Bypass ?

[cperky]

I was bushhogging today going up a very steep hill. The briars and weeds were between knee and waist high going up the hill. At one point there was a sudden loss of power and it seemed liked the rpm's dropped.The forward pedal went to the floor like a brake pedal on a car. I quickly raised my foot from the forward pedal and the tractor just as quickly recovered. I went on my way with no further problems. This has happened one time before also on a steep hill while bushgging. I have read in other posts here that sometimes the hydro will go into bypass? Does this sound like bypass or do I have another problem?

Thanks,
Chris

 

[LBrown59]

What's by pass

I was bushhogging today going up a very steep hill. The briars and weeds were between knee and waist high going up the hill. At one point there was a sudden loss of power and it seemed liked the rpm's dropped.The forward pedal went to the floor like a brake pedal on a car. I quickly raised my foot from the forward pedal and the tractor just as quickly recovered. I went on my way with no further problems. This has happened one time before also on a steep hill while bushgging. I have read in other posts here that sometimes the hydro will go into bypass? Does this sound like bypass or do I have another problem?

Thanks,
Chris

 

[cperky]

What's by pass

I guess I really don't know what bypass is. I was just hoping that there was a simple answer, and like I said I have seen others mention this term.

 

[jinman]

I guess I really don't know what bypass is. I was just hoping that there was a simple answer, and like I said I have seen others mention this term.

Bypass is. . . well . . .bypass. It's what happens when the pressure relief valve lifts. It happens at 5000 psi inside the transmission to route fluid around the hydraulic motor portion of the HST. Nothin' wrong with your use of the word "bypass."

I think you described whet many of us have happen with the NH HST pedals. This occurs when the engine bogs down to a low rpm and the tractor is under a heavy load. Because the HST's charge pump cannot maintain enough flow as the engine bogs, and the transmission is under high pressure, the swashplate in the pump pulls itself to maximum angle without any foot pressure. It's kind of a dangerous situation if you are in close quarters. but out in the open, it seems to recover as soon as the pedals go far enough down that the transmission is forced into bypass if you don't have your foot pressing on the forward pedal. The real solution is to always maintain a high rpm above 2000 or use a low range where the engine will not bog down. It does not take a very steep hill to cause the tractor to bog in High/Turtle. I usually mow in Low/Rabbit on small inclines and sometimes on really steep inclines where I'm backing down with a mower, I'll drop down to Low/Turtle to ensure I have enough power and torque to prevent surprises.

You can also increase the return spring pressure on your pedal, but the more spring pressure applied, the harder you have to push on the pedal and that may bring about foot/leg fatigue if you don't use cruise.

I think you have just experienced what many of us have with these tractors. It's always a little disconcerting when it happens, but reminds me to use the correct range and keep rpm up.

 

[dynasim]

There is a relief valve on the HST that will lift (bypass) if the tractor if the tractor is pushing hard. On my TC45, the pedal does the same thing(drops to the floor) if that happens.

Were you in high range? I haven't had this happen in low range, except when digging dirt. You may have some tough! weeds.

Chris

 

[cperky]

The real solution is to always maintain a high rpm above 2000 or use a low range where the engine will not bog down. It does not take a very steep hill to cause the tractor to bog in High/Turtle. I usually mow in Low/Rabbit on small inclines and sometimes on really steep inclines where I'm backing down with a mower, I'll drop down to Low/Turtle to ensure I have enough power and torque to prevent surprises.

You can also increase the return spring pressure on your pedal, but the more spring pressure applied, the harder you have to push on the pedal and that may bring about foot/leg fatigue if you don't use cruise.

I think you have just experienced what many of us have with these tractors. It's always a little disconcerting when it happens, but reminds me to use the correct range and keep rpm up.

There is a relief valve on the HST that will lift (bypass) if the tractor if the tractor is pushing hard. On my TC45, the pedal does the same thing(drops to the floor) if that happens.

Were you in high range? I haven't had this happen in low range, except when digging dirt. You may have some tough! weeds.

Chris

Thanks for the input guys. Sounds like you have both described exactly what happened. I was in low turtle at pto rpm's but the hill I was climbing will sometimes give a 4x4 truck trouble when the weeds are cut, This is the first time this hill has been cut in one year so i think I may have been pushing the limits of the tractor.

Once again thanks for the input. I always learn a little every time I login here

 

[dynasim]

That must have been a steep hill. If it were me, I may question whether the relief valve set pressure was to low. However, I really don't know enough about the specifics of these things to be able to judge.

In turtle/low, my TC45 will spin 3 tires in dry dirt without bypassing(I don't have weight on the rear of it, though).

Chris