Just confirmed that the driveshaft was not high speed tested. It was only taken to about 500-700 RPM and brought in to no worse that .005-.007” runout.

I am beginning to look at having a 3”, .0083” wall thickness, driveshaft built, that is .750” longer on the body to get more engagement in the trans.

I would butt the yoke you plan to use all the way into the trans then measure the C to C you have at that point then subtract 3/4 from that dimention & this is with the suspension loaded (axle on stands). give that number to your shop. EDIT I would locate the front/rear axle position first & I like to have the bottom of the rear shackles point slightly rearward so that the springs "work" when they are compressed when you get on it as opposed to raising the car when the springs arc over center which they do if the bottom is pointing forward from "vertical". keep an eye on shock fitment when you change that position.

That is pretty much how the DC books say to do it.

As fro finding the angles, I have two of these I use.

I have bought from that eBay shipper "Zoro", no issues. Definitely get a digital one as opposed to a cheapie with a magnet & gravity needle.

Uppn more measuring, the body of the driveshaft definitely needs to grow 3/4" to be right. Should have a new DS tomorrow.

Using a bigger 3” driveshaft, am I still okay to use the same 4 bolts and caps for the rear yoke? They are all in good shape.

As log as your keeping the same size U joints your good on the straps and bolts
Do NOT over tighten them

No sir on over tightening; it is bashed into my brain from testing and design with fasteners as part of my every day gig.

The ujoints will be the same. Specified to the builder that the rear yoke WILL NOT be changing and he is going to work around that.

Are you going by rear ujoint endplay (I hope so) or by front yoke appearance/it's end play?

In the existing form, there was 1.5-1.75” of slip yoke exposed with the driveshaft installed. Pushing the shaft all of the way into the trans then backing out .750”-1” left about .500-.750” of slip yoke exposed.

.750” longer on the body should push the slip yoke into the trans .750” further.

I would suggest .750" max (springs loaded)

Yep, .750" additional length is the max and what I specified, to be safe and conservative.

The additional diameter of the driveshaft and the extra engagement should help eliminate the driveshaft from the potential problem list, even if this doesnt solve the issue. I do believe it will though.

Source another front yoke and pony up the coin for new u-joints...

Checked the front yoke and all seems well for now. I'll pull it apart later if I need to.

New ujoints in the same number and size as the 2.750 inch are being added onto the 3 inch unit.

might be too late, but Inland Empire is not too far from you.... I've had pretty good results using their stuff on my race car. A little more reading from their web site

https://www.iedls.com/?a=Critical_Link#Power_Train

UPDATE: new 3" shaft is in. Engagement into transmission is improved. Pinion angle is good. Same issue is still there.

Drove it more tonight and even felt that minor soft vibration between 35-40. Drove it in 3rd at highway speed and couldn't tell if its still there, due to increased engine vibes. Starting to feel this more from the fron, maybe something in the OD gear wearing, or elsewhere in the trans. Maybe those new motor mounts are not the best at dampening harmonics? I am going to check the wheel bearings in the front.

At least the driveshaft is now eliminated from potential issue list.

It sucks when you think you have a problem pinpointed and spend money only to see that the symptoms continue. ALL car guys deal with this!

I have a friend whose Mopar mechanical and automotive skills I have great respect for, insists that a driveshaft yoke shoved into a transmission bushing with too much clearance is the root cause of many unexplained intransigenet driveline vibration issues.

He recommends a new bushing which is too tight and honing it out to fit the specific yoke you are using. He suggests with the transmission out of gear to relieve stress on driveline, to attempt to move the yoke up and down. Any permitted movement is indication of potential problem.

I will forward this thread to him for comment.

And have we checked pinion angles yet?

It verified right in line upon measuring everything up. Angle is good.