So went from a Posi and stock axles to a Strange spool and axles this past winter on my Mom's bracket Duster. Now the car is un stable going down the track. It just moves around and searches a lot. I thought maybe the spool was highlighting the fact that the frontend didn't have much caster so I rebuilt the frontend with all new ball joints, tie rod ends, and new QA1 upper control arms with 3.5 degrees of caster. This didn't change the way the car handles at all. It has old Comp Engineering shocks on the back with HD springs and the front has some old Koni shocks. All the suspension and tires have been on the car for a while and the only change that seemed to cause this problem was the spool and axles. Any ideas what may be causing this issue?

What tires are on the front and back of the car?
Have you measured the circumference of the rear tires?
Is the rear of the car sitting much higher than the front?

Is it an 8-3/4 ?? did you check to see if the housing is bent?

It has M/T ET fronts and M/T slicks. They can from the M/T truck and were matched when new to 1/4" of rollout. The rear does have some rack to it being a stock suspension car. It does have a 8 3/4 rearend in it. I haven't measured to see if it is bent but the old axles came out very easily and the new ones went in very easily.

The really weird thing is it doesn't go right or left every time. It leaves straight and then just starts to sashay around.

what did the clutches look like?
one tire may have been spinning less than the other.
check circumference again.

Don

I will check the slicks again but wouldn't that cause the car to pull one way or the other? This car sways back and forth all the way down the track until you let off the gas.

check air pressure it's probably low

Air pressure is checked before every run in all 4 tires.

FWIW, I'm also wondering if the housing is "tweaked" and/or is the rear is "square" in the chassis. But whatever it is, it seems like the Sure-Grip was absorbing some of the problem through slippage and the spool doesn't.

Strut rods and steering box tight?

The only time I had a wandering problem was when I tried 165/15 radial front tires on my bracket car.

tires growing at different times

With it going both directions an arbitrarily moving each direction I would look real hard at the housing. It sounds to me like each slick is trying to force the direction of the car going down track. I would not think that it would take much to cause a problem.

I run the exact same combo on the street and it`s a wandering fool for sure.........

What is the best method to measuring to see if the rearend is square?

Find the factory jig holes in the frame and measure to the housing

Check the rear spring front bushings to see if they are loose.

When they hunt like that something is moving.

I bought a set of SS springs (way back in the day) off a dude with the hangers and everything. Just bolted them in. After damn near getting the tree, the left guardrail, back over the center line, back to the left guardrail, back across the center line and almost into the door of the dude in the right lane I lifted.

25 different pit heros tried to tell me the front end was jacked up, but I kept telling them every time I shifted or lifted it changed directions. I spent a considerrable amount of money on the front end but still, you NEVER knew which way you were going.

I caught it by plumb bobbing off the axle faces and measuring to find that the axle was not square in the car. I started taking stuff apart and that's when I found out the dude used bolts that were too small in diameter throught the front spring eye! So literally, every time you changed load (shifted, lifted, braked etc) the axle could move front to rear in the car. Sometimes the wheel base would be longer on the right and shorter on the left, or it could be shorter on the right and longer on the left.

I ran into the dude several years later and he told me that's why he sold them.

So any time they move around like that I look to the rear end.

A non square housing will cause the car to dog track. A bent housing that has toe-in or toe-out will drive very poor. I've driven cars that were in accidents prior to doing the alignment. Those with bent rear housings would drive similar to driving a boat. It feels like it steers from the rear and very twitchy. If everything is tight I would definitely check the rear toe.
Doug

Agree front bushings could be loose or worn. I use aluminum front bushings on my rear springs.

the question is how much pressure. I see so many people running way to low of air pressure. if your sure about everything else try raising the rear pressure up a little at a time.

If the only change is the spool it would have to be in the tires.

I suspect one is larger than the other, run into this myself. I lost a slick at an event and had to pop on a backup and the car walked around like crazy.