Not good to use 4WD on pavement (power, wheels, different)
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Do all part-time 4x4s have the front axle turning at a higher RPM than the rear axle?
I have found a few trucks made in the 60's that had different ratio front to rear. My 76 Blazer had the front very slightly faster, 3.73 and 3.72 front.
It really depends upon the four wheel drive system. There are a bunch of different systems out there and they all work just a little bit different. Some of the systems are "all wheel drive" and the power only goes to two wheels until they start slipping, then power is diverted to the other two wheels. (Subaru for example.) .
Not necessarily true. Subaru has a handful of cars for which this is the case, such as Legacy, Impreza and Forester with automatic transmissions and the base, non-turbo 4-cylinder engine. Models with a 6-cylinder or turbo-4 engine have a default torque split of anything from 50-50 for most manuals, 55/45 rear/front for automatics, and driver-controllable variable torque split that can adjust anywhere from 50/50 to 65/35 rear/front on the 6-speed manual gearbox found in the STi and the Spec B trim of the previous Legacy GT.
Most Audis also default to 50/50 torque split though some such as the A3 and TT are "part-time" AWD as you describe where they're really FWD until the front wheels slip or under hard acceleration. BMW's AWD system on the 3 and 5 series default to 65/35 rear/front. I think that's also the case for Lamborghinis. Most other AWD cars are 2WD most of the time as you describe.
The only time all that is true is if all the axles were welded to the carriers and not allowed to "differentiate".
Not quite true.
I had a Chevy 4X4 half ton years ago that once wound up so tight I had to jack up a front tire to get the transfer case out of 4HI. The left front wheel turned almost 1/4 turn as it left the ground. Both differentials were open, no posi-trac or limited slip.
I once bought a Jeep wagoneer that was stuck in 4HI due to a broken shift lever. On the way home, on a patchy ice/snow road, the drive train bound up to the point where it threw the vehicle into the ditch when it hit a slick spot and unwound. Turned out some idiot had put three different size tires on it, and THIS idiot never thought to check! Again, open diffs on both ends.
YES, drive train windup CAN happen, even with open differentials.
AWD and fulltime 4WD vehicles have a differential in the transfer case, between the front and rear driveshafts to prevent windup.
1. Do all part-time 4x4s have the front axle turning at a higher RPM than the rear axle?
2. Why would you be driving in 4-wheel drive on dry pavement anyway?
1. It really has more to do with the fact that your rear wheels always point forward, and your front wheels turn from side to side. The diagram on the link was accurate and provoded a good visual indication of the differing turning radii of each wheel.
With part-time (traditional) 4WD, the front and rear axles are locked together, either by gears or by a triple-row chain. When you turn the wheels, even slightly, it results in each wheel needing to travel a different distance. This creates the binding situation described in the link. Eventually you will wear out parts prematurely.
Most full-time (all-wheel-drive) transfer cases contain basically a limited-slip differential. This is a bit of an oversimplification, but you get the idea. That's why they can handle the different front and rear wheel speeds, because they are clutched, allowing the transfer case to slip a little.
Locking front or rear diffs change this slightly, but the concept holds true.
This would not apply if the vehicle is AWD or full time 4WD? The necessary engineering was added to prevent damage from occurring if the wheels would slip.
1. Do all part-time 4x4s have the front axle turning at a higher RPM than the rear axle?
2. Why would you be driving in 4-wheel drive on dry pavement anyway?
I was wondering why one would use 4 wheeled drive on pavement anyway... If you want the wear and tear on tires and drivetrain and severely diminished fuel economy.
Quote:
Originally Posted by 73-79 ford fan
Trucks with the New Process 203 transfer case can be used in 4wd on pavement.
Isn't the 203 a full time 4x4? The 204 was the part time 4x4
While the website is almost close on some things he missed the boat on other things. And almost close only counts in horseshoes and hand grenades
I was wondering why one would use 4 wheeled drive on pavement anyway... If you want the wear and tear on tires and drivetrain and severely diminished fuel economy.
Isn't the 203 a full time 4x4? The 204 was the part time 4x4
While the website is almost close on some things he missed the boat on other things. And almost close only counts in horseshoes and hand grenades
Yep, the 203 is full time 4x4 but it can be converted and the 205 is part time 4x4.
My 76 Blazer had the front very slightly faster, 3.73 and 3.72 front.
Whats the point of having different ratios like that?
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Rugged
