raise hst relief valve pressure on tc33 ?

[schlen]

has anyone been able to raise the relief pressure on a tc33? i know there are many threads about these hst's, but none I found on changing the pressure relief setting. I know it must be possible. These tractors would be much better if I could put all of the engine's power to the ground.

 

[RickB]

Have you checked your drive pressures yet? I didn't think so. I'm pretty sure the tractor has to be split to access the main F and R reliefs. Substandard drive pressures are not at all common in NH hydrostatic units

 

[jinman]

To add to what Rick said, changing the HST relief pressure would be very hard to accomplish and extremely unsafe. The forward and reverse pressures both have relief poppet valves under spring pressure. There is no adjustment or shimming like the main hydraulic pump pressure. Changing to a stiffer spring or shimming the existing spring would most likely result in your tranmission blowing up. I'd sure say to check the HST pressure. If it is within spec., leave the valves as they are.

 

[schlen]

thank you both for the informative responses.
It's not that I want to somehow push my tractor beyond the limits for which it was designed. Its that I think it should live up to what it is--a 33hp tractor. call me old school but I just think one should be able to kill the engine with the hydro pedal(meaning all engine power is usable). I partly own a JD 855 hydro, and although it is less power and 1000 less pounds, it will probably outdo my tc33 doing loader work. the hydro on that unit (JD)is very tight and responsive, it is much more enjoyable to operate. I know you all have been over this, so please pardon my rant--there is no reason a hydrostatic transmission cannot be designed to handle the rigors and power of a CUT while still being responsive, powerful and "tractor-like". my JD 855 is proof of this, so are my ZTR mowers that get pushed to their limit. are these modern HST transmissions just reflective of how so many things are becoming these days--not as good as they should and/or could be but with just good enough to ensure profit and still be able to sell a tractors? Word is that it is not just NH HST but others. Why do you think they are making HST trannies like this (low pressure relief)?

 

[dynasim]

Does your 33 really have 5100 hours on it?

Chris

 

[RickB]

I'm pretty certain that you have no idea whether the 855 has substantially higher drive pressure relief setting than your TC.
I'd also speculate that if the TC33D actually has 5100 hours, it may well have low drive pressure. The cause most likely is NOT the relief valves, but wear within the rotating group components.

 

[SPYDERLK]

I'm pretty certain that you have no idea whether the 855 has substantially higher drive pressure relief setting than your TC.
I'd also speculate that if the TC33D actually has 5100 hours, it may well have low drive pressure. [[The cause most likely is NOT the relief valves, but wear within the rotating group components.]]

If you think about this I think youll see that it cannot explain it in any systemthat has even a semblance of normal function. Your premise would require the group components to be bypassing a great deal of flow at full pedal when there was a moderately high load. This would quickly degrade all components not specifically made to handle it. The relief is the only component made to handle this.
I agree with schlen on this. His system could use a couple hundred psi relief increase.
larry

 

[slowzuki]

I don't know much about these little NH's but the hydro unit may be undersized compared to the tractor. If you end up operating at the high pressure range of the unit you will hit the relief frequently. I find that the case when in high range with my Kubota L5030. In low or medium I can stall the tractor but high just operates the relief to protect the hydro.

Rick could be right if the wear was limited to the output pump (I think this is the variable displacement one on the NH's)

This is not the normal wear pattern as normally the components all wear at similar rates and leakage is noticed by poor performance as the fluid heats up. 5100 hours is a lot on a hydro...

 

[RickB]

If you think about this I think youll see that it cannot explain it in any systemthat has even a semblance of normal function. Your premise would require the group components to be bypassing a great deal of flow at full pedal when there was a moderately high load. This would quickly degrade all components not specifically made to handle it. The relief is the only component made to handle this.
I agree with schlen on this. His system could use a couple hundred psi relief increase.
larry

Well, Larry, we seldomn agree anyway. This is no exception. I'm not a bit worried.

A 5100 hour hydro can be bypassing oil just about anywhere, in any quantity.

Or the OP simply needs to select a lower range and higher throttle setting for loader work.

 

[schlen]

thanks for the input

I just got this tractor last year and thought it was worn out until I read many posts here about NH and other modern hst transmissions.

My tc33 has about 5200 hours on it now. the spring at the bypass may have weakened and the components are surely loosened up so I may not be in the best position to pass judgement--however one can tell when a relief valve is popping off as opposed to excessive fluid shear in the transmission.

the tractor will still go 15 mph in 3rd--do you guys think it would go this fast if the hydro was worn out? I'm not sure . . . it does lose a little speed as it heats up but did fine in the summer mowing

Rick--I don't know if the 855 has higher pressure, but whatever the specifics of its transmission are it makes for more usable horsepower and just a better feel as though it is a better fit to the size and power of the machine.

I'm not knocking NH, just curious.