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Is this too much exposed slip yoke and not enough on the spline?

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72 SSP with 340 and 727. Was wondering if I need a longer driveshaft. My car has a vibration somewhere in the drive line and was considering a balancing of the driveshaft but upon further inspection, I noticed about 3.5 inches of the yoke is exposed. It may have been a little smaller area exposed and increased after adding + 2 new leaf springs. I have not pulled the yoke out to see what's left on the spline but it would have to be about 2.5 to 3 inches?
I've read that 1-2 is the most that should be exposed. Do you think I need a new drive shaft to close this space to maybe 1-1.5 inches?
Yoke.jpg
 
I just got a shaft for my 66. When speaking to the local driveline shop, the fellow told me to push the yoke in all the way and then pull it out 1". Measure u-joint to u-joint from there.
 
X2...
If your rear suspension unloads completely there is a very good possibility of it coming all the way out and if it is at speed bad things will happen!
I would not drive it like that!
 
Adding leaf springs should not have caused that.
You did center the axle housing on the alignment pins after installing the extra leaves? Drive shafts do not shrink somethings wrong.
 
I would say that's a bit much. Here is what my 73 340 and 727 looks like, factory drive shaft at factory ride height and there is just about 2.25 inches exposed and about 1/4 inch polished due to suspension travel.


20171105_213542.jpeg
 
I have heard that same suggestion from Drive Shaft shops about slipping the yoke in until it bottoms, then pulling it out an inch, but.....
MOST factory built cars seem to have more than one inch sticking out. Most of my junkyard experience is with A bodies since they made so many more of them. Most had between 1 1/2" to 2" sticking out. Now, this is with the rear axle at full droop. Still, looking at it in terms of geometry, As the axle droops, it also swings forward because the leaf springs are hinged at the front eye and shackled at the rear. Downward travel causes the yoke to slip out but the arc of the axle as it droops minimizes how much. I have not closely studied this but I would suppose that even at full droop, the yoke probably does not move more than one inch. This may explain why the driveshaft shops use the one inch guideline. They surely do not want to have the drive shaft bottom out.
I currently have a 65 Dart that I'm working on. It too has about 3 1/2" of yoke exposed with the tires at full droop. This car was originally a slant six/904 but when I got it, there was a 318 and a later slip yoke 904 in it. I have no way of knowing what this driveshaft was in originally but the car drives fine with this setup. If I were to have bought this car and it had no drive shaft, I would defer to the common suggestion for measurement.
Final note:
In 1984, I had a friend that was given a 74 4 door Valiant. He really had no use for the car so he decided to have some off road fun with it. He cranked up the torsion bars and did something to lift the rear end as well. Driving down the road, the car had an annoying hiss type sound, almost like what you hear when brake drums are on a lathe....This went on for a couple of days. Something fell out of the rear suspension and the rear ride height was back to normal. That hiss sound was gone too. We thought back then that maybe the sound was from either driveline angle or from the shaft not being in the transmission deep enough.
 
I just got a shaft for my 66. When speaking to the local driveline shop, the fellow told me to push the yoke in all the way and then pull it out 1". Measure u-joint to u-joint from there.
I`ve had 4 made , all were done the 1" way . I think u found ur vibration, surprised it hasn`t knocked the seal.
 
Agree with what all these folks are saying. Just went through all this with mine.
Yours looks dangerously close to dropping out - and you do NOT want that pogo action. People get seriously messed up when that happens at speed.

Figure out what changed when you did the springs and correct it. Polish up that yoke when things are back where they should be.
Also figure on replacing the bushing and the seal in the rear of the tranny. They're probably trashed by now.
 
In my opinion that is WAY too much yoke sticking out. I had a similar vibration issue when I installed super stock leaf springs & used the upper holes in the front spring hangers. The nose of the rear end went way up & pulled the driveshaft out of the transmission quite a bit. (I fixed all that now).

My suggestion is to check your tailshaft bearing (maybe just wobble the yoke by hand?) and get a longer driveshaft.
 
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