Correct Driveshaft Length

[cv70chall]

I posted a while back regarding a clunk whenever I& would first place the car into reverse. If you drop it into reverse, then back to park- and right back into reverse- it shifts into reverse nice and normal.
I've checked the U joints- they were nice and tight. We shifted with the car on a lift and could tell the noise wasn't coming from the pumpkin either, so we can rule out an adjustment.
That being said, we did notice the driveshaft was a bit short. (I had the car upgraded from a 904/ 360 to a 727/440 a few years back and the guy apparently used a different driveshaft.
My question is- what is the correct length for a driveshaft for a 70 E-Body, 727 and 440 combo?

[70chall440]

Google is your friend 

This is a chart of common 1966 and later RWD Mopar slip yoke driveshafts. It is sorted by length to help with interchange.
Mopar Slip Yoke Driveshafts Part No Years Dia" Length" Trans Rear Engine Body
2883775 1970-71 3.25 42.60 727,833 9-3/4 426 440 Barracuda
2996134 1974 3.25 43.29 727,833 8-1/4 318 360 Barracuda
2883636 1970 3.25 43.60 727 8-3/4 383 426 440 Barracuda
2996134 1971 3.25 43.79 727/833 8-3/4 340 Barracuda
2883769 1970-71 3.25 43185 727/833 8-3/4 340 Barracuda
2883667 1970-71 3.25 44.60 727/833 9-3/4 426 440 Challenger
2883690 1970-72 3.00 44.99 727 8-3/4 340 Duster Demon
2883656 1970-71 3.25 45.60 727/833 8-3/4 340 383 440 Challenger
2996142 1971 3.25 45.79 727 8-3/4 340 383-2 Challenger
2883782 1970 3.25 45.85 727/833 8-3/4 340 Challenger
3578138 1974 3.00 47.40 904/230 8-1/4 318 Barracuda
2852228 1967-69 3.25 47.81 727 8-3/4 340 383 Dart
2883693 1970 3.25 47.99 727 8-3/4 340 Dart
2852206 1967-69 2.75 48.60 904 8-3/4 273 318 Barracuda Valiant
2852206 1967-69 2.75 48.60 833 8-3/4 273 318 340 383 Barracuda Valiant
2852216 1968-69 3.00 48.88 727 8-3/4 340 393 Barracuda
2996157 1972 3.25 48.89 904/230 8-3/4 225 318 Duster Demon
2883760 1970-72 2.75 48.96 833 8-3/4 340 Duster Demon
2883760 1970-72 2.75 48.96 904 8-3/4 198 225 318 Duster Demon
2883752 1971 2.75 49.27 904/833 8-3/4 198 225 318 340 Valiant
3578146 1973 3.00 49.40 727/833 8-3/4 318 340 Challenger
2996105 1971 3.25 49.50 727/833 9-3/4 426 440 Belvedere Coronet
2781952 1966 2.75 49.58 904/833 8-3/4 170 225 225 273 Barracuda Valiant
2996146 1971-73 3.25 49.89 727/833 8-3/4 318 340 Challenger
3467151 1973-76 3.25 49.90 904/833 8-1/4 225 318 340 360 Duster Dart Sport
2883779 1970-72 3.25 49.95 727 8-3/4 318 Challenger
2883766 1970 3.25 50.18 727 7-1/4 225 318 Barracuda
2781955 1966-67 3.00 50.27 833 9-3/4 426 Belvedere Coronet
2853247 1968-69 3.00 50.39 833 9-3/4 426 440 Belvedere
2996101 1971 3.25 50.68 727/833 8-3/4 383 426 440 Belvedere Coronet
2996109 1972-73 3.25 50.80 727/833 8-3/4 400 440 Belvedere Coronet
2852326 1968 3.00 50.96 833 9-3/4 426 440 Coronet Charger
2660628 1967 2.75 51.03 727 8-3/4 225 318 383 Belvedere
2781953 1967 2.75 51.15 727/833 8-3/4 426 440 Belvedere Coronet Charger
2660628 1966-67 2.75 51.28 745 8-3/4 225 273 318 383 Belvedere Coronet Charger
2996268 1974 3.25 51.34 727/833 9-1/4 360 400 440 Belvedere Coronet
2781953 1966 3.00 51.40 727/833 8-3/4 426 Belvedere Coronet Charger
2533192 1967-69 2.75 51.43 904/833 7-1/4 225 273 318 Barracuda Valiant
2852161 1968-69 3.00 51.50 727/833 8-3/4 383 426 440 Belvedere
2852212 1967-69 3.00 51.53 833 8-3/4 273 318 340 383 Dart
2996137 1973-76 3.25 51.89 904/833/230 8-1/4 225 318 340 360 Duster Dart Sport
2883758 1972 3.00 51.96 904/230 8-3/4 225 318 340 Dart
2660635 1967-68 2.75 52.00 727 8-3/4 318 383 Belvedere Coronet Charger
2852162 1968 3.00 52.07 727/833 8-3/4 383 426 440 Coronet Charger
2852118 1967 3.25 52.27 727 8-3/4 440 Charger
2660635 1966-67 2.75 52.28 727/833 8-3/4 361 383 426 Belvedere Coronet Charger
3467155 1973-76 3.25 52.70 904/833/230 8-1/4 225 318 340 360 Duster Dart Sport
2883696 1971-74 3.25 53.18 727/833 8-3/4 225 318 340 360 400 440 Belvedere Coronet
2996113 1974 3.25 53.30 727/833 8-1/4 400 Belvedere Coronet
2996195 1970 3.25 53.64 727 8-3/4 383 440 Belvedere
3578322 1974 3.25 53.80 727/833 8-1/4 400 Belvedere Coronet
3578331 1974 3.25 53.84 727/833 9-1/4 400 440 Belvedere
2853237 1967-76 3.00 54.36 904 7-1/4 170 225 273 318 Dart
2660622 1966 3.00 54.54 904/833 7-1/4 273 Valiant
2996201 1971-73 3.25 54.86 727/833 8-3/4 318 Belvedere Coronet
3578301 1974 3.25 54.92 727/833 8-3/4 225 318 Belvedere
2533148 1966 2.75 55.42 727/833 8-3/4 225 273 318 Belvedere Coronet Charger
2660550 1968-69 3.00 56.17 904 8-3/4 225 273 318 Coronet Charger
2660550 1966 2.75 56.42 904/903 8-3/4 225 273 318 Belvedere Coronet Charger
2660607 1966 3.00 56.61 904/833 7-1/4 170 225 273 Dart
2883735 1972-73 3.25 57.36 727/833 8-3/4 225 318 Belvedere Coronet
2996121 1972 3.00 57.42 727/833 8-3/4 225 318 Belvedere Coronet
2852253 1968-69 3.00 57.65 904/903 7-1/4 225 273 Belvedere Coronet
2996121 1974 3.00 57.82 727/833 9-1/4 360 Belvedere Coronet
2852222 1968 3.25 57.93 727 8-3/4 383 440 Chrysler

[70chall440]

Here is something that you can copy and keep if you would like

[cv70chall]

Thanks!
So, based on what I have, it would be this?

2883656 1970-71 3.25 45.60 727/833 8-3/4 340 383 440 Challenger
Might you know of anyone wanting to sell one? Mine is shorter, which leads me to believe it might be for a larger rear end?

[70chall440]

You are far better off ordering a new one than buying a used one, there are many places online that make/sell them but you will need to provide the length and U joint type to be used. That said, I would actually measure your drive line (center to center on the U joint caps) just to confirm, you need the rear suspension to be under load meaning it needs to be held up, on stands, etc. so that it is where it would be when on the ground.

[cv70chall]

Hey thanks again for the input.
I have a drive on lift available to me, so having the suspension under normal load won't be an issue.
When you say measure from center to center of the u-joint caps, can you clarify? And I would need to remove the shaft from the transmission to get the full measurement as well, right?
Lastly, who can you recommend for ordering a new driveshaft?

[70chall440]

So here is the procedure;

1. remove the drive shaft currently on the car; you are going to need the transmission yoke either from that shaft or another one. It may be possible to do this if you just unbolt the U joint caps at the rear end.

2. push a yoke into the transmission until it bottoms out, then pull it back out slowly until you have approximately 3/4" clearance from the end of the tail shaft of the transmission to the body of the yoke where the U joints are (the big part of the yoke)

3. you want to measure from the center of the cap (or cap hole) of the yoke to the center of a cap (or cap hole) on the pinion (usually this where the U joint straps are flat on the pinion yoke.

You need to be relatively accurate on this measurement.

The only place I can personally recommend is

The driveshaft specialist Inc.
San Antonio, TX

I am running a 3.5" aluminum shaft they made me and I am very happy with it.