My '69 Chevelle is squirrely above 60 mph, especially when changing lanes on the highway. The front end kind of rolls a bit and needs correcting from the steering wheel. Here's what I have:

Originally a 350/350 car.
454 with TH 400.
Stock front control arms
New steering box, 3 1/2 turns lock-to-lock
Grant 13" steering wheel
A/C
Small block A/C springs (about 2" lowered)
Stock rear springs
Complete front end poly rebuild 3 years (15,000 miles) ago.
Boxed rear control arms
12 bolt 2.73 open
7/8" rear sway bar
15/16" front sway bar
Caster + 2.25 degrees
Camber - 0.5 degrees
Toe in 1/16" each side
235/60/15's in front
255/60/15's in back

As far as cornering, the car handles great. Flat and even. The only problem is high speeds. I feel like I have to pay too much attention to keeping things centered. I recently had the toe in increased and while it did help, it's still not all the way there. I had a bone-stock small block '72 Cutlass convertible for more than 10 years and it never had this problem.

I've talked to a lot of people and they tend to fall to one camp or the other:

1.) Install a 1 1/8-1 1/4" front sway bar to compensate for the extra weight of the BBC.

2.) Install offset upper control arm shafts and take the caster to approx + 5 degrees.

The first option is the simplest and cheapest, but will it do the trick?

Any insights are much appreciated!

I just rebuilt the front suspention of my 68 and here's my observations. I couldn't get positive caster and negative camber on my setup with the stock control arm shafts. I "settled" on -.5 degree camber and -.5 degree caster with 1/16 inch toe in. My car is stable at high speeds but I intalled an 1 5/16" sway bar from Spohn Performance. It made all the difference in the world! (ps. I haven't installed the rear anti-roll bar yet but it is next on the list! Right now I don't have a rear sway bar.)

I would check your alignment and shocks.
A 1 1/8 front bar would better match(in most cases)the 7/8 rear bar.
a shock upgrade will do wonders-stockers usually leave much to be desired.

Warren,

Thanks for replying!

Where did the 1 5/16" sway bar make the difference? Was it primarily in cornering, or was it stability at high speeds? Or somewhere else?

It really tightened everything up. The car feels very stable (even at 100+). Now the rear needs attention. I'm looking at Sphon's rear pro-touring anti-rollbar. My car did not have a rear bar from the factory so this is a viable option since the lower rears have no sway bar provision.

Note that springs can make a big difference too in roll.

A lane change manuever is a very dynamic situation. The suspension is constantly in motion and never really hits a stable state in this manuever. The first order tuning mechanism for dynamic behavior is the shocks.

I would hazzard a guess that second order tuning here is tires. Running 15" tires will leave quite a bit on the table compared to modern 17" lower profile tires.

Those apply to the lane change manuever... for straight line stability I would go in search of more positive caster. That will likely require adjustable upper control arms from SPC (available from SC&C or Summit). But if you are going to go there it is likely worthwhile to also go for the Howe tall ball joings that SC&C offers. They will help static steady state cornering and make your tires last longer (reduce outside edge wear).

Steve,

Thanks for the input. I'm still leaning towards the problem being the extra weight of the big block in a small block car. The '72 Cutlass I had was bone stock and didn't even have a rear sway bar. Plus, the front end was rubber and pretty worn out, and the wheels were stock 14" with high side walls. That Cutlass would cruise smoothly at 75 mph all day long, and in the decade that I owned it, I took it coast to coast at least 11 times. I'm think that the lower weight of the Olds small block vs. Chevy big block is what made the difference.

The shocks are good and I'm going to try a beefier sway bar and see if it helps. If not, then I may try to improve the caster, or the shocks, or the springs.

Does it go straight well, or do you feel it unstable trying to go straight too?

Interesting. My suggestions would be lower it, by cutting the springs, which will give you a stiffer spring rate, and install stout shocks and a bigger sway bar.

I would then find a custom alignment old guy. One with no computer if you can, that does a lot of older cars, particularly streetrods and stuff, and go to him. Ask for a "I want it to go straight and not wear the tires alignment."

I went through this when lowering my first 5.0. Got caster camber plates and all that. Went to my local shop who aligned it twice, gave me all the fancy printouts. Car would go anywhich way but straight. He explained that it was within specs and it was, and that was the best he could do.
I have forgotten the numbers, but I reviewed them all at that time.

Found a shop, Jackies Alignment in Seabrook SC, who does street rods, race cars, lots of older high dollar antiques, and Jaguars. 30 minutes and it went straight and true forever after.

My 66 still sits too high in front for my liking, so I am going to try to cut the springs some more. However, it does not feel uncomfortable to me to drive at 80 or so, for the 10 - 20 mile jaunts I have taken it on down I10. The front has decent bushings, cut springs, new cheapo shocks, a stock 6 cylinder sway bar, and new 205-65-15 el cheapo tires. Has no rear sway bar, but has wore out lca and uca bushings, and new el cheapo shocks. Has a somewhat worn out manual steering box, tightened up by another buddy who worked for GM for 40 years. Between these two guys it goes down the road decently.

Do you have deep-offset wheels in the front? Sounds to me like a possible scrub-radius problem, if the car is just following cracks in the road.

too basic but is there any loose play in steering linkages and steering gear box? positive caster helps. most of us old guys that have done alignments with non-computer equipment also set the front end for the "crown" in the road

note that front end can be "aligned" and the frame still be "diamond". it still won't drive right

go like was mentioned earlier...find an old traditional alignment shop.

The alignment sounds good. The more caster the better, but I doubt you will be able to get any more without affecting the camber. Tubular arms would help that. I'm suprised you were able to get that much postive caster out of it with the factory arms. Most crossmembers have sagged so much that you can barely get it back to 0.

check the idler arms and the rest of the steering linkage for play.

Just my $0.02...

This guy has it right...

RKD wrote:

"I went through this when lowering my first 5.0. Got caster camber plates and all that. Went to my local shop who aligned it twice, gave me all the fancy printouts. Car would go anywhich way but straight. He explained that it was within specs and it was, and that was the best he could do.
I have forgotten the numbers, but I reviewed them all at that time.

Found a shop, Jackies Alignment in Seabrook SC, who does street rods, race cars, lots of older high dollar antiques, and Jaguars. 30 minutes and it went straight and true forever after."


You've "talked to a lot of people". Just talk to somebody who knows what they are talking about. Einstein wasn't a committee.

Your '72 with the worn-out suspension and skinny tires went straight as an arrow. Stock suspension engineered by engineers. Your present setup has been engineered by ??? Is he an engineer? Not a very good one apparently.

I wouldn't lose sight of the forest for all of the trees. How many things can you afford to change taking shots in the dark? Good luck on it.

My $0.02