Tractor squeals under load after getting warm

[Soundguy]

I think i'd flush it into a bucket first.. easy enough to do a poor mans pressure and flow test at home with common tools and parts.. if a hst has failed.. the cooler will be the least of the expense or worries..

soundguy

 

[hlukeh]

Thanks for the suggestions!

The more I do myself the more I'll learn about hydraulics, and it's a field I've always wanted to learn. Three years ago I didn't know much, but I feel like I'm now learning a lot.

I'll see if there's a bypass valve next to the HST to look at and clean. The service manual shows that the tractor has to be separated to get to the high pressure relief valve, and I don't know how I'd ever get the tractor halves re-lined up if I were to separate it. It sounds like I will probably have to separate it anyways to get to the HST, but I may as well fix the flow through the cooler since I know it's blocked or bypassed somewhere.

There is definitely no fluid going through the cooler because after driving the tractor for about an hour today the cooler wasn't even warm (80F vs the 120F of most of the other hydraulic components).

Luke

 

[Soundguy]

yikes!

 

[jinman]

There is definitely no fluid going through the cooler because after driving the tractor for about an hour today the cooler wasn't even warm (80F vs the 120F of most of the other hydraulic components).

Luke

Luke, just remember when you are making comparisons that the main hydraulic system and the HST system are different. Don't compare the temperature of the HST to the main pump's temperature. Feel your HST filter and use that as a comparison. Your HST is working, so it must be getting oil. If it is not going through the cooler then it must be bypassing at the pressure bypass at the filter. Otherwise, your HST would starve for oil and self-destruct in short order. Also, one side of the HST cooler should be much warmer than the other side.

The flow of oil is as follows. The charge pump pulls oil from the reservoir and sends it through the filter and cooler before supplying it to the HST main pump. The HST pump then supplies oil to the motor based on how far the pedal is depressed. The pedal changes the amount of oil the HST pumps. The HST works the same for all transmission ranges. Only the gearing changes after the transmission when you select another range.

I think you can probably remove the HST relief valve and a couple of checkvalves from outside the transmission housing. From the parts diagram, it looks like there are round ports in the casting to allow access to the transmission valves. I'm not sure of that since I've never worked on a 1520, but you said the maintenance manual said you have to split the tractor to do that. I know for sure on my larger TC45D that the relief valve can be changed without splitting the tractor. It's worth double checking.

 

[hlukeh]

I got a gauge and tested the hydraulic pressure today.

I engaged the parking brake, put the tractor in high range, and turned up the revs to 2500rpm. I then pressed on the hydrostatic pedal to go forwards and backwards.

The service manual says to use the left test port and press reverse, but there is no pressure when I do that. If I press forward the pressure builds.

When I first started the tractor and pressed forward, the pressure built to 2600psi before squealing (I assume that's the fluid going through the high pressure bypass valve).

As the tractor continued to run and warm up (just sitting) the max pressure that the gauge would go to before squealing slowly decreased. After a few minutes the pressure would only build to 2300psi.

After 10 minutes the pressure would only go to 2000psi.

The service manual says that the pressure should build to 3839-4124

My hope is that either the relief valve just has to be adjusted and maybe replaced, and that it's not something more. The painful part is that the tractor has to be separated in order to adjust the valve, and possibly multiple times, and that means unhooking hydraulic hoses, draining fluid, unbolting the tractor halves, somehow wheeling it apart, adjusting the valve, somehow wheeling it back together and getting it lined up and back together, hooking up all the hydraulic hoses, replenishing the fluid and trying it out. Then do it again if it wasn't adjusted enough.

Luke

 

[tnewbern]

Check your charge pressure.

If the pressure is low then you may have a restiction like the oil cooler or a worn supply pump.

If it is up to spec then your pump/motor are worn and bypassing the fluid.

I'm with jinman though and think its time for an HST overahaul.

Coyote Machine funny how we both found this thread...

 

[hlukeh]

Thanks for the suggestion about the charge pressure. It's too bad New Holland didn't provide an easy test method. The manual says to remove the Banjo bolt, drill and tap it, test the pressure, and then I guess put a plug into the banjo bolt, although it doesn't say to plug the hole afterward, unless of course they want a person to buy a new Banjo bolt for $300+...

It's probably worth while to do that before separating the tractor, especially considering how dirty the fluid was and there may be a restriction in those lines.

Luke

 

[tnewbern]

Post the page with the recommended way for testing the charge pressure. If its possible post a picture or page with the hydraulic schematics. There has got to be a better way to test the charge pressure. This may even be as easy as using thew same test port for the HP relief. At the very least you should be able to put a guage before and or between the filter and HST and measure it outside the unit.

 

[hlukeh]

That's a good idea to just measure the pressure in the line instead of trying to drill and tap that bolt.

I took some pictures of some of the pages. Thanks a lot for the continued suggestions. I think I'm getting closer to the problem and haven't had to take the tractor anywhere which is great!

Luke

 

[hlukeh]

I think it might be easier to look at some pictures of the manual in pdf format rather than jpg...