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By slumlord444 - 2 Years Ago
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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?
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By Ted - 2 Years Ago
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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.
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By slumlord444 - 2 Years Ago
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Still looking for other ideas?
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By miker - 2 Years Ago
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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.
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By FORD DEARBORN - 2 Years Ago
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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?
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By slumlord444 - 2 Years Ago
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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.
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By Deyomatic - 2 Years Ago
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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.
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By Joe-JDC - 2 Years Ago
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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 
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By John Mummert - 2 Years Ago
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Its putting too much power to the left rear tire for one reason or another.
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By slumlord444 - 2 Years Ago
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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.
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By 55blacktie - 2 Years Ago
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Were your tires still wet after burnout? Track? My Ram 1500 will go sideways on a wet road, if I give it too much gas when the traffic light turns green.
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By slumlord444 - 2 Years Ago
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On the street, not the track. My Dakota with limited slip does the same thing on wet pavement. So why does my T Bird do it on dry pavement?
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By 55blacktie - 2 Years Ago
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Condition of tires-inflation? Road temperature? Probably a stretch, but you don't have an answer yet.
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By slumlord444 - 2 Years Ago
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Tires in excellent condition. 32-35 pounds. Air temperature around 80%. No idea about road temperature.
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By miker - 2 Years Ago
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On a flat road, street tires, they all pretty much move right in the rear if you’re spinning them hard. I think it’s the reaction to engine torque. But given yours is severe, and the other way, I’d be looking at the rear gears/traction loc. Might be worth a phone call to Randy’s Worldwide (used to be Randy’s ring and pinion). Tell them the problem and ask what to look for when you pull it, which is what I’m afraid you’re going to have to do.
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By FORD DEARBORN - 2 Years Ago
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There is a test that in this case, might be worth doing. It's described in the 50"s and 60's shop manuals how to check the holding force along with the smoothness of the axle clutch pack: Raise only one wheel and with the transmission in neutral, there is a specified minimum torque as measured with a toque wrench to breakaway and rotate the free axle. It also should provide a feel of the clutches while slipping. Checking a 1959 shop manual, 200 lb. ft. of torque is mentioned. Personally I don't think I could pull 200 lbs but maybe a breaker bar and a cheater pipe would work? Hope this helps..................
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By slumlord444 - 2 Years Ago
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Found the front spring clamp on the drivers side spring was unhooked and wedged between the spring and the frame. Fixed it and tried another burnout. Better but still wanting to fishtail at the end of first gear. Finally checked the black marks on the road. Both sides seemed to be equal which indicates that the traction loc is working. Pattern was dark on the outside edges and light in the middle which indicates low tire pressure. I was running around 32 psi. Re checked tire manufacturers recommendations and discovered they recommend 38 to 40 psi. Tried 38 psi and another burnout but still squirrely. Burnout pattern on the road a little better but still indicates low tire pressure. Will try more air pressure. In researching the factory tire pressure recommendations i realized that the tires are 7 years old which I had lost track of. Could that be the problem because the rubber is probably getting hard? Tires always inside and probably around a thousand miles. Diamondback radials.
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By 55blacktie - 2 Years Ago
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Normally tire pressure is lowered for better traction on the track. If you're running street tires, there's nothing to be gained by doing a burnout.
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By slumlord444 - 2 Years Ago
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Not trying to gain anything. Trying to figure out why it won’t go in a straight line on a hard launch. I’ve been doing hard launches with this car since I bought it in 1965. Used to launch it on the drag strip at 5,500 rpm’s with 6” recap slicks and it always went straight.
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By miker - 2 Years Ago
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Glad you found a suspended problem that fixed most of it. Better than a broken posi. Maybe it’s getting squirrelly because you’ve got a lot more torque and horsepower?
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By Hoosier Hurricane - 2 Years Ago
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It left straight with slicks, now it doesn't with street tires. Wouldn't that suggest a tire problem? What if you tried switching the rear tires side for side. If it goes crooked the other way, that would tell you if it was a tire issue.
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By slumlord444 - 2 Years Ago
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That’s a definite possibility that I’m considering.
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By slumlord444 - 2 Years Ago
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I haven’t tried switching or rotating the tires yet. It’s on my list of things to try. The added horsepower and torque is also a definite possibility. Had a conversation about the problem at a local car cruise with a Ford guy tonight and he bought up the fact that CLTrac’s worked very well with keeping high horsepower cars going straight. The fact that they ar adjustable makes sense. I’ve been thinking about trying them. I don’t find a part number for my 57 T Bird on their website. Does anyone have a part number?
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By slumlord444 - 2 Years Ago
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It actually went straight with street tires until I upped the horsepower and torque with headers and exhaust system.
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By slumlord444 - 2 Years Ago
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Any comments on how well CalTrac’s work?
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By miker - 2 Years Ago
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Old post on Caltrac. Note Vic’s comments towards the end. If it’s leaving straight with a wheel pulled………
http://forums.y-blocksforever.com/Topic118990.aspx
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By charliemccraney - 2 Years Ago
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CalTracs are the best option for a street / strip car. They provide the traction capability and for me, I could not tell any difference in the everyday ride quality. They may or may not address your problem, depending on what that problem ends up being.
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