Driveshaft length-replacing 8.2 with a 12 bolt

I am about to change my existing 8.2 rear end with a built 12 bolt.I will be using the standard short 12 bolt pinion yoke with a 1330 size u-joint.The question is whether my driveshaft length needs to be changed.I couldn't find anything using the search function on the site.
Has anyone converted a '70 GS from an 8.2 to a 12 bolt? I would appreciate any advice.This project has taken me way too long!
Many thanks
Rod

 

My cousin took the 10 bolt out of his 65 GTO and put in a 70 Cheby 12 bolt. He didnt need to change anything. I dont see a problem with this unless your new U-joint is longer. Let us know how it turns out. Oh hang in there most projects take at least 4 times longer and 4 times money than anticapated. Dave

 

Thanks Dave.You are indeed right about the multiplier factor both as to time and money.I know from experience that installing an 8.2 in a '71 car requires driveshaft shortening.I just hope that I am not now in a bit of a pickle.
Rod

 

Driveshaft length

Rod, I have a 71 GS 350/350 combo. I replaced the original 8.2 with a 12 bolt Chev and everything bolted right up with the original driveshaft.
Hope this helps and good luck. Jim

 

Thanks for the info Jim.Are you sure you originally had an 8.2 in that '71?They came with the 8.5(except those built in Canada had the 12 bolt).My '71 was a U.S. car and thus had an 8.5.I replaced that with an 8.2 and it required a driveshaft shortening of about 1.25 inches.Would you mind confirming that you started out with an 8.2?
Many thanks,
Rod

 

Rod, my mistake, :spank: it was the 8.5, sorry about that. ou:

 

I have replaced olds, pont. buick, rear ends in all years from 1964-1969 and have never had a change in drive shaft length. Maybe i have just been lucky I currently have a 12 bolt in my 1964 Lark which i belive had a 8.2

Ken

 

Rod you got me puzzled. Did you change the trans, yoke, control arms, or anything else when you changed that rear in the 71!! From my understanding a rear from and A-body from 64-72 (weither it was a 8.2 10bolt,Olds 12 bolt, Pontiac 12 bolt, or Cheby 10 or 12 bolt)? will all swap....no mods.
The swaps I have done personally are 67 and 68 Olds 12 bolts, 69 8.2 10 bolt and 67 Chevelle 12 bolt into my 67 Cutlass. Others.. 64 8.2? into a 65 and a 66 GTO, 70 El camino rear into a 65 GTO.
Anyone else want to chime in on this? Iam going to look at a (71 I believe) 12 bolt for my 67. Dave

 

The forth pargraph answers my previous question. I dont like it when Idont know the answers!!!! So I just had to search. :Smarty:
www.oldsmobility.com/10boltPont-rebuild.htm

And this site also have alot of info. thought this could help anyone that may read this thread.
www.442.com/oldsfaq/ofdif.htm#Differentials

Now I can sleep easy tonight. :sleep:

 

Thanks for all your efforts Jim,Dave,Ken and anyone else I missed.I must say I am now thoroughly uncertain about the proper driveshaft length I need.this is not based on the most helpful info you guys have provided,but I am wondering now what I used for a driveshaft when I did the original swap from a '71 8.5 to the'70 3.64 geared 8.2.
It was a Buick shaft because of the 1330 joints.According to my read of the Olds site the '71 and'72 8.5 Buick cars used a longer pinion yoke,thus requiring a shorter driveshaft.Therefore,if I was using a '71 shaft in my conversion to the '70 rear end I should have needed to lengthen the shaft not shorten it! I do have an old uncut shaft in my "junk" about 100+ miles away which I will retreive,sandblast and have ready to slip in the car after the 12 bolt is installed so that I can possibly get home with the old boiler.I will let all know in a week or so how it goes.
Thanks again,Rod

 

Hello all.I just wanted to advise that yesterday I finally got the 12 bolt installed.I had found a 1330 yoke for the 12 bolt and the driveshaft which was previously in my car with a Buick 8.2 was a perfect fit.No problems.Went with the Eaton posi with the heavy springs and ceramic clutch discs and a 3.08 gear(instead of the 3.64 that was in the car).The swap was worthwhile.The car is much nicer at 60mph plus you get a bit of the "freewheeling" effect as opposed to keeping your foot in it a bit to maintain speed.Acceleration doesn't "feel" like it is affected adversely.With all that torque Buicks really don't care(street motors anyway) what gear is installed.I gave it a shot last night in low stall from a standing start and the car is as squirrely as ever.The fun is still there.Best thing I have done other than the Jim Weise switchpitch.I'm all smiles!
Rod

 

Good going Rod! But why did you originally put the 8.2 in the 71?

- Bill

 

Bill,
You know I have no idea why except the original rear was a pegleg and I had a chance to get a rear out of a Stage car.This was back a bunch of years when I knew even less than the little I know now! Oh well,a couple thousand bucks later and all is well.At least the 8.2 is,and was,a good rear and will be ending up in a board member's 4 speed '70 Stage car.
Rod

 

shafts

Buick u-joints are 3RL series (saginaw) NOT 1330. 1330 is FORD, 1310 Chevy & 3RL series B.O.P. You guys are going to get confused. Don't get me wrong here. Various earlier year cars (Skylarks & big Buicks) did use different series u-joints especially on 2pc. carrier bearing and CV shafts, so it can get confusing. If your driveshaft has inside snap rings (lock-up) its 3RL. Outside lock-up (pretzel clips) its 1310 / 1330/ 1350 respectivly. :Smarty: Just try'n to help ......Tim :Brow:

 

Always get the 1330 & 3RL lingo mixed up as they are the same diameter :eek2: When doing 8.2 to 8.5 rear swaps, I always have the driveshaft shop to shorten the original; 8.2 driveshaft 1", then have them install new u-joints.

Miss the old driveshaft shop I used up till 2003... $22 to propperly shorten & weld the end back on a steel driveshaft. Whattadeal :ball:

Roger