propshaft vibration

[anupbansal13]

Hello all I recently replaced my fuel tank due to rust and in doing so had to remove the propshaft. Ever since I noticed when I floor it around 5k rmp there severe rattling/vibration of the propshaft (which there wasnt before). It can be felt through the seat and is quite severe. Once of the car the centre bearing was NOT replaced so the propshaft was not split. The rubber guibo was replaced and im pretty sure the bolts were put through in the correct direction corresponding to the arrow marks.
Am I right in thinking the propshaft only needs to be realigned correctly if its split?
Also what does it mean when you need to preload the bearing? On reading up a few sources is it just pulling of the bearing toward the transmission?
And what could the issue be?

Any help would be appreciated.

Cheers

[HairyScreech]

How is the UJ at the back of the prop?
A lot seem to be on their way out and causing prop issues now.

Regarding preloading the bearing, you slide it about 5mm towards (the cv attached to the splined bit that goes through the bearing, cant remember if that's forward or back) from it's static resting position.
It just keeps a small amount of side load on the bearing and stops the balls skidding across the races which can be a big cause of early failure in bearings.

[Rtaylor2208]

Sounds exactly like the symptoms of a failed bearing carrier on the prop. Mine had the exact same issue and the rubber on the carrier had started to split.