L785

[Tazza]

I just swapped the servos. The problem, however, remained on the left side. Today, I discovered that the left drive motor had no seal on the shaft that goes through the resevoir wall to connect up with the main drive sprocket. When I took it off all there was, was two large washers and a bunch of form a gasket. I'm assuming the previous owner just made his own seal. I'm suprised it lasted so long though, or I guess that's why it felt weaker on that side. Anyway, I put everything back together, with a new seal, thinking I was Mr. fix-it and nothing. Still does not move. I put the pressure gauge back on the out-put line, #19 if you're looking at figure 096 on the new holland web site, and removed the servo to work the control by hand. when no pressure was applied my reading now comes up ZERO. When I grabbed the control arm, directly connected to the rear piston pump, and worked it myself the pump got a mind of its own and shot up to at least 5000 psi. I dove out of the loader thinking my gauge was going to explode...but then the machine stalled out. Still the wheels did not move on the left side. Tomorrow, I'll see if the hoses will reach to hook up to the right side motor with the rear pump, or the forward piston pump with the left side motor, if those hoses will reach. I can't see that #17 is blocked (same figure), because i had it completely unhooked and blew through it, thinking there may be a plug. While I was re-testing though fluid would come out of #19 from the motor not hard and fast but at a steady pace.

If you are getting 5,000 PSI i do believe the pump is working correctly.
Be very careful installing pressure gauges on the hydrostats, 5,000 PSI is more than enough to kill you. Its normal for the machine to stall as there is no where for the fluid to escape, thats why when testing these sort of things they use a restricting valve so the fluid is still moving but you can control the pressure build up. They say to bring the pressure up slowly and not to exceed 5,000 PSI.
I would say it is indeed the motor, i still think the best way is to swap motors if you can, then you will know for sure.
If you are getting constant by-pass like that there has to be something broken, if it has worn, it will by-pass slowly but it will still have drive power. Test the *good* motor from the other side on the bad side and if it works, pull the dead motor down and have a look. You can't cause more damage if it is already broken.
Thats what i would do at least.
Remember, be carefull with those pressures, i can't stress it enough! if a hose split you could get a jet of oil that can cut you badly.

 

[sterlclan]

If you are getting 5,000 PSI i do believe the pump is working correctly.
Be very careful installing pressure gauges on the hydrostats, 5,000 PSI is more than enough to kill you. Its normal for the machine to stall as there is no where for the fluid to escape, thats why when testing these sort of things they use a restricting valve so the fluid is still moving but you can control the pressure build up. They say to bring the pressure up slowly and not to exceed 5,000 PSI.
I would say it is indeed the motor, i still think the best way is to swap motors if you can, then you will know for sure.
If you are getting constant by-pass like that there has to be something broken, if it has worn, it will by-pass slowly but it will still have drive power. Test the *good* motor from the other side on the bad side and if it works, pull the dead motor down and have a look. You can't cause more damage if it is already broken.
Thats what i would do at least.
Remember, be carefull with those pressures, i can't stress it enough! if a hose split you could get a jet of oil that can cut you badly.

high pressure oil causes gangrene in a very short amount of time that type of cut needs immeidate surgery safety first Jeff

 

[onyxtour]

If you are getting 5,000 PSI i do believe the pump is working correctly.
Be very careful installing pressure gauges on the hydrostats, 5,000 PSI is more than enough to kill you. Its normal for the machine to stall as there is no where for the fluid to escape, thats why when testing these sort of things they use a restricting valve so the fluid is still moving but you can control the pressure build up. They say to bring the pressure up slowly and not to exceed 5,000 PSI.
I would say it is indeed the motor, i still think the best way is to swap motors if you can, then you will know for sure.
If you are getting constant by-pass like that there has to be something broken, if it has worn, it will by-pass slowly but it will still have drive power. Test the *good* motor from the other side on the bad side and if it works, pull the dead motor down and have a look. You can't cause more damage if it is already broken.
Thats what i would do at least.
Remember, be carefull with those pressures, i can't stress it enough! if a hose split you could get a jet of oil that can cut you badly.

Why isn't there any pressure now when the control arm remains idle? (As opposed to me moving it by hand and it just grabbing and jumping up to 5000 psi). Also when I was driving the machine, after reinstalling the drive motor today, the machine would lock up on the left side, the side that is not operating, i.e. wheels turning. I'd have the control arm pushed all the way forward, but nothing. Only the right side was moving me along, in a big circle. And then all of a sudden the left side would jump and lock up, sending me in a dead spin to the left.

 

[Tazza]

Why isn't there any pressure now when the control arm remains idle? (As opposed to me moving it by hand and it just grabbing and jumping up to 5000 psi). Also when I was driving the machine, after reinstalling the drive motor today, the machine would lock up on the left side, the side that is not operating, i.e. wheels turning. I'd have the control arm pushed all the way forward, but nothing. Only the right side was moving me along, in a big circle. And then all of a sudden the left side would jump and lock up, sending me in a dead spin to the left.

The way axial piston pumps work is by vairing the amount the postons travel, when the arm is in the neutral position the pistons do not move back and forth generation pressure. As soon as you move the control the pistons will move back and forth with respect to how far the lever has been moved (a very simple yet effective design). Pressure will build up quickly if the line is pluged with a pressure gauge even if you only move it a little bit.
When hydraulic motors are full of oil they don't turn easily with external pressure, like if you shut the machine down on a hill. The oil inside would resist the pull of gravety trying to drag the machine down the hill, it will move with small internal leakage but it will not move quickly. All i can think of is the motor is full of oil which has essentially locked it as the oil passes through it and back to the tank.

 

[onyxtour]

The way axial piston pumps work is by vairing the amount the postons travel, when the arm is in the neutral position the pistons do not move back and forth generation pressure. As soon as you move the control the pistons will move back and forth with respect to how far the lever has been moved (a very simple yet effective design). Pressure will build up quickly if the line is pluged with a pressure gauge even if you only move it a little bit.
When hydraulic motors are full of oil they don't turn easily with external pressure, like if you shut the machine down on a hill. The oil inside would resist the pull of gravety trying to drag the machine down the hill, it will move with small internal leakage but it will not move quickly. All i can think of is the motor is full of oil which has essentially locked it as the oil passes through it and back to the tank.

I found a good explanation of how the piston pumps operate at this web site http://www.answers.com/topic/axial-piston-pump; and on another learned that any scoring on the valve plate or block can be stoned up to .0002, so as not to remove any hardness. This is not to say i observed any scoring, but if there were scoring it would keep the block and plate from making a tight enough seal to produce the required out-put energy; in that rather than the fluid going directly through the hole in the valve plate a greater percentage would be lost between the plate and block due to the seperation and therefore not enough juice to produce...internal leakage. After reading the information on this above-referenced web site, however, it appears that as long as the pistons are properly following the surface of the swashplate, with the swashplate properly functioning, everything should work fine; with no blockages in the pistons themselves, of course.

 

[Tazza]

I found a good explanation of how the piston pumps operate at this web site http://www.answers.com/topic/axial-piston-pump; and on another learned that any scoring on the valve plate or block can be stoned up to .0002, so as not to remove any hardness. This is not to say i observed any scoring, but if there were scoring it would keep the block and plate from making a tight enough seal to produce the required out-put energy; in that rather than the fluid going directly through the hole in the valve plate a greater percentage would be lost between the plate and block due to the seperation and therefore not enough juice to produce...internal leakage. After reading the information on this above-referenced web site, however, it appears that as long as the pistons are properly following the surface of the swashplate, with the swashplate properly functioning, everything should work fine; with no blockages in the pistons themselves, of course.

If you were to "flat plate" the swash plate, you will need to do the face of the rotating group. The marks in the swash plate will match the rotating group, if you flatten one, you will need to do the other or you will have achieved nothing.
The swash plates in my 743 are actually bronze that have been fused to a steel backing, there is no hardness there.

 

[onyxtour]

If you were to "flat plate" the swash plate, you will need to do the face of the rotating group. The marks in the swash plate will match the rotating group, if you flatten one, you will need to do the other or you will have achieved nothing.
The swash plates in my 743 are actually bronze that have been fused to a steel backing, there is no hardness there.

Well today I switched out the right side drive motor with the left side...What a job, nothing like working on a bobcat, i suppose anyway. The final problem turns out to be..........the motor. Once switched the left side took off like a rocket, throwing dirt, while the right side was now dead in the water. Right now I'm trying to find a rebuild kit, or a motor...used first, then if nothing new. Anybody know where they sell used drive motors? Tazza I wasn't talking about the swash plate. I was talking about the other end where the block, piston holder, rests against the back cover. If that back side of the block is scored then the pressure would be lost from the pistons shooting it through via leakage around the raised area, or scoring, on either the back plate or block.

 

[Tazza]

Well today I switched out the right side drive motor with the left side...What a job, nothing like working on a bobcat, i suppose anyway. The final problem turns out to be..........the motor. Once switched the left side took off like a rocket, throwing dirt, while the right side was now dead in the water. Right now I'm trying to find a rebuild kit, or a motor...used first, then if nothing new. Anybody know where they sell used drive motors? Tazza I wasn't talking about the swash plate. I was talking about the other end where the block, piston holder, rests against the back cover. If that back side of the block is scored then the pressure would be lost from the pistons shooting it through via leakage around the raised area, or scoring, on either the back plate or block.

I know what you were refering to, don't worry
I think the encypedia has it a bit mixed up, as far as i was aware, the swash plate is the part where the rotating group rubs on, this is where pressure is created. The other end is the yoke, this is hardened and where the hardened shoes of the pistons run, no hydraulic pressure is generated here. Either way, if its working don't touch the pump, there are a lot of close tollerence parts you don't want to touch if not needed.
Glad you found out it was the motor, call around a few hydraulic shops and see if they can offer a re-build kit. I would open it up and see if you can work out just what is broken so you know what you need to buy.

 

[onyxtour]

I know what you were refering to, don't worry
I think the encypedia has it a bit mixed up, as far as i was aware, the swash plate is the part where the rotating group rubs on, this is where pressure is created. The other end is the yoke, this is hardened and where the hardened shoes of the pistons run, no hydraulic pressure is generated here. Either way, if its working don't touch the pump, there are a lot of close tollerence parts you don't want to touch if not needed.
Glad you found out it was the motor, call around a few hydraulic shops and see if they can offer a re-build kit. I would open it up and see if you can work out just what is broken so you know what you need to buy.

I did open it up and can find nothing wrong. Nothing is broken. Is there some web site I can go to get an exploded view, or discussion on the same?

 

[Tazza]

I did open it up and can find nothing wrong. Nothing is broken. Is there some web site I can go to get an exploded view, or discussion on the same?

The eaton site should give you details on them, just finding them on the site can be a bit of a pest to find.
Does it have a model stamp on it?

 

[onyxtour]

The eaton site should give you details on them, just finding them on the site can be a bit of a pest to find.
Does it have a model stamp on it?

So far I've come up with (1) Canadian patent number, or year 1969-1971; (2) 71442 DAR; (3) 71442-3000; (4) 8C48 JJ; and the following are the U.S. patent numbers it may be under: (a) 3,396,536; (b) 3,508,817; (c) 3,621,761; (d) 3,486,334; (e) 3,611,879. I can find no other numbers or marking, other than "Cessna - Made in the USA".

 

[onyxtour]

So far I've come up with (1) Canadian patent number, or year 1969-1971; (2) 71442 DAR; (3) 71442-3000; (4) 8C48 JJ; and the following are the U.S. patent numbers it may be under: (a) 3,396,536; (b) 3,508,817; (c) 3,621,761; (d) 3,486,334; (e) 3,611,879. I can find no other numbers or marking, other than "Cessna - Made in the USA".

I don't know how that stupid angel thing got in there.

 

[Tazza]

I don't know how that stupid angel thing got in there.

ooh... its a cessna motor, not vickers.
I still think your best bed is to take it to a hydraulic shop and get them to identify it and see what they think is wrong with it. I would suspect something like a valve is playing up. I'm not too sure how these motors work, but for it to just stop and by-pass and to show no obvious breaks it has to be something simple....
From what i have seen, they are fairly simple in design, but they will need some sort of valve to control the oil, i would start there.....

 

[onyxtour]

ooh... its a cessna motor, not vickers.
I still think your best bed is to take it to a hydraulic shop and get them to identify it and see what they think is wrong with it. I would suspect something like a valve is playing up. I'm not too sure how these motors work, but for it to just stop and by-pass and to show no obvious breaks it has to be something simple....
From what i have seen, they are fairly simple in design, but they will need some sort of valve to control the oil, i would start there.....

Just returned from Heavy Equipment Repairs. They told me that the piston block, the end that connects to the back plate, needs the surface ground, because it's raised. That the back plate must be re-hardened, because it has worn through the hardness; this they have to send out to have done. That the flat brass tops on the pistons, that are against the swashplate, must be re-surfaced, because they have minor-here and there- scratches. And, that the spider must be completely replaced, because it's groved from the pistons. I'm waiting to here the estimate. When I asked what caused the damage, Glen told me that it's more likely than not water damage...a lack of quality oil flowing through the motor. He's also going to see what a rebuilt motor would cost. I priced the spider at NH and it's $57.00. Do I truly need the back plate re-hardened, and if i don't what can I expect for the life of the motor as well as loss in power?

 

[onyxtour]

Just returned from Heavy Equipment Repairs. They told me that the piston block, the end that connects to the back plate, needs the surface ground, because it's raised. That the back plate must be re-hardened, because it has worn through the hardness; this they have to send out to have done. That the flat brass tops on the pistons, that are against the swashplate, must be re-surfaced, because they have minor-here and there- scratches. And, that the spider must be completely replaced, because it's groved from the pistons. I'm waiting to here the estimate. When I asked what caused the damage, Glen told me that it's more likely than not water damage...a lack of quality oil flowing through the motor. He's also going to see what a rebuilt motor would cost. I priced the spider at NH and it's $57.00. Do I truly need the back plate re-hardened, and if i don't what can I expect for the life of the motor as well as loss in power?

$810.50 plus shipping to have my cessans rebuilt. I send it out they send it back 4-6 weeks. 180.00 they re-harden the back plate, and I also pay shipping, out and back. Takes 4-6 weeks. $50.00 to re-surface pistons and piston block. spider $57.00 this way equals approximately $320.00. Does any one know where I can buy a used back plate? I really need to save on the 4-6 week deal.

 

[Tazza]

Just returned from Heavy Equipment Repairs. They told me that the piston block, the end that connects to the back plate, needs the surface ground, because it's raised. That the back plate must be re-hardened, because it has worn through the hardness; this they have to send out to have done. That the flat brass tops on the pistons, that are against the swashplate, must be re-surfaced, because they have minor-here and there- scratches. And, that the spider must be completely replaced, because it's groved from the pistons. I'm waiting to here the estimate. When I asked what caused the damage, Glen told me that it's more likely than not water damage...a lack of quality oil flowing through the motor. He's also going to see what a rebuilt motor would cost. I priced the spider at NH and it's $57.00. Do I truly need the back plate re-hardened, and if i don't what can I expect for the life of the motor as well as loss in power?

The hardness is only a few thou thick, after the wear and a surface grind is taken into account it most likely will be gone. But with hardening the first say 11 thou will be super hard but after that it is still hard, but it tapers off the further down you go.
Wear on the brass swash plate is normal, that is where the rotating group runs. These can be ground flat again and i thought the rotating group could be ground flat to.
As for hardening, in the scheme of things it will not be that expensive.
Did they give an estimate of the repair? and what kind of warranty do they give on it too?

 

[onyxtour]

The hardness is only a few thou thick, after the wear and a surface grind is taken into account it most likely will be gone. But with hardening the first say 11 thou will be super hard but after that it is still hard, but it tapers off the further down you go.
Wear on the brass swash plate is normal, that is where the rotating group runs. These can be ground flat again and i thought the rotating group could be ground flat to.
As for hardening, in the scheme of things it will not be that expensive.
Did they give an estimate of the repair? and what kind of warranty do they give on it too?

$180 plus shipping there and back for the hardening. $110. for the re-surfacing and spider. Total @ approx. $320.00. I'll put it back together myself. The shop guy said though that it was the raised surface on the piston block and the back plate that shut the motor down. No warranty was talked about. I have to call back tomorrow with my decision. Having my totally rebuilt would be the 810 plus shipping etc. Can't I just get away with having the surface of the back plate ground for now...can I wait to send it out for hardening....say in a month? Will that hurt things too bad?

 

[Tazza]

$180 plus shipping there and back for the hardening. $110. for the re-surfacing and spider. Total @ approx. $320.00. I'll put it back together myself. The shop guy said though that it was the raised surface on the piston block and the back plate that shut the motor down. No warranty was talked about. I have to call back tomorrow with my decision. Having my totally rebuilt would be the 810 plus shipping etc. Can't I just get away with having the surface of the back plate ground for now...can I wait to send it out for hardening....say in a month? Will that hurt things too bad?

To do the job correctly they will grind the surfaces flat then send to get hardened then give it a light grind to ensure it is still flat. Some metals will get a slight furry coating from the hardening process that is easily polished up for a good smooth finish.
Just having the surfaces ground will work for a while depending on how deep the scoring is. You may be lucky enough to get away with it like that as you may not remove all the hardening as it does taper off after a few thou. If you run it and decide to get it hardened later they will need to re-grind it. Its your choice, you may get a good life with just a grind but again it may only last a few hours before it picks up and causes more damage than it had before ( i do doubt it would do that but it could).
Any other input guys?

 

[onyxtour]

To do the job correctly they will grind the surfaces flat then send to get hardened then give it a light grind to ensure it is still flat. Some metals will get a slight furry coating from the hardening process that is easily polished up for a good smooth finish.
Just having the surfaces ground will work for a while depending on how deep the scoring is. You may be lucky enough to get away with it like that as you may not remove all the hardening as it does taper off after a few thou. If you run it and decide to get it hardened later they will need to re-grind it. Its your choice, you may get a good life with just a grind but again it may only last a few hours before it picks up and causes more damage than it had before ( i do doubt it would do that but it could).
Any other input guys?

I tried to relocate another drive motor, used, or for parts, but no luck. If I wasn't in such a bind I'd go ahead and have it sent out to be hardened...but the 4-6 weeks will kill me right now. I told the shop to go ahead and grind everything down and I'll pick up the motor monday. I figure I'll only be running it 8 hrs. I hope the hardness goes deep enough to handle that. Once done I'll go ahead and bring the machine back here to the shop and have the back plate sent out to be hardened. No sense in having it rebuilt since the grinding and hardening, along with the new bearing in the back with seal and gasket...a spinder plate, will pretty much constitute a rebuild motor. If anyone has any idea as to why I shouldn't try and run it for the 8 hrs, or knows that it will cause more damage, please advise. My only other alternative is to have a flat bed tow truck go out and try pulling the machine up and transport back here.