1980 L48 Auto

I recently ordered front sway bar bushings for my 80 Vette. I looked up what I thought was the stock sway bar size and ordered 7/8" bushings. It turns out the car has a 1 1/8" sway bar installed. I assume it was installed as an upgrade at some point in time. The car does not have a rear sway bar. When I bought the car I noticed it had a pretty severe oversteer. I'm wondering if the 1 1/8" front bar (which I assume is not stock) combined with the lack of a rear sway bar could be the problem (oversteer). I'm thinking my options are get a rear bar or install a stock bar on the front. Any ideas or suggestions?

 

What are the driving conditions that makes you think it is over steer ? Are you taking a corner @ 50 MPH and the back end starts to swing out ? both on and off throttle acceleration out of a corner?

Alignment of the wheels can have a large effect on producing over and under steer conditions. eg more camber on front wheels with toe out will produce over steering. Its very hard to experience over steer under normal street driving related to sway bars. The car is just moving to slowly. Once you speed things up and the weight shift is not smooth then the sway bar effects can be felt.

 

Most noticeable at above 35 MPH, e.g. when entering a curving freeway ramp. The alignment was done recently so I don't think that is an issues (if it was done correctly). Front end wants to aggressively steer into the curve. Rear end stays planted however (of course I am not really going that fast that the rear end should break free). The reason I thought about adding a rear bar is because other threads in this forum talk about that issue.

 

A C3 with an 1 1/8" front bar, no rear bar and stock springs would most likely UNDERSTEER like an old Buick.
If the car is oversteering, something is loose, maybe in the rear suspension. Or the alignment was done improperly.

 

MY experience with MY 69. All cars, because of different springs, shocks, tires, sway bars, etc. drive differently. My 69 BB has a 1 1/8" front bar and no rear bar. This gives me fairly neutral steering. I have 550# front and 360# rear springs, etc. The kit supplied 7/8" ?? rear bar indused severe oversteer while pushing it through the mountains. Even the origional/smaller rear bar induced oversteer.
MY understanding is to use a large front bar, then use the rear bar to get the results you want. In your case, from my experience, a rear bar would give you more oversteer.

 

Until the tires start to slide I would not call this over or under steer. I think what you are feeling is just the suspension loading and the tires holding the grip, and turning as it should. If you give more gas during the turn the car will shift more weight to the back wheels and produce more under steer effect. It's near imposible to work this out without a autocross track or road track. You cannot drive the car hard enough to really feel either over or under steer related to sway bars. Its a question of which tires want to let loose first, something you dont want to do on the street. I would first look at alignment and tire conditions. Can you post your alignment printout ?

 

After the Ralph Nader fiasco in the 60's, all GM cars were setup from the factory to understeer. Base late 70's cars with the base suspension had a 7/8 inch front bar and no rear bar and would understeer severely at the limit. A C3 with a front gymkhana 1 1/8 inch bar with no rear bar would understeer severely-more so than the base cars. The Sport suspension on my 78 with the 7/16 inch rear bar and stock aluminum wheel with 255/60/15 tires would UNDERSTEER at the limit-my experience and from the articles written from the day. Only sport gymkhana later C3's received an rear 7/16 inch rear bar to reduce the front understeer from the 1 1/8 inch bar. All BB cars received a big front bar AND a rear 9/16 inch sway bar. The BB cars are nose heavy relative (front 51-52% weight bias) to the SB C3's (front weight bias 48-50%) and needed a rear bar to offset the more natural tendency of the BB cars to also understeer. I cannot explain a BB C3 with a large front bar with no rear bar oversteering….Any rear bar on any C3 should be an OEM type bar with the OEM type rear end links that are different from the front end links. Using the aftermarket rear bars with the front type end links on a rear bar will induce oversteer…There is a very good reason that GM chose NOT to use the rear bars on C3's with the front style end links-they designed a distinct end link for the rear sway bar C3's...

 

Funny how opinions differ among enthusiast on a specialist website regarding one piece of equipment:

https://www.corvetteforum.com/forums...-sway-bar.html

I suppose the first step to determine my issue is to install a stock sway bar, 7/8", on the car and assess the results. Then move on to other causes if that doesn't clear it up. As an aside, there was a sticker on the installed 1 1/8" sway bar that when cleaned up proved to be a GM sticker. Couldn't read the numbers. The previous owner who owned the car for 15 years said he didn't add the sway bar. Thanks everyone for the input, very helpful and informative.

BTW, according to the literature and my experience you don't need to break the rear wheels lose to have oversteer.

 

I went with the factory 1 1/8 and 7/16 rear. Bilstein HD and the car handles the best it ever did in the 15 years I've had it.

 

Uh Oh. Another option That was my original plan based on previous threads here. But the advice given above caused me to question it. Is your car a BB or SB. I would guess the weight bias of a BB might have some influence on the OS US situation. My car is a SB.

 

My stock 78 L-82 4 speed had a 1 1/8 inch front bar and a rear 7/16th GM rear sway bar with 550 front springs-my addition, 360 mono spring-my addition, Bilstein HD front and Bilstein Sports rear and its handling was terrific….If you go with the stock gymkhana sport suspension system to start with you can't go wrong and you can adjust from there…which I have done over the years as well.

 

I have the vb&P street and salmon kit on my 78. 1 1/4" front with 3/4" rear. From there I have adjusted the alignment to have more bias towards under steer. I have different settings I use depending on the track I drive. Sometimes I have added more front camber and more toe out in the front to produce over steer conditions. But the best improvement I found is going from the stock 15" TA tires/ Wheels to 18" michilen Super Sports. Improved cornering (less effect of over / under steer ) due to much better grip levels and much better braking. The stock 15" TA Tires are ok for daily driving, but are so so for performance driving.

What are you running for tires ?

 

I currently have the stock 1 1/8 inch OEM front bar with poly mounting and end link bushings and a rear 3/4 inch OEM type sway bar with poly mounting bushings along with a front spreader bar and rear competition adjustable strut rods with heim joints. My car is very neutral at the limit of adhesion. I also run 255/45/17 ZR ultra high performance summer only tires and you are correct, the tires make a HUGH difference in grip for handling and braking. I am not so kind about the OEM 15 inch tires which are basically a mass market standard passenger car tire with raised white letter-most compact cars with 17 inch tires have a MUCH superior tire on them than the 255/60/15 S rated tires available for our cars. I switched to 17 SLP rims a few years ago since I could not tolerate the stock type tires on the car any longer...

 

The current tires are Mastercraft (never heard of them) P255/60R15. After I get the suspension sorted I will look at better tires but the Michelins are probably over kill for my freeway entrance ramp slalom driving. From your comment about producing more oversteer I assume you adjust less camber and less toe out for understeer. By less would that mean less than the factory settings?

 

The Mastercraft tires I believe are from one of the chain auto parts stores like PEP boys, Advanced etc and are no better and no worse than any of the other 15inch tires available for the C3-just a generic branded tire probably made by one of the big boys-Goodyear, BFG, Cooper etc. There are no performance tires from any manufacturer that makes a ultra high performance tire for the C3 in a 15 inch-that is the problem. Everyone has to do what is right for them but my belief is there is no such thing as overkill with tires for any car. I buy the best I can get for safety and performance on my DD's as well-2001 pontiac Grand prix-225/55/16 ZR ultra high performance Cooper RS3-A, as an example, Traction AA, Temperature A, 40,000 miles warranty-Speed rated to 168 MPH (safety, tire construction strength, handling/steering, braking). My C3 has 255/45/17 ZR ultra high performance summer only tires-one of the best things I have done to my C3 in 30+ years of ownership….

 

I get your point about the tires. But what about the less camber, less toe in for understeer. Do you have any advice on that. I guess I'm asking if by less you meant stock settings as opposed to the more you dial in for oversteer. Or are you saying less than stock for understeer?

 

Here is a reference I have used as a starting point.
http://tech.corvettecentral.com/2011...ignment-specs/
Also read the comments below the chart to see additional changes and what they produce.
These settings for street driving will setup the car for best tire life and setup based on the stock suspension to be more toward under steer under harder cornering.
Most settings outside of the street settings will produce additional tire wear but also change the handling characteristics. eg note the autocross settings which has the front wheels with toe out and more camber on the front vs the rear. This will produce more over steering, allowing the car turn in faster when pointing the wheel left or right.

When I setup my car for road track driving, I am looking for best track performance which is not best for Street Driving.

The stock suspension with the street alignment should produce a car that should be biased toward under steer. This is the safer condition the manufacture designs for. To have over steer is usually when something is worn or moving that shouldn't.

 

Thanks, that is very helpful. I appreciate your taking the time to provided so much info.

 

Replaced existing sway bar rubber bushings with Poly bushings (with grease fittings). The old bushings were worn but not badly. I wonder if the worn bushings on the sway bar could result in oversteer. Need to find a lift where I can tighten the suspension bolts with the weight of the car fully supported by the wheels. I'll report back after I drive the car.

 

OK, front suspension rebuild is done and front end has been aligned. The car corners beautifully. But what caused the severe oversteer? Was it sloppy bushings or ball joints? Unfortunately, since I changed everything I can't say for sure. I didn't find anything particularly worn, although I suspect it was the first bushing/ball joint replacement the car has ever had (78,000 miles). Only thing not stock in the rebuild were poly sway bar bushings. So it appears to me the 1 1/8" sway bar was not contributing to the oversteer since it is still on the car and the oversteer is gone. So I can't say for sure what caused the excessive oversteer but it is history.