C-3 Rear Diff.

[David M.]

April built 68 small block roadster, 3 speed stick, stock drive train from trans out, aprox 375-400 flywheel HP.
While tearing into the rear end to install a new axle bearing assembly on one side,(the other sides been recently replaced), I had to bead blast the outer half shaft flange to clean it up. That got me to thinking, "this part doesn't look all that stout". This car is a driver. I know SOME of the week spots in these rear ends. Isn't this one of them? Does anyone offer billet inner/outer flanges or any other bolt on improvements for these early C3 rears? Big Block parts? Maybe a shop that does this for one of you guys that I can contact etc???
What interchanges with the stronger later C3 stuff say from the inner flange out to the wheel bearings?
I'm in there, so nows the time for up grades in the interest of safety/reliability.

Thanks,

Dave

[Joe L.]

Re: C-3 Rear Diff.

Dave-----

First of all, understand that any 1963-82 Corvette rear drive and differential assembly is not a particularly stout set-up, at all. They were never designed for serious drag racing. Notwithstanding that, the stock assembly will handle without problem for street applications the power and likely torque level that you're talking about.

There were 3 different half-shaft flanges used over the 1963-79 period. The 63-only flange is manufactured of cast nodular iron. It is the weakest of all, although it appears stouter because it's larger in cross section. The 64-74 flange is a forged piece of thinner cross section but much stronger. It was also SERVICE for 1963. The 1975-79 piece was manufactured by Spicer and is also a forged piece. Although its configuration differs somewhat from the 64-74 flange, it has approximately equal strength. It is also SERVICE for all 63-74 models. There were no special half shaft flanges used for big blocks of any year; the half shaft flanges for any given year were the same for all engine applications.

Once again, for your application and power level the stock half shaft flanges should be adequate for normal street use, if not even some racing use. Generally, the stock flanges were used for most road racing applications. Stronger parts may be needed for serious drag racing applications, though. I don't recommend drag racing IRS Corvettes, but to-each-his-own.

There are no other changes in later C3's (i.e. after 1968) that will provide any parts for up-graded rear drive. Through 1979, most of the parts are pretty much the same (as they are pretty much the same from 1963 to 1968, too). In 1975, Corvettes went to a larger OD half shaft. However, contrary to popular opinion and the intuitive, these larger OD half shafts were not significantly stronger than the smaller OD 63-74 shafts.

You can somewhat improve rear drive strength by adding the cap-type axle yokes used for 65-74 big blocks and some 1970+ small blocks.

There are aftermarket parts available to significantly improve 1963-79 rear drive strength. Primarily, these parts are for drag racing applications, but folks who "over-power" any 1963-79 Corvette may be wise to use them, too. I don't recommend such conversions (or, "over-powering" any 63-79 Corvette), but to-each-his-own. If you're interested, check with suppliers like Tom's Differential (www.tomsdifferentials.com) for such components.

[Mark #28455]

think road racer

If you have watched 12 and 24 hour endurance racing, you have seen how some of the higher powered cars lose the race due to breakage. I have run 600HP big blocks with a stock F41 BB corvette rear suspension, BUT, I don't drag race and I don't BANG the gears, I let up on the gas when I shift and don't pop the clutch. More than 20 years later, not one failure in the stock parts.

Mark

[David M.]

Re: think road racer

Thanks guys, thats what I needed to hear. I cant find any fine thread grade 5 or 8 hardware locally with out purchasing boxes of 50. I'm thinking ARP should have what I need. Its probably over kill but I reassemble anything drive train or engine related with the finest hardware I can buy. Now, if I can just stop ordering parts and get it on the road, its a sickness!

[Joe L.]

Re: think road racer

Dave-----

Orchard Supply Hardware carries grade 8 SAE fine thread fasteners and they sell them "per each". At least, they do in my area in California.

Some sizes of SAE grade 5 and 8 fasteners are also still available from GM on a "per each" or small quantity package size basis. The problem is that many now carry a pretty stiff price when purchased from GM. But, if you don't need that many, it's not a problem.

[Gary R.]

Re: think road racer

Joe,
What is Orchard supply- local to CA or do they have a web site?

Dave,
You can beef up the differential a lot with some old time mods. I have documented the steps in a very long post on another forum. If you search you can find it or contact and I'll go over how I build them. A simple bearing cap bolt change to socket head screws will add soem strength.
Last week I opened up a 75 diff that was ripped in 1/2 at the cross shaft, the stock caps and SHCS were still tight. In fact they were the only thing that wasn't destroyed in the diff.

[Joe L.]

Re: think road racer

Gary-----

Yes, they have a web-site. I think it's www.osh.com

I thought that they were a national chain, but I'm not sure if they are. It's been owned by Sears for about the last 5-10 years. In other states, it might be called "Sears Hardware", but I don't know if they have the same product line.

[Gary R.]

Re: think road racer

Joe, Sounds like the Sears hardware we have around here. Thanks