Propshaft vibration

Hi,i have a 2 inch lifted, 87 defender 2.5 TD, it was equipped with cranked radius arms 3 degree, possibly slotted swivel house, standard axels plus spacers, and 35 inch tires.
after removing lift block from the vehicle and lowering it by 1.5 inch in the front (now down to 2 inch), a vibration showed up. its coming between 32 mph and 37 roughly.. and is only there while accelerating, goes away while coasting or de accelerating.
i have since then fitted new tcase output bearing and fitted a double cardan prop in the front. but after changing driveshaft the same vibration is there, i have also tried phasing it, to see if this had made any difference, but the vibration only gets worse.
the diff nose seems to be point pretty straight toward the shaft, maybe pointing a bit up in relation to it (will measure tomorrow)
what could be the cause of this??

Could be diff nose is high because castor correction bushes have been fitted.

it also seems that the vibration is only present when driving in 4th or 5th gear at this speed.
have already tried removing the front prop and driving with diff lock, this eliminates the vibration. could it be a problem with the tcase differential, maybe output shaft spline wear?
when i changed the transfer case bearing it had almost emptied all the oil because of heavy vibration, did a flush and filled it up with some Castrol Syntrax Longlife 75W-90
there is no leak at this point but maybe some damage has been done on the transfer case from running low on oil ?

Check output flange movement,that is up and down and side to side not rotary.If none should be good.Grab
shaft in the center and do the same to check spline fit. Check diff input flange the same way and make sure all UJ's are free and smooth moving.

coming back, i still have the vibration, to specify more, i tried removing the front prop shaft and that eliminated the vibration. so definitely a prop/diff/CV vibration ?? i also think the diff nose is a bit high in realtion to the axle, and to my knowledge this could make a horrible vibration, as i am perceiving. is this also the case with a double cardan / CV propshaft ?
should i try fitting some caster correction bushings to bring the the diff nose down, though making the angle worse it would bring the diff nose on the ''correct'' side of the prop.
thanks for any input, as i seem to be a bit lost on this one

Further experimentation have helped, but not resolved the problem entirely. I decided to buy some offset bushes for the radius arm, this way i would be able to play with different diff pin angles, by ''simply'' adjusting them (pressing them out and turning them a bit) to see if that would change anything.
I started out by installing them as per manufacturer, this made a big change in diff angle. And the pinion flange is now pointing down in relation to the propshaft, where it was pointing a bit up before.
it resulted in almost eliminating the 40-60 km/h vibration, its now only present at 50 km/h, and only half as ''bad''. i think this is bacause of the extreme change. ( pointing too much down..)
next up is make a smaller adjustment, i aim for the pinion to point down in relation to the axle by 2 degrees, i have yet to measure, but would think its around 6 degrees now.
so, it might be a sort of weird setup, with 3 degree caster correction arms, plus offset bushing, but im slowly dialing myself in to an almost vibration free drivetrain.
hope this could help people in the future!

Are you following the Haynes manual? If so, it tells you to put the front prop on back to front which causes vibration

... Male end of the prop should be towards the transfer box

I finally tracked it down to being the center differential, which was badly worn. And I guess the more direct pulsing waves that comes In 4 gear, must have resonated in the gearbwheels in the diff and transmitted it through the driveshafts.

kaae said:

I finally tracked it down to being the center differential, which was badly worn. And I guess the more direct pulsing waves that comes In 4 gear, must have resonated in the gearbwheels in the diff and transmitted it through the driveshafts.

Click to expand...

Thanks for letting us know, too many threads just stop when the poster has found a fix, and we are none the wiser.

Kaae thanks for posting all that you've tried, I have a vibration that sits between 35 and 40, on accel and decel, so will look into what you have found to see where it gets me.