69 RR pulls to right on acceleration

[Garys1969RR]

My 69 Roadrunner pulls right when the front end lifts on hard acceleration. Then you let off the gas, and it goes back to the left. Makes it a little scary to drive. All the front end parts feel tight, with no loosness noticed anywhere. Had a good front end alignment done after I bought the car. Any ideas? Has anyone else experienced this ?

 

[Kern Dog]

Rear end out of square? Mancini Racing sells shims that can correct that. They fit between the front spring eye hanger and the body. An alignment shop can tell you if your thrust angle is out of spec and tell you how much.

 

[RT K_line]

How are the lower control arm bushings? They need to be checked a certain way. With the load off but can't remember where to lift to check them. You can also check the visually with a good flashlight.

 

[Garys1969RR]

Rear end out of square? Mancini Racing sells shims that can correct that. They fit between the front spring eye hanger and the body. An alignment shop can tell you if your thrust angle is out of spec and tell you how much.

That would certainly account for the pulling right on a hard pull. Never thought of that. Thanks!

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How are the lower control arm bushings? They need to be checked a certain way. With the load off but can't remember where to lift to check them. You can also check the visually with a good flashlight.

I am pretty sure they are tight, everything else is.

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Would the torsion bar tension need to be totally released to check them?

 

[HEMI-ITIS]

Have you changed anything since this condition arose??

 

[Garys1969RR]

Haven't changed anything yet. But it has had subframe connectors welded in by a previous owner. The front end lifts and angles to the right on full throttle in first gear, then you let off and it wants to go left. Not as much effect in second and third gears.

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I suppose it has always done this, just really noticed how much after not driving it all winter.

 

[Garys1969RR]

Would this be caused by the left rear tire being closer to the front wheels than the right rear tire? Propelling the front end to the right under acceleration?

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I guess I can measure the distance from the axle housing to the lower control arm on each side, compare the 2 measurements, and get a general idea as to whats going on.

 

[miller]

Hey, Gary...left rear closer? Front spring hangers the same?

First thing you might do is be sure the frame is square. In the service manual, it shows the four measuring points, how to check it, and the measurement. If it's good, the rear could be mounted not in line with the frame. Key measurement on that would be from the front hanger mounting pad, to the axle itself...as long as the frame is good.

 

[Garys1969RR]

Thanks, Miller. I will check it maybe on Sunday.

 

[Garys1969RR]

Hey, Gary...left rear closer? Front spring hangers the same?

First thing you might do is be sure the frame is square. In the service manual, it shows the four measuring points, how to check it, and the measurement. If it's good, the rear could be mounted not in line with the frame. Key measurement on that would be from the front hanger mounting pad, to the axle itself...as long as the frame is good.

Hi Miller, can you tell me what measuring points the factory says to measure? For frame in square? Or can I find that on line? Thanks.

 

[miller]

Right off hand, Gary, it 'should' be in the service manual, either under frame, or alignment.

Those measuring points, through all most years, are alike. At the bottom of the main frame rails, should be four holes, about 3/4" I think, maybe bigger. To check frame square, you measure in a 'X' pattern, from front hole on one side, to the rear hole on opposite side. Think somewhere around 1/16" is allowed difference, but that should also be in the book.
Service deal on that uses a long rod, with adjustable ends with pins that fit into those holes.

If frame is okay, take in consideration the frame connectors you mentioned, or even a possible previous accident. Past that, only thing I know of is either frame pad where front (rear) spring hangers mount, hangers themselves, or springs themselves. Also possible the line-up pin on your springs, that location axle to spring, is out-of-wack.

 

[AR67GTX]

I believe a bad front leaf spring bushing could cause that. Can't imagine a factory bushing getting sloppy enough to cause the darting but if someone has replaced them with Poly bushings and they have deteriorated, crumbled, cracked, etc, there could be enough play there.

On checking the LCA bushings - not sure releasing the torsion bar tension will tell you much as the strut rod tension takes up the LCA play unless there are a bunch of worn bushings. If you pull the torsion bar out and back off the bolt on the strut rod you could see if the LCA shaft is still locked tight in the bushing or if the arm and bushing rotate loosely on the shaft. There's a lot of play in the LCA between the torsion bar socket and the arm itself when the strut and torsion bar are removed - unless someone has clamped the sides of the arm together and welded reinforcement plates across the bottom.

 

[Cranky]

Does the car have a good Sure Grip in it or did it not have one and does now and you're using the same rear tires? If so, measure the roll out on the rear tires. If one tire is a bit taller than the other, it'll do this. It's a quick and simple measurement too. Ask me how I know this lol It's a good idea to measure the roll out on rear tires when you're using a Sure Grip anyways because uneven tire height will also make it wear out faster....

 

[Garys1969RR]

As far as I know, the tires appear the same height. Do you make a chalk mark on the tire and ground, then roll one complete revolution and make another mark on ground when the mark is straight down again, and measure the distance between marks? That seems like a good way to do it. Also, does the taller tire push the front end to the other side? Like taller left rear tire pushes the front end to right?

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Pretty sure the differential is working ok. We raced it down the 1/4 mile last summer several times, and the burnouts were pretty even on both rear slicks.

 

[Cranky]

Best way to measure roll out is to wrap the tire with a flexible tape measure and yes, the taller tire on the left will push the front end to the right. Measuring the height of the tire on the car isn't accurate enough and wrapping the tire with the tape is the best way. It doesn't take much difference to push the car around either. Even brand new tires should be measured! Make sure both are at the same psi and I even like to make sure both are at the same temps. A tire on the sunny side of the car will increase psi and grow a bit.

 

[Garys1969RR]

Measuring from front of tire forward to wheelwell, the left tire is closer to the front of the wheelwell on the left side by a good 1/2 inch. I know this isn't real accurate, but gives an indication as to whats going on.

 

[AR67GTX]

Given how unit bodies were built up of so many parts I'm not sure how meaningful that may be. A couple other measurements to check are:

- With front wheels set dead straight ahead, measure between the front hub and rear hub on both sides and compare the dimensions.

- With front wheels set dead straight ahead, stretch a taunt piece of fishing line from the front wheel to the rear wheel. You can wrap it around a lug nut or center cap - as long as it runs tight to the tire sidewall and is tight. Then find a good straightedge, the longer the better. Lay the straight edge on the sidewall of the rear tire, extending towards the front tire. Measure the deviation from the straight edge to the string line at some specific point ahead of the rear tire - say 4 ft if you have a long enough straightedge. If the deviation from one side to the other varies significantly, your rear end is not tracking straight with the unit body and the front suspension. It's important that the front wheels are as straight ahead as you can get them. The straightedge can be laid against the sidewall of the front tire and deviation checked to the body from side to side to try and verify they are straight.

 

[miller]

Just curious if you've checked any of those 'hard' frame/rear alignment measurements, Gary?

Sure sounds like something out of sorts. Hard pulls like your doing can shift your rear axle around, if things aren't locked down, or certain parts aren't up to snuff. One easy check is that locating pin I mentioned, spring to spring pad on the rear housing. Should be able to touch inside that housing mount pad, feeling for the locating pin rounded end, in the hole drilled in the pad. (I've seen them snapped off...letting the spring move off it's location) Something worth checking!

 

[Garys1969RR]

Ok, I'll check that tomorrow!

 

[HEMI-ITIS]

Have you done a comprehensive inspection of the front and rear suspension components???
Take a good look at the rear spring perches,had the same issue at South Mountain Dragway.
Bent up the left spring perch!