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Power-Trac Variable volume pump and Hydroback

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Aaron60
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2002-04-29          37948


Anybody had any trouble with the Variable Volume Pump (the hydraulic pump located just behind the seat in the engine compartment)? I just bought a used 1997 PT 1425 (similar to the PT 425) and believe a seal blew out on the bottom of the shaft. Just want to know if anyone has replaced this before and how difficult it may be.

I also think the hydroback or push pull cable from the treadle to the hydroback is acting up. I can't get full power. Any suggestions?

Also, does anyone make their Power-tracs climb hills? Mine just seems surprisingly underpowered.

Thanks.




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Power-Trac Variable volume pump and Hydroback

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Charlie Iliff
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2002-04-30          37960


Mine is an 1845, but I have been in communication with a number of 422 and 425 owners on this board. I think with any Power Trac, and with most HST machines, they will bog badly if you floor the forward pedal while gioing uphill. They climb well if you only depress it a small amount, which is essentially low gear.
I think if you call Power Trac, they will help on the seal question, and talk you through a fix, as well as your linkage question. ....


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bubenberg@netzero.co
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2002-05-02          38067


hi charlie,

that is a must, and sometimes i forget do do my chores, to clean underneath those pedals. but that does not last for very long, when i move up hill with my attached wing mowers and don't make any headway. out i go and clean-up under there.

am glad you are making the point of not using the pedals as a car accelerator when working with appliances, less becomes very powerful. ....


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Power-Trac Variable volume pump and Hydroback

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Aaron60
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2002-05-02          38090


Unfortunately I am going to have to get the entire pump rebuilt or replaced. When I removed it from the machine, I opened it up to find a lot of broken metal pins and brass. Anyone have any good ideas on how to flush the system to remove any metal that is now residing in the lines and other motors? ....


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Power-Trac Variable volume pump and Hydroback

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bubenberg@netzero.co
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2002-05-02          38091


hi, have you contacted power trac yet? terry and dan in the tech support have their own pts and here all our questions about our problems. share your problem with them especially an older machine and let us know what happened, please! ....


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Power-Trac Variable volume pump and Hydroback

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TomG
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2002-05-03          38103


That's very unfortunate. There are a lot of parts in an axle flow pump, which would be the type often used to drive HST's. I guess that's one of the reasons why HST's are sometimes thought to have higher maintenance costs than gear TX's. I know it's of little help now, but maybe somebody knows of typical symptoms of a failing HST pump. I've got a gear TX myself.

I guess because there's a potential of this kind of failure, there's a good chance that there's a screen between the pump and motor. I'd check a manual to see if one is present. I'd also seek opinions if a screen would adequately strain metal particles from the oil before worrying too much about flushing the system.
....


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Aaron60
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2002-05-03          38114


Yes, I did contact Power-Trac and they recommended flushing the wheel motors by putting one hose in new oil and rotating the wheel to pull the oil thru the motor. Then do it with new oil in reverse. The pump is going to be replaced by the person I purchased the PT from a couple weeks ago. Still, no one is able to give me a good reason why this happened, which makes me wonder if it will happen again. All Power-Trac could tell me is that there must have been air in the pump. They thought that would cause the breakdown within a minute. I bought the machine with 378 hours on it and drove it for about an hour before buying it. I got it home and drove it another 2 hours before this happened. I did not change the filter, so it is hard for me to figure out how air got in the pump. ....


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TomG
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2002-05-04          38127


Aaron: At least it sounds like most or all of the repair costs aren't going to come out of your pocket. With tractor remote system hydraulics you hear of air or vapour in the pump due to breaks or obstructions in the pump suction line. Breaks obviously admit air, while obstructions lead to cavitation in the pump. Both conditions can lead to loss of hydraulic power, hot frothy oil and eventual pump damage. Clogged filters qualify as suction line obstructions.

You also sometimes hear of pumps loosing their primes, but mostly on older farm tractors. I haven't heard of the problem with a reasonable modern compact. In addition, for all I know the powertrac pump may operate in an oil-bath and loss of prime and suction line breaks would be all but irrelevant. However, an obstructed inlet would still cause cavitation even in an entirely submerged pump.

Cavitation also can occur on the high pressure side of a pump, but that's another issue because the resulting vapour is unlikely to ever reach the pump.

Anyway, there are a number of not all that uncommon conditions that can result in vapour in a pump. The times I've heard that are required to damage a pump are a lot longer than a minute, although these times may be for gear rather than piston pumps. A reaction off the top of my head is that if the failure did result from a suction line type of problem and the pump is capable of destroying itself in a minute, then a sensing system that would provide warnings seems like a good idea.
....


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Aaron60
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2002-05-04          38153


Thanks Tom. That makes sense since the person I purchased the tractor from told me that there were about 70 hours on the filter, which is 20 more than Power-Trac specifies everywhere you turn. I'll be sure to keep up with the filter changes.

Do you think a little air in the line after the pump will cause any damage when I start up? It seems like it will be difficult to keep those lines airfree when I break them to flush the sytem of any remaining metal from the failed pump. I would assume that any air will be pumped back to the tank and not be a problem, but I wonder if that air would damage any of the wheel motors.

Thanks again Tom,
Aaron ....


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TomG
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2002-05-05          38157


AAron: I have to talk about tractor hydraulics rather than specifically about Powertack, which I don't know. Tractor hydraulics, unlike automotive brake systems are open. They normally carry and air through the system, which then bubbles out of the oil in the sump.

Occasionally some air may stay in a cylinder and is normally is purged by cycling the cylinder. Cycling is done by simply running a cylinder to the limit of its travel and holding for a few seconds while the relief valve opens. I don't know if there's is an equivalent to cycling for hydraulic motors.

I'd guess that the motors are going to be fairly full of oil after drawing new oil through them when flushing them. Continuing to guess, I imagine that small amounts of air remaining would be self-purging and would not damage the system. It's always wise to check with a dealer though.
....


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Aaron60
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2002-05-05          38184


Thanks again Tom. I believe the same to be true and Power-Trac never mentioned having to bleed the wheel motors, just the pump. I suppose I'll have to fill the pump (prime) with oil before starting it up, but other than that and bleeding it, I think the other little pockets of air should end up in the resevoir. ....


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