Tuning alignment for road crown pull?

[pitts64]

This is for a 69 el Camino 454.

It has the SC&C uppers and lowers with Delrin and .9/.5 Howe ball joints.

The rear has 4 Spohn adjustable control arms with there Del sphere bushings..

Also has a new Lee 14:1 with 30lb valve.

8/8.8 caster, .45/.65 camber. Toed in around 1/16

I handles great but drifts towards the curb because of road crown..



What should I be concentrating on?

[dontlifttoshift]

I have to look this up because for years I had it backwards and can't unlearn it.

Unequal caster causes the vehicle to pull to the side with the least positive caster.

I don't adjust for road crown with the alignment.

[David Pozzi]

We run a half degree more positive caster on the right front. You might try more toe in. Is the idler arm in good shape?

[pitts64]

Idler arm and linkage is tight.. I'm taking it in for a 4 wheel alignment on Monday. I'm thinking it might be the rear end. I did even out the camber yesterday and it made a big difference.

Here's the SC&C specs that came with the package.. I think I'm going to try the second one..

Street Performance
camber: -1/2
caster: +5 to +5.5
toe in: 1/16" total

Mild Competition Aggressive street
camber:-1
caster: +5 to +5.5 degrees
toe: 0"

Autocross/Road Race
Camber: -1.5 degrees
Caster: +5.5 degrees
Toe: 1/16" toe out (Autocross)/ 0" Road Race

[pitts64]

I had it put on Hunter Hawkeye rack. I ended up using the street performance specs.

I had the caster at +9/10, the camber at -1 and toe out 1/8 on each side. The thrust angle was .09 and now it's .02..

It felt a lot better before but I needed to get a base. It feels neutral now but goes down the road straighter but still has a drift to the right. Adding more +caster and more -camber to the passenger side doesn't seem to make any difference. I'm going to check those rear brakes out, they might be causing the drift.

I think I'm going to try -1 camber and zero toe. Maybe take the caster up to 8 since the SIA is 8.75 on these cars.

[a67]

If the rear has a posi of some sort, torsen, locker, clutch/cone posi, check the rear tire pressure. And more important measure the circumference of the rear tires. Need to have the two rear tires match, otherwise it will impart a pull.

I've run into this with a Zexal Torson unit, the tire pressure was uneven and the car was all over the road.

Bob.

[pitts64]

Thanks for the posts..

Turns out the bearing race in the passenger side rotor was spinning.. I ordered new slotted and drilled rotors, since I use pads with asbestos. I also ordered new Timkin bearings also..

[NoMoneyZ]

Your tow out will cause the car to follow the road more. I would set tow in. With what you have, it should drive straight down the road, but there is only so much correction you can do to correct road crown pull before you start affecting flat road manners. Also a separating or odd wearing tire can create a radial pull. Try swapping tires side to side and see what happens.

[pitts64]

I notice most only use a half of degree more caster on the right side for road crown. Right now I have everything even, caster 5+, camber .50- and toe in 1/16 both sides..

Once I get the new rotors and bearings on I'll know were I stand..

I think I'm going to try 7.5 / 8 positive caster with 1 degree negative camber..

With the new alignment it goes down the road pretty good but the bad bearing race is throwing everything off.. It makes a weird squeak/squeak sound..

[NoMoneyZ]

I didn't see that last post, must have happened while I was typing. Definitely let us know how it is with a new bearing and race installed. General rule of thumb that were taught here is .5 to .75 degree more positive caster on right side but other things can skew that either way. For street driving -1 degree of camber is good IMO. I have run up to -1.5 without much abnormal wear if I kept my tires rotated.

[pitts64]

Thanks.. I have installed the new rotors, pads and bearings.. It's better but still slightly favors the right.. I'll try adjusting it myself since I have the SPC adjustable uppers..

I was also thinking on taking it back to the alignment shop and having the caster moved up to 6.5 drivers/7 passenger side with maybe 1 degree negative camber and 1/16" toe in.. I don't think I can adjust it with my home made set up like that rack can.. It had more snap back when it was at 10 degrees positive but it steers right to left faster at 5 positive..