Higjh or low RPM when going down steep grade with HST?

[furnone]

Just wondering... when I go down a steep grade with my JD 2210 HST, do I have more braking with higher RPM' s or does it matter? I don't fully understand how the wet braking works, but it would seem that higher RPM's would allow more hydraulic pressure and thus more braking action.

 

[Wagtail]

To be honest I don't think it matters. With HST, as soon as you take your foot off of the directional (FWD or RVS) the tractor stops, which is a function of the HST transmission to an extent. The brake is then applied to hold against any creep due to the gradient you're on.

 

[jenkinsph]

I would raise the rpm above idle a little (1200 to 1500 rpm) just to make sure the engine doesn't stall. Make sure the transmission is in low range and 4x4 is engaged. As long as the tires can maintain traction you should be fine. If you start to slide down the hill make sure someone is there to make a video to post for us.

 

[Thomas]

Going down steep slope/grade I like low range most of when FEL loaded.

 

[ruffdog]

Also, lock the rear differential. It has happened that one tire spins forward and the other loses traction and spins backward. At that point, you have lost control.

 

[furnone]

Wagtail, that is what I'm wondering about, since the stopping or holding action is a function of the HST transmission, do higher revs equal more hydraulic pressure and thus more holding or braking power?

I always use low range and keep the bucket low to the ground, but each time I go down, I wonder if I should be at low, medium or full throttle. I have learned that it's a mistake to go down with a loaded bucket without 4 wheel drive engaged. I almost turned it over the first time I went down and made a turn at the end.

 

[vsteel]

Wagtail, that is what I'm wondering about, since the stopping or holding action is a function of the HST transmission, do higher revs equal more hydraulic pressure and thus more holding or braking power?

.

Wagtail is saying that the stopping and holding function is a brake, not related to the hydraulic pressure.

Personally I would go at least medium throttle to allow me enough power if I had to try and back up for some reason.

 

[oldnslo]

Engine RPM does not equate to more pressure in HST systems. What you need to be cautious of is over speeding the diesel engine if you have enough traction and a steep slope the HST can now drive the diesel engine to an over speed condition. Like others have said run around 1500 - 1800 RPM and you should be fine.

 

[Gary Fowler]

Engine RPM does not equate to more pressure in HST systems. What you need to be cautious of is over speeding the diesel engine if you have enough traction and a steep slope the HST can now drive the diesel engine to an over speed condition. Like others have said run around 1500 - 1800 RPM and you should be fine.

I have found that my B26 will go into a coast mode when in high range and traversing a slight downhill slope. It then has to kind of catch up to the wheels when it reaches the bottom of the hill. I haven't noticed this effect when in M range where the braking action of the HST keeps everything in sync.
I haven't found that RPM make any difference in braking action. You can always use the brakes to slow down if you start going too fast regardless of the RPM.

 

[MHarryE]

If you are using the hydro to control your downhill speed, it doesn't make any difference. Torque = pressure X displacement. Braking is the torque required to hold position on the hill. Speed does not enter into the equation. Displacement in this case is motor displacement as under braking, the motor and pump switch positions - the motor is pumping oil and the pump is resisting. Except for needing control pressure to set the position of the pump smash plate, the engine could be off. In fact it f you shut your engine off while on a steep slope, the swath plate will go to zero and you will slowly creep down the hill - until control oil is depleted from the servo piston, the swash plate goes to max, and your tractor rolls down the hill and into the river.