Replaced a Posi with a spool now the car moves around

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.

I have a feeling it's in the rear somewhere especially since I rebuilt the whole frontend and it didn't change anything about how the car handled. I will check the front spring bushings because I believe they were rubber when I installed the springs years ago, and will also check to see if the rearend is square. I will also roll the tires and check them. I will keep you guys updated on what I find.

My guess is that the car is rear steering from spring wrap up or bushings.

Assuming the springs, shocks, and bushings are good I vote for bent housing or axle misaligned in the chassis. The 'grip will help smooth out differring amounts of grip. The spool will just ensure the car gets pushed around.

Does the car feel like its moving by the seat of your pants or steering wheel correction??

Are you using a pinion snubber?

No pinion snubber.
The car requires steering input all the way down the track. It felt this way when we first bought the car many years ago where it would sway back and fourth requiring a lot of steering input. I was able to eliminate the problem when I put it on a alignment rack and saw it had negative caster in the frontend. It now has a good amount of caster but has started swaying again but is more controllable this time around. My mom is 65 years old and races for the fun of it. The car run 6.80-90's with a pump gas small block in it and she doesn't feel very comfortable in the car with it moving around so much.

Given the history and steerring input needed I would think it's not the tires. I've driven cars that move around (I call it wallowing) but you shouldn't have to go crazy driving it to keep it going straight even if the sidewalls move around a little.

I think this steering input is PART of the problem. Some cars with slicks, especially smaller ones, tend to sashay a bit going down the track. If you are trying to correct every little wiggle with steering input, you are simply compounding the issue and soon the sashay will be bad. I run into this often with guys who are used to drag radials and bolt on bias tires for a race at a bad track. The radials drive SO good, that on slicks they tend to try and control the car TOO much. Once I tell them to just keep the wheel straight and let the car just go down the track...the ill handling usually goes away

My old pump gas Duster had a 8 3/4 that was bending while I raced and drove it, it would wonder on the street with mix type tires, bias in the front with radials in the back and do the same with radials in the front and bias in the back It wouldn't wonder as much on the street with the same type tires front and back but it would go straight at the tracks with either combination, both 1/8 and 1/4 with mixed type of tires I ended up finding a worn idler arm, it had been replaced when I first assemlbed the car and it had less than 3000 miles total on it whe I replaced it the second time, that straighten all the problems out after that

I actually thought that she might be overdriving the car also until I made a pass in it.
I have driven a lot of different cars ranging from all types or tire sizes, suspension setups, and power and some cars will move around and not require any type of steering input. Super Stock cars will get that radial wobble sometimes, but this car has to be corrected going down the track. It swayed with the old alignment with the posi in it and was corrected with the alignment to where it would drive straight down the track in all conditions. Now that the axles are locked together it is highlighting a different issue I need to find. I have two travel races the next two weeks with a LODRS event in Noble,Ok and a National in Dallas so the car is on the back burner since the bracket season is all but over this season.

Can you get any more caster in it?

Kevin

Just for grins, what size are the slicks/wheels. I had a car that would move around from too narrow of a wheel in the slicks with too little air.

I'm of the opinion that something is loose in the rear. Do you have shackles or sliders? Springs or ladders? One of those back tires is moving forward or backward, meaning something is bent, broken or wore out making it self-steering. Find it before it breaks completely, wouldn't want your mom to get hurt!

I experienced that same issue using 28 x 10 slicks on 8-inch rims. I couldn't get a decent footprint unless the air pressure was so low the back end would start to sway back and forth right about the time I'd shift into high gear.

It's the M/T 28x9" slick with tubes on a 8" rim. We run 13psi in the tires. It is a stock suspension car with just a set of HD leaf springs on it. I plan to check the spring bushings as well as the housing. If I don't find anything I'll recheck the frontend and maybe put it on a alignment rack.

Do you have access to a go pro camera? They are awesome tools for problems like this

Slick rollout sizes the same?

What bearing did you use on new axels?

Did you use the green bearings or the taper?

Put a radial on it and enjoy going faster and not dancing around.

I agree with 1980volare..........

I think its tire circumference since the only thing that has changed is the swapping in of a spool.

Considering drag radials for my next tire purchase, my friends car launches like a fiend with them. Slicks don't bother me though, some walking around the track is just part of the experience in my opinion. If the rest of the car is tight it really should not be a huge problem.

On my Duster the idler arm would move up and down about 3/4 inch before making the tie rod move, that tiny bit of play made mine a bear to drive with mix tires. Once I replaced it and had the front end alignment recheck it was good

Green bearings on Strange axles.

I got the car up on jackstands yesterday and checked everything out. Looks like the rearend is in there straight, shackles and bushings on the leaf springs are tight, idler arm and pitman arm are tight. I don't know about the tires yet and I don't know if the housing is flexing or not.

Measure the rollout. Try adding some pressure just to see if it helps it. I like another 2-4psi in mine than what you do.

Measure the distance between the slicks front and back and see if there is any toe in or out. I bet it has always been bent.

Another vote for adding 3-4 psi and see if it makes any difference. If nothing else it's free.