Well those of you with a McLeod Twin disk and have broken an output/mainshaft or two like me. Well I have a fix being made as I type. It is made of 300M and is 4.5 times stronger than the stock shaft. I am only having 5 made right now to see if it will be a popular item.

Of course I am getting one of them so that leaves 4 left for grabs.

If interested please call Paul at Corvettes of Houston to order or to ask any questions. 281-821-1222

I believe the price will be $750


Thanks.
Sean

 

TTT

Sean

 

Sean: I called, sounds promising. So it's the same dimensions as a stock shaft but stronger?

Rich Krause

 

What did you guys identify the stock material as?

I'm interested, but I'm not sure that a simple material upgrade (if you can call a switch to 300M "simple" ) will cure the problem, or if I'll be better off switching to the larger-diameter Viper mainshaft (which is a less-expensive change but requires that I send off some parts for machine work).

 

To change to a viper shaft you will have to bore the tail housing, get a viper tail housing seal and bushing and get a viper slip yoke for the driveshaft. Not sure what you will have to do about the speedo reluctor.

The special thing about the 300M is its elastisty (chromium and silicon content). The stock (viper and F-body) material is just a cast ductile iron (pretty fragile).

Sean(Pig)

 

Yes, the 300M shaft is the same dementions as the stock F-body shaft and is right at 4.5 times stonger than the stock shaft.

Thanks,
Sean(Pig)

 

What's the shear modulus (G) compared to the stock material? The elastic modulus won't affect the materials response to torsion.

 

Have you guys tried a cryogenic treatment on the output shaft?
Wouldn't that make it stronger, at a better price?

 

I wouldnt waste money having the shaft cryoed. These stock cast shafts are very inconsistant as far as air bubbles and misaligned atoms. All cryoing does is straightens the material.

Sean(Pig)

 

All I can tell for now is that the 300M's elastisty is 19% and the stock material is 7%.

Basically a spung hub clutch and a bit of tire spin will help the stock shaft live, but with a solid hub clutch (like the twin disk) and slicks your asking for a disaster if you hook up well after 6k rpm launch.

I will get more specs on the shear modulus tomorrow. I cant remember right now.

Thanks,
Sean(Pig)

 

300M is modified 4340, right? It can be heat treated to a maximum tensile strength up to 290,000 psi, so to be 4.5 times stronger, the stock output shaft would only have a TS of about 65,000 psi which is less than almost any low-carbon or mild steel which has received no heat treating, or even cold working. I suspect the stock shaft is a little stronger steel than that.

Are you sure it's cast? Even ductile iron is usually above 65K psi. It's a fully machined piece, with no big flanges, so from a manufacturing point of view, a casting would be much more expensive to machine than a steel bar, and not offer the same strength.

Will you really be using 300M it at it's ultimate strength point? Isn't it kinda brittle there? Sure, top-of-the-line bolts are that strong, but they don't get repeated torsional impact loads like an input shaft.

Not that 300M isn't a good material, but $750? It might just push the failure point to the next weakest link.
My $.02

 

I'd be OK with that - the transmission mainshaft is probably the most difficult part to service in my entire drivetrain.

 

I meant other internal transmission parts. If they fail they usually take lots of friends with them.

 

Just an FYI, you would want to use the yield stress instead of the ultimate in designing/comparing the shafts. Ultimate=broken. Yield=shaft survives without permanent deformation, though fatigue would possibly need to be considered. Most important, the new shear modulus and allowable shear stress (which is related to the tensile strength) are necessary to determine how much better the shaft is.

 

Yep. It would help to know what the stock shaft is made from and it's hardness, and whether it's a thru-hardened steel or case hardened or maybe pre hardened (like Stressproof). The failure mode and point of failure would also be critical to know.

If impact loading if causing the failures, the type of heat treating could be critical. Martempering (marquenching) might be useful. We produce Top Fuel/Top Alcohol blower drive parts which take very high rpm and extreme loading. Martempered 4340 works well in this application. Choosing AQ (aircraft quality) material is worth the slight extra bucks; there are fewer chances of inclusions, voids, impuities, etc. in the steel.

The jury is still out on "misaligned" atoms, however. I'm happy just to get 99% martensite on the blower drive parts. With the relatively small diameter of this shaft, that's a good bet.