Please Sign In

Please enter a valid username and password
  • Log in with Facebook
» Not a member? Take a moment to register
» Forgot Username or Password

Why Register?
Signing up could earn you gear (click here to learn how)! It also keeps offensive content off our site.

AnswersASK YOUR QUESTION

Answers

Q:
ok so there was just a question on here about tires for a truck, and somebody brought up rear differential, i was wandering what exactly it is, my truck has a center differential, is this the same concept/does it do the same thing.

Question by tbogg10. Uploaded on February 02, 2010

Answers (7)

Top Rated
All Answers
from Ontario Honker ... wrote 4 years 10 weeks ago

On a 4x4 (or convention two-wheel drive) the rear differential is the hub in the center of the rear wheels axel. It contains the ring gear, etc. for transferring the power from the drive line to the wheels. Older 4x4 pickups had a solid front axel similar to the rear one and therefore they also had a "front" differential. Most 4x4s these days have an independant suspension front drive with CV joints/axels instead of the conventional differential. I'm sure this makes it about clear as mud for someone who had no idea what a differential was in the first place. Did my best.

+3 Good Comment? | | Report
from Clay Cooper wrote 4 years 10 weeks ago

tbogg10

I'm the one who suggested the rear locking differential.

A locking differential, diff-lock or locker is a variation on the standard automotive differential. A locking differential may provide increased traction compared to a standard, or "open" differential by restricting each of the two wheels on an axle to the same rotational speed without regard to available traction or differences in resistance seen at each wheel.

A locking differential is designed to overcome the chief limitation of a standard open differential by essentially "locking" both wheels on an axle together as if on a common shaft. This forces both wheels to turn in unison, regardless of the traction (or lack thereof) available to either wheel individually.

When the differential is unlocked (open differential), it allows each wheel to rotate at different speeds (such as when negotiating a turn), thus avoiding tire scuffing. An open (or unlocked) differential always provides the same torque (rotational force) to each of the two wheels, on that axle. So although the wheels can rotate at different speeds, they apply the same rotational force, even if one is entirely stationary, and the other spinning. (Equal torque, unequal rotational speed).

By contrast, a locked differential forces both left and right wheels on the same axle to rotate at the same speed under nearly all circumstances, without regard to tractional differences seen at either wheel. Therefore, each wheel can apply as much rotational force as the traction under it will allow, and the torques on each side-shaft will be unequal.(Unequal torque, equal rotational speeds). Exceptions apply to automatic lockers, discussed below.

A locked differential can provide a significant traction advantage over an open differential, but only when the traction under each wheel differs significantly.

All the above comments apply to central differentials as well as to those in each axle: full-time four-wheel-drive vehicles have three differentials, one in each axle, and a central one between the front and rear axles.

http://en.wikipedia.org/wiki/Locking_differential

Detroit Locker Automatic Locking Differential

http://www.locked-drive.com.au/dl.php

Your local 4x4 shop can help you with this!

+3 Good Comment? | | Report
from Ontario Honker ... wrote 4 years 10 weeks ago

Posi-track, or the locked differential described above, also has the significant disadvantage of gobbling fuel. My experience has been that posi-track was a good option in some two-wheel drive pickups in the old days before the bugs were worked out of 4x4 systems. Our new (2006) Pontiac has some kind of "low trac" system that apparently locks the front-wheel drive differential for a bit if it senses a loss of traction. A light comes on telling us that this has happened and goes off when the differential is unlocked again. Not sure if it has been adapted to 4x4s yet, but it would be a great idea for the front end of those outfits.

Incidentally, when I was a kid the automakers had to drop their positraction rear differentials for several years after the whale hunting ban went into effect. Yep, the gear case lubricant was obtained from those poor devils. Anybody else old enough to remember that?

-1 Good Comment? | | Report
from Wapiti wrote 4 years 10 weeks ago

This is a tough subject to write about, but sometimes easier to see. Here is a link to an instructional film from about the 1930's that explains the concept very well:

http://www.youtube.com/watch?v=K4JhruinbWc#t=1m50s

Give it a look, and suddenly these descriptions will make a lot of sense.

+1 Good Comment? | | Report
from MLH wrote 4 years 10 weeks ago

Differentials are pure genius. Wapiti's link is excellent.

The center differential acts like the rear or front differential and allows the front wheels to turn at different speeds than the rear wheels on 4WD and AWD vehicles. They can be locked by various methods. They can also be set up to split (vary) the torque between front and rear wheels.

Posi-Trac was really a limited slip differential. Still a great thing.

+3 Good Comment? | | Report
from Bob Sawyer wrote 4 years 10 weeks ago

WHEN YOU 'BUY A 4X4' YOU ARE USUALLY GETTING A 2X2 UNLESS THE WINDOW SAYS POSI-TRACTION THEN YOU GET A 2X3 IN REALITY UNTIL YOU PUT A POSI IN THE FRONT !
I HAVE AN OLDER (79 CHEVY AND I HAVE POSI IN FRON AND REAR SO WHEN I SAY 4X4 IT REALLY IS)AND WHEN OFF ROAD IT SHOW THE DIFFERENCE TO ALL THE NEWER MODELS!AND THE POSI ONLY WORKS WHEN ONE AXLE IS STARTING TO SLIP SO IT DOESN'T USE ANY MORE GAS THAN A NON-POSI UNIT !

0 Good Comment? | | Report
from blackdawgz wrote 4 years 6 weeks ago

Most modern 4X4's have a center rear differential. You have to go back to very old CJ's and 'Cruisers to get an offset diff.

0 Good Comment? | | Report

Post an Answer

from Ontario Honker ... wrote 4 years 10 weeks ago

On a 4x4 (or convention two-wheel drive) the rear differential is the hub in the center of the rear wheels axel. It contains the ring gear, etc. for transferring the power from the drive line to the wheels. Older 4x4 pickups had a solid front axel similar to the rear one and therefore they also had a "front" differential. Most 4x4s these days have an independant suspension front drive with CV joints/axels instead of the conventional differential. I'm sure this makes it about clear as mud for someone who had no idea what a differential was in the first place. Did my best.

+3 Good Comment? | | Report
from Clay Cooper wrote 4 years 10 weeks ago

tbogg10

I'm the one who suggested the rear locking differential.

A locking differential, diff-lock or locker is a variation on the standard automotive differential. A locking differential may provide increased traction compared to a standard, or "open" differential by restricting each of the two wheels on an axle to the same rotational speed without regard to available traction or differences in resistance seen at each wheel.

A locking differential is designed to overcome the chief limitation of a standard open differential by essentially "locking" both wheels on an axle together as if on a common shaft. This forces both wheels to turn in unison, regardless of the traction (or lack thereof) available to either wheel individually.

When the differential is unlocked (open differential), it allows each wheel to rotate at different speeds (such as when negotiating a turn), thus avoiding tire scuffing. An open (or unlocked) differential always provides the same torque (rotational force) to each of the two wheels, on that axle. So although the wheels can rotate at different speeds, they apply the same rotational force, even if one is entirely stationary, and the other spinning. (Equal torque, unequal rotational speed).

By contrast, a locked differential forces both left and right wheels on the same axle to rotate at the same speed under nearly all circumstances, without regard to tractional differences seen at either wheel. Therefore, each wheel can apply as much rotational force as the traction under it will allow, and the torques on each side-shaft will be unequal.(Unequal torque, equal rotational speeds). Exceptions apply to automatic lockers, discussed below.

A locked differential can provide a significant traction advantage over an open differential, but only when the traction under each wheel differs significantly.

All the above comments apply to central differentials as well as to those in each axle: full-time four-wheel-drive vehicles have three differentials, one in each axle, and a central one between the front and rear axles.

http://en.wikipedia.org/wiki/Locking_differential

Detroit Locker Automatic Locking Differential

http://www.locked-drive.com.au/dl.php

Your local 4x4 shop can help you with this!

+3 Good Comment? | | Report
from MLH wrote 4 years 10 weeks ago

Differentials are pure genius. Wapiti's link is excellent.

The center differential acts like the rear or front differential and allows the front wheels to turn at different speeds than the rear wheels on 4WD and AWD vehicles. They can be locked by various methods. They can also be set up to split (vary) the torque between front and rear wheels.

Posi-Trac was really a limited slip differential. Still a great thing.

+3 Good Comment? | | Report
from Wapiti wrote 4 years 10 weeks ago

This is a tough subject to write about, but sometimes easier to see. Here is a link to an instructional film from about the 1930's that explains the concept very well:

http://www.youtube.com/watch?v=K4JhruinbWc#t=1m50s

Give it a look, and suddenly these descriptions will make a lot of sense.

+1 Good Comment? | | Report
from Bob Sawyer wrote 4 years 10 weeks ago

WHEN YOU 'BUY A 4X4' YOU ARE USUALLY GETTING A 2X2 UNLESS THE WINDOW SAYS POSI-TRACTION THEN YOU GET A 2X3 IN REALITY UNTIL YOU PUT A POSI IN THE FRONT !
I HAVE AN OLDER (79 CHEVY AND I HAVE POSI IN FRON AND REAR SO WHEN I SAY 4X4 IT REALLY IS)AND WHEN OFF ROAD IT SHOW THE DIFFERENCE TO ALL THE NEWER MODELS!AND THE POSI ONLY WORKS WHEN ONE AXLE IS STARTING TO SLIP SO IT DOESN'T USE ANY MORE GAS THAN A NON-POSI UNIT !

0 Good Comment? | | Report
from blackdawgz wrote 4 years 6 weeks ago

Most modern 4X4's have a center rear differential. You have to go back to very old CJ's and 'Cruisers to get an offset diff.

0 Good Comment? | | Report
from Ontario Honker ... wrote 4 years 10 weeks ago

Posi-track, or the locked differential described above, also has the significant disadvantage of gobbling fuel. My experience has been that posi-track was a good option in some two-wheel drive pickups in the old days before the bugs were worked out of 4x4 systems. Our new (2006) Pontiac has some kind of "low trac" system that apparently locks the front-wheel drive differential for a bit if it senses a loss of traction. A light comes on telling us that this has happened and goes off when the differential is unlocked again. Not sure if it has been adapted to 4x4s yet, but it would be a great idea for the front end of those outfits.

Incidentally, when I was a kid the automakers had to drop their positraction rear differentials for several years after the whale hunting ban went into effect. Yep, the gear case lubricant was obtained from those poor devils. Anybody else old enough to remember that?

-1 Good Comment? | | Report

Post an Answer

bmxbiz-fs