Newbie Hydraulic Question

[jmerola]

Hey guys, I apologize in advance for the stupid question(s). I recently picked up a used NH TZ24DA. It has 98 hours on it, and was sitting at the dealers (as a trade in) for a year prior to my purchasing it. I want to go through it and change all the fluids / filters, but I think it would be wise to understand, conceptually, what exactly each fluid "circuit" does before digging in. My questions are these:

1) What is the distinction between the transmission and HST fluid "circuits" (ie, what exactly does the HST do, and what does the transmission fluid do)?

2) Does the tractor have a power steering pump, or is that part of HST circuit?

3) Anyone know of a good online source for filters/fluid?

Thanks for the help, and I apologize for the uninformed questions.

- Jason

[jinman]

That's not a stupid question...very few are. Your tractor has one hydraulic reservoir and one main hydraulic pump. That pump supplies pressure to the power steering system, your implement lift (3PH), and FEL. The main system filter will have all hydraulic fluid flowing through it as it leaves the reservoir. That is the most expensive filter on your tractor, about $75 I believe.

The HST system draws fluid from the main hydraulic system reservoir, but it has its own special filter that makes sure no contamination makes it to the HST. After the HST uses fluid, it drains back into the main reservoir.

The lower part of the transmission and differential form the main hydraulic fluid reservoir. The gears pick up lubricant from being bathed in the fluid reservoir and sling that fluid around some to other transmission and rear differential gears. To my knowledge, there is no pressure lubing of transmission or differential gears.

The front axle, drop boxes, and differential have their own reservoir of fluid that is not associated with the main reservoir nor the power steering system. The front axle case is it's own isolated reservoir.


Your power steering pump is the main hydraulic pump. You do not have a separate pump for it.

Two good online sources are TBN advertisers and sponsors. They are:

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and Partspring

I have ordered from Messicks.com and found their service to be excellent. They are both a Kubota and New Holland dealer in PA. Good folks!

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[jmerola]

Thanks for taking the time to respond with that very insightful post Jim - I very much appreciate it.

So is it safe to say that the tractor has 1 hydraulic pump (contained somewhere in the main reservoir), and that the variability in speed afforded by the hst transmission comes from a variable displacement motor (located ?).

- Thanks again,

Jason

[dqdave1]

hydraulic pump is attached to right side of the engine at front end. Follow lines from filter on right side under rear fender well and it will lead to hydraulic pump. One side is for hydraulics and other is for power steering I believe.

[jinman]

Originally Posted by jmerola

Thanks for taking the time to respond with that very insightful post Jim - I very much appreciate it.

So is it safe to say that the tractor has 1 hydraulic pump (contained somewhere in the main reservoir), and that the variability in speed afforded by the hst transmission comes from a variable displacement motor (located ?).

Jason, the main hyd pump is located where dqdave1 said. It has nothing to do with the HST transmission. The HST transmission has its own pump and motor. When you press on the HST pedal it changes the amount of fluid the pump supplies to the motor instead of changing the motor as you stated. That's how it provides variable speed. The motor in your tractor is fixed and responds only to the amount of fluid supplied by the pump. Some tractors can change both the pump and motor, but yours, the TZ24DA, is not one of those.

Both the HST's pump and the main pump draw fluid from the main reservoir which is the transmission case. The simplicity is that you only have to drain one reservoir for the whole tractor, with the exception of the front axle and differential.

BTW: The area where the HST transmission is located is in front of the transmission case. It's a dry casing that just supports the HST. The transmission where the gears are for the ranges is behind the HST case and that's the one with all the fluid (the reservoir).

[jmerola]

Thanks guys! It's starting to make more sense now.

The sales guy said something about the power steering being on a "separate fluid circuit", such that steering is never lost, regardless of how hard the implements are being worked. Sounds like that is not quite correct. Maybe that is with a different model.

Thanks again for all the information.

- Jason

[dqdave1]

If you open your hood; you shoould see a black canister about 4" in diameter and about 10" tall with a black cap that says OIL. This is your power steering fluid resivoir. The power steering is seperate from hydraulics. when you find pump you will see it is actually two pumps. Do not add engine oil to this canister; it taes 134 hydraulic fluid. This canister is actually the filter for the power steering fluid and can be changed as per maintainance guide suggests. I will say, not many change this filter.
Sorry for the confusion.
Did you get a manual? If so, I would recommend reviewing it.

[jmerola]

Thanks dqdave1 - I did get a manual, but it didn't mention anything about power steering fluid or a filter. I will check again tonight. I think that was the initial source of my confusion. Maybe I should just spring for a service manual, and hopefully that will have more detail.

I appreciate the information,

- Jason

[jinman]

Originally Posted by dqdave1

If you open your hood; you shoould see a black canister about 4" in diameter and about 10" tall with a black cap that says OIL. This is your power steering fluid resivoir. The power steering is seperate from hydraulics. when you find pump you will see it is actually two pumps. Do not add engine oil to this canister; it taes 134 hydraulic fluid. This canister is actually the filter for the power steering fluid and can be changed as per maintainance guide suggests. I will say, not many change this filter.
Sorry for the confusion.
Did you get a manual? If so, I would recommend reviewing it.

Dave, what you describe is true for your TC29D and my TC45D, but I believe the TZ24DA only has one main hydraulic pump. The power steering is tapped off that supply and routed to the PS valve at the base of the steering column. It's function is similar to a power beyond circuit or flow divider.

I'm attaching a copy of the complete hydraulic system for the TZ24DA. You can see the piping for the power steering and the HST filter in the lower portion of the illustration. By used the circled reference letters and details, you can piece together how the system flow works, but there is only one main hydraulic pump and no separate power steering system like we have.

Jason, if you will go to Messicks.com and go to the parts section, you can enter your tractor model and look at detailed parts diagrams like the one posted below. Earlier, I mentioned that the hyd filter was around $75. That was an error on my part. That filter is about $15 and the HST filter is about $26. If you want the special rugged HST filter that is designed for temperatures below zero degrees (and associated high pressure), then the price is $75 to $80. That's the one I first saw and reported in error.

EDIT: Here's another item about the TZ24DA that you can see in the diagram. The HST filter receives flow through the same pipe as the power steering valve. Therefore, the main hydraulic pump serves not only as the power steering pump, but it also is the charge pump for the HST. Larger tractors like the TC29D and my TC45D have their own charge pump that draws oil from the reservoir and supplies it under pressure to the HST for more efficient operation. On the TZ24DA, the main hydraulic pump supplies this function, eliminating the need for a charge pump on the HST. These are things NH did to keep the price of the TZ24DA as low as possible and reduce the number of components.

[jmerola]

Wow Jim, thank you! This site/posters are really a wealth of knowledge and understanding.

Once again, I appreciate your time.

- Jason