Still chasing vibration!!

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Originally Posted by nedflanders

Cheers for all the replies, I understand castor and the need for it, I could live with it as it is as I still get self centering and the steering isn't noticeably twitchy. My concern is prop vibration, having read lots it seems that the angles at each end need to be the same to cancel out the vibration, the diff end is a lot less angle than the t box end. To increase the angle I need in fact to lower the pinion which is what off set radius arms do, as long as the prop is phased correctly won't increasing the diff joint to match the t box joint stop the vibration?? I've seen plenty of lifts much higher that don't have issues. A DC may stop the vibration but won't bring back my castor.

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The engine, gearbox, and transfer case slope down from front to rear.

The front diff slopes up from front to rear. If the drive flange end of the front diff is rotated down, as would need to occur to correct the castor change due to suspension lift, the operating angle of the uni at the transfer case will increase. The uni joint at the transfer case is already operating at too great an angle and increasing it further won't help.

Because the angles of the front and rear uni's on the front drive shaft are not equal, Land Rover assemble the front drive shaft so the uni's are out of phase to compensate.

You could try changing this by one spline more, or less to see if that helps.

However the reliable, proven, but $$$$ solution is to fit a double cardan drive shaft for the vibration issue, and fit slotted swivel balls to correct the castor issue. It seems you don't need to do the last as steering is not bothering you. With 50 mm lift, some drive fine, but others wander badly, another of those luck of the draw things. I had over 75 mm lift and steering was great with no castor correction, but I thank the tru-track front diff for that.

Spicer, one of the largest manufacturers of drive shafts for all types and sizes of vehicles, say IIRC the operating angle should be not greater than 3 degrees for vibration free operation. Have a read through the two drive shaft technical documents that I uploaded to the files section about halfway down the page.

Managed to get hold of a DC cheap, going to change the UJ's for grease able ones then all I need to do is change the t-box flange, going to fit some castor correction bushes as well as it's fine round town but twitchy at highway speeds, plus the bilstein damper makes the car pull slightly right so hopefully castor (and checking kingpin preload) will cure this too.

Quick update, finally changed the prop for a DC, right enough all vibration gone. I had the UJ's changed as well as the centre bearing and then balanced. Also went for QT castor correction arms, just need to adjust the kingpin preload now but that can wait until I change the discs at the weekend. So all in all a bloody expensive exercise for a 2" lift :(