Drive shaft length

I have a 70 Skylark with a 350 and a th350 trans with a chevy 12 bolt rear.
Car currently has the stock 2 piece drive shaft in it.
I am going to a 455 with the same th350 and need to upgrade my drive shaft to a 1 piece.
Question is what length drive shaft do I need to match up to the 12 bolt chevy?
Also should I measure from center to center of the u-joints?
Thanks

 

I've always measured center of the cap to center of the cap and have never had an issue.

Someone might have an answer for you on length, but I do recommend measuring it and be sure to measure it with the rear axle on jack stands and not free hanging and have the yoke about 50% into the transmission. I did have success cutting down a drive shaft by looking up the difference in length of a TH400 and a TH700r4 and told the shop to remove "X" number of inches. They didn't like those instructions but did the work anyways. In general driveline shops want to know actual length not the change.

 

Should be the same driveshaft length I do not believe the motor will make the difference just the tranny. Jim

IF and when you are going to make a drive shaft call your drive shaft shop and ask them how you want the drive shaft length measured as THAT IS ALL THAT MATTERS. Some shops will measure different areas . NEVER assume everyone does it the same. Jim

 

I agree with Jim as unless you move the trans rearward your shaft length will be the same. I've not personally hade to move a trans rearward on a 350 to 455 engine swap yet. For me only installing a TH400 has made a difference in shaft length. As a former driveshaft builder of many years i can tell you that shops do sometimes differ in the way they'd like the measurement taken. Some prefer a seal to center measurement others may want you to push your trans yoke all the way in (bottomed out) then pull it out 3/4 to 1" and then measure centerline (cl) to centerline (cl). Always done with the rear "up" in a "riding" position. Centerline of the rear end yoke (looking at it sideways) will be roughly where the straps sit flat against the yoke and if you have U-Bolts then right where they start to go into the yoke holes. Personally i prefered seal to center as i liked to pick the cleanest spot on a trans yoke for the seal to ride when i was building shafts. I know everyone likes to call the rubber element shafts "two piece" and yes since they are not technically "welded together" they are seperate pieces but to a drive line guy they are one piece. "Two piece shafts" have a carrier (center) bearing and actually have a front and rear section using some type of "slip and spline" as the front half is generally fixed and only the rear half moves with the suspension as found on the Buick Rivieras / Wildcats / LeSabre etc. Also the OEM "chevy" 12 bolt yokes normally have two types of ways to lock in the u-joints. The Saginaw 3RL series u-joint (1 1/8 cap dia.) uses inside clips located on the u-joint caps to center them. The 1310 and more rare 1330 series u-joints (1 1/16 cap dia.) use tabs cast on the outside ends of the yoke to keep the u-joint locked in. The problem with the one piece rubber element shaft is that the rubber has hardened over the years and the shaft under acceleration torque starts to twist the front to rear yokes "out of phase" of each other. I've seen the shafts react one of two ways, either it starts to collapse causing the trans yoke to work out of the trans and effectively shortening it or it expands (but this is rare) and pushes the trans yoke into the trans effectively lengthening it and making the shaft harder to remove. Also beware that the TH350 trans yoke in high HP/Torque applications also tends to "twist" the splines internally and will not "bottom out" when pushed into the trans which can make shaft length seem incorrect. I've seen TH400 trans yokes do it too but it is uncommon due to the difference in ID/OD thickness. Sorry didn't mean to write a book LOL! Just being informative.

 

I would assume I will need the same length that I currently have. Just need to switch to a 1 piece shaft.
I was hoping someone would know the length off hand. I can measure mine when I get it up in the air again.
Good info Tim.
Found this.

http://www.v8buick.com/showthread.php?113759-Drive-shaft-length-needed

Since I swapped the Buick rear for a Chevy 12 bolt is there any difference between the 12 bolt chevy yoke and the factory Buick yoke length that I need to worry about?


Thanks,

 

GSX678 I had that same set-up in my 70 Stage 1 car - 455, T350 and Series III 12 bolt. I still have the driveshaft and can measure it for you if you would like. I would need to know how you want it measured. I also used the cross member from the 350 tranny. (Sorry, I don't remember why I did that). regards, buickstaged

 

Real easy go here:http://www.dynotechengineering.com/

 

Because your rear end it not stock there is a strong possibility that:

1. Your stock driveshaft is not in fact stock length but shorter.

2. Your stock driveshaft is in fact still stock length however it may be too long with the rear end swaps. Check the engagement depth of the driveshaft into the trans to find out if the shaft is the right length for your car as it sits. To do this put the rear up on jack stands or a lift, unbolt the J joint bolts at the rear end and see how far the shaft pulls out of the trans and hopefully it is engaged about half way with the suspension loaded up.

I know a guy who used a rear end that required a 3/4" shorter driveshaft but he used a stock length shaft and when he went over a massive set of railroad tracks the driveshaft bottomed out into the trans causing fatal damage to the trans.

After you check the engagement of the driveshaft then if you are happy bring it in and have a shop measure it up "their way" and then make you a shaft.

Why take a short cut, do it right, do it once.