My 57 T Bird with a Mummert head 312 with around 425 horsepower insists on making a right turn on a hard launch from a dead stop. Toploader 4 speed, 3.89 traction loc rear end, rebuilt set of original Traction Masters, Diamond back radials, station wagon rear springs. The first time it happened I ended up setting sideways in the road headed straight towards the ditch on the right side of the road. Scared the crap out of me. It’s never done anything like that before. Easy enough to light up the tires but it always went in a straight line before. Not that it should make a difference but it didn’t happen until I replaced the antique Headman headers with FPA headers and switched the stock mufflers and tailpipes with Turbo mufflers and 2 1/2” tailpipes. Picked up horsepower and torque with the change. I’m thinking a problem with the Traction Loc or the rear suspension?  It starts to go straight and then the back end comes around and it starts to spin out and head for the ditch. Goes straight down the road otherwise. What’s the problem?

For now, I’ll rule out suspension or tire issues as your problem sounds more mechanical.

I’ll suggest removing the passenger (right) side axle and examine the splines that go into the rear differential carrier.  When looking at the axle splines for that side, you can observe where the axle engages within the carrier with a double row of splines.  The Traction Lock diff has two gears on one side of the unit with each of those gears having splines that must be aligned in which to fully install the axle on that side.  If the axle splines are stripped, shallow, or worn, then that can allow the clutches to disengage within the posi unit and just pull with one tire instead of both.  That can make the rear act like a broken axle and twist the car sideways.  Beyond that, you may need to pull the posi-traction unit apart and give it a thorough examination.

Other suggestions always helpful as I'm only touching on one potential cause for the problem.

Lorena, Texas (South of Waco)

Still looking for other ideas?

I’ve got the Dana 44 (from a truck) with a limited slip in the back of my bird. With new stock leafs, old fashion traction masters, it left straight on the stock size Coker’s, and on the 235/60 BFG T/A’s. Spin em hard enough, the engine torque will move the rear end over, or it’ll fall off a crown in the road, but nothing like you’re talking about. If it’s not a wheel drive problem, something is broken loose. I did break a main leaf years ago (different ‘bird), it got a little squirrelly and sent me looking, but not like your case.

miker
55 bird, 32 cabrio F code
Kent, WA
Tucson, AZ

Sounds like quite a lot of asymmetrical thrust, or drag going on. Could be something going on inside the differential as Ted suggested or an issue with the clutch pack? You stated this didn't start happening until you performed major exhaust work. Did you need to loosed up a motor mount and possibly forget to retighten it? Could something be against one of the parking brake cables causing tension when the body/axle is under torque stress? 

64F100 57FAIRLANE500

I’ll be looking under the rear end this week. I do know that the headers and exhaust system added a lot of horsepower and torque. Hopefully I’ll find something. 

I may be wrong but I can't imagine that a header and exhaust swap would have added enough power to do that.  I had a broken rear leaf spring pack once that made the car feel like it was "sidewinding" down the street.  I'd look into that suspension. 

On my 345Y that we dyno tested at Ted's shop, it made 402hp/405tq with FPA headers for my '55 Thunderbird.  I had a pair of ported exhaust manifolds for the Thunderbird, and we swapped them to the 345Y on the dyno, and promptly lost 35hp/35tq.  The exhaust manifolds were ported/cleaned up and the exits enlarged for 2 1/2" exhaust pipes with about two feet of exhaust pipe installed.  Ted said that was inline with what he had seen with dyno testing different exhaust manifolds/headers on several tests.  Probably would have been a little more lost if I hadn't ported the exhaust manifolds.  Joe-JDC  

JDC

Its putting too much power to the left rear tire for one reason or another.

http://ford-y-block.com 

20 miles east of San Diego, 20 miles north of Mexico

Jacked it up and carefully examined everything under the rear end. Nothing broken or obviously wrong. Turn a wheel and the other one turns as it should. Equal air pressure in both tires. Could possibly be the crown in the road causing the problem. Will try it out a different stretch of road that is definitely flat and possibly play with tire pressure. Haven’t pulled the axle’s yet but will at some point. The funny thing is that my Dodge Dacota with factory limited slip rear end also tends to go sideways when the rear end breaks loose. I seem to recall that when limited slip rear ends first came out there were some problems with people crossing the car up if the tire’s really broke loose.