HST pedal sticks under load

[tpaulson]

I have a TC45D. The HST pedals return to neutral slowly when under load. I know this has been discussed several times already. I was wondering if someone has found a fix or if NH has released a service bulletin on it? Going up a slight incline with lower engine rpm (1300 to 1500) or pulling a heavy load will almost always cause this problem. It also seems to happen more when getting close to something you don't want to run into, like the house or car (probably just coincidence). You have to quickly step on the opposite pedal to stop the tractor from moving forward. I have about 100 hrs on my TC45 now, it has always had this problem and hasn't gotten any worse or better. I have talked to 2 mechanics at the dealer and they say they have seen the problem before but can't do anything about it. They also said they are unaware if NH has released a bulletin on it yet. But, they were also unaware of the running cold problem due to the lower drain hose (until I brought in a TBN post and proved it to them by clamping the hose). I have greased the 2 zerks on the pedal mechanism, checked for any binding of the pedals, and the cruise control mechanism. All seem to be working ok.

I see this as a safety issue, it is just a matter of time before myself or my wife runs into something with the tractor. It always seems to happen when you are least expecting it.

Spencer200 have you seen this problem and what is the current NH position on this?

Thanks
Tim

 

[jinman]

There are two things I know that you can do. One is to apply lube to the "B" shaped piece along the edge where the roller rides. Also, you can adjust your return spring a little tighter (effectively the same as stepping on the opposite pedal). My tractor has 328 hours and the problem has essentially gone away.

 

[tc35dforme]

I've noticed the same thing on my TC35D but it seems to be related to the temperature of the hydro fluid. Once everything is warm...I haven't noticed the hang-up. I did crank up my return spring a while ago just to add a bit of 'under foot' resistance to the pedal.

Just one of those quirks we've got to live with ???

 

[deepsnow]

Jinman, I hope your suggestion solves my sticky HST pedal. I like simple fixes. Late last winter the pedal started sticking (not returning to neutral postion from both foward and reverse position) no problems this past spring & summer. Couple days ago (temp upper 40's F) sticky pedal. Forcast for snow tomorrow. Still don't own a snowblower. If I purchase one I'll probably jinx the snowforcast for the season.

 

[TCowner]

I had the same problem with my TC40D earlier this summer. I told the service manager that it was a little irritating because I had to be ready to hit the reverse pedal or it would kill the tractor (I was moving heavy,wet sand). He said he would send a service tech in a couple of days to look at it. I told him that it was dangerous and that I almost ran over the spouse. He sent someone within the hour. It was fixed by tightening the return spring adjustment. It hasn't misbehaved since. I think anytime you raise an issue that concerns safety the dealerships seem to respond a little quicker.

 

[RickB]

Adjust the return spring tension all the way to the end of the threads. If this doesn't cure the problem, get after the service dept.

 

[jinman]

Noel, I don't live in really "cold country" so I may not have experienced the same problem a lot of folks are having. I do know that I've had my assembly completely apart and there is a nylon bushing on the outside pivot point of the "B" shaped actuator. I'd squirt a little light lube on this pivot, but anyone will tell you that the nylon is supposed to not require lubricant and lube may attract dust and dirt. That's also true for spraying lube on the roller which runs along the "B" shaped piece. I strongly suggest not to use grease for lube in these areas. A light lube will rinse off the old residue and any dirt everytime you apply fresh lube.

There is another thing I've noticed about the action of the pedals as the tractor's engine lugs down. In this situation it does seem like the pedal action is more sluggish. When I first had my tractor, I would constantly push the pedal too far (treating it like an accelerator pedal). As I became more familiar with the action of a hydro tranny, I realized that if the engine is lugging down, I need to shift to a lower range rather than push harder on the pedal. Pushing the pedal is like shifting to a higher gear and the engine just lugs down more and will eventually die. A point about this that is normally not discussed relates to the way a hydro tranny works. It requires hydraulic flow to operate. When the engine starts to lug down, hydraulic flow is reduced to nearly none. Everything just quits working. The internal transmission pressures which aid in returning the pedals to neutral are no longer there and the return spring is all you have to put the pedals in neutral. So in my opinion, for everthing to work properly, the engine must be running at normal speeds. That's why I think shifting to a lower range is a wise move.

 

[Mosey]

My TC29D has always had this problem. I was hoping it would go away as it got broke in more, but I have over 250 hours now and it still does it. It does it the most when it's cold and will do it under load like you said. I have just one pedal, so I have to push on the back of it to get it to stop. I had the dealer look at it and they replaced the cruise control magnet. That helped but didn't solve the problem. I don't know how the TC45D works, but on the TC29D I can push the clutch in to stop quick if I have to and sometimes that's faster than pushing on the reverse side of the pedal. I'm so used to it now that it really isn't a problem, but I have to remember to tell anyone else who drives it. It's very rare for anyone else to drive it anyway.

 

[djradz]

Did you try some lube on the roller. I used some 30w oil and mine now actually seems to move too fast. /w3tcompact/icons/shocked.gif

 

[jtn]

This is normal.

A quick lesson in how hydrostatic transmissions work to illustrate my point. The engine turns a variable displacement hydraulic pump. This is plumbed directly to a hydraulic motor that has two positions, high and low (on Class III NH tractors). When you press the petal down you are increacing the displacement of the pump. As pump displacement INCREASES you are going FASTER and MORE POWER is going to the ground. When you flick the high/low switch on the dash you switch the motor from high displacement to low displacement. When you decrease motor displacement you will go FASTER but have LESS POWER to the ground.

Now what does this have to do with the petal sticking? When you are trying to push an immovable object one of two things will happen. 1. you will start spinning the tires in poor traction conditions, and/or 2. The drive petal will floor itself. This occurs because you are exerting a demand on the tractor that the pump displacement you specified can not match. Remember, the greater the pump dislacement the greater the power. In effect the tractor is powering itself up to meet the demand. If you floor the petal yourself you will get the same effect. When the petal is floored you are getting the most power to the ground.

There is not much that can be done about this until NH releases an electronically controlled hydrostatic system (I wonder what the JD owners with eHydro would have to say about this). An electronically controlled system will still try to power up but you would not feel the petal moving, as pump displacement would be controlled by a computer.

So, to sum it all up, when trying to dislodge that big stump or move Mt Everest, be ready to hit the reverse petal so you do not stall your engine.

JT

 

[tc35dforme]

Jtn, Is there a typo in your post ?? You reference FASTER in two separate sentences apparently outlining two separate modes of operation. Can you break it down a bit or am I just missing something on this one ???

I may regret this....but......doesn't the 'power' and 'speed' run on an inverse relationship. I was under the impression that the maximum 'power' ( traction assumed to be 100 % ) was obtained at the beginning of the pedal stroke. As you squash the pedal, you go faster, but you give up traction force or 'power'.

I find that when I'm really trying to push something...a slight nudge of the pedal to a creep seems to do the trick.

I defintely don't know the physics behind the hydro transmission, but I do know that if I'm in Hi range - "bunny" and slam down the pedal...the tractor isn't too happy.

I guess some time reading the repair book is in order. It never hurts to learn....or ask questions.

 

[RocketJSquirrel]

I wonder if this is a long time Ford/NH problem. Our 1995 Ford 1320 does the same thing. OTOH my JD 755 stops immediately when you let off the pedal. I'll check out the spring tension.

 

[DK35vince]

tc35dforme,
Your version on how hydro works is more accurate.

 

[jtn]

There are two ways to go FASTER with a hydro tranny. First is to INCREASE the displacement of the PUMP (depress the travel petal all the way); the second way to go FASTER is to DECREASE the displacement of the MOTOR (shift to rabbit mode). The gear shift lever on the right side has no effect on the hydro; it is a two speed transfer case (you are right, if this is shifted into high range you will get less power to the ground).

The hydro tranny will have the most power when the pump and motor are both at maximum displacement. This is turtle mode with the travel petal floored. With a hydro tranny you are increasing tractive effort and speed until the pump is at maximum displacement. I agree this does not seem to make sense unless you understand the workings of the hydro system. If you shift to rabbit mode or high range with the transfer case this will decrease your tractive effort and cause you to go faster.

I will see if I can get some diagrams or more info on the web to try and make this a little more clear for anyone interested.

JT

 

[jinman]

I think you are correct on your description of what happens with our tractors. JTN's description of added power is only true if you have unlimited torque from the engine. If you change the angle of the pump swashplate in any range, you will only increase the tractive power up to the limits of input power. Pressing the pedal further will cause the engine to lug down and stall unless the relief valve's pressure is exceeded.

 

[jlong]

Hope you tried the "quick fix" of lubing the roller and tightening the spring because it worked great for me. My TC35D has acted the same since I got it. Now with 275 hours on it, and two trips to the dealer, who explained it as "Characteristics of a Hydrostatic tractor", I tried it and it worked. I was a bit skeptical since my adjustment spring was all but 1/2" from the tightest setting, but I tightened it all the way and sprayed some silicone on the roller. Immediately tried it on a slope that always caused the tractor to keep going in low, and the tractor stopped on a dime.

Good luck. Hope it works as well for you.

And again, thanks to all of the knowledgeable people on this website

 

[djradz]

I'd suggest something a little heavier than silicone spray, like 30w, but anything is better than dry for the roller.

 

[tpaulson]

Just a quick update. I adjusted the return spring tension almost all the way to the end of the threads. When I got the tractor the spring was already set about a 1/2" away from the end. I made this adjustment about a month ago and have not had the pedal stick since.

Thanks for everyone's help and suggestions.
Tim

 

[Mosey]

tpaulson - After you tightened up the tension on the spring, did it make it noticeably harder to push the pedal?

 

[tpaulson]

Mosey
It may have made the pedals slightly harder to push, but I don't think it is very noticable.

I am not sure if your TC29 would have the same type of tensioning spring to adjust.

Tim