66BBCoupe

Are midyears set up from the factory with front end geometry that induces oversteer? I believe my 66BB exhibits this tendency - I am used to it - just curious if this is the norm.

66BlkBB

Having only driven my car I can't really say. I don't notice anything like oversteer but I may not know what to look for. I ran a real curvy rural MN highway yesterday and I did not notice my car heading for the ditch on either side of the roadway. Again, maybe I am just used to my car and mentally adjusted for the oversteer already. Fat Chance of that!!!

Steve

mid-year crisis

In my experience, it could be as much the way the rear end is set up (as far as alignment & toe) as the way the front end is. After I redid all of my suspension and had a great shop align all four, I now had a condition that I would consider oversteer.

JohnZ

Nope. GM cars have always been designed with some level of terminal understeer, for safety reasons. Anything that adds rear roll stiffness (like adding a rear stabilizer bar without changing the front one) or reduces front roll stiffness (like removing the front stabilizer bar or going smaller) will bias handling toward oversteer, as will incorrectly set rear toe-in, especially in transient maneuvers near the limit. Chassis dynamics are a function of many different variables, and the factory suspension system configuration is pretty close to neutral.

66BBCoupe

Thanks John - Guess I'll get the alignment rechecked!

66since71

I agree with John with one exception. The factory rear suspension has a relatively high roll center. That means if you do something really stupid in a corner, and near the limit (like lifting or tapping the brakes) you can get some exciting oversteer. The phenomenon is called "jacking". As the rear end raises up, the rear wheels see more and more positive camber (and lose "camber thrust"). The cornering forces act to maintain or accelerate the phenomenon. C-3's got a new camber bracket with a lower roll center. That was related mostly to the wider wheels and new (then) low profile tires, but it also fixed the jacking problem.

Harry

Kensmith

How about darting? My 65 has been aligned properly with 225/50X17 radials and traveling at freeway speeds it darts when I steer left or right but only when first moving the wheel. It is smooth after that first initial movement. Steering box too tight? Tires too aggressive? Or normal?

rgs

I'd check toe.

RobRace10

I'd check front caster. I know some guys machine the UCA cross shaft to achieve more caster.

Kensmith

Front toe .06" left front .07" right front.

Rear toe .08" left rear .07" right rear.

Kensmith

Caster is 2.4* left front and 2.6* right front.

rgs

Toe out or toe in? A toe out in the front will cause exactly what you are experiencing.

I'm assuming that the tie rod ends, ball joints, etc are all in good shape.

Kensmith

Toe-in. New box, all else is good!

magicv8

Power steering or manual?

Checked the idler arm?

Checked all the rear rubber bushings?

DansYellow66

I'm no alignment expert but I don't think 2.4/2.6 deg of caster is anything exceptional for straight ahead stability. It could probably benefit from even a little more caster at the risk of more steering effort. Of course 50 series tires probably have a mind of their own anyway on anything other than a pretty smooth road.

Kensmith

No P/S

Idler arm good

New poly bushings everywhere

wmf62

add more caster; ~5 would be better.
Bill

MikeM

[QUOTE=66since71;1567196663]I agree with John with one exception. The factory rear suspension has a relatively high roll center. That means if you do something really stupid in a corner, and near the limit (like lifting or tapping the brakes) you can get some exciting oversteer.

I agree with the above. I can't tell you why but mid-years react as described and I know the C-3's are a little tamer.

Another factor is weight distribution which is different than most American cars. Depending on options, the weight front/rear bias is more nearly equal on these cars than most. That'll add to the sensation of looseness rear end.

If you want to try something cheap and easy, take one of the links off your BB rear sway bar and take it through some corners. It it starts pushing the front rather than hanging the rear out, it's probably behaving normally.

MikeM

[QUOTE=66since71;1567196663]I agree with John with one exception. The factory rear suspension has a relatively high roll center. That means if you do something really stupid in a corner, and near the limit (like lifting or tapping the brakes) you can get some exciting oversteer.

I agree with the above. I can't tell you why but mid-years react as described and I know the C-3's are a little tamer.

Another factor is weight distribution which is different than most American cars. Depending on options, the weight front/rear bias is more nearly equal on these cars than most. That'll add to the sensation of looseness rear end.

If you want to try something cheap and easy, take one of the links off your BB rear sway bar and take it through some corners. It it starts pushing the front a little, rather than hanging the rear out, it's probably behaving normally.

If it seems loose in the rear during normal driving, I'd have the rear toe-in checked.

magicv8

Years ago after 3 different 4wheel laser alignment shops couldn't get the rear right (although they said they did), I started mapping the rear wheels on my garage floor. As a result I do my own rear wheel alignment now and I have no problems. I do have a PS car and I use the factory settings for a 1976 Corvette (radial tires).

Since all the bushings are poly, can I assume you've had a recent alignment? If so, you may want to take an hour and map the rear wheels against the front end and verify the rear toe and the thrust angle.