Superior Braking Power in the PT

[smartguyz]

Hi guys -

I was just thinking - after using my PT all over my property, I noticed something really critical to safety and stability.

As you know, all normal tractors usually have 2-wheel-brakes, with braking power to the rear wheels. Those with significant seat time on any significant grade realize that when carrying a load in the front loader, that your best bet is to go in reverse down the grade. There's a good reason why.

A fully-loaded front-loader tends to act as a counterweight, which lifts the rear end of the tractor - that's why normal tractor owners put fluid in the tires, or weights on the rear. When going downhill with a full front-loader, this changes the center of gravity and further exascerbates the problem. In many cases, seasoned tractor guys have experienced how the back end of the tractor will be so 'light' going down the grade that you lose traction on the rear tires, and since the front wheels in a normal tractor are free-wheeling (i.e. have no brakes) - you can find yourself in situation where you have no brakes (since the rear has no traction) and the tractor is plunging downhill. Normally, the only solution is either to have avoided the situation by going in reverse down the hill, or by dropping the front loader if you have started downhill and encounter this situation. However, the superior design of the PT avoids much of this.

First, the PT has the engine in the rear, which naturally acts as a counterweight. This helps to balance the weight situation, as a traditional tractor design with the engine up-front simply makes the load on the front axel (with a full front loader) extremely heavy, and contributes nothing to balancing the load. Second, the PT has no traditional braking system, rather the wheel motors act as 4-wheel brakes under all conditions. Think about it - when you go downhill with a PT, you don't 'hit the brakes' - rather, you let up on the treadle pedal, which causes fluid flow to decrease to the wheel motors, and ALL FOUR wheels brake. Third, the PT has identically-sized tires at all four corners, which maximizes and balances traction at all corners. Fourth, the articulation and oscillation help keep traction regardless of grade. As a result, much of the drama of going downhill with a load is reduced. Even if the center of gravity shifts and 'unloads' the rears, the fronts, which are bearing nearly all the weight, have 'braking' action available. The only issue is whether the front tires have enough traction to bring the inertial load to rest. All in all, I have found through direct experimentation that loads that would be death-defying with a traditional tractor are easily handled, even going down a grade, using the superior PT design.

Your comments and feedback are welcome.

Sincerely,

Rob /forums/images/graemlins/grin.gif

 

[bmac]

Makes perfect sense to me. However, if your front load was heavy enough to lighten the rear wheels, it seems to me that you would lose or diminish your ability to steer. I would think with articulated steering, the rear end would just swing around under these conditions. But, at least you could stop.

 

[SnowRidge]

The PT's 4 wheel braking is superior--until you blow a hydraulic line to a wheel motor. Then you have no brakes, and rapidly no steering either.

What is the chance of blowing a line? Highly unlikely, I would think, but then I'm the guy that blew a line on my nearly new Branson at the top of a steep hillside.

In that case, it was the steering that went away, so nothing prevented me from stopping. If I lost a line in the PT up there, it would get a lot more interesting fast.

SnowRidge

 

[Bob999]

Most newer CUT's are 4wd and hydrostatic transmission (HST) is available for them. The HST has some simililarities to the PT drive system--when you take your foot off the pedal they stop. However, modern CUT's also have brakes and if they are in 4WD the brakes effectively act on all four wheels. I believe a separate braking system is a significant safety advantage. Some PT units also have brakes (automatically applied on the slope mowers and manually actuated on certain other models) and can safely stop with a burst hydraulic hose. I am not referring to the pin type parking brake system on the PT 425 or the PT 1430. This system is strictly a parking brake system and has little utility for stopping a moving tractor.

 

[wasabi]

I too have broken hoses, but it takes quite a while to lose hydraulic power because of the size of the resevoir. I agree with the point that the PT all-wheel braking system is safer. It was a factor in my decision as we have steep /forums/images/graemlins/shocked.gif hills.

Sabi

 

[MossRoad]

I think any 4wd HST unit has that benefit when the rear wheels lose traction. That's just another reason why I prefer HST over gears.

 

[MossRoad]

<font color="blue"> I would think with articulated steering, the rear end would just swing around under these conditions. But, at least you could stop. </font>

That's exactly what can happen. You notice you aren't turning and look to one side and all is well... you look to the other side and you rear end is next to you /forums/images/graemlins/shocked.gif Gives you a big dose of reality and you start paying attention reeeeeaaaalll well. You learn to keep your hand on the joystick when on a hill so you can dump the load if needed. Also teaches you to travel with the load as low to the ground as needed. Same things you should do with a traditonal CUT.

 

[davesisk]

Hey Rob:

Your observations are precisely correct. However, don't let that make you feel a little too confident. I think the PT's are about the safest design possible, but there's still safety issues to consider.

You should still back down a hill with a heavy load in the bucket, IMHO. As you start downhill, the COG (center of gravity) still shifts forward, and the tractor will still tip forward until the bucket hits the ground. If you've got the bucket low, then you're probably OK. If you've got the bucket high, you might still find yourself underneath this machine. You can flip any machine with a front-loader over (or at least on it's side) without too much difficulty. Regardless of the design, it just takes enough weight in the bucket.

You'll also notice that, with a heavy load in the bucket, if you turn the steering, this essentially "shortens" the machine and moves the COG forward. End result is that when you turn the wheel, the PT tips forward...when you straighten it back out, the rear end settles back on the ground.

We've affectionately named these phenomena "the PT pucker". Obviously, if you don't have the loaded bucket low (like in inches above the ground), the PT pucker-factor can increase exponentially. /forums/images/graemlins/cool.gif

One other big safety factor that I like is the fact that powered attachments use a hydraulic PTO rather than a spinning shaft. I've read that some huge percentage of deaths from tractor-related accidents involve either 1) ending up with a tractor on top of you rather than underneath you, and 2) getting something (hair, shirt, whatever) caught in the PTO shaft. I think both of those are considerably harder to do with a PT (although anything is possible).

Enjoy your new machine!
Dave

 

[johara1]

for years in the heavy equipment, if the engine stopped or you lost oil pressure in the trans. the dozer would run off. you could drag the blade, thats about it. now they are made a little safer brakes are spring on and hyd. pressure off you loose anything it will stop. i would pay a little more to have this safety feature.i think i would change all the wheel motors to gain this brake plus higher torque.the cost of the new wheel motors would be less than a engine,pick up more torque, a parking brake on all 4 wheels and the safety if you blew a hose or the engine quit,the tractor would stop! /forums/images/graemlins/cool.gif