How much movement should I have when sliding my front driveshaft back?
 

How much play or movement(front to back) should I have in the spline on the front driveshaft in my 420SEL? Mine is totally compressed, with nut loose,no movement to rear of car at all. Flex disc is unable to come loose even with carrier bearing loose. I've changed the engine in car, and am in process of bolting everything together.I feel I should have enough movement to allow flex disc to be removed . I think I need to shorten my driveshaft, but need to have an idea of how much.

Um, 0.0

Once the nut is completely relaxed, you should be able to compress the driveshaft far enough to clear the pilot bushing at the flex disk.

Occasionally, a good sized pry bar will encourage the driveshaft to move.

Jim

Mine is totally compressed when in place, can get not get enough movement to get away from flex disc at all. Looks like I've got to do some more measuring and shorten my driveshaft a little, maybe about an inch?

how do you know that the driveshaft is totally compressed?if the parts on the car are the same as the original that driveshaft will compress enough at the slip joint to enable you to remove or replace the flexdisc.suggest that you take off rear flex disc and carrier bearing and put complete shaft on the ground and take apart slip joint and lubricate well.you will find that it is jammed.check for balance marks on shaft and yoke,if not there mark it before you take it apart.

New engine/trans is different from stock? If yes, then you may have a length issue (I get email about that all the time:D).

If same as stock engine/trans, sometimes the bushings in the flex disc are tight in the yoke. Factory manual says to insert a dowel to move around, free them up. If you can't get clearance to remove the front disc, your not going to have any for the rear either. Removing the carrier bearing bolts may give enough angle in the shaft to allow a bit more clearance. A little leverage as Jim suggested "should" be all it takes.

Engine is not stock, is 617 diesel from 300SD. I found that I need to shorten shaft 1", am working with Driveshaft Specialist Inc in San Antonio to remedy the problem. Fully rebuilt,shortened shaft is around $525, so will probably go that route. Thanks.