I know this has been beat to death. But i didnt really find what i was looking for....

Specs
samurai
yota axles 4.88s spool in rear detroit in the front
35s
ML yjs

When i go over 20 mph the rear driveshaft vibrates bad.... I figure ill call up tomwoods and get a CV or a double carden....

But i took the rear out and front it in 4x4 with the front hubs locked and it still had some vibrations.... would this just be because i was locked up front and on pavement?

I would like to be able to run my zuk up to 40 mph from trail to trail

let me know what you think

do front and rear d shafts need to be replaced?
currently have stock with spacers.
Brad

To take advantage of the YJs and droop - I'd replace both driveshafts with non-cv, Toy IFS rear shafts.

also, check out your t-case mounts.

x2,
And also make sure your pinion angle is set the same as the t-case one. Should be right around 6 degrees if the t-case is in the stock location. This would be optimal for the non-cv type shafts.

6 degrees may not be too bad if you only go up to 40mph. but both u-joints need to be within 2-3 degrees of each other. also check to make sure the yokes are 'in phase'.
what that means is that both yokes on the driveshaft itself(not counting the pinion yoke or the t-case yoke) need to be aligned with each other, and not offset. if one is absolutely horizontal, the other should be too. if you go for a cv at the t-case, the bottom u-joint by itself should be set to about -2 degrees(downward) so that when you apply torque the axle-wrap effect will lift it up to about zero or no more than +2 degrees(upwards).
my buddys driveshaft had 17 degrees at the top and 12 at the bottom and he wondered why he threw the shaft out at about 90mph. I was surprised it went that fast before exiting the vehicle, stage right, stage left eveen. we simply put a cv on top, and set the bottom to -2 and he can go 120mph in his blazer(seriously not recommended though)