when you purchase a sye it does it adapt to the orig. shaft or do you have to
use a specific drive shaft never done one of these before all info would be a gret help thanks in advance

 

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You need a double cardon drive shaft, you can get one made from a place like tom woods... or some xjs are able to use a stock front driveshaft as the rear.

 

a SYE kit (slip yoke eliminator) is making it so you will not loose any fluid from the transfercase should you flex your rear end so bad that the driveshaft will come off of the transfercase.or if your rear seal on the transfer case is shot you can potentially loose fluid from around the slip yoke on the driveshaft.
currently as you go offroading and your jeep flexes over rocks/ditches the rear driveshaft slides in and out of the transfercase.this is what the SYE kit is eliminating for you.
when you buy a SYE kit it comes with a new rear output shaft for the transfercase. that is what you are basically replacing and you will have to get a new driveshaft.the stock driveshaft does not expand or contract at all.if you were to try to just put a universal joint connector to the end of the stock driveshaft you would punch in the rear of the transfercase the first time you went offroading. that would be very costly.most SYE kit manufactures will tell you what you will need to purchase.your driveshaft will now be the place where the expanding and contracting of the rear end flexing will occur. so your drive shaft will now have to be able to expand and contract with the flexing of the rear end of your jeep.hope this makes sense to you.