Thread: Detroit rear locker

Originally Posted by DiscoMick

True, but Tru Tracs can go in the front.

Yes because they are not a diff lock but a type of LSD.

Originally Posted by mattg

I have test driven a disco with a true track in the front and steering was great

I've been driving my D1 with a true track in front for years now - no problems whatsoever. It's duties run from daily driver to tourer to (mostly Japanese) recovery vehicle. With the Detroit in the back, it's damn near unstoppable.

Originally Posted by garrycol

Yes because they are not a diff lock but a type of LSD.

Arent they torque bias diff as opposed to limited slip? My understanding is they work quite differently more like the ATBs.
I have just fitted an ATB to the front of mine and apart from a bit of a return to centre tendency no issues with steering.

For sure but at the end of the day when traction gets lost it is only one wheel drive on the axle - might be a different wheel but still one wheel drive and is not locked. That is my point - it is still essentially an open diff that limits slip on on one of the wheels not both. It is still a LSD type diff - just with a different method of operation.

Originally Posted by CraigE

Arent they torque bias diff as opposed to limited slip? My understanding is they work quite differently more like the ATBs.
I have just fitted an ATB to the front of mine and apart from a bit of a return to centre tendency no issues with steering.

Yep Garrycol was commenting on truetracs being "like an LSD, so they can go in the front"... And that is loosely true. They are actually torque biassing, like the Ashcroft ATB units. (Not exactly LSD's)

As opposed to detroit lockers, which are best defined as "unlockers" - which do not allow "differentiation" in the usual way differentiation is understood.

The normal understanding of "differentiation" means both wheels (half shafts) either side of a diff are actually constantly driven proportionally. e.g. in a straight line both half shafts are driven at the same speed... when cornering both half shafts are driven constantly but of course the half shaft attached to the outer wheel, in a turn, is revolving faster - but nevertheless both wheels/halfshafts are being driven all the time by the driveline.

With a detroit locker, an unlocker, both half shafts MAY be driven at the same speed in a straight line. When turning a corner, only the inner wheel is driven, the outer wheel is not driven (by engine/driveline), it is allowed to revolve faster than the inner wheel by an unlocking/ratcheting style mechanism - in essence the outer wheel is freewheeling, driven by the road surface to rotate at the speed it needs to.

Where I wrote "...both half shafts MAY be driven at the same speed in a straight line." - I mean that even when driving along in a straight line there may at times be only ONE half shaft/wheel actually driving the vehicle along the road. Arguably they may be small instants in time.... times where one half shaft started to overrun (perhaps a previous curve moment) but didnt click one full ratchet period forward. Thus that arguably freewheeling wheel/halfshaft may be matching the rotational speed of the driven halfshaft whilst not actually being driven - the ratchet mechanism partially disengaged.

This is where the occasionally-complained-about "bang! thud" happens when tramping on the throttle hard with a detroit fitted... the one driven wheel gets a sudden push forward by the driveline, then at the very point where it might have started to spin - the ratcheting mechanism catches up to the wheel that had been idling along previously. It then locks in and drive is now definitely on both half shafts.... as it is in any other situation where wheelspin may have started. It now behaves like a full locker - until traction is regained, wheelspin stops and one or the other halfshafts is driven by roadwheels a little faster. (i.e. curves or cornering).

Of course a Torsen or ATB (incl truetracs) never ever fully locks. Never drives just the inner wheel in a curve. Vastly different to the "unlocker" or detroit.

An ATB always drives both half shafts proportionally like an open diff in the "normal" understanding of differentiation.... and just like an open diff is useless whenever either side of the diff can freewheel (like a wheel in air situation)

Originally Posted by garrycol

For sure but at the end of the day when traction gets lost it is only one wheel drive on the axle - might be a different wheel but still one wheel drive and is not locked. That is my point - it is still essentially an open diff that limits slip on on one of the wheels not both. It is still a LSD type diff - just with a different method of operation.

You are talking ATB? Not quite 100% correct... Yes an ATB, like an open diff, is utterly useless when either wheel on an axle gets airtime (or any other situation, like broken halfshaft - where freespinning on one side of the diff can happen). Of course things like TC or LFB can mitigate to a degree...

But ATBs still work fantastically where "traction gets lost" in any slippery/slidey situations that fall short of a total loss of traction on just one side....

Examples of what I mean are:
- dirt roads
- muddy trails
- ice (where wheels on both sides of the diff are on the ice, the baseline biassing of the diff will see both sides spin, not just one)
- water on the road

Lets not get bogged down in minutia - with any of these diffs, if ultimately one wheel completely looses traction you dont have drive - up until that point not matter if it as a ATB, Torsen, LSD or some other version they provide various levels of traction to the wheels where a normal diff may not. They all have the function of limiting slip but using different means.

Garry

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