Re: Radial Tire Alignment

[Joe L.]

Alex-----

I don't think that wheel alignment is your problem. After you check to make sure that the trailing arm alignment shim packs are TIGHT, I'd suspect a failing power steering control valve or a steering gear box in need of rebuild.

[Alex Gilmour]

Re: Radial Tire Alignment

Hi Joe, Could you elaborate a little on your response? The control valve is good, as is the ram, and the hoses are new. The box could probably use a rebuild, but I'm not sure how this could unsettle the car. When I say that steering inputs unsettle the car, I mean that as I turn the wheel, the car feels really "loose" like the car would oversteer and the backend would come around. It seems like Corvettes in general tend to want to "push' or understeer if pushed hard.

The reason that I asked is that I saw a brief letter in this month's Vette magazine mentioning that alignment settings need to be changed with Radial tires. I trust you guys more that something that I read in the car rags.

Thanks, Alex

'66 A/C Coupe

[Chuck G.]

Re: Radial Tire Alignment

Hello Alex: An "old time" alignment man here in my home town told me that radial tires are basically set at a zero "toe in", while the old bias ply tires were set with about 1/8 inch total toe in. This is why, if you have your car aligned for radial tires, it feels "squirrelly" when you switch back to bias plys....as in for driving to a judging meet, etc. With a zero toe in on bias ply tires, the car will track all over the road. Now, I don't know if this helps you, because you seem to have the opposite situation, but you might check your front end alignment....toe, caster, and camber. Chuck Gongloff

[Joe L.]

Re: Radial Tire Alignment

Alex-----

A few more comments relative to your questions, but first I will describe some of GM's specifications for front wheel alignment for several different model year spreads for Corvettes. For simplicity's sake, I'm just going to present the "preferred" settings, not the acceptable ranges. Also, caster and camber are in degrees; toe-in is in inches:

66-67 w/PS caster=+1;camber=+3/4;toe-in= 3/16 to 5/16

68-72 w/PS caster=+2-1/4;camber=+3/4;toe-in= 3/16 to 5/16

73-79 w/PS caster=+2-1/4;camber=+3/4;toe-in= 3/16 to 5/16

As you may be aware, in 1973 Corvettes switched to radial tires. However, as you can see from the above, GM did not change the alignment specifications from the bias ply tire equipped cars of the 68-72 period. Also, with one exception, the alignment specifications for 66-67 are the same as for 68-79. That exception is caster. As you can see, the caster specification for 66-67 is considerably less than 68+. If you increase your caster setting to the +2-1/4 degree setting of the 68+ Corvettes, you might improve your handling problems. However, I would not recommend changing the other settings from the GM specifications. I use the 68+ specifications with my 69 which has been equipped with radial tires for years and I have none of the problems that you describe.

Your problem still sounds much more like the classic symptoms of power steering control valve deficiency or steering box deficiency. Steering box problems account for more handling problems than any other component. If your box has never been rebuilt, you won't be wasting any money by rebuilding it. Bear in mind, though, that if the worm and sector gears show any wear at all, you won't get ideal performance unless you replace them. Most rebuilders do not replace these parts unless they're really bad. That's because they're expensive and the 70+ worm gear is discontinued. The 63-69 worm gear is still available, though. And, as far as I know, the 63-82 sector gear is also still available.