big block vs small block rear ends
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Safety Car
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big block vs small block rear ends
Hi, guys I have been off here for awhile. I have 1969 small block 350 350 hp vette with some mods headers alluminum heads , cam , march pully set up , allumnum radaitor, borgeson box, and a t56 magnum 6 speed.I am curoius I would like to make the rear end a big block rear end,also changing out the 370 gears for 411 gears. what I have been told is the half shafts are different, and the side yokes coming out of the diff are beefier as well as the ,what I call input shafts that come out of the trailing arms are heavier as well ,so that the half shafts connect with a beefy bolt and bracket, verses the one I have now that uses a nut with a u shaped peice of metal or strap.sorry about my spelling.some day I want to run about 550 to 600 hp out of the engine. alot of people have told me to run the big block stuff and have some light weight chromeoly half shafts made., thanks for your help. .
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From: North of Toronto - Ontario
Other than the side yokes using the caps rather than the u-bolts I don't think there was any difference SB to BB on the rear drive-train.
Half shafts were the same (2-1/2") and everything out on the arm was the same.
Now that said, there are aftermarket HD shafts and Yokes available so maybe that's what people are telling you about rather than what GM did. Also the later C3 went to a thinner wall / 3" half-shaft which is arguably stronger
M
Half shafts were the same (2-1/2") and everything out on the arm was the same.
Now that said, there are aftermarket HD shafts and Yokes available so maybe that's what people are telling you about rather than what GM did. Also the later C3 went to a thinner wall / 3" half-shaft which is arguably stronger
M
Tech Contributor
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From: Connecticut, USA
Moser nailed it except the BB vs SB had different stampings if that is important.
Personally I think too much is put into the notion that the "HD" axles are superior to the standard U-bolt axle. With the exception of the u-joint retention there is no difference. In fact new and some rebuilt axles sold today are not as good as possibly the original 69 axles you have. I just built a 69 diff and reused the axles, they were factory hardened and had little face wear and no spline twisting.
If you are going to run 600hp that you might want to so some homework as a stock diff was designed for 300-450hp and many came apart once more power and abuse were applied.
Now if you have an original 69 diff then there are some issues in it that should be addressed. While this was the first year for the 2nd design Eaton posi, which was an improvement over the 65-68, it wasn't as good as later units. They still had parallel seam castings as the earlier cases and still were prone to cracking. The posi cases were slightly revised by 72 and are the best to use. The posi needs to be addressed if you going to follow this path.
411 gears by Tom's are made to use with a 3 series case so all you need are the gears.
Personally I think too much is put into the notion that the "HD" axles are superior to the standard U-bolt axle. With the exception of the u-joint retention there is no difference. In fact new and some rebuilt axles sold today are not as good as possibly the original 69 axles you have. I just built a 69 diff and reused the axles, they were factory hardened and had little face wear and no spline twisting.
If you are going to run 600hp that you might want to so some homework as a stock diff was designed for 300-450hp and many came apart once more power and abuse were applied.
Now if you have an original 69 diff then there are some issues in it that should be addressed. While this was the first year for the 2nd design Eaton posi, which was an improvement over the 65-68, it wasn't as good as later units. They still had parallel seam castings as the earlier cases and still were prone to cracking. The posi cases were slightly revised by 72 and are the best to use. The posi needs to be addressed if you going to follow this path.
411 gears by Tom's are made to use with a 3 series case so all you need are the gears.
Thread Starter
Safety Car
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thanks for the help.I did notice on the big block cars 425 hp they did have bigger half shafts.I will be installing my ride tech coil over suspension, so I wanted to do rear end up grade while doing suspension.thanks again.
Tech Contributor
Joined: Aug 1999
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From: Connecticut, USA
All vettes from 63-74 used 2.5" shafts, 75-79 used 3" either will work. They all used 1350 u-joints.
Toms offers 3.5 x 134" Wall in 1350 or 1480 for extreme use.
Toms offers 3.5 x 134" Wall in 1350 or 1480 for extreme use.
Last edited by GTR1999; May 19, 2019 at 09:12 PM.
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As far as I know, GM only made 2-1/2" half-shafts until 75 when they switched to 3". SB, BB Standard, Automatic all got the same.
M
M
Last edited by Mooser; May 20, 2019 at 01:08 PM.
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Never seen anything except 2.5" ones until the later 3" that were used in the mega-lo HP versions in the later 70's. There never was an LS-7 factory Vette.
Nothing that special about the u-joint retention. You'll break something else before the straps give you any troubles.
Listen to Gary (GTR1999)...he knows what he's talking about.
JIM
Nothing that special about the u-joint retention. You'll break something else before the straps give you any troubles.
Listen to Gary (GTR1999)...he knows what he's talking about.
JIM
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