Anybody know if an 8.25" axle is liable to fail in a roadrace, side loaded environment? Not really worried about the strength of the axles as much as the c-clip retention.

Car should generate some good g's, so I expect to put some load to it.

I would just jump to an 8.75" axle, but I kind of like the lighter 8.25", and I don't see that the car will need the 8.75" unless the c-clips are a real issue. Putting an 8.75" in the car feels a bit like put a Dana 60 in a mild SB car.

Figure the least I will do is upgrade to 29 spline axles as I will probably need a custom axle regardless. 29 spline axles are just a touch smaller in diameter than Ford 8.8 31 spline axles (1.29" to 1.32"). The Ford FR500S turnkey racecars use a 31 spline 8.8, so my 8.25 should be adequate, right?

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'15 Chrysler 200S V6
'74 Duster 360, factory 4 speed car

There are many things to consider. An 8 3/4 is not much heavier than an 8 1/4. If you are road racing you'll probably want more than one ratio to choose from. Fast tracks you'll probably want 3.55s. Slower tracks like Laguna Seca will need 3.91s or 4.10s.

I would not bother upgrading an 8 1/4. I only own one because it was cheap and had the 3.21 gears I wanted. I feel the money is much better spent on narrowing an 8 3/4 even if you use cut down factory axles. Factory axles might even be better than aftermarket is some instances. I saw a Mustang loose an aftermarket axle shaft at Laguna Seca as the bearing retainer evidently wasn't a tight enough press fit on the axle. This was coming downhill from the corkscrew

Where are you going to race? You can't go to an SCTA sanctioned meet at Bonneville with C-clip axles. Then again I wouldn't expect failure from a modern C-clip rear end. To me the ability to change gears and loose the C-clips by going to an 8 3/4 makes a lot of sense. I'm still planning on replacing my 8 1/4 with an 8 3/4 when I have the funds.

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Joshua

I don't really expect to change the ratio once I get it set. More like a regularly driven street car that get's tracked once a month or so.

At the same time, being able to change the ratio easily does lend itself to finding the right all around ratio.

One additional advantage to the 8 3/4 is the possibility of fixed caliper brakes in the rear. The c-clip axle eliminates that completely. I had decided that I could live without them, but it would be nice to have the option.
I'm hoping to get my feet wet here in Spokane. Someday, I'm hoping to make it to SFSF (?), but that's a little ways off.

The ultimate goal is to have a car I can comfortably drive to some far away racetrack and have some fun at an open track day or something. Think daily driver M3 weekend warrior kind of car.

If this was a single purpose track car, the only axle option I would consider is the 8.75".

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'15 Chrysler 200S V6
'74 Duster 360, factory 4 speed car

From my sources, an 8.25" axle is MAYBE 5-10 lbs lighter than an 8.75". Not worth it unless you already have an 8.25".

Lou

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Home of Slant6-powered fun machines since 1988

I thought it was about 25#, but never did verify it.

I do have an 8.25" in the car now. It's an F-Body one, and a bit wider than I hoped, but it will fit the Duster fine. Problem is, the Duster is a 4 speed car in which I expect to spend some time at the strip this summer, and I don't think the an 8.25 rear will handle it very well. Dilemma is do I build two 8.75 rears, or just one for the Duster and get some custom length axles for the 8.25" axle in the Valiant.

For 8.75 parts, I currently have (2) housings, (4) axles, a 3.55 742 pumpkin and an extra pumpkin of unknown ratio with a clutch style sure grip. To build (2) complete axles, I would need (2) housing ends (one of the housings is an early one) and one more pumpkin and another sure grip.

Side comment -> I realize now that my heading was probably misleading. "Roadrace" most likely means 20 hard laps of racing, combined with a bunch of tuning and qualifying laps, every weekend or so. I probably should have said "track days".

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'15 Chrysler 200S V6
'74 Duster 360, factory 4 speed car