TJefferson2020

As I get my car back on the road, it is one squirrelly handling ****. I definitely had a bad power steering pump, new one is starting to finally get the air out and working well (still makes a chirping sound at full left - but I think it still needs some bleeding).

That was part of the problem. If you recall, I put in 215/70/15's on and to get the clearance I needed, I swapped my vintage TT's with some new TT-D's.

Nothing else was changed in the suspension (other than replacing front sway bar bushings and links).

The car doesn't self center. I know the steering boxes of these old cars don't do this automatically but previously the alignment would straighten the car with minimal effort.

Now it seems to dive into turns and you have to really pull it back. Previously it handled really well - went straight with no hands. Drove mostly like a modern car.

These tires are quite a bit bigger than the 215/60/15's I had on previously and the wheels have different offsets. (The tires fit with good clearance all around - surprisingly the worst clearance issue was at the sidepipe not the front of the fender.

I may disconnect the front anti-sway to rule that out and I'm hoping to get it aligned this coming week.


Two questions:

1. Is an alignment required after changing wheels and tires (especially sizes and offsets?)

2. Can alignment or lack thereof cause such extreme changes in handling?

wmf62

caster is what makes steering self-center, and any change in 'rake' will affect caster; and not enough caster will make the steering light, especially with power steering, and squirrely.

get a 4-wheel alignment with the caster to the high end (numberwise) of the tolerance range, maybe even a bit more.

Bill

davekp78

Radials require more caster than the OEM bias ply tires so the OEM caster numbers are too low. Get as much as you can- you'll probably only get about 3 degrees without adding some negative camber but 1/2 degrees negative camber is not an issue.

TJefferson2020

Could have sworn I replied to this.

I’m glad you reminded me. I was going to give the tech the factory specs. He actually a young guy that knows old cars. Plus state of the art 4 wheel alignment machine.

I’ll have him dial in max castor and a bit of camber. If I recall the AIM says 0 camber all around.

Took it for a short drive today. Power steering pump is smooth, actually feels pretty good except it is overly sensitive to steering input. When you turn the wheel that car TURNS - I would describe it as diving into the turn.

I’ll get it aligned and report back. The larger tires feel great. And very grippy. *technical term.

SWCDuke

You're recollection is wrong.

Duke

warrenmj

And the factory specs will be incorrect for radial tires. They were for bias ply. Check out these threads for more info.
https://www.corvetteforum.com/forums...h-radials.html
https://www.corvetteforum.com/forums...ent-specs.html
https://www.corvetteforum.com/forums...ent-specs.html

C4toC2

I had a problem a while back with a sloppy power steering piston rod bushing (the one on the shaft the pushes the on the center link.) On a bumpy road it would violently shake - scary - as the power steering would try to correct and re-correct. It is important that this bushing is in good shape and compressed sufficiently.

C2Dude

What width TT-D wheels did you use? Same width front and back?
Thanks

BB767

As to your comment about overly sensitive steering inputs here's my observation.

I have 2 '66 small block cars. One has manual steering and one has factory power steering. They are both equipped with nearly identical tires and wheels. The car with power steering has noticeably more "lively" steering. When I drive it right after driving the manual steer car I find I tend to over steer the car until I adjust to it.

As I recall, Corvettes with power steering from the factory have a quicker steering ratio than a manual steer car. As such they require smaller steering inputs and a lighter touch than a manual steer car.

Zora loved road racing and might this relate to the mind set of road racing where you think the car through a corner as opposed to driving the car through a corner?

Anyway, driving a factory power steering Corvette is definitely much different than driving a power steering non-Corvette of the same era and takes some adjustment IMHO.

Thomas

TJefferson2020

It’s been known to happen. I’m using your specs.

Yep. Found Duke’s detailed discussion and specs.

Mine entire system was new 11 years ago. Very few miles. I will get under there and check it.

7” wide all around.

TJefferson2020

That’s pretty interesting. Mine definitely has the short ratio steering. It could be that I’ve been driving my C5 for two years while this car was getting painted and refined. So it seems but it’s just normal.

I can tell it needs an alignment. It didn’t dive into corners before with BF Goodrich Comp TAs 215/60/15s. It was lively but this is scary at freeway speeds.

Although I took it out yesterday and it’s running like a banshee. I think I have a little sagging at high RPMs but probably just a timing slip of the dizzy. I think it coulduse a touch more advance.

Per trinity is known for that too. But super minor. I don’t race it anyway.

davekp78

One other thing- the PS control valves had two different springs. The OEM Corvette spring was 55lb. The full-sized Chevrolet and Chevy II used 30 lb springs. Later on all valves used the 30 lb spring. 55 lob springs are unobtanium, unless you can steal one from an old OEM valve. All currently rebuilt valves use the 30 lb. I cannibalized an old valve for the 55 lb spring. I can feel the difference. Less "squirelly", but I have 3.2 degrees caster with -.17 degrees camber.

SWCDuke

...just the opposite. Radials have more self-aligning torque than bias ply tires, so for the same tire diameter and caster, radials will have stronger self-centering action.

Duke

davekp78

So you are saying radials don't need as much caster?
I don't think that is what I found after a lot of research here on the Forum.
But I could be mistaken.

wmf62

interesting... but with you

Bill

C2Dude

Thanks, I will be shopping for wheels/tires when I finally get her home.

MidYearRoadster

I got these specs yrs ago and have seemed to work just fine for my 67. Non power steering car. FYI

Front camber 0
caster +1.5
toe in each wheel 1/32"

Rear camber -0.5
toe in 1/32"

TJefferson2020

Did not know. Mine was replaced (entire system) 12 years ago. I'm sure I have the 30lb spring. Overall the PS is very good on these cars. Surprising for the era.

Mine with happily drive off the road right now... (alignment scheduled for Thursday)

My understanding is that would be a moderate setting. I think Duke's is for a bit more aggressive driving and for cars that have uprated suspension.

I put a lot of effort and money into the suspension on this car. A bit kidney rattling but a very tight car. One thing I should disclose is I dumped the rag joint.

Put in a hard joint. Really don't notice a difference in terms of vibration at the wheel but yuge difference in general feeling of steering accuracy.

Didn't hurt to get the box rebuilt either.

Avispa

That's probably more of it than you might have thought. The red thing was off the road for about 2 1/2 yrs while trying to sort out some major engine block issues. The shifter felt like rowing a boat after that amount of time behind an MGW short throw in the Cobra. The feeling is only going to get worse as new cars get better and better. We just didn't know how crude these cars were back in the day, mainly because there wasn't anything better to compare them to.

SWCDuke

...not at all. I prefer as much positive caster as I can get out the alignment adjustment, and with radials it creates more self-centering and "steering feel" than bias-plies. I installed a set of 6.70-15 Michelin X radials on my SWC in 1964 when it was a year old. A day hot lapping Kent began to shred the tread off the OE General JetAires. I knew they were junk from day one.

Back then radials were relatively unknown, but were generally described as "driving on rails" because they operate at much lower slip angles than bias-plies, so the steering is much more precise.

Not long after installing the Michelins, I switched to the fast steering ratio, and it was even better. I don't think there was a better handling car in Seattle than my SWC in 1964, and I proved it to several other sports car drivers including in pouring down rain.

Anyone who has ever experienced even some cheap modern radials compared to bias-plies knows that compared to radials, bias-plies are like driving on slime.

I remember reading way back when that Duntov recommended against installing radials on early Corvettes. I never figured out why. IMO they were the best handling improvement you could make back in the sixties and seventies, but early American radials were junk. Many suffered from tread separations.

Only the Europeans made good radials back then and my next two sets were 205HR-15 Pirelli CN-72s, which required 7" wheels to work better than the Michelins, followed by 225/70VR-15 CN-73s, Both sets of Pirellis had fabric cap belts, not steel because they had more benign breakaway characteristics than early steel belted radials, but the industry has since learned how to make steel belted radials with more gradual breakaway, especially if they are H or above speed rating with spiral wound nylon cap belts.

I now have a set of the last of the Firestone 225/70R-15 102V PV41 "police pursuit tires". They are steel belted with a spiral wound nylon cap belt.

Duke