Truetrac diff carriers: general behaviour and front/rear orientation

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Originally Posted by workingonit

I have a conventional locker up front. When engaged on hard surfaces the steering will be 'heavy' as the locker pulls it straight all the time - soft stuff, steering not so much of an issue. Wonder if a True Trac really is the thing to have up front? With a conventional locker you can turn it off for regular road use.

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Torque biasing diffs are factory fitment in front wheel drive hot hatches, they are pretty benign.

My steering is pretty heavy anyway, I guess due to 265/70 tyres. The angle of the draglink probably doesn't help either. Physically impossible to turn the wheels whilst stationary even on loose surfaces.

Driving in 2wd with the hubs locked, I need to use both arms to turn the wheel pulling into side roads etc. Well I need both arms to steer anyway at town speeds, but with the hubs locked it's both arms putting a lot of force on the wheel. In 4wd it's an unpleasant characteristic when going down hills that have bends in them. I think I'd be struggling to get the steering to full lock without getting on the gas.

I hadn't noticed any torque steer, and I have plenty of low down grunt with the 13bt, get 10psi of boost at about 1500rpm and the pump is maxed out.


I didn't take photos, but I'm pretty sure you could only see a small bit of the helical gears from the ends only. I think I might pull it just to be sure. I'd heard about the trick of pulling the whole swivel balls rather than stripping, might try it. Though i probably need to get some longer soft brake lines and I've read it's pretty hard to bleed the tls brakes without laying the backing plate horizontal.

Interesting read.

Detroit TrueTrac? Differential

I've never had a True-Trac, so tell me if I'm wrong here, but aren't True-Tracs unlocked unless a wheel spins, causing the diff to lock? Isn't that why they can be used in the front without affecting the steering?
Isn't that the opposite of automatic unlockers like the Detroit one, which is locked unless the vehicle makes a sharp turn, like on a roundabout, causing the locker to temporarily unlock to make the turn?
That how the Detroit auto-unlocker worked in the rear of our D1. It was fine in the rear, but I wouldn't have one in the front.

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Originally Posted by DiscoMick

I've never had a True-Trac, so tell me if I'm wrong here, but aren't True-Tracs unlocked unless a wheel spins, causing the diff to lock? Isn't that why they can be used in the front without affecting the steering?
Isn't that the opposite of automatic unlockers like the Detroit one, which is locked unless the vehicle makes a sharp turn, like on a roundabout, causing the locker to temporarily unlock to make the turn?
That how the Detroit auto-unlocker worked in the rear of our D1. It was fine in the rear, but I wouldn't have one in the front.

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no, they are torque biasing, and they do behave funny if you're not expecting it.

if the ratio of the turn rate on the tyres in the turn (inside speed to outside speed) isnt above the freeplay limit of the troit it wont do squidly, but as you start to invoke its magic it will try to drive the torque to the slower moving wheel (which is the inside the turn wheel) this then tries to straighten the car up. Its no where near as bad as when you have an unlocker (which simply means the slowest moving wheel must be turning at crownwheel RPM) or a locker (both wheels turn at crownwheel RPM.

in a series you can get some extra interesting results when in 2wd, especially if you have an early version of it. No, dont ask why, I dont know, its not supposed to happen but sometimes it does my guess is that without input torque the detroit is all happy until theres a rotational difference when it tries to act like a traditional unlocker (but winds up locking both sides to the crown wheel) or a full locker.