Tractor squeals under load after getting warm

[jinman]

Good job so far Luke. Looking at the mouse-house, it sure makes you wonder why all openings aren't plugged. My tractor is the same way with ports going into the relief valves. I sure don't envy your having to clean up that mess. From the looks of things, your problem was probably that clutch slipping because of the throwout bearing being so far out of adjustment. I bet you keep that 3/4" freeplay the next time around after getting this replaced. You have to be pretty pleased that it was something simple rather than an HST rebuild. Many HST tractors also have a clutch. This is a very good lesson in why you need to keep that clutch adjusted properly even on an HST tractor.

I think it's funny how we all zeroed in on the HST. Had this been a gear tractor, many of us would have immediately said to check the clutch. I never considered the clutch because my tractor is one of those HSTs that doesn't have one. Hindsight is 20-20.

EDIT: The pressures you got during your test still indicate a problem with the HST. That and the looks of the old oil from your change that you posted have me thinking that you may have reduced performance from the HST. There are still questions that need to be answered.

 

[winslet]

Hey,
Sorry I am not understand with this.

 

[hlukeh]

I took off the clutch housing and removed the HST. The HST looks beautiful inside and the high pressure relief valve looks fine. I guess there's a possibility that the high pressure relief valve spring is slightly weaker, but because of the underlying symptom - pressure drops as engine heats up but not necessarily as hydraulic fluid heats up, points me to the clutch being the entire problem. If the clutch was slipping, then theoretically the longer the tractor ran, the more it would slip and heat up and thus the easier it would slip.

I just wanted to take out the HST and open it up to see if there was any obvious wear inside, and to see if there was any obvious problem with the relief valve, but it all looks fine to me.

I could add an extra washer to the relief valve to increase the pressure that the valve would open, but it's probably smart to replace the clutch, put it all back together, test it out, and if there is still a problem try to pinpoint the issue further and then re-take it all apart and fix the next thing that it possibly could be.

Let me know if anyone has any thoughts on the HST or relief valve.

For anyone trying to take the HST out of this tractor in the future and not being able to remove the clutch housing, the bearing going to the front drive axle, as shown in some of the attached pictures, was completely seized to the shaft and finally came loose after spraying anti seize spray (liquid wrench) around the axle and let it sit for a while. I then had to lightly tap the shaft tip with a hammer to get it to slide backwards through the bearing.

Luke

 

[SSdoxie]

Looking at the clutch it's wonder it drove at all. The valve plate on HST looks like new yet. I wouldn't change anything there, put in new clutch and throwout bearing and try it.

 

[hlukeh]

Here are some more pictures of the hydrostatic drive. It looks brand new inside!

 

[jinman]

Looking at your sparkling clean HST's inside and the dirt on the outside of the transmission, I just hope you are being extremely careful to keep any crud out of the transmission. I'm sure you will be very meticulous, but seeing the contrast in your photos makes me cringe a bit.

 

[hlukeh]

Well, my clutch finally arrived and I put it back together enough to test it out. Guess what?! It works just as well as it did before I took it apart!!!! That means I haven't made it any worse, but it still bypasses fluid somewhere and squeals around 2600psi and gets worse the longer it's driven.

A few weeks ago I bought a few implements that I got a good deal on. Yesterday I tilled a couple of acres with the rototiller and it didn't squeal at all in low range until I started tilling up a not so steel hill. The tiller runs off the PTO and actually helped to push the tractor up the hill when the tractor started losing power.

The squeal sounds like it's coming from inside the HST somewhere, but I'm not sure what else to look at in there, not to mention that it takes a couple hours to open the tractor up - draining power steering fluid, hydraulic oil, engine oil (the filter blocks a bolt)...

Luke

 

[hlukeh]

Today I decided to make a high pressure relief valve removal port instead of splitting the tractor. It was very easy to drill a hole through the housing, and I don't think it will weaken the mid section at all. I'll just have to find a nice plug to put in the opening.

I removed the high pressure relief valve, took it apart and found an o-ring that had a very slight slit in it, so I replaced the o-ring. I also added an extra washer to the ones that were already installed as spacers to slightly compress the spring. I figured I should see a difference if the spring has weakened and the issue is the relief valve.

I put the relief valve back together and back into the tractor (30min total procedure!!). There was no change whatsoever at the point that the HST started squealing with the brake on, engine running at 2500rpm, in high range, and then pressing slightly on the pedal either forwards or reverse.

Unfortunately I don't think there is an issue with the relief valve, but now I have no idea what else it could be.

Does anyone have any other ideas?

Thanks,

Luke

 

[dynasim]

I would look for air ingress into the suction side of the charge pump. It is a relatively common problem, and the specific symptom is squealing.

Good luck
Chris

 

[hlukeh]

Thanks for the suggestion Chris.

Yesterday I checked the charge pressure at the drilled out banjo bolt, and at idle it was just under 90psi. What I hadn't tried before was putting the tractor in high gear with the brake on and pressing on the pedal while watching the charge pressure. As soon as the tractor started loading, the pressure started dropping, so it appears that there is a problem either with the charge pump, charge relief valve, or as you mentioned air getting into the suction line.

I guess air getting in could be as simple as the hydraulic pipes that go into the charge pump could be allowing air past the o-rings. The two pipes that go into both sides of the charge pump are just pushed in and are sealed with o-rings and don't really have much holding them in place other than a plate and screw on the outside of the tractor. I'll have to check those seals as I didn't pay too close attention to the o-rings when I had the pipes off.

Thanks,

Luke