So Jim - how about a direct answer to the question ... ... Say you have a nice street/strip 500-550hp 455 for your 69-72 GS and over ----> there you have a stock non-posi 71/72 Buick 8.5" 10-bolt and sitting right next to it is a non-posi 12-bolt out of a canadian built skylark. Both will need a posi unit, both will get upgraded axles and need a going through including new bearings etc ... you're going to have a new beefy driveshaft made with new U-joints etc. Since its a STREET car your going to gear it somewhere between 3.08 - 3.73 ... which would you build for your car ?
That's not what the OP has. If the 12 bolt is out of a Canadian built Skylark, I believe it will have bolt in axles, and the bigger Buick U-joint already. In that case, build the 12 bolt for sure. The OP probably has a regular Chevy 12 bolt, but an 8.5, in the car now. I still say it's much easier to just build the 8.5 in the car now. I believe John Jr.'s procharged car has an 8.5 in it. That's a testament to it's strength.
I can build either to do the job - The question is how much of a BUICK guy are you to keep it all buick compare to the chubby rear...??? If your going to do street strip I can build the 8.5 cheaper with the stock axles to do the job. The 12 bolt will need AXLE no matter what- I would NOT reused stock chevy c-clip axles with a torque monster buick motor. I would always want the bolt in axle. FOR me it would come down to MONEY. and how often I was going to the track. you will need about 1050.00 excluding LABOR to set up the 12 bolt with alloy c-clip axles, NEW bearings, NEW posi, new gears, 1350 yoke. this would be for the street strip more street than strip action 1250.00 NO laber for set-up and welding billet ends on to do the 12 bolt with MOSER 33 spline custom race axles, GM flange bolt pattern and ford large bearings billet ends, 33 spline posi unit, ring and pinion, new bearings... IF I was to do the 12 bolt THIS is the way I would build it for MAXIMUM strength and street ability. 800.00 for the 8.5 excluding labor again - new bearings and seals, new ring and pinion, new posi, new 1350 yoke base street strip with more street than strip. Original 28 spline bolt in axles. 1185.00 will add the Moser 30 spline race axles this will do 10 sec range pretty easy - So for all out strength YES the 12 bolt chevy set-up with all the best will out do the 8.5 BUT will cost you more. remember someone has to buy the housing and that will BE A HUGE difference - 300-500 just for a housing 10 bolt 8.5 I have bought for 50-200 core open diff. There you go. I would say you have to determine HOPW much power you will actually get to the ground and how much track time your really going to do to pick. Think about how much money you can sell the 12 bolt to a chevelle guy to and then build 1/2 your 8.5 with that money... Jim:TU:
Oh I included a 1350 yoke in the builds because it sounded like you were intent on doing so. I consider the 8.5 yoke superior to any 12 bolt chevy yoke. I also believe the 1350 yoke is way over kill and NOT necessary as yokes and u-joint do not break unless you have a faulty part or YOUR drive line is set wrong and or NO pinion angle control is used. we have a 1310 yoke on a 10.90 car... pulls the front and 1.40 sixty foot. stock shorten GM drive shaft ... AGAIN not because I am cheap...It is to prove a point. we use the 8.5 rear with stock gm 30 spline axle and c-clip elim kit. again to prove a point...put the parts together correctly and true and your parts will go A LONG WAY for you. YES there are limits to everything and size usually helps in most applications for strength. Jim
Bump for a great infomative rear thread and question to Monzaz 30 spline 12bolt vs 33+ spline equiped 12bolt would the 33 and or 35 spline shafts make the carrier journel's too thin for a street car? Not building one, just read this a few times and we all know you're the rearend Guru ps everyone should inquiry about a Wavetrack for a 10 bolt!!
I have a 10 bolt with 3.91's and it is holding up great! I am really happy with it. Of course, I'm not racing it. My car is street only. Dave
Seeing the thread has been revived, I went with a 8.5" for my 65 Skylark. Upgraded to the 30 spline axle and Eaton posi unit. Also running 3:23 gears for my application.
I got mine rebuilt a few years ago with prettymuch bought all goodies from Monzaz excluding detroittru-trac, 3.08 gear and ta cover. for anyone thats hardcore into auto-x roadrace, best thing for the rear http://www.pro-touring.com/threads/81164-NEW-GMR-Pro-Touring-Rear-Floater-Hubs
