CDL Question

[Chris Green90]

Thanks Chris. That was the info I was looking for. Never even thought about this and never really had a.need.for it but just figured that if it was as.easy as the 80 to do then why the hell not.

 

[Ecoman]

I hear what your saying Brett but I wanted full control over the diff locks. I got into a situation recently where I needed to turn sharp right at the top of a steep incline. The truck easily made it up the incline with all 3 diffs locked but as soon as I tried to turn right the transmission wound up and brought me to a stop. I had to unlock everything to get the truck round the corner but it was not an elegant manoeuvre as I could have done with the front and rear diffs locked to cut down on the amount of wheel spinning and soil flying.

 

[Brett]

You would still have the same problem even with the centre diff open, a locked front diff doesn't like going round corners! The only way round this (IMHO) would be some deft unlocking of the front diff just before you want to steer (not easy with electrically actuated diff locks)

 

[Dave Docwra]

Hi Brett, what happens if you disengage the rear diff lock & leave the front engaged on corners

 

[Towpack]

A full time 4 wheel drive with open diffs is basically a one wheel drive when you lose traction!

..............unless you have a VC in the centre diff.

 

[BobMurphy]

Hi Brett, what happens if you disengage the rear diff lock & leave the front engaged on corners

I'll be interested in Brett's response . . But I suspect it wouldn't help you go around the corner.

With the front locked both front wheels are going to move at the same speed so always try to follow a straight line in whichever direction they are facing.

You get the same effect at the rear with the rear diff locked but it is more obliged to follow the front. It causes the tyres to scrub though.

I doubt that 'hanging the tail out' would help much either though it might 'threepenny-bit' around the corner - the centre diff would also have to be unlocked for this to happen.

This is why it is more usual to have a limited slip diff at the front and a locker at the back (and in the middle).

Bob.

 

[IRLGW]

I suppose that if you are in an extreme offroad situation (which I assume this topic is based around) or a tight spot and you have the ability to lock the front diff -while disengaging the rear diff and center diff, then you might be able to apply the handbrake and wheel the front of the vehicle around. I don't think any manufacturer out there has made a vehicle with fully independent selection of lockers.

My old 96 V6 swb shogun had the vacuum driven super select system.. when you start the engine and the vacuum is formed then the front diff and center difflock are disengaged automatically so you are effectively on rear wheel drive with open rear diff. When you move the transfer lever into 4wd then this activates the vacuum solenoid and releases the vacuum going to the front diff and engages the front axle. 4wd with cdl is also engaged by vacuum on the center diff for high and low ratios. Rear difflock can only be selected by electric switch which runs a compressor to activate the rear diff once the CDL has been locked for safety reason.

Most people fit a switch that earths the vacuum solenoid for the front diff so that you can have low box without 4wd and this leaves the cdl locked, but because the front diff is completely disengaged it doesn't matter. However you can now have a rear locked diff with no drive to the front axle and I can tell you from experience that this is really dangerous on the road and offroad the vehicle is virtually undriveable. I don't think a locked front diff with would be much better although in the landcruiser you will always have the rear axle turning unless you fit the 2wd conversion kit.....

I intend fitting a cdl switch to my 93 manual cruiserfor low ratio towing but going to leave everything else well alone this time

 

[Brett]

Hi Brett, what happens if you disengage the rear diff lock & leave the front engaged on corners

I think you know what would happen Dave

It certainly wouldn't steer

 

[Brett]

A full time 4 wheel drive with open diffs is basically a one wheel drive when you lose traction!

..............unless you have a VC in the centre diff.

This is true, then you would have an "amount" of drive split between front & rear.

 

[Dave Docwra]

I only ask this question as a lot of South African vehicles without axle diff locks have an ARB retrofitted to the front only, and reading some off road mags over here some of the off roaders have spoken about engaging the front lock only on loose twisting sections, as for not steering surely the wheels will attempt to go in the direction they are pointing & as they are travelling at such slow speed tyre scrub surely would be off little effect & also the vehicle has nothing at the rear pushing it straight, could someone experiment next time they are off road & see what happens.

 

[Towpack]

With the front DL locked the front wheels will TRY to go in the direction they are pointing but the outside wheel has to travel further and hence, faster but cannot due to the lock so it is, in effect, a brake holding the car back.
I tried this on nothing more challenging than wet grass. Locking the rear diff didn't seem to have much effect but with the front also locked the turning circle was massively increased. At an estimate, probably by a factor of at least 10!