteristics are present. It does not appear that the damper is asking up, it always smoothly returns to neutral and the lever always moves according the input on the pedal. If I am gentle and move the pedal slowly, the brake works and forward and rearward engagements are smooth (normal) but if I start to move more quickly (e.g nothing more than normal use moving dirt around, cutting the lawn etc.) the harsh engagements and lack of braking return. It looks as if something must be going on with whatever is connected to that shaft into the HST (swashplate?). I have never had a HST apart so I am not sure exactly how the swashplate assembly works and if this could be simply something sticking or a worn/failed seal or broken spring, etc.

    Any words of wisdom is greatly appreciated! cheers!

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    SulleyBear's Avatar
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    Quote Originally Posted by Techspec360 View Post
    Hey guys, in advance I would like to preface that this is a Yanmar SC2450 (SC2400) which from my not-to-educated SCUT knowledge is very similar to the 1025R.

    I have searched high and low on the cub and Yannie sites with no luck, I have studied the technical manual for the machine and nothing really stands out, hence me asking hear. Plus I imagine many of these HST's operate similiarly anyhow. If not, or this is an unacceptable post, please move or delete, my apologies.

    Here's what I got going on. Since I bought the 2010 SC2450 with 30hrs on it, when I work it hard (e.g box scraper, heavy FEL work), the brake function would start to diminish. When releasing the forward (or rearward) pedal direction it would feel roll and not stop. Sometimes the brake would slowly engage, other times not at all. I never really cared to much since at that point I'd been pushing it to the limits for a while and it was time to quit anyway. The next day it was back to normal, forward/reverse/brake all HST working normal.

    Up until recently after a decent hard working, it did not resolve itself after the cold soak. Now when I let off the pedal (mainly going forward but sometimes reverse) there is no braking function. Not all the time but more often than not. Also, now with that happening, when changing directions (with the rocker-style pedal) it engages harshly into forward from reverse. E.g. If I back up rather quickly and let off, it normally slows down in reverse, but rocking the pedal to forward there will be a noticeable change in the resistance (lighter) felt in the pedal and while continuing to depress it will suddenly very harshly engage forward range. Sometime so harshly that it pops the high/low lever out of low into high range.

    From what I can see, all of the linkage is moving freely and the damper is returning it to neutral position every time. Even though the "arm" connected to the shaft into the HST returns to the neutral position and moves forward and rearward with the pedal movement, the above characteristics are present. It does not appear that the damper is asking up, it always smoothly returns to neutral and the lever always moves according the input on the pedal. If I am gentle and move the pedal slowly, the brake works and forward and rearward engagements are smooth (normal) but if I start to move more quickly (e.g nothing more than normal use moving dirt around, cutting the lawn etc.) the harsh engagements and lack of braking return. It looks as if something must be going on with whatever is connected to that shaft into the HST (swashplate?). I have never had a HST apart so I am not sure exactly how the swashplate assembly works and if this could be simply something sticking or a worn/failed seal or broken spring, etc.

    Any words of wisdom is greatly appreciated! cheers!
    OK, I will take a bite at the apple, so to speak.....

    First, how many hours are now on the machine?

    Second, when you talk about "braking engagement" are you talking about the machine stopping forward or reverse movement on its own when you let off the pedal? Or are you referring to something else like when you actually apply the brake it doesn't stop the movement? ( I doubt this is what you mean)

    Basically, here is what I would check.

    1. - The directional dampener which is the shock absorber looking device on the pedal linkage at the swash plate shaft area. Make sure its connected and that it applies pressure in both directions. Unhook the unit if necessary and make sure it has pressure when the shaft moves in and out of the unit. It provides the "smoothness" of the pedal operation and the hydro engagement. Just because its hooked up doesn't mean it's not internally broken or malfunctioning.

    2. - Your machine should have a free wheeling lever or a way to put the machine in neutral so that you can roll it with either the engine on or off. Usually, they are at the rear of the machine and you either lift the lever up or push it down. What this does is it simultaneously engages the forward and reverse directional control valves, bypassing them so you can manually move the tractor. Make sure this linkage is full in the "disengaged" or "not in use" position so the directional control valves. If this is partially engaged, from the "violent movements", it could be causing some of the issue.

    3. - Swash plate shaft and bushing / seal. Does the rear assembly leak any fluid? If so, does it leak out the area near the swash plate shaft? Sometimes, a worn swash plate shaft or bushing will cause this erratic behavior.

    4. - When did you last change the hydro oil and filter? If its been "awhile", consider changing the hydro fluid and filter.

    5. - Also, are you using the specified hydro oil and not some "just like the OEM" type discount fluid?

    6. - Does the hydro unit build excessive heat, which either you sense from the heat emanating from the operators seat? Is the engine temp higher than usual because the oil cooler on some machines is part of the radiator or its mounted immediately against the radiator and transferring heat to the radiator because it's so hot? Does the erratic behavior worsen as the unit builds heat?

    7. - The neutral adjustment of the hydro unit could be off, which is directly affected by the movement of the swash plate. Usually, this occurs after the unit is reassembled or the repairs to the swash plate, etc. The neutral adjustment will cause the machine to "creep" and not stop when you let off the pedals of either direction. The technical service manual for the rear hydro drive unit should cover the proper way to adjust this.

    8.- You could have a malfunctioning relief valve in the hydro unit.

    9. - Abrupt movements forward and backwards can be a result of the wear on the pump plates.....and they are often affected by the temperature of the unit. You would need to pressure test the hydro system to determine the pumps output.

    I would suggest using a infrared temp gun and checking to see what the temps are of the hydro unit. Check different areas of the case, the spin on filter, the oil cooler itself. See if the hydro oil coming into the cooler is hotter than the oil leaving the cooler by pointing the infrared temp gun at the top and bottom areas of the cooler. Just as you see the coolant coming into the radiator hotter than the coolant exiting out of the lower hose.

    There are things I would check. Also, if the hydro oil hasn't been changed in the last year or more, I would change the hydro oil and filter and make sure to carefully look at the bottom of the fluid catch pan to see if there is any "debris" in the oil.......there shouldn't be. Sometimes it looks like clutch matter or other debris. The fluid should just be "dirty" from use, but no material in the fluid or pan.

    The other thought is maybe the hydro oil filter is partially collapsed, partially plugged, fully plugged or has a malfunctioning bypass valve.

    There are where I would start. First and foremost with the hydro fluid.

    Does the PTO engage and disengage like it should?

    Try and get a Technical Service manual for the hydro unit as this will help you properly adjust the neutral bias and make other diagnostic tests to the hydro unit.

    Please Let us know what you find............and the answers to the questions above.......




    O

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    Quote Originally Posted by SulleyBear View Post
    Quote Originally Posted by Techspec360 View Post
    Hey guys, in advance I would like to preface that this is a Yanmar SC2450 (SC2400) which from my not-to-educated SCUT knowledge is very similar to the 1025R.

    I have searched high and low on the cub and Yannie sites with no luck, I have studied the technical manual for the machine and nothing really stands out, hence me asking hear. Plus I imagine many of these HST's operate similiarly anyhow. If not, or this is an unacceptable post, please move or delete, my apologies.

    Here's what I got going on. Since I bought the 2010 SC2450 with 30hrs on it, when I work it hard (e.g box scraper, heavy FEL work), the brake function would start to diminish. When releasing the forward (or rearward) pedal direction it would feel roll and not stop. Sometimes the brake would slowly engage, other times not at all. I never really cared to much since at that point I'd been pushing it to the limits for a while and it was time to quit anyway. The next day it was back to normal, forward/reverse/brake all HST working normal.

    Up until recently after a decent hard working, it did not resolve itself after the cold soak. Now when I let off the pedal (mainly going forward but sometimes reverse) there is no braking function. Not all the time but more often than not. Also, now with that happening, when changing directions (with the rocker-style pedal) it engages harshly into forward from reverse. E.g. If I back up rather quickly and let off, it normally slows down in reverse, but rocking the pedal to forward there will be a noticeable change in the resistance (lighter) felt in the pedal and while continuing to depress it will suddenly very harshly engage forward range. Sometime so harshly that it pops the high/low lever out of low into high range.

    From what I can see, all of the linkage is moving freely and the damper is returning it to neutral position every time. Even though the "arm" connected to the shaft into the HST returns to the neutral position and moves forward and rearward with the pedal movement, the above characteristics are present. It does not appear that the damper is asking up, it always smoothly returns to neutral and the lever always moves according the input on the pedal. If I am gentle and move the pedal slowly, the brake works and forward and rearward engagements are smooth (normal) but if I start to move more quickly (e.g nothing more than normal use moving dirt around, cutting the lawn etc.) the harsh engagements and lack of braking return. It looks as if something must be going on with whatever is connected to that shaft into the HST (swashplate?). I have never had a HST apart so I am not sure exactly how the swashplate assembly works and if this could be simply something sticking or a worn/failed seal or broken spring, etc.

    Any words of wisdom is greatly appreciated! cheers!
    OK, I will take a bite at the apple, so to speak.....

    First, how many hours are now on the machine?

    Second, when you talk about "braking engagement" are you talking about the machine stopping forward or reverse movement on its own when you let off the pedal? Or are you referring to something else like when you actually apply the brake it doesn't stop the movement? ( I doubt this is what you mean)

    Basically, here is what I would check.

    1. - The directional dampener which is the shock absorber looking device on the pedal linkage at the swash plate shaft area. Make sure its connected and that it applies pressure in both directions. Unhook the unit if necessary and make sure it has pressure when the shaft moves in and out of the unit. It provides the "smoothness" of the pedal operation and the hydro engagement. Just because its hooked up doesn't mean it's not internally broken or malfunctioning.

    2. - Your machine should have a free wheeling lever or a way to put the machine in neutral so that you can roll it with either the engine on or off. Usually, they are at the rear of the machine and you either lift the lever up or push it down. What this does is it simultaneously engages the forward and reverse directional control valves, bypassing them so you can manually move the tractor. Make sure this linkage is full in the "disengaged" or "not in use" position so the directional control valves. If this is partially engaged, from the "violent movements", it could be causing some of the issue.

    3. - Swash plate shaft and bushing / seal. Does the rear assembly leak any fluid? If so, does it leak out the area near the swash plate shaft? Sometimes, a worn swash plate shaft or bushing will cause this erratic behavior.

    4. - When did you last change the hydro oil and filter? If its been "awhile", consider changing the hydro fluid and filter.

    5. - Also, are you using the specified hydro oil and not some "just like the OEM" type discount fluid?

    6. - Does the hydro unit build excessive heat, which either you sense from the heat emanating from the operators seat? Is the engine temp higher than usual because the oil cooler on some machines is part of the radiator or its mounted immediately against the radiator and transferring heat to the radiator because it's so hot? Does the erratic behavior worsen as the unit builds heat?

    7. - The neutral adjustment of the hydro unit could be off, which is directly affected by the movement of the swash plate. Usually, this occurs after the unit is reassembled or the repairs to the swash plate, etc. The neutral adjustment will cause the machine to "creep" and not stop when you let off the pedals of either direction. The technical service manual for the rear hydro drive unit should cover the proper way to adjust this.

    8.- You could have a malfunctioning relief valve in the hydro unit.

    9. - Abrupt movements forward and backwards can be a result of the wear on the pump plates.....and they are often affected by the temperature of the unit. You would need to pressure test the hydro system to determine the pumps output.

    I would suggest using a infrared temp gun and checking to see what the temps are of the hydro unit. Check different areas of the case, the spin on filter, the oil cooler itself. See if the hydro oil coming into the cooler is hotter than the oil leaving the cooler by pointing the infrared temp gun at the top and bottom areas of the cooler. Just as you see the coolant coming into the radiator hotter than the coolant exiting out of the lower hose.

    There are things I would check. Also, if the hydro oil hasn't been changed in the last year or more, I would change the hydro oil and filter and make sure to carefully look at the bottom of the fluid catch pan to see if there is any "debris" in the oil.......there shouldn't be. Sometimes it looks like clutch matter or other debris. The fluid should just be "dirty" from use, but no material in the fluid or pan.

    The other thought is maybe the hydro oil filter is partially collapsed, partially plugged, fully plugged or has a malfunctioning bypass valve.

    There are where I would start. First and foremost with the hydro fluid.

    Does the PTO engage and disengage like it should?

    Try and get a Technical Service manual for the hydro unit as this will help you properly adjust the neutral bias and make other diagnostic tests to the hydro unit.

    Please Let us know what you find............and the answers to the questions above.......




    O
    Sulleybear, thanks a bunch for taking the time to respond in such great detail, I truly appreciate it.

    So I think I determined what it is. The HST disconnect lever was stuck “up” about a quarter inch. The lever which is a pull up to disconnect and push down to engage is fastened by a through bolt and nut which also provides resistance to its movement. It is difficult to see on this machine and blends in to the other brackets nearby. I pressed down and to my excitement it moved. After using the machine over the weekend, it hasn’t displayed any of the aforementioned characteristics. I haven’t really worked it yet, but I’m willing to bet the issue will be resolved.

    I’ve had this thing since 30hrs and it looked essentially brand new when I got it. I did not ever think that the disconnect lever could be partially open/closed, figured it was all or nothing. Why it wasn’t fully seated, who knows. Maybe it can work it’s way up if jarred around? Or maybe like that from previous owner or even back to assembly/ transport?

    Either way, I’ve never had an HST apart and definitely wasn’t looking forward to that, and after 3 fluid changes in 150 hours, I’m relieved that is out of the realm of causes as well.

    Cheers and thanks again!

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