Auto Racing: Rear Differential Weld?, traction unit, sarasota florida

Question
QUESTION: Do you know if welding the rear differential is legal in autocross? I'd like to be able to practice drifting at a track but still compete in autocross. My car is F Stock class. I wouldn't wanna change classes so I'm wondering if they'd allow it. I looked through the rule book at least twice for it now and saw no mention. Also, the extra traction from it wouldn't hurt. Also, do you know the pros and cons of welding the differential? I know that when you do that, your tire will skip and bounce a little bit at low speeds and backing up but that it gives you a solid axle where both spin at the same speed. This is something that I probably would do if I had an extra car to spare so I could still compete. And yes, I'm the same 16 year old that asked about rally racing.

ANSWER: Welding a differential is an ancient way of 'locking' it so it can't differentiate.  It does increase traction in the rear wheels, but only in a straight-ahead direction.  They work well on drag racers, but in corners it causes trouble because the outer wheel in a corner needs to go a little faster due to the fact that it's following a longer path through the corner.  It would be a poor choice for an auto cross or solo car, causing it to slide fiercely in the corners, and make it hard to steer.   

If you can find a posi-traction unit for your car, you should install that, it won't affect street driving and it will lock up under load. In corners it stops the inner wheel from spinning, and forces it to continue to drive the car.
Used units can be had for $200 on up and are worth the investment.

You are thinking about this stuff, that's a good thing. Remember keep those grades up so you can get into a good university.

Dan Liddy]
Sarasota Florida

---------- FOLLOW-UP ----------

QUESTION: Okay. Do you know where I could get a used posi? Or should I just check out some of the local junkyards or order a used one from Ebay or something? Also, do you know if stripping the car of things like extra seats and such to decrease weight would put me into a different class than just leaving it there? Or could I do that and live with my friend's scrutiny of my car?

Answer
Try e-bay, that's where I find that sort of thing. New ones usually run in the $7-800 range, and still require the services on a highly skilled mechanic,  NOT the average garage guy but a mechanic with race experience and a professional set of equipment. Gears are real sensitive to adjustments, and you can turn an expensive diff into gravel right quick if you do it wrong.

So yea, e-bay is your best bet.  Or look around local race shops.

Dan