How does castor correction work

Dear boffins!

After a 2 inch lift my Def 90 steering was poor. The mechanic fitted castor correction bushes and it was much improved and a kick-back/shudder effect on the clutch pedal when turning the landy off, disappeared.

I am using a double carden prop to avoid vibration - although I am still getting it!

So tell me...

Does the castor correction actually drop the diff nose down towards the ground a bit to counter the fact it was lifted a bit and put the steering out, thereby bringing the steering back on track (pardon the pun).

Normally is the diff nose meant to actually point to just above the transfer box, so that the UJ's at both ends operate at the same angle and therefore do not 'wind' each other up due to differing speeds on each rotation? (the inside of an angled UJ rotation is faster than the outside of an angled UJ rotation, whereas the inside and outside of a non-angled turn rotation are the same speed - combine both on one prop and you get a vibration effect caused by altering speeds at one end - a double carden compensates for the former effect by cancelling the altering speed on a single UJ rotation by using an extra joint). Watch what happens when you try applying the same techniques to a skipping rope!

My castor correction bushes have the diff pointing directly at the t box so that there is no angle on the diff UJ but a big angle at the T box UJ. I can't use ANYTHING but a double carden as I can actually hear the normal prop winding up - not binding - but putting wind-up strain on the T box.

I can't point the T-box at the diff, so I am stuck, unless there is some way to get the diff nose pointing higher again without losing good steering control.

Any advice welcome! Thanks.

I should also mention I have a big heavy winch bumper on the front. Not sure about the effect of this on the whole matter.

you sure diff lock is disengaged? I'm not so sure. Check that you are getting enough throw cos when they installed your gearbox they may have buggered the setup up. This problem has been crazy. Have you changed diffs at all? Some numpty hasn't put a 4.7 ratio one in there by mistake drom a series mota have they?

I mean not put one diff in leaving you with 2 different final ratios front to back. You been having serious issues and you have replaced the tranny box and propshafts.

Hi Jai - diff lock disengaged - got under the 90 and checked it myself - when diff is on it is right and clunky and can't turn tight circles - none of those probs. But it is so much lighter and smoother with the front prop off in diff lock. Maybe I need to change the front diff anyway - I have a 12 spline defender one ready to go in. I note that there is quite a dent on the front diff housing from when I bought it but the wheels spin freely and it worked fine before the lift but I got a different gearbox and t box fitted at the same time - r380 and 1:22 box.

Jai - surely an easy way for me to test that both diffs are the same ratio would be to jack a back wheel and a front wheel - then measure the distance turned by the each diff flange for one full rotation of a tyre?