Fiat 600 Rear Stub Axles
If you own or drive a Fiat 600 or 600-based car, you may or may not be aware of a weakness these cars have. Many of us are running a lot more horsepower than these little cars originally came with; we have lowered and stiffened the suspension, and are running new sticky tires that are pretty wide. I know on my own modified 600 AMY I have 175/70HR13 Yokohama A001R tires, which are no longer available today, but were recommended for Autocross for this weight of car at the time. Today many of you are running even lower profile, even stickier tires!
In the old days, even with modified cars, the best tires (remember Firestone Blue Streaks?) were bias-plied tires. If you were going as fast as you should, the inner front tire was in the air and the car was sliding in a nice drift. With today's tires, the car doesn't slide, so the tires and the car needs to absorb what you are asking it to do.
Consequently, the rear hub snaps off the stub axle and the outside rear tire, brakes and all, exits the wheel box, and the suspension digs into the pavement, usually flipping the car. This all happens so fast I am told (it has never happened to me, yet) that there is nothing the driver can do other than go along for the ride.
There are supposed "fixes" for this: PBS thought going with a solid spacer between the rear wheel bearings would solve some of the stresses. It doesn't - I have had customers with this fix flip their cars. Others thought using 850 stub axles and carriers in modified 600 swing arms would solve the problem - it doesn't either. No matter what method you use, if you are campaigning a 600-based car, everyone agrees that you should magnaflux the stub axles yearly to check for cracks.
But we all know that a good, non-cracked stub axle can still crack and fail next weekend. Consequently, I personally do not corner my car like I used to, or like I know it could. ...
However, I found a company that does racing axles, and sent them a used and a failed stub axle. They agree that the stock unit is not designed to be used with today's stresses, and have proposed a new stub axle that addresses the problems that they observe. The radius between the axle and the flange is addressed, the material is changed to 4340 chrome moly steel, and then the stub axle is subjected to the "full thru heat treat" process.
Is this the solution? We don't yet . . . but I believe that if the obvious faults are addressed, then the next weakest link, whatever it is, will fail next. And I would sure like to drive AMY as hard as I know she will go.
Unfortunately, these new racing axles will not be nearly as cheap as a new, current production stub axle (part #4070039). For one pair they have quoted me $750.00, for 5 or more pairs $550.00 each. Are there enough of you out there willing to purchase these so we can find out if these finally solve the problem???
If you have a fast 600 that looks like a Berlina Corsa, or maybe not something quite so serious but that you enjoy driving the way it begs - what is your peace of mind worth? Would you like to be able to run at your limit into a corner, instead of finding out all-of-a-sudden that you've run up to and beyond your stub-axle's limit only when you are on the way over to your roof?
