Thread: True Trac or Detroit locker

CDL = Centre Differential Lock, and almost all Landies have one (except a few Discoveries in 2002 or 2003 I think).

In most models you just push the Hi/Lo lever across to the left to lock the centre diff. Newer rangies have auto locking CDLs (Viscous, and now electronic?).

HTH David

Originally Posted by yosh

Hello,

can you please explain what is the CDL?
and, can you clarify and elaborate on the usefulness and efficeancy of the front LSD for better traction, concidering it as not a full locking differential, which I suppose should make it less effective?

thanks very much...
(pardon for the broken english)

an lsd in the front generally outshines the locker as it provides for a limited amount of rotational difference on the wheels which helps you corner but it still provides a proportion of positive drive to a wheel that has traction when its partner has none.

Limited slip diffs come in a few varieties and achieve their drive distribution in various ways.

the simplest way is what I call a sprag locker. these are sometimes called an unlocker. Its essentially a normal open diff with a pair of one way clutches attached to the carrier, one for each axle. When the crown wheel turns in the normal direction of operation both axles are driven forwards by the clutches. When you corner and one wheel speeds up it overruns the clutch and is free to turn faster than the crownwheel.
This type of diff has a couple of drawbacks. 1. They dont work in reverse and 2. depending on the exact situation they can cause some havoc with the vehicles handling if you have two of them fitted. 3. I have heard of a couple of cases where with 2 fitted and four wheel drive accidentally engaged on high traction surfaces they have taken out driveline components.

youve then got what I call a Cam'n'clutch locker which essentially has a set of springs and cams worked into the guts of the diff that when the axles start to turn at different rates the cams are activated to start engaging the clutch which then transmits the drive to the slower axle. they work in both directions, are a little more maintenance intensive needing occasional adjustment and more attention to the oil you use in them and are adjustable in how much slip you want to have before they engage. some are rough in there engagement but generally this is not the case

Torque biasing diffs are next and are pretty much the ducks nuts of the LSD world they are fairly unique in the way they work through the magic of helical worm gears driving clutch members. Their engagement is usually silky smooth and they apply torque to the axle that can use it at a proportionally larger amount than the slipping wheel this is refered to as the the torque multiplication factor and it can be as high as 3:1. its not a magic increase in available power but a multiplication of the resistance offered to the spinning wheel for instance If a wheel was spinning on a diff setup for 2:1 multiplication and it had 50Nm of resistance applied to it then the wheel that wasnt spinning would recieve 100Nm of drive.

this has some unique advantages which I'll delve into later.

Yosh CDL is “Central Differential Lock” or locks up the central or 3rd open differential sitting in the transfer case. If you have one LSD locker like a TruTrac on one axle (and no CDL) you are guaranteed that 1 wheel must get traction. However this is really little different to having open diffs all round and no CDL.

Engage CDL (having no lockers) 2 wheels must get traction (1 on each axle). However having 2 LSD lockers with no CDL little different as still only 2 wheels (on the same axle) are guaranteed of getting traction. However with just one LSD locker and with CDL engaged 3 wheels must get traction.

This is the reason why D2 owners go to all that trouble to get CDL’s hooked up.

I have found a TruTrac up front is 70- 80% efficient but a lot easier to steer than having a 100% locker on the front axle, particularly at speed in sand. I also think most people put TruTrac on front axle first planning to put a 100% locker on the rear.

What happens when you're in reverse? Have you got better steering with the Detroit locker (in the rear) than with the TruTrac?
Do you need to take extra care driving into tight windy places with TruTrac's as you might have no (or restricted) steering reversing out?

Deano

DeanoH

A TruTrac is geared style limited slip diff that is very smooth and effective engaging and there are no impediments to reversing. Detroit is a auto locker that is 100% locked up and unlocks on hard surfaces cornering etc when required. Detroits should only go on rear axles not stering axles because of this style of operation.I am unaware of any reversing limitations with a Detroit howver the unlocking probably requires getting used to. The only impediment with auto lockers is some people prefer on demand lockers (ARB,Maxi etc) not auto lockers on the rear axle when on loose slide slopes.

I think with a truetrac you won't notice any change to the steering either forwards or backwards. I know the one fitted to the rear of my RRC is completely transparent, I don't notice it at all.

thanks very much for the remarks.

CDL engaged at any offroad condition where my wife private car wouldn't pass.

The point is, I'm trying to figure out how much better traction I'l achive with the truetrac at the front. I've allready implemented Detroit on the back and can only say good things about it.
no doubt on demand lockers - ARB will give better effect as 100% lockable but it cost twice the LSD.
I rarely drive on sand so it's effet on this condition is irelevant for me.

I understand the mechanical clarification Dave kindly offered.

Can drivers who add LSD to the front after allready have 100% locker at the back tell how they impressed with the improvment?

if you're going to run any of the lsd's that arent an unlocker in the front and you already have a selectable locker down the back you're laughing in all respects and will have the best of all worlds with downsides that in reality just arent worth worrying about. Especially if you already have TC.

with the CDL in you achive positive drive to all wheels yet still maintain the ability to have a differential action on the front wheels which will allow you to maintain most of your steering ability.