F40 and F41 suspension identification

[John G.]

I have seen in a parts supplier book reference to F40 and F41 suspension for C3 I believe F40 is 7 leaf rear spring and .9375 front sway bar can anyone tell me what make up the F41 kit and my LT1 has 7 leaf rear spring with .75 sway bar would this have been a normal configuration
john

[Joe L.]

Re: F40 and F41 suspension identification

I have seen in a parts supplier book reference to F40 and F41 suspension for C3 I believe F40 is 7 leaf rear spring and .9375 front sway bar can anyone tell me what make up the F41 kit and my LT1 has 7 leaf rear spring with .75 sway bar would this have been a normal configuration
john

John-----


F-40 was never an RPO designation for C-3 Corvettes. It was used for 1964-65 Corvettes and was also part of the Z-06 package for 1963. Beginning with the 1966 model year, the RPO designation changed to F-41. I really don't know why this occurred since there was really no difference in components for F-40 or F-41.

For 1970 and 1972, F-41 suspension was only available as part of the ZR-1 special performance package. Only a handful of these cars were ever made. Some say that F-41 was available for any 1971 Corvette, regardless of engine. That may be or it may not be.

In any event, your car, if it's a 1970 or 72, should most likely not have F-41. If it's a 71, who knows?

In any event, F-41 included the following components:

15/16" OD front sway bar;

HD front springs (11/16" wire diameter)

HD shocks

HD 7 leaf rear spring

HD rear lower shock mounts (forged 3829265 LH, 3829266 RH)

The 7 leaf rear spring and the HD shock mounts later became SERVICE for all 1963-72 Corvettes, so it's possible if your car has these, they may have been a replacement.

I would look for the HD front springs by measuring the wire diameter. If you have these, the chances are the car was an original F-41. If not, I'd say you have a standard suspension car that has had the rear spring replaced. Most LT-1's were standard suspension which would have included a 3/4" front sway bar and front springs with a wire diameter of about 19/32".

[John G.]

Re: F40 and F41 suspension identification

Thanks again for the detailed information Joe will check out other measurements tomorrow. I am considering a rear sway bar any thoughts on this?
john

[Duke W.]

Re: F40 and F41 suspension identification

Adding a rear bar will bias your car toward oversteer. The base suspension has a tendency to oversteer at the limit, so I would certainly not recommend adding to this tendency, and replacing the base rear spring with the HD rear spring has already increased oversteer bias.

Begining in 1975 the FE7 suspension consisted of HD springs (same rates as '63 Z-06) with a 1.125" front bar and 7/16" rear bar. This would be a good starting point, but keep in mind that tires are what ultimately limit grip, so if you have typical low speed rated, hard compound tires, messing with springs and bars won't have much measureable effect.

Unfortunately, most suspension component changes are made willy-nilly without any understanding the underlying vehicle dynamics. Before you embark on such a project, obtain and read Fred Puhn's "How to Make Your Car Handle". It's old, but the basics haven't changed.

If you want to improve handling the first place to start is tires. Then do a "performance alignment" (-1 deg. camber at each corner, maximum front caster available within the adjustment range), add adjustable rebound shocks, then balance the car with bars, changing one at a time until the optimum balance is obtained.

The last thing that should be changed is springs, and spring changes should only be made based on achieving a computed ride frequency for the driving conditions. As a general rule, the OE ride frequency is in a proper range unless you are running on high speed race tracks.

Duke

[Joe L.]

Re: F40 and F41 suspension identification

Thanks again for the detailed information Joe will check out other measurements tomorrow. I am considering a rear sway bar any thoughts on this?
john

John-----


I agree with Duke. I would not add a rear sway bar for your application.