Bypassing on a TC45D

burtrl · Jan 4, 2009

I recently read an old thread started by jinman comparing TC35D & TC45D tractors and how the extra horsepower does not give the TC45D any advantage of the TC35D in terms of pulling power. This got me thinking about my own TC45D and how easily it is to get bypassing to occur. On your tractors does your engine load up much before the hydrostat bypasses? On mine in high range the engine doesn't seem to load up all that much. Heck on ice in 4WD rabbit (high range) I have trouble spinning the tires!

jinman · Jan 7, 2009

I waited a few days to respond to see if anyone else would. On my tractor, in high range and either turtle or rabbit, the engine doesn't load much at all to put the transmission into bypass. However, I can hear the HST whine a bit before it goes into bypass.

You are right about high/rabbit being unable to spin tires on ice or a banana peel. That's a road gear and with a slight grade on a smooth road you have to really feather the pedal to get going. I usually start in turtle and then punch the rabbit button as the tractor starts to roll. It feels like an automatic transmission shifting up in my opinion.

I think NH probably figured 5000 psi was the maximum pressure they trusted in our transmissions and they won't go any higher. That's why the TC48 and TC55 never offered an HST. That would require a whole new level of engineering to get up to 6,000 or 7,000 psi or even design a higher torque transmission that operated up to 5,000 psi. What they seem to have decided is that the CVT is the future. I'm looking forward to the first CVT tractor so I can go test drive it. However, I'm still really happy with my TC45D for what I use it for. I'm not ready to give up that HST yet.

burtrl · Jan 9, 2009

Last weekend I drove the tractor into a frozen manure pile to see just how much the engine would bog down before bypassing in all ranges. What I found was that the engine would drop a couple hundred RPM, stay steady for a couple of seconds, then load up until she stalled. I was able to do this in both high ranges, but in the lower ranges the tires broke loose before the engine became that loaded. Another observation I made, was that when the engine became loaded to the point of stalling, if I took my foot of the pedal, the transmission would not release on its own. I had to hit the reverse pedal to get it to release just prior to stalling. Does this sound normal to you?

I do agree with you Jim, in that I would definitely not give up the convenience of the hydrostat for loader work.

Ross

DocHeb · Jan 9, 2009

burtrl said:
Another observation I made, was that when the engine became loaded to the point of stalling, if I took my foot of the pedal, the transmission would not release on its own. I had to hit the reverse pedal to get it to release just prior to stalling. Does this sound normal to you? Ross

That is "normal" for the HST. Jim may chime in and explain it better (he knows all about those swash plates, etc.), but you need enough RPM and pressure in the transmission charge pump to affect the change in direction. If you really bog the engine down, the charge pump doesn't give you enough pressure to reverse the transmission. The same thing happens if you put the tractor under significant load with the RPM set too low. This is not a New Holland issue, but is an issue with other HST brands also.

Also, the HST pedals do have a zerk for greasing, make sure they're lubed up. Also, adjust the return spring on the pedals to maximum return strength. The early models had a weaker spring, and there is a replacement spring that gave a better return. Always run at proper RPM when the tractor is under load.

See:
Follow-up to sticky hydro. pedals
and
HST Just Won't Stop, Quit, Woah - this post gives the part number for the new spring.

jinman · Jan 10, 2009

DocHeb said:
...Jim may chime in and explain it better....

Chris, here's my "chime," but it ain't better. You did a great job of explaining what happens. Our HSTs do not work well when loaded in low engine rpm situations, period.

RickB · Jan 10, 2009

jinman said:
I think NH probably figured 5000 psi was the maximum pressure they trusted in our transmissions and they won't go any higher.

Somewhere around 5000PSI is about the limit for most hydrostatic systems in consumer, Ag, and construction equipment. Applications transmitting more torque and HP than TC's use more flow and bigger displacement pumps and motors with similar relief pressures. It gets expensive trying to contain operating pressures much above 5K.

6sunset6 · Jan 10, 2009

ah hah I asked a question a long time ago and did not get an answer ,probably because I did not know how to ask the question.
I have a MF shuttle shift TLB around 47 HP. two pedals. 1st 1/4 pedal move picks an electrical solinoid for foward or reverse. More pedal travel increases engine rpm until you are going as fast as you want. I also have a NH TC 34DA HST and was wondering why the RPM's had to be up all the time. Now I know. I was also interested if the next frame size uo TC 35, 40, 45 etc was the same HST as the TC34 though it has 2 pedals. I was trying to find out if the two pedals were like the TC 34 or like the MF shuttle shift. I was toying with the idea of upgrading because I like the MF shuttle shift better.
But I think the HST's are the same. Obviously no variable throttle with HST.
Next Question What RPM's for what? I sort of set it at 2000 unless I am running the PTO then at the PTO mark which is a little more

RickB · Jan 10, 2009

6sunset6 said:
ah hah I asked a question a long time ago and did not get an answer ,probably because I did not know how to ask the question.
I have a MF shuttle shift TLB around 47 HP. two pedals. 1st 1/4 pedal move picks an electrical solinoid for foward or reverse. More pedal travel increases engine rpm until you are going as fast as you want. I also have a NH TC 34DA HST and was wondering why the RPM's had to be up all the time. Now I know. I was also interested if the next frame size uo TC 35, 40, 45 etc was the same HST as the TC34 though it has 2 pedals. I was trying to find out if the two pedals were like the TC 34 or like the MF shuttle shift. I was toying with the idea of upgrading because I like the MF shuttle shift better.
But I think the HST's are the same. Obviously no variable throttle with HST.
Next Question What RPM's for what? I sort of set it at 2000 unless I am running the PTO then at the PTO mark which is a little more

I'm not familiar (at all) with the MF system, but it sounds like it is electronically controlled similar to Deere's E-hydro system. To date all NH hydros are not electronic, therefore the throttle has to be set manually. The NH transmissions are similar between classes, but not identical. Single or dual pedal design is purely external; both systems operate a single pintle shaft. I tell my customers to operate the NH hydros at a minimum of 1500 ERPM even when doing light work so as to provide sufficient charge pressure flow and oil cooling. Heavy loader work and similar tasks should be done at a higher ERPM setting. PTO implements should not be overspeeded. Most will function just fine at less than 540 PTO RPM. But you already know that part. If you are considering making a trade, let's wait on the new Boomer with the CVT transmission. Ted was out to Las Vegas to the product intro just this past week.