Shortening driveshaft

[Rick Bollinger]

On my 68 lwb 2 piece drive shaft is there any reason I cannot shorten it at the splined end of the front driveshaft? The reason I am thinking about that end is because the balance weights are on the other end and would need to be moved. I assume there is a shoulder on the splined end that slips into the driveshaft similar to the yolk end. And also when the front driveshaft is together the yokes do not line up. But I believe they are suppose to. Can someone please confirm so when I weld it back together it will be right.
Thanks
Rick

[Overdriven]

You do not want the yokes for the u-joints to be lined up, they need to be offset. If you watched the speed of the shaft after a single u-joint, the shaft will slow down, then speed back up as it rotates. If you add a second u-joint and offset it, the second u-joint counteracts the first and the output rotates at the same rate as the input. This is why you’ll never see a driveshaft with a single u-joint and why you want the front and rear u-joints to have as similar of an angle to them as possible. If one u-joint has more angle than the other they will rotate at different speeds, introduce vibration and wear out faster.

Personally I wouldn’t modify a driveshaft or recommend anyone do it themselves. Driveshaft shops have the tools to get the u-joints aligned correctly and balancing is required after any modifications. Get it wrong and you could end up with a broken transmission, driveshaft coming through the floor and who knows what else.

[Rick Bollinger]

Well its done anyway. Ended up cutting it at the front yoke. I used a 4 blade pipe cutter to get a nice cut. And then was just able to chuck the short end up on my 7" hobby metal lathe. Cut the weld out then slipped the yoke out of the 2 3/4" piece of drive shaft. The yoke slips up inside the driveshaft about an inch with a firm fit so you would have to try really hard to get it crooked. Leveled out the two yokes and welded it up. I do a lot of custom fab and welding at work so it really wasn't that bad. Just need to be careful to get a straight cut in the driveshaft and to be careful not to mess up the end of the yoke that slips into the driveshaft so it goes in straight. I did sand blast the entire thing to clean it up. There was no way it was balanced with all the paint and undercoating and grease on it. After checking my angles I will try it wort case is that I will have to balance it.