What would be a better choice for my '69?

I put my new Moser 12 bolt in and find out my driveshaft is now too long(I'll know for certain today). I am fighting speed vibes, (which is one of the reasons for the new rear) and was looking at going to a 3.5 x .125 aluminum(see shaftmasters thread) over a .83 steel shaft.

What are the advantages of one over the other?

That's a great question.

We're really not talking about a lot of weight difference between the two now are we? As explained to me by a vendor the chromoly-steel driveshafts are stronger and not much heavier so that's why I went with that choice for my engine.

You should probably state your engine's HP & Torque so people can better advise you though.

I only have maybe ~300hp to the wheels, so not too concerned with strength. I'm looking for opinions on which would be better at reducing vibes.

If you have vibes , I would be looking for the source of that. Not trying to find a shaft that would help reduce the feel of that. Either the alum or steel shaft will be a great shaft. I would be checking your pinion angle if you have vibes. mike

You could get yours cut down and balanced.

As for vibs ???? while the driveshaft is out install a plug and see if its in the motor/tranny first ?

Do what Mike said; check your pinion angle. Mine vibrated since new. As of this summer, it's smooth. I raised the pinion 6*. Wonderful. The new aluminum drive shaft had nothing to do with it. The original shaft was balanced several times with no improvement. It's kinda pretty, don't you think?
http://epitomesrebuild.com/images/236.JPG

Ok I took the 1350 yoke(supposed to 1310) off and put my old 1310 yoke on for now. The driveshaft is back in so I'll be testing the new rear today after some break in.
If I still have vibes I'll look to have the driveshaft balanced for a 3rd time.
Funny thing is everytime the shaft is balanced, the guy says it's way off, and this is two different shops. Around here we only have shops that balance at 500 rpm.
Do I need to find a shop that will hi-speed balance?

And yes I have done the pinion/trans angle thing already.

Fred, I think I've asked already, but what angles(trans down/pinion up) are you at now?

I just talked to the local driveshaft shop. I am putting an aluminum one out of a 4th gen in my 77 this winter. He felt the aluminum ones balanced well. He is going to balance it at 3300 rpm.

If someone is doing their job properly, I can't see how a steel or aluminum one would balance better than the other. It's either balanced within tolerance or it's not. Oh and yes, I do agree that your alumuminum one looks nice under there.

Heard of a little trick about drilling a 1/8" ? hole in driveshaft, pouring in 1/2 qt of oil and welding closed. Someone here ? said it's what the circle track guys used to do ? (self balances)

Ok I took the 1350 yoke(supposed to 1310) off and put my old 1310 yoke on for now. The driveshaft is back in so I'll be testing the new rear today after some break in.
If I still have vibes I'll look to have the driveshaft balanced for a 3rd time.
Funny thing is everytime the shaft is balanced, the guy says it's way off, and this is two different shops. Around here we only have shops that balance at 500 rpm.
Do I need to find a shop that will hi-speed balance?

And yes I have done the pinion/trans angle thing already.

Fred, I think I've asked already, but what angles(trans down/pinion up) are you at now?
It's not a matter of angles, such as 2* up at the trany. The measurements can be done with the car tilted. (not good, but possible) You see, the drop of the trany has to be off-set by the upward angle of the diff-pinion. One degree of error is plenty good, but mine was off 6 degrees. Why do they do that? They must figure we all load up our cars to the max. These guys explain it very gooder,,,:D http://www.iedls.com/measure.html

I have balanced thousands of driveshafts over the last 25 years. From one shop to another there may be slight inconsistencies in the way a shaft will run in a particular balancer depending on the fixtures being used to chuck the shaft into the balancer. For one shop to another to say that it is way off or way out of balance would tell me one or both of them are either not being truthful, don't know what they are doing, or have inferior equipment. The things that greatly influence the way a shaft runs are the runout of shaft, the condition of the yokes and u-joints. Yokes that are bent or sprung can cause a u-joint to either be too tight or loose which will both cause balance problems. Greaseable u-joints can cause problems with the joint floating from side to side at higher rpm's. Greaseable joint do not have tolerences as tight as non-greasable because they have to be able to purge when greased. My experience has been that a aluminum driveshaft with quality non-greasable u-joints will hands down run 10 times better than a steel shaft with greasable u-joints. The difference, especially at higher rpm's is night and day.
Robert

I have balanced thousands of driveshafts over the last 25 years. From one shop to another there may be slight inconsistencies in the way a shaft will run in a particular balancer depending on the fixtures being used to chuck the shaft into the balancer. For one shop to another to say that it is way off or way out of balance would tell me one or both of them are either not being truthful, don't know what they are doing, or have inferior equipment. The things that greatly influence the way a shaft runs are the runout of shaft, the condition of the yokes and u-joints. Yokes that are bent or sprung can cause a u-joint to either be too tight or loose which will both cause balance problems. Greaseable u-joints can cause problems with the joint floating from side to side at higher rpm's. Greaseable joint do not have tolerences as tight as non-greasable because they have to be able to purge when greased. My experience has been that a aluminum driveshaft with quality non-greasable u-joints will hands down run 10 times better than a steel shaft with greasable u-joints. The difference, especially at higher rpm's is night and day.
Robert

That's great experience talking there which is worth a lot - What about strength Robert? a.k.a Shaftmaster.

When we first started repairing and manufacturing aluminum driveshafts 3 1/2 years ago I'll admit I was skeptical about their strength and how well they would hold up in the long run. I am no longer a skeptic. We follow Dana Corp. gudelines as far as the proper tube diameter and wall thickness depending on the length of the driveshaft and the maximum rpm's it will turn. We have built 100's of custom aluminum shafts that are being mostly used in street rod, race car applications. We have yet to have any complaints of a shaft shattering, bending, breaking, vibrating, etc. To the contrary, we have received nothing buy rave reviews about them.
Robert