Difference between Diff Lock and Centre Diff

Submitted: Thursday, May 29, 2003 at 20:08
ThreadID: 5177 Views:21820 Replies:6 FollowUps:1
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Been discussing with a friend the difference between a diff lock like the airlocker, and a centre diff in a a full time 4wd.

Does the centre diff do the same as a diff lock like the airlocker or are they 2 completey different things?

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Reply By: Mark - Thursday, May 29, 2003 at 20:31

Thursday, May 29, 2003 at 20:31
Basically a diff lock will lock both wheels on the same axle whereas a centre diff will lock (at least) one wheel on the front axle & one on the rear. Without the centre diff locked it is possible to have drive to only one wheel.
AnswerID: 21413

Reply By: Rob - Thursday, May 29, 2003 at 21:21

Thursday, May 29, 2003 at 21:21
Does the centre diff do the same as a diff lock like the airlocker or are they 2 completey different things?

No, and no.

The basic problem is that a 4WD's front axle travels further than the rear axle when going around any corner. If both axles are driven at the same speed, stress results in the drivetrain (transmission windup).

Therefore, some form of device is needed between front and rear axles to permit the front axle to rotate faster than the rear during cornering. This is a centre diff, referred to as such to differentitate (sic) it from the diffs all cars have between wheels which do exactly the same job, permitting the outside wheel to travel faster around a curve than the inside whilst maintaing drive to both.

Differentials do have a major disadvantage for offroad use, and that is the fact they direct most drive to the wheel that is easiest to turn. So if you have one wheel on mud and another on rock, the differential will send almost all the drive to the wheel on mud, and you'll be going nowhere.

Difflocks prevent this by effectively "locking" the differential, so it doesn't act as a differential at all. In the previous example, equal amounts of drive would go to each wheel, so you could still move. Turning ability would be restricted becuase the wheels would be forced to move at the same speed.

This is a very much misunderstood topic, but there are plenty of links on the web for further reading. I've only covered it at a high level here. There was a 4WD Monthly article on the subject a while back.



AnswerID: 21419

Follow Up By: Tony - Friday, May 30, 2003 at 07:25

Friday, May 30, 2003 at 07:25
The above only refers to vehicles with full time 4WD where it has a totaly different meaning than is being sujested.
FollowupID: 13975

Reply By: Outnabout David (SA) - Friday, May 30, 2003 at 08:18

Friday, May 30, 2003 at 08:18
Someone can correct me if they like. I will talk about constant 4WD vehicles. In normal road mode the drive is probably 70/30 or 80/20 or whtever to the rear/front wheels. This allows the vehicle to drive around corners without winding up.
With the centre diff locked the drive is split 50/50 so in essence the vehicle is now no different to a part time 4wd. Whether the diff is locked or not if you have diagonally opposed wheels off the ground or slipping then you could have no drive at all. in other words your 4wd just became a no wheel drive because of the wheels spinning.

The air lockers lock the wheels on the same axle so you could have one wheel off the ground and the other would be driving. In the scenario above you would be at least getting drive to one wheel.We have so little time to enjoy our land
AnswerID: 21434

Reply By: Member - Rohan K - Friday, May 30, 2003 at 09:17

Friday, May 30, 2003 at 09:17
Mark J, check this out:

http://auto.howstuffworks.com/four-wheel-drive.htmLife just ain't that serious.
Rohan (Sydney)
AnswerID: 21439

Reply By: Matt M - Friday, May 30, 2003 at 15:47

Friday, May 30, 2003 at 15:47
Mark, to keep it simple a diff lock refers to eny means of locking a differential, be it in a rear or front diff or in the centre between the two axle assemblies!
A centre diff lock only is referring to a constant 4wd. With constant 4wd you need a means to let out any wind up between the front and rear axle as you would from left to right in any conventional axle assembly!
So a diff lock, be it centre or rear/front does the same thing in principle, eliminates the differential action that can take place between two axles. The only difference is the location on the vehicle and what is does to the vehicles driveline output!
So to answer you question about the difflock (centre) and airlocker, in principle they are doing the same thing, locking out the assemble from any differential action (slip) between two axles. Oly one acts in the axle assembly and the other in the transfer case ie one acts from left to right in the exle and the other front to rear in the transfer case!
Clear as mud, we I hope its clear!

AnswerID: 21464

Reply By: Mick - Friday, May 30, 2003 at 23:10

Friday, May 30, 2003 at 23:10
Mark, you have 3 diffs. One in the centre and one on each axle. The centre diff lock locks the centre diff (are you still with me?). The other diffs can be locked by fitting other diff locks. All diff locks lock diffs (hence the name) and it's just a matter of knowing which diff you can or want to lock.
AnswerID: 21490

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