Bleeding the closed loop PT drive system

[KentT]

I'm thinking about my upcoming wheel motor upgrade and have a couple of questions...

1. To bleed the drive system after it has been opened up at each wheel, do I just bleed it at the charge pump the same way I would when changing the filter?

2. Should I also push the treadle in, while cranking with the spark-plug wires removed, to allow the tram pump to push the air out of the lines? If so, how would I know how long to crank it? When bleeding after changing the filter, you crank long enough to make sure the charge pump is fully primed and pumping a steady flow. Since the air introduced into the system would be on the other, output side of the tram pump, would this still be a good indicator?

3. Given the fact that it is a closed-loop system where the oil stays in there all the time (not going back to the reservoir) and only replenished by the charge pump as needed to overcome "leakage" -- do you think it would be beneficial to try draining ALL the oil out of the lines that run to the wheel motors, just to get rid of any possible contaminents in those lines?

Thanks -- I look forward to the insight...

 

[J_J]

I'm thinking about my upcoming wheel motor upgrade and have a couple of questions...

1. To bleed the drive system after it has been opened up at each wheel, do I just bleed it at the charge pump the same way I would when changing the filter?

2. Should I also push the treadle in, while cranking with the spark-plug wires removed, to allow the tram pump to push the air out of the lines? If so, how would I know how long to crank it? When bleeding after changing the filter, you crank long enough to make sure the charge pump is fully primed and pumping a steady flow. Since the air introduced into the system would be on the other, output side of the tram pump, would this still be a good indicator?

3. Given the fact that it is a closed-loop system where the oil stays in there all the time (not going back to the reservoir) and only replenished by the charge pump as needed to overcome "leakage" -- do you think it would be beneficial to try draining ALL the oil out of the lines that run to the wheel motors, just to get rid of any possible contaminents in those lines?

Thanks -- I look forward to the insight...

Kent

I am assuming the machine is up on blocks. I think you should use plugs in the lines when you remove the wheel motors, When you have them all hooked up, remove the bleed plug, and crank until there is no air coming out of the system . Do you have a case drain going from the tram pump to the hydraulic cooler? I think any air left in the system, will be compressed and forced out the case drain. The charge pump is always at standby to keep the system pressurized. I wouldn't crank the starter very long, give the starter a rest , and crank some more. Just my opinion.

 

[KentT]

JJ,

My PT doesn't have case drains at all, as far as I know. I should've mentioned that.

That's one of the reasons why I asked about draining the lines while I had it open. Otherwise, any contaminants there may be are "trapped" in the drive system until they happen to get out as "leakage."

Char-Lynn also cautions to fill the motors with fluid when replacing them, and to not run them without oil. That's why I was thinking of cranking it with the treadle mashed down -- to get some oil back to the wheel motors as soon as possible.

 

[marrt]

This is an excellent question. I plan on replacing my “hydraulic fluid” with real hydraulic fluid at some point. However, if the wheel circuit is closed, how do I replace the fluid in this critical circuit? Also, what is filtering this circuit? If a wheel motor starts to suffer a catastrophic failure, does this mean it potentially damages every other motor (and the pump) in the circuit? It think I’m missing something.

 

[J_J]

Kent.

Do you have a hydraulic circuit schematic for the 425? Please post one if you have one.

 

[J_J]

JJ,

My PT doesn't have case drains at all, as far as I know. I should've mentioned that.

That's one of the reasons why I asked about draining the lines while I had it open. Otherwise, any contaminants there may be are "trapped" in the drive system until they happen to get out as "leakage."

Char-Lynn also cautions to fill the motors with fluid when replacing them, and to not run them without oil. That's why I was thinking of cranking it with the treadle mashed down -- to get some oil back to the wheel motors as soon as possible.

Kent,

You can partially fill the wheel motor by removing the pressure fitting at the tram pump. I would think that if you just replaced the wheel motors, and started the engine and let it idle, and then press on the treadle to get the pump pumping, it will fill the wheel motors all by itself. The motors are not going to turn until they receive the fluid. The wheel motors will start turning, and the first motor that is closer to the pump will turn first. After they have turned for a few minutes, they should be ready to go.

 

[marrt]

Kent.

Do you have a hydraulic circuit schematic for the 425? Please post one if you have one.

I think so...take a look at the attached image.

 

[marrt]

I think so...take a look at the attached image.

Actually, I mis-read your post. Obviously, that image is for my 1845...not the 425.

 

[toy]

JJ,

My PT doesn't have case drains at all, as far as I know. I should've mentioned that.

That's one of the reasons why I asked about draining the lines while I had it open. Otherwise, any contaminants there may be are "trapped" in the drive system until they happen to get out as "leakage."

Char-Lynn also cautions to fill the motors with fluid when replacing them, and to not run them without oil. That's why I was thinking of cranking it with the treadle mashed down -- to get some oil back to the wheel motors as soon as possible.

When you get the new wheel motors they will probably have plastic plugs where the hoses fit inorder to keep contaminents out. If you take the plugs out when you are installing the wheel [which you will have to do anyway ], with the plastic plugs out if you pour oil into one of the holes as you are turning the shaft of the motor by hand that will fill the motor for you so that the motor will have oil in it when you first apply tram pressure . It might be possible to take the hoses off closer to the pump and fill them at the same timeas you are filling the wheel motor. Anotoher thing as you are getting ready to install the new wheel motors already have the proper fittings in the wheel motors to hook the hoses up to, already having this done will cut down on the time from the time you take the hoses of the old wheel motors and hooking them up to the new wheel motors. Another thing you might want to do is have some rags already handy to stuff into the end of the hoses that you take off or some other means to plug the end of the hoses to keep from loosing too much or all of your oil in the system. Plan your project out ahead of time say forinstance if you can pull the hoses up above the oil level you won't loose very much oil that way . After saying all this seems like projects seldom go the way you plan but that way you will be thinking and planning ahead. Good luck with your change over. Oh yes have some screw drivers handy within reach and also any other tool that you think you might need that way you won't be having to hunt them while the oil is a flowing. Oh yea don't leave the rags in the hoses when you reconnect them and I know some might say that fragments from the rags will contaiminate the system that might be true but I also know that sometimes all things that you wouldn't do goes out the window when you are actually doing the job. I hope some of this is a help to you . Another thing take the plugs that you took out of the new wheel motor and put them in the old wheel motor to help protect them.

 

[KentT]

JJ,

I don't have the hydraulic diagram handy -- the Owner's Manual is with the PT down in Tennessee.

toy,

Thanks for the tips. I'm leaning toward draining the lines to the wheel motors, to try getting rid of any metal particles that may be in there. Hopefully this is a "one time" opportunity to clean any contaminents out.