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Message
Mechanically Inclined/Lawn Service Individuals - ? About Hydraulic Pump
Posted on 9/5/16 at 2:14 pm
Posted on 9/5/16 at 2:14 pm
Equipment:
I am running a Scag Tiger Cub SMTC-48A.
Here is Link to parts diagram if needed:
Drive System Components
Fuel & Hydraulic System
Hydraulic Pump Assembly
Pertinent Info:
Last week I was in process of replacing the left hand spindle assembly on the deck. I ran into difficulties with this repair. The tapered hub had seized onto the shaft eventually forcing me to forcibly separate the pulley and hub. This required ordering both a new pulley and tapered hub.
Relevance to current problem:
1)This lawn mower sat on clean concrete for about 48hrs as I waited for these new parts. when they arrived, I moved the mower to a new area to give me better access to finish the repair. When mower was moved the concrete under it was clean and had no signs of any fluid leaks.
2) Mower was moved and was only running for 1-2 minutes to move to new area for repair.
3) Repair was made in the morning and then sat in this new spot for 3-4 hrs. During this time a large pool of hydraulic fluid became visible under the mower.
Initial "repair" of hydraulic leak.
1) Visual inspection of hoses and clamps showed no indication of leaks.
2) I did notice a wet dust build up on what I though was a drain plug on the right hand pump. (Part #30 under diagram labeled "Hydraulic Pump Assembly")
3) I was able to tighten this plug for about 1/2 turn.
4)I filled fluid reservoir, cleaned the area around the leak and under to help determine if it continued to leak.
5) No further leaking.
Current Issue:
As I was running this mower this morning, a sudden metallic noise and loss of significant drive power occurred. I immediately stopped mower and raised the seat.
A massive hydraulic leak was noticed again on the right hand side.
All hoses check out visually. No apparent hose failure.
Fluid is visible dripping from the tapered pulley hub which connects to the hydraulic pump on the right hand side of mower. (Part #11 on diagram "Drive System Components")
This pulley connect to the hydraulic pump shaft. (Part #11 on diagram "Hydraulic Pump Assembly")
So, I am certain that I had a seal failure around this shaft and the metallic sound was a shaft bearing failure as a result.
NOTE: The drain plug I originally tightened has now been identified as a "Relief Mechanism"
1. My thinking is that I had a pressure build up with the hydraulic pump last week. This pressure was released by the relief mechanism. That was the cause of my original leak.
2. I tightened the system relief mechanism as I mistakenly thought it was a loose drain plug.
3. The pressure build up continued until the next weakest point failed. That being a seal around the shaft. This caused a drastic failure in the system.
My questions are:
Does this sound like a reasonable guess as to what has happened to cause this leak.
If so, Replacing the shaft and seals and bearings will only be addressing the symptom of my problem. Something is failing in the pump to cause the pressure buildup? Correct?
A shaft kit is $140. But that repair is above my current skill level and tool level. So I would then have a substantial labor expense since I would need to take my mower to the shop.
Or I can buy a new pump at $520. This would hopefully be a repair I can complete myself. I forsee the most difficult part being the removal of the pulley and hub from the pump shaft.
Those knowledgeable in this area, does it make more sense to buy a new pump rather than repair/rebuild the current pump?
ETA: To the internet bad arse that down votes a request for help/advice. Must he difficult spending holidays by yourself.
I am running a Scag Tiger Cub SMTC-48A.
Here is Link to parts diagram if needed:
Drive System Components
Fuel & Hydraulic System
Hydraulic Pump Assembly
Pertinent Info:
Last week I was in process of replacing the left hand spindle assembly on the deck. I ran into difficulties with this repair. The tapered hub had seized onto the shaft eventually forcing me to forcibly separate the pulley and hub. This required ordering both a new pulley and tapered hub.
Relevance to current problem:
1)This lawn mower sat on clean concrete for about 48hrs as I waited for these new parts. when they arrived, I moved the mower to a new area to give me better access to finish the repair. When mower was moved the concrete under it was clean and had no signs of any fluid leaks.
2) Mower was moved and was only running for 1-2 minutes to move to new area for repair.
3) Repair was made in the morning and then sat in this new spot for 3-4 hrs. During this time a large pool of hydraulic fluid became visible under the mower.
Initial "repair" of hydraulic leak.
1) Visual inspection of hoses and clamps showed no indication of leaks.
2) I did notice a wet dust build up on what I though was a drain plug on the right hand pump. (Part #30 under diagram labeled "Hydraulic Pump Assembly")
3) I was able to tighten this plug for about 1/2 turn.
4)I filled fluid reservoir, cleaned the area around the leak and under to help determine if it continued to leak.
5) No further leaking.
Current Issue:
As I was running this mower this morning, a sudden metallic noise and loss of significant drive power occurred. I immediately stopped mower and raised the seat.
A massive hydraulic leak was noticed again on the right hand side.
All hoses check out visually. No apparent hose failure.
Fluid is visible dripping from the tapered pulley hub which connects to the hydraulic pump on the right hand side of mower. (Part #11 on diagram "Drive System Components")
This pulley connect to the hydraulic pump shaft. (Part #11 on diagram "Hydraulic Pump Assembly")
So, I am certain that I had a seal failure around this shaft and the metallic sound was a shaft bearing failure as a result.
NOTE: The drain plug I originally tightened has now been identified as a "Relief Mechanism"
1. My thinking is that I had a pressure build up with the hydraulic pump last week. This pressure was released by the relief mechanism. That was the cause of my original leak.
2. I tightened the system relief mechanism as I mistakenly thought it was a loose drain plug.
3. The pressure build up continued until the next weakest point failed. That being a seal around the shaft. This caused a drastic failure in the system.
My questions are:
Does this sound like a reasonable guess as to what has happened to cause this leak.
If so, Replacing the shaft and seals and bearings will only be addressing the symptom of my problem. Something is failing in the pump to cause the pressure buildup? Correct?
A shaft kit is $140. But that repair is above my current skill level and tool level. So I would then have a substantial labor expense since I would need to take my mower to the shop.
Or I can buy a new pump at $520. This would hopefully be a repair I can complete myself. I forsee the most difficult part being the removal of the pulley and hub from the pump shaft.
Those knowledgeable in this area, does it make more sense to buy a new pump rather than repair/rebuild the current pump?
ETA: To the internet bad arse that down votes a request for help/advice.
Must he difficult spending holidays by yourself. This post was edited on 9/5/16 at 2:33 pm
3
Posted on 9/5/16 at 2:39 pm to Bama323_15
On a Dixie Chopper, they say to never move mower when not under its own power. Damage to the hydraulic system can occur. The dealer told me I would have to loosen a bolt in the oil system that is like an emergency by pass if the mower needs to be pushed or pulled. Just a heads up on some hydraulic systems. How many hours on the mower, my chopper needs hydraulic filters and fluid changed every 1000 hours.
Posted on 9/5/16 at 2:45 pm to TIGER2
The leak at the pressure relief might have been from the locked up pulley causing the pump to dump some oil at the relief valve. Check all the other belt hubs that they are free and not going bad too.
Posted on 9/5/16 at 3:06 pm to Bama323_15
My Exmark 48" Hydro is in the shop right now getting seals replaced on both motors. Initially brought it in because it stopped on me and had to pull that bitch up on the trailer by myself. Right after that I broke my ribs and didn't have time to look at it. Plus I physically couldn't with my ribs. Sent it in to get looked at. Needed a new pull chord, broke on me the day it stopped moving, New drive belt, had them go ahead and do a hydro flush and change the filters while it was in. Then they call and tell me the seals are bad and need replaced. All in all it's going to be about $850 for everything. So it depends on how much time you have on your hands to replace the seals yourself or buy new pumps. Or you could buy new ones now, replace the seals in the old pumps later and sell them.
Posted on 9/5/16 at 4:58 pm to TIGER2
Thanks Tiger2.
Not sure of exact hours on system currently. I have changed filters and fluids on it previously. Mower 1s 10 years old and original pumps...may just be time for them to wear out.
Not sure of exact hours on system currently. I have changed filters and fluids on it previously. Mower 1s 10 years old and original pumps...may just be time for them to wear out.
Posted on 9/5/16 at 4:59 pm to TIGER2
quote:
The leak at the pressure relief might have been from the locked up pulley causing the pump to dump some oil at the relief valve. Check all the other belt hubs that they are free and not going bad too.
Did not realize both these were your replies.
The idler pulley in the drive system did have a little movement in it. Going to replace it as I am doing this repair.
Posted on 9/5/16 at 5:03 pm to YNWA
quote:
Initially brought it in because it stopped on me and had to pull that bitch up on the trailer by myself. Right after that I broke my ribs and didn't have time to look at it. Plus I physically couldn't with my ribs.
Sorry to hear about ribs and mower. I bet that was a load getting it onto a trailer yourself. I had already started worrying about that myself.
I have a 2 ton chain hoist in my lawn mower room. Was going to rig it up to pull my scag onto trailer if needed.
quote:
All in all it's going to be about $850 for everything.
That hurts about as much as the ribs I bet.
quote:
So it depends on how much time you have on your hands to replace the seals yourself or buy new pumps. Or you could buy new ones now, replace the seals in the old pumps later and sell them.
Good idea and I have planned on doing something similar. Will tell you what I have decided in next post so this will not be so long.
Thanks.
Posted on 9/5/16 at 5:10 pm to Bama323_15
Thanks for the advice from both of you.
I have just removed everything. I removed the pulley and hub. Both of those are still in good shape...will reuse those. Drive belt is still in good shape.
Idler pulley has a little movement...took it off so I can go ahead and replace it while I am under the mower.
Pump is off. Shaft is sitting at an angle now. Is that bad?
So I am ordering a new pump.
I am going to donate my old pump to local high school small engine class. If they can fix it I will pay for parts and have it on hand if my other hydraulic pump goes out. If not, the class gets to have a pump to break down and examine in class.
I have just removed everything. I removed the pulley and hub. Both of those are still in good shape...will reuse those. Drive belt is still in good shape.
Idler pulley has a little movement...took it off so I can go ahead and replace it while I am under the mower.
Pump is off. Shaft is sitting at an angle now. Is that bad?
So I am ordering a new pump.
I am going to donate my old pump to local high school small engine class. If they can fix it I will pay for parts and have it on hand if my other hydraulic pump goes out. If not, the class gets to have a pump to break down and examine in class.
Posted on 9/5/16 at 6:22 pm to Bama323_15
1. Assuming you moved the unit w/o bypassing hyd. you likely blew the pump shaft seal at the time of your initial repair. There should be (or sometimes is) a lever to allow the fluid to go back to tank for freewheeling. Relief should have saved it, but it could have been mal-adjusted from go. I bet it was hard to push until it went over relief?
1. Relief started to weep a little for an undeterminded reason- as hydro sytems age, things start to weep. Weeping isn't a symptom of bypass- once the relief opens, it just goes back to tank. In fact, you ever stall the hydraulics going up a hill or through a ditch? Makes a whining noise with no movement? That's going over relief.
2. When you tighetened the relief, you raised the pressure that it takes to open it. Could be a big adjustment- it's a spring that opens up a poppet under pressure- let's say it was set at 2000 psi, quarter turn could have raised it to 2500 psi. Now you would have less protection on the system.
3. Either the pump seal decided to let go at the time of the initial repair, or the pushing it over relief caused it, sounds like the shaft seal failed first (obvious, right?) but the metal noise means pump failure, or worse- you cooked both pumps, the other pump, or one or both of the drive motors beacuse of a lack of oil (we don't know where). Remember, the oil on that system is not closed loop it's just normal (meaning both pumps share a common reservoir). So, yeah, you may have a catastrophically leaking shaft seal, but you may have killed the other pump, one or both of the motors, or the pump you are diagnosing because of oil starvation due to seal failure at the leaky pump.
Take it to the dealer. Piston components aren't to be trifled with.
ETA- read your last post. Rotating group on the pump or shaft bearing/bushing sounds like it's shot. You are probably in the right direction, but no guarantees something else didn't die in the process- i.e. motor seals are good, but the rotating group is scarred, causing internal leakage and loss of performance.
Make sure you get a 2 new filters if you DIY- this stuff NEEDS MUST HAS TO BE clean. You need to run it, and then change the filter again.
1. Relief started to weep a little for an undeterminded reason- as hydro sytems age, things start to weep. Weeping isn't a symptom of bypass- once the relief opens, it just goes back to tank. In fact, you ever stall the hydraulics going up a hill or through a ditch? Makes a whining noise with no movement? That's going over relief.
2. When you tighetened the relief, you raised the pressure that it takes to open it. Could be a big adjustment- it's a spring that opens up a poppet under pressure- let's say it was set at 2000 psi, quarter turn could have raised it to 2500 psi. Now you would have less protection on the system.
3. Either the pump seal decided to let go at the time of the initial repair, or the pushing it over relief caused it, sounds like the shaft seal failed first (obvious, right?) but the metal noise means pump failure, or worse- you cooked both pumps, the other pump, or one or both of the drive motors beacuse of a lack of oil (we don't know where). Remember, the oil on that system is not closed loop it's just normal (meaning both pumps share a common reservoir). So, yeah, you may have a catastrophically leaking shaft seal, but you may have killed the other pump, one or both of the motors, or the pump you are diagnosing because of oil starvation due to seal failure at the leaky pump.
Take it to the dealer. Piston components aren't to be trifled with.
ETA- read your last post. Rotating group on the pump or shaft bearing/bushing sounds like it's shot. You are probably in the right direction, but no guarantees something else didn't die in the process- i.e. motor seals are good, but the rotating group is scarred, causing internal leakage and loss of performance.
Make sure you get a 2 new filters if you DIY- this stuff NEEDS MUST HAS TO BE clean. You need to run it, and then change the filter again.
This post was edited on 9/5/16 at 6:29 pm
Posted on 9/5/16 at 6:33 pm to subMOA
quote:
. Assuming you moved the unit w/o bypassing hyd. you likely blew the pump shaft seal at the time of your initial repair. There should be (or sometimes is) a lever to allow the fluid to go back to tank for freewheeling. Relief should have saved it, but it could have been mal-adjusted from go. I bet it was hard to push until it went over relief?
This initial movement was made while under power. I did not make that clear in my original post.
quote:
2. When you tighetened the relief, you raised the pressure that it takes to open it. Could be a big adjustment- it's a spring that opens up a poppet under pressure- let's say it was set at 2000 psi, quarter turn could have raised it to 2500 psi. Now you would have less protection on the system.
Yep, this was what I was guessing happened in general. However, since hydraulic systems are new to me I was not 100% certain.
quote:
3. Either the pump seal decided to let go at the time of the initial repair, or the pushing it over relief caused it, sounds like the shaft seal failed first (obvious, right?) but the metal noise means pump failure, or worse- you cooked both pumps, the other pump, or one or both of the drive motors beacuse of a lack of oil (we don't know where). Remember, the oil on that system is not closed loop (meaning both pumps share a common reservoir). So, yeah, you may have a catastrophically leaking shaft seal, but you may have killed the other pump, one or both of the motors, or the pump you are diagnosing because of oil starvation due to seal failure at the leaky pump.
I really had not considered that possibility until you mentioned it.
Currently I am planning on ordering a completely new pump and was planning on talking with a technician to make sure the relief mechanism comes pre set on a new pump as I don't want to attempt to set it.
Also found a video of the exact model pump I have. This guy is doing a complete rebuild on the pump.
Pump Rebuild
Definitely looks like something that I will attempt with the old pump at some point.
Thanks for the advice.
(I am stubborn enough to always think I can figure this stuff out eventually. Most of the time it works out. Sometimes I end up costing myself extra time and money.)
ETA: You added-
ETA- read your last post. Rotating group on the pump or shaft bearing/bushing sounds like it's shot. You are probably in the right direction, but no guarantees something else didn't die in the process- i.e. motor seals are good, but the rotating group is scarred, causing internal leakage and loss of performance. Make sure you get a 2 new filters if you DIY- this stuff NEEDS MUST HAS TO BE clean. You need to run it, and then change the filter again.
This post was edited on 9/5 at 6:29 pm
Thanks. Will do. Was also going to research how to do system flush.
This post was edited on 9/5/16 at 6:39 pm
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