robison
Silver Member
- Joined
- Apr 27, 2005
- Messages
- 120
- Location
- Western Massachusetts
- Tractor
- John Deere 4510 / John Deere GT235 / DR mower
</font><font color="blue" class="small">( </font><font color="blueclass=small">( Applying a right or left wheel brake while in 4wd will not produce the result it will in 2WD. )</font>
If you had just made that statement, I would have to agree. I think differential braking works better/easier in 2WD, but it is very effective and safe in MFWD also.
Very few of our CUTs are true 4WD. At best, with differential lock, we get 3WD. I can't tell you how many times I've been in MFWD and looked down to see one rear wheel turning and one front wheel turning and two tires just sitting there because they had more traction than the ones turning. Would you say this is bad on the differential? I don't think so. I think most people would say the differential is working just like it should. Then why would you think it's bad on the driveline if I force this same circumstance with one of the rear brakes?
**** Here is why:
When you are in 4wd with a compact tractor the front and rear axle driveshafts are locked together, rotating at constant speed.
You have differentials in front and rear but none in the center. That's why you rip the grass turning in 4wg - by the way - the front axle needs to run a little faster in the turn but there is no diff to allow that so the wheels are skidded on the turf.
Anyway, when you are in 4wd you will indeed always see one front and one rear wheel spin. You won't normally see a single wheel spin.
The reason? With a constant input speed from the drive shaft for one wheel to speed up (spin) the opposite wheel has to slow down (stop). But with 4wd engaged the opposite wheel won't stop because the front axle is pulling you along. Unless it loses traction on one wheel, too, in which case you are stuck with one front wheel and one rear wheel spinning.
In that circumstance stepping on the brake for the spinning rear wheel will transfer power to the other rear wheel and you may well drive out of the situation.
But if you are not stuck stepping on one brake increases the stress on the driveline because all the other wheels are still turning at the constant rate.
It will tend to turn you into the direction of braking but less effectively than if you were in 2wd and with considerably more stress.
For that reason if you are not stuck it's better to do brake turns in 2wd.
But if you are stuck in 4dw applying one brake may well get you out.
Hope that explanation helps.
If I'm in loose or soft soil, it is surely not hard on the driveline (beyond design) to do this kind of "turn assist" braking. In many instances, we are not talking about oversteering, but just keeping the front end from understeering. Granted, the end-row spin around is going to happen with a locked tire, but that will be in field soil and tire slip on the front should be aided by the weight of the raised implement on the 3PH.
I use differential braking a lot on my tractor and my driveline responds well in 4WD and 2WD. I have noticed that in 2WD there seems to be less front end push and it's a little easier to produce oversteer if I step down on the brake.
Essentially, I'd say I would not recommend using MFWD on hard surfaces or pavement. It goes without saying that I would not use MFWD and differential steering on those surfaces. I'd first change to 2WD. In dirt or especially in tilled or loose soil, I just use differential braking anytime I need it. )</font>
I think you have it right above. The stress on the driveline will probably not exceed the design limits as you say. But stress has a cumulative effect on the gears so you may do that fine for 5 years and one day the teeth strip off the gear for seemingly no reason - it was a failure from accumulated stress.
Given the lack of a center differential, you are placing significantly increased stress on your driveline anytime you run in 4wd on hard ground when you don't need it.
Most of the time, for most jobs, 2wd will suffice as proven by the experience of all the farmers up to the advent of 4wd in recent times.
Your equipment will last longer in 2wd in most cases because of the lack of a center differential.
If you had just made that statement, I would have to agree. I think differential braking works better/easier in 2WD, but it is very effective and safe in MFWD also.
Very few of our CUTs are true 4WD. At best, with differential lock, we get 3WD. I can't tell you how many times I've been in MFWD and looked down to see one rear wheel turning and one front wheel turning and two tires just sitting there because they had more traction than the ones turning. Would you say this is bad on the differential? I don't think so. I think most people would say the differential is working just like it should. Then why would you think it's bad on the driveline if I force this same circumstance with one of the rear brakes?
**** Here is why:
When you are in 4wd with a compact tractor the front and rear axle driveshafts are locked together, rotating at constant speed.
You have differentials in front and rear but none in the center. That's why you rip the grass turning in 4wg - by the way - the front axle needs to run a little faster in the turn but there is no diff to allow that so the wheels are skidded on the turf.
Anyway, when you are in 4wd you will indeed always see one front and one rear wheel spin. You won't normally see a single wheel spin.
The reason? With a constant input speed from the drive shaft for one wheel to speed up (spin) the opposite wheel has to slow down (stop). But with 4wd engaged the opposite wheel won't stop because the front axle is pulling you along. Unless it loses traction on one wheel, too, in which case you are stuck with one front wheel and one rear wheel spinning.
In that circumstance stepping on the brake for the spinning rear wheel will transfer power to the other rear wheel and you may well drive out of the situation.
But if you are not stuck stepping on one brake increases the stress on the driveline because all the other wheels are still turning at the constant rate.
It will tend to turn you into the direction of braking but less effectively than if you were in 2wd and with considerably more stress.
For that reason if you are not stuck it's better to do brake turns in 2wd.
But if you are stuck in 4dw applying one brake may well get you out.
Hope that explanation helps.
If I'm in loose or soft soil, it is surely not hard on the driveline (beyond design) to do this kind of "turn assist" braking. In many instances, we are not talking about oversteering, but just keeping the front end from understeering. Granted, the end-row spin around is going to happen with a locked tire, but that will be in field soil and tire slip on the front should be aided by the weight of the raised implement on the 3PH.
I use differential braking a lot on my tractor and my driveline responds well in 4WD and 2WD. I have noticed that in 2WD there seems to be less front end push and it's a little easier to produce oversteer if I step down on the brake.
Essentially, I'd say I would not recommend using MFWD on hard surfaces or pavement. It goes without saying that I would not use MFWD and differential steering on those surfaces. I'd first change to 2WD. In dirt or especially in tilled or loose soil, I just use differential braking anytime I need it. )</font>
I think you have it right above. The stress on the driveline will probably not exceed the design limits as you say. But stress has a cumulative effect on the gears so you may do that fine for 5 years and one day the teeth strip off the gear for seemingly no reason - it was a failure from accumulated stress.
Given the lack of a center differential, you are placing significantly increased stress on your driveline anytime you run in 4wd on hard ground when you don't need it.
Most of the time, for most jobs, 2wd will suffice as proven by the experience of all the farmers up to the advent of 4wd in recent times.
Your equipment will last longer in 2wd in most cases because of the lack of a center differential.
