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Car Drifts Left During Burn Out

Posted By: patosmith

Car Drifts Left During Burn Out - 10/13/19 09:07 PM

Can anyone give me some ideas on where to look for reasons why my 72 Challenger drifts to the left during a burn out?
I get into the water box, begin my burn out but before i can really get the slicks warmed up, I have to lift because the car gets out of shape. Then it spins at the launch.
I have the same issue when I run with street tires so I don't think it is the slicks.
Here is my set up:
Car runs around 12.1 to high 11's in 1/4.
Big block
727 Automatic with 3000 stall converter. No trans brake.
Dana 60, 4:10 gears and Detroit locker.
Cal Tracs mono leafs and adjustable shocks.
M/T ET Street Radial Slicks

Shocks were set pretty light during a test pass but I then stiffened them up. Same setting on both. Same results.
Air pressure for the slicks were both at 17. Also tried 18 and 19.
Cal Tracks are adjusted to "just touching" on both sides.

I put the car on jack stands. Weight being on the suspension. I took measurements and the car is square.
I took diagonal measurements LF to RR and RF to LR.

I am going to check the slicks to make sure they measure out the same just to be sure but I have the same problem with street tires .

Any ideas on what else I should look for?
Posted By: AndyF

Re: Car Drifts Left During Burn Out - 10/13/19 09:32 PM

Get the car scaled. You probably have a weight bias. You could also have an issue with the differential. Maybe your Detroit Locker has a little bias built into it. Measure the diameter of each tire, sometimes they vary by quite a bit.
Posted By: Tempest

Re: Car Drifts Left During Burn Out - 10/13/19 09:48 PM

Because we have torsion bar front suspensions, the front can have an effect on the rear and weight distribution. I have a narrowed, back half coil over rear suspension car. I had to adjust the front in addition to the rear for the car to go straight.
Posted By: Cab_Burge

Re: Car Drifts Left During Burn Out - 10/13/19 10:08 PM

[quote=AndyF Measure the diameter of each tire, sometimes they vary by quite a bit. [/quote] iagree scope get them within a 1/4 inch on the circumference with a cloth seamtress tape using air pressure, if possible luck
If they are more than a 1/4 inch now and you can't get them near that try swapping the big tire with the small tire on opposite sides.
Good luck, let us know what you find out wrench
Do you have a manual valve body trans? If so are you starting in 2.nd gear and shifting into high gear as soon as the rear tires start to spin? If not try that and get the rear tire spinning as fats as possible to get them hot sooner scope up
Posted By: RiskyRickey

Re: Car Drifts Left During Burn Out - 10/14/19 02:00 AM

ck front brakes one not holding letting your car get sideways .I had same problem. Found a bad brake hose
Posted By: dvw

Re: Car Drifts Left During Burn Out - 10/14/19 12:02 PM

What are you scale weights? I'd be the RR is lighter than the LR.
Doug
Posted By: Cab_Burge

Re: Car Drifts Left During Burn Out - 10/14/19 08:33 PM

Originally Posted by dvw
What are you scale weights? I'd be the RR is lighter than the LR.
Doug
iagree Every near stock Mopar from 1962 on that I have weighed all four corners on had the least amount weight on the right rear, every one whiney shruggy
I've raced cars with spools in the rear end like that did not move around in the water box, a lot of them shruggy work
Posted By: dart4forte

Re: Car Drifts Left During Burn Out - 10/14/19 09:45 PM

Possible you have a bent or twisted axle housing?
Posted By: Magnum

Re: Car Drifts Left During Burn Out - 10/15/19 02:04 AM

Originally Posted by RiskyRickey
ck front brakes one not holding letting your car get sideways .I had same problem. Found a bad brake hose


+1
Posted By: TC@HP2

Re: Car Drifts Left During Burn Out - 10/15/19 10:01 PM

Would rear axle thrust cause this?
Posted By: patosmith

Re: Car Drifts Left During Burn Out - 10/16/19 12:21 AM

I thought about the weight issue too.
I will need to find someone local that has scales so i can check on that.

Would it help any to soften up a shock on one side?

Also, someone asked about the axle housing. This rearend is a new Moser Dana 60 so i hope it's not bent or twisted!

I hadn't thought of the front brakes. That will give me something to check also.

I don't think I would be able to get back out to the track this year to test. Seattle rainy season is just about upon us!

I will spend the winter checking on why it is doing this.

I appreciate everyone's input. Good stuff.

I will post what I find.
Posted By: Cab_Burge

Re: Car Drifts Left During Burn Out - 10/16/19 06:10 PM

It wouldn't hurt to take two carpenter squares and set the car up on jack stands with both rear wheels remove and have someone help you use the carpenter squares push up tight the axles and use a tape measure to see how far apart the squares are measured out around 15 inches from the center of the axles under the car to the other square as close to the rocker panels in front of the rear end and then reverse the measuring to the rear and compare the results to see if it is wider (more than 1/8 inch) front or rear scope And then measure straight up and down to see if it is bent that way or not also up wrench
Posted By: dvw

Re: Car Drifts Left During Burn Out - 10/16/19 06:27 PM

I log
Originally Posted by patosmith
I thought about the weight issue too.
I will need to find someone local that has scales so i can check on that.

Would it help any to soften up a shock on one side?

Also, someone asked about the axle housing. This rearend is a new Moser Dana 60 so i hope it's not bent or twisted!

I hadn't thought of the front brakes. That will give me something to check also.

I don't think I would be able to get back out to the track this year to test. Seattle rainy season is just about upon us!

I will spend the winter checking on why it is doing this.

I appreciate everyone's input. Good stuff.

I will post what I find.

Tightening the left torsion bar adjuster will jack weight to the right rear. As long as the car doesnt wheel stand this will help.
Doug
Posted By: topside

Re: Car Drifts Left During Burn Out - 10/17/19 12:34 AM

Aren't Caltracs supposed to be pre-loaded on the right ?

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