can anyone explain what it means when a diff has been 'locked'? can it be un-locked?

Normally a diff thats had the planet gears welded up so that both wheels will only turn at the same speed. Lots of tyre scrubbing on cornering or plenty sideways.

This reminds me of the thread on another forum with the guy that welded his crownwheel and pinion up!

Locking a diff usually entails either welding , or pinning the planet gears inside the diff so that there is no speed difference between the two driven wheels. Ok if you need to drive straight, but or and corner you will either lose control, rip the tyres to shreds or break whatever link you have from the diff to the wheels.

This reminds me of the thread on another forum with the guy that welded his crownwheel and pinion up!

Locking a diff usually entails either welding , or pinning the planet gears inside the diff so that there is no speed difference between the two driven wheels. Ok if you need to drive straight, but or and corner you will either lose control, rip the tyres to shreds or break whatever link you have from the diff to the wheels.

You might also see diffs referred to as 'lockable' - mostly in off-roaders. They are essentially an on/off LSD - either fully open or fully locked with a manual control in the car. Of course this type of diff can be unlocked as well as locked!

Liam

Normally only used for drag racing and drifting. Be carful if welding it yourself though as if the weld breaks, its bye bye diff!

its when you fill the diff with lock tight and not diff oil

Welded diffs are used in Autograss quite a bit, I did mine on a front wheel drive & it made the car more predictable than a plate LSD but you did have to be a bit rough with it to get it to turn into the corners. Once turned in though it was fine.
The only real trouble was you had to be careful when moving about in the pits etc, it was quite easy to pop an outer CV if you wer'nt careful but it was never a problem when you were thrashing it!
& if you do weld it up have the halfshafts/driveshaft stubs in while you tack it up as they'll likely be out of line otherwise.
I've heard of them being filled with lead too to do the same thing.

Locked or welded diffs have been used in circle track racing, early days of NASCAR.
I believe they now use a Spool, which is similar to the spider gear carrier. The crown wheel is bolted to the spool and the axles slide into the splines in the spool, no spider gears, therefore no differentil gearing.
The 105E Anglia and Datsun 1200 I raced in the 60's and 70's had welded spider gears, no problems on the track, just as stated in the pits, hard to steer.

As above really, they are welded up. I'm assuming you've seen the 3,38 7" sierra diff on ebay . It wont be much use in a kit car unless you want to try racing it on the ovals.

some diffs can also be described as locking , ie when the stop the inside wheel spinning , they lock up 100% and usually result in opposite lock and lots of swearing if it catches you out .

search on ebay for a detroit locker