For those of you who have changed from a 727 to a 518, how much did you have to remove from your driveshaft? On my 70 Cuda, I get about 2 1/4" difference. But I have read some other posts that say more like 3" or even 3 1/2" has to come off.

I suspect you are just asking generally, and any exact number has to be measured when installed, correct?

I have had the engine/tranny installed a couple of times as test fits and expect to permanently install it tomorrow. But I cannot get full weight on the differential the way that I am doing the engine/tranny test fits. The diff probably lacks a couple of inches from being all the way up into it's usual running position. When I measure the driveshaft length with the differential at full drop and as high as I can get it now, there is maybe 1/4" difference. And it doesn't appear that moving the diff the rest of the way up into running position will affect the length much more. And would shorten the driveshaft measurement if anything.

It is a 3 day turn-around on the driveshaft mods and it will probably be Wednesday or so before I get the car down on all 4s so that I can measure the driveshaft that way. Which would put me into week after next before I could test drive the car rather than next week. So, I was hoping to send the driveshaft off tomorrow in order to have it this week.

If others here came up with about the same driveshaft difference as I did rather than some of the larger differences, then I would have the confidence to go ahead and send the driveshaft off with these measurements.

Hope others concur here for you, but it sounds like you are close enough then to get the dimension you need, only thing not mentioned, is if you need to reangle rear axle housing, that can change the dim a bit, and not sure if it would be in a favorable direction.

70 340 Challenger, I shortened by DS 2 1/8" and wish I'd only did 1 5/8.
Not sure if my DS was the original but I think it didn't have enough engaugement.
With the large factory seal, there's at least 1" of compression available.

on my 68 Charger i cut 1 3/4 off

1 5/8", 1 3/4" and my 2 1/4" which was sliding the yoke out a good 1/2" too much to allow for any forward movement from the diff.

I think that I will go with 2" which will allow for just a bit of additional forward movement.

Thanks guys for taking the time to respond. I really appreciate it!

The 2WD 518 is 3.25" longer than the 727 with the standard slip yoke tail.

See, now that's another part of this puzzle. I measured the 2 trannies and got that they were about 3" different. But in the car, I get the 2" measurement. There is a different K and engine in front of the 518, but they don't appear to be an inch farther forward.

I really want to get this thing on the road. I think that I will still have the driveshaft cut down 2". If it doesn't fit, at least it will be too long so that it can be cut again.

Street Machines is right around the corner and a group of us always spend that weekend with the cars. I don't want to have to ride there in a Pontiac or a Mustang while my Hemi sits at home.

After reading these replies Im very sure I only trust an actual measurement.

Not only for the reason of being sure but the factory yoke to seal clearance is too generous. It should be run closer. Unless its an off road vehicle. 1/2 " is plenty.

Do you have an adaptor plate that maybe where the inch difference is coming from? Or perhaps the mounts are loose on the engine allowing to move some once the trans is in?

I got weight on it and it still measures out at 2" +/-. So that's what I told the driveshaft shop to take out. Hope to get it back tomorrow and install it.