HST Problems

[rockin]

Hi
I'm having problems with the HST on my 1620 ford tractor, after steady use for a couple of hour it seems to lose it push power. I think after the hydrolic oil heats up it is bypassing. Could it be a faulty high pressure releif valve. Any input would be greatly appreciater. thanks

 

[jinman]

Yes, it could be a relief valve. However, the only way you'll ever know for sure is by doing a pressure test. Those high pressure relief valves are normally very expensive parts. I've seen some over $300 each. So, it's something you don't want to replace just to 'see' if that's the problem. On my tractor, there is both a forward and reverse valve that are identical. They could be swapped if I had doubts. On your tractor, I think there is a single relief valve, so it's not so easy. Often, getting to the valve requires a special tool and two elbows on the same arm without dismantling the operator's platform.

What I'm trying to encourage is to check with your dealer about testing. The relief valve will lift at it's rated PSI whether you have cold oil or not. You could have some wear inside your HST pump/motor that's allowing thinner oil to bypass. Do you use the specified Multi-G 134 fluid? If you are using a single viscosity fluid instead of the Multi-G or compatible, then that could be part of the problem. TSC has a premium transmission fluid that works well in my TC45D, so you do not have to have NH oil if you purchase a multi-grade oil designed for transmission use.

BTW, we all get used to the operation of our HSTs and I admit thinking sometimes that it is bypassing early. Then, I notice that I'm spinning tires and just asking a bit too much of the tractor. The only way to know for sure is with testing pressure. My objective evaluation of my tractor's power becomes subjective when I want to do a particular job just a bit too big for it.

 

[rockin]

I know what you mean about doing jobs to big for the tractor, there is times I have worked it to capasity and beyond. I have always used the recommended oil which is hydrol 56 I also changed Filters and checked for clogged screens. Had the main hydrolic filter assembly, and also the HST filter assembly apart looking for a plugged screen didnt find any screens. I Did a Pressure test on the charge pump and also the high pressure pump. The charge pump Pressure is good but the high pressure seems to be down a bit it is at 3800 PSI. to check the relief valve on my tractor I have to split the tractor to get at it. In the maual it says relief valve can be adjusted, but to take it out adjust it put it back together it is a lot of work. If i go that far I might as well take the transmission out and have it checked out. I am 8 hour Ferry boat ride than another 8 hour drive to the closest Dealer. I priced the high pressure relief valve from the ford dealer and they give me a quote of $700 for a new one. After I have worked the tractor steady for a couple of hour it loses forward power and starts to make a noise when I try to push into a load with the frontend loader. Thanks for your insight.

Ron

 

[jinman]

Ron, I'm not sure what your pressure should be. My 45HP tractor has a relief pressure of 5000 psi. It makes sense that yours would be less considering your reduced weight. Of course, gear ratios/ranges come into play also, but 3800 psi sounds like a reasonable amount for your power-weight ratio.

The noise you are hearing when the tractor warms is what concerns me. As I mentioned before, the relief valve should lift at the same pressure no matter what temperature, but the rate of flow in bypass might change due to viscosity thinning. Is your oil clear? Have you ever taken a sample to have it tested for metal particles? There is the possibility of internal pump/motor wear. If so, there should be an elevated metal content in your fluid. Of course, I regularly push my HST into relief when loading from a pile or digging. I'm just deaf enough that I can't hear it. Relief is normal, but early relief seems to be what you are experiencing. That's something only you know and just can't be fully described on a forum.

It's a bummer being so far away from a dealer. I'm 25 miles from mine and that seems pretty far sometimes. I knew the relief valves were expensive, but I was shocked at your $700 price. Wow! Shibaura parts sure have skyrocketed in price since New Holland split with them. Everything seems to be two or three times it's original price.

I can't help much except to be a 'coach' from afar. I hope you find a good solution. If there is any data I can help you research, let me know. Nothing seems quite so bad as being isolated with equipment problems. Good luck!

 

[Hooked_on_HP]

I know what you mean about doing jobs to big for the tractor, there is times I have worked it to capasity and beyond. I have always used the recommended oil which is hydrol 56 I also changed Filters and checked for clogged screens. Had the main hydrolic filter assembly, and also the HST filter assembly apart looking for a plugged screen didnt find any screens. I Did a Pressure test on the charge pump and also the high pressure pump. The charge pump Pressure is good but the high pressure seems to be down a bit it is at 3800 PSI. to check the relief valve on my tractor I have to split the tractor to get at it. In the maual it says relief valve can be adjusted, but to take it out adjust it put it back together it is a lot of work. If i go that far I might as well take the transmission out and have it checked out. I am 8 hour Ferry boat ride than another 8 hour drive to the closest Dealer. I priced the high pressure relief valve from the ford dealer and they give me a quote of $700 for a new one. After I have worked the tractor steady for a couple of hour it loses forward power and starts to make a noise when I try to push into a load with the frontend loader. Thanks for your insight.

Ron

Are you sure that is the correct oil. To me that apears to be a strait hyd oil not a uthf type.
Bill