Rear end spins out to the left.

[landmass]

I've recently started 1/4 mile drag racing. I notice that during burn out at the track, and when I do a burnout on the street, that the rear end immediately starts moving to the left and does not track straight during burn out like the other cars at the track. I have a Ford 9" rear end with 2 trailing arms, a Panhard bar, and a 3rd link bar. What adjustments could I try to get the Cobra to track straight during the burnout?

[RET_COP]

How does the car leave the line? Do you have to fight it to keep it straight after shifting?
If tire pressure is equal, check the lower control arm bushings for any play. Also make sure your rear is square with the chassis.

[Detroit Bill]

Welcome to the forum

Who made the car? FFR, superformance?

[Dwight]

Your getting to much traction on the driver side (left).

Check tires to make sure you have the same pressure on both sides.


If you have adjustable coil overs on the rear you can raise the driver side a little to shift weight to the passenger side.

Trial and error

Mine pulled to the right. I bought adjustable QA1 coil overs and increased the pressure on the passenger side by two click and decreased by two on the driver side. It now pulls straight

Dwight

[Tommy]

It's the Coriolis effect. It'll go straight if you race at the equator. ;-)

[Cashburn]

Originally Posted by Detroit Bill

Welcome to the forum

Who made the car? FFR, superformance?

9"

[mrmustang]

Originally Posted by landmass

I've recently started 1/4 mile drag racing. I notice that during burn out at the track, and when I do a burnout on the street, that the rear end immediately starts moving to the left and does not track straight during burn out like the other cars at the track. I have a Ford 9" rear end with 2 trailing arms, a Panhard bar, and a 3rd link bar. What adjustments could I try to get the Cobra to track straight during the burnout?

Who's chassis are you running (yes, it makes a difference on how we will respond)?



Bill S.

[landmass]

It's a Hurricane Motorsports Cobra with a 347 cu in. 500 hp - fastest time yet is 11.3 secs at 121 mph. Tire pressure is equal on rear tires(and front). Has adjustable QA1 shock system which has been weighed and setup for road racing. I adjust the shock knobs one way(softer) for drag racing and the other way(harder) for road racing. Right now it's set up for drag, so the shock knobs are adjust to 5 on the passenger side and 3 on the drivers side. This setting is supposed to help keep the rear of the car level during launch. And this is the setting that I need to run straight, instead of going to the left at burnout. I'm thinking that adjusting the panhard bar may solve the problem. Also, maybe the trailing arms(or track bars) are not adjusted equally in length, and are "kicking" the axle off at a slight angle. Thanks for the advice so far. Tuesday, I'll be calling the factory for advice and talking to a couple of mechanics with drag racing experience. Thanks for all the tips, and I'd like to get more advice from anyone who has experience on this matter. I've been studying up on the internet, but I feel like I'm missing something...

[Gaz64]

My car runs a 9 inch LSD, it will always slide to the left on hard launch.

My mates car runs a 9 inch Truetrac, it is dead straight on launch.

Trait of LSD diffs.

[Ron61]

The LSD could be taking just a fraction of a second to get the right side rear tire hooked up. I have seen this on several that didn't have the LSD built to where it is almost a locker.

Ron

[vector1]

What was the thrust line when you did the alignment? I know, you didn't do an alignment. The thrust line needs to point either straight ahead or slightly to the right no more than 6-7 deg. to compensate for the engine assy. turning direction for drag racing from what I have read.

[Jerry Clayton]

Is your 3rd link on the upper right hand side of the center section??
How much adjustment do you have in it??? On my drag car with a 3 link pulled my hair out trying to get it to go straight---------- adjust location of 3rd link sideways will effect direction it pushes the car---------I went thru over 30 coil over shocks before I found ones that were what they were supposed to be-----------

[landmass]

I have an Eaton Detroit Truetrac differential. I got some advice this morning that sounds promising. Basically, using the panhard bar adjustment, I should center the rear axle housing to the frame(not the body) by using measurement points on the frame. Then, using the trailing arm adjustments, make the rear wheels the same distance from the front wheels. This procedure would make the rear end, frame, and the front wheels plumb and square. I'm going to do this in the next couple of hours, then I'll retest the results. I'll mount a GoPro camera under the car looking at the pinion angle under full load to make sure that has still proper after the other adjustments have been made. I've mounted the camera at that location before, and the footage was very dramatic and informative. I didn't believe the amount of movement going on with the rear end under race conditions - everything moves, flexes and bounces around. If I knew how to post a short video clip, I would do it. Thank all you guys for the tips and information. I'll report the results when testing is complete. Vector1 - is this the type of alignment you are referring to?

[landmass]

Jerry Clayton, yes, the 3rd link is at the upper right hand side of the center section. I'll be checking it out in a short while. How did you know that your final adjustment was correct - that is was straight under full load conditions?

[landmass]

After adjustment of the system, I did a couple of burnouts and the car tracked remarkably well, and I am satisfied. However, the pinion angle is off now, the differential actually goes slightly nose up under load. I've already called a mechanic friend and will be seeing him tomorrow at 3pm for him to adjust the pinion angle. It looks like poor alignment of the rear end was at fault. Thank all you guys for the advice. I sure learned a lot about my Cobra(and this web site) from this experience.

[Detroit Bill]

Originally Posted by Cashburn

9"

That's a helpful comment. Why not take the time to explain the significance of 9" instead.

[twobjshelbys]

Mine would not do a straight line burnout either. Always wanted to go clockwise. The nature of the beast with a short wheelbase and lots of torque.

For what it's worth my Ford GT does the same thing.

[patrickt]

Originally Posted by Detroit Bill

That's a helpful comment. Why not take the time to explain the significance of 9" instead.

SPF cars do not come with a Ford 9" rear, they come with a ZF Limited Slip. It is understandable that you might ask that considering the fact that you are new to SPF cars, and even though you have one on order. The same poke in the eye would have followed if a new "ERA on order" member had asked the same thing.... <maybe> ... because ERA cars don't come with 9" rears either -- same with CSX cars, Kirkhams, etc. although you could always fab one in, I suppose.

DetroitBill, you need to relax a little bit. This is all just a game and most of us have been playing it for years.

[cycleguy55]

Patrickt: Perhaps I took Detroit Bill's comment differently than you did.

Cashburn posted '9" ', with the 'smiley' indicating 'sarcasm'. I took that as his questioning why someone would have a 9" Ford rear end in their car, especially when he has a Backdraft with an IRS.

My perspective on Detroit Bill's comment was he was merely challenging Cashburn to do more than take a 'cheap shot' and explain his concerns or issues with a 9" live axle. Perhaps, as a purchaser of a car with an IRS, he'd like an informed opinion from someone who has one.

Just my $0.02.

[patrickt]

Originally Posted by cycleguy55

My perspective on Detroit Bill's comment was...

Hmmm, perhaps you're right. That Cashburn is a tricky devil, though. But you don't tend to hear too many Cobras breaking Ford 9" rears coming off the line. I can't say that's true with some of the other fully independent rears with Jag origins (mine included). With racing slicks, stub axles tend to get twisted relatively easily. If I wanted a Cobra for drag racing only, I wouldn't have my fancy IRS in it.