&F40 / &F41 Rear Spring ID

[Ray K.]

Is there a "known" way to identify if a F40/F41 rear spring?
I have a F40/F41 heavy duty spring and I'm trying to determine if it could be an original, service or aftermarket spring.
The 1965 6th Edition Technical Information & Judging Manual doesn't provide much to help identify it (stampings, part number, date code, manufacture letters/numbers, etc).
Can anyone help?
Here are a few jpegs:
Ray K (#43777)65 Vette - F40 Rear Spring_1 - 06Sep22.jpg65 Vette - F40 Rear Spring_2 - 06Sep22.jpg65 Vette - F40 Rear Spring_3 - 06Sep22.jpg65 Vette - F40 Rear Spring_4 - 06Sep22.jpg65 Vette - F40 Rear Spring_5 - 06Sep22.jpg

[Richard M.]

Re: &F40 / &F41 Rear Spring ID

Ray, For reference, here is a F40 spring on a '65 fuelie. Best of my knowledge original. Appears identical to yours.

The only caveat is that I believe service replacements used that flat extra leaf on top. Not sure if 65 used that or not.

Rich

[Gary B.]

[Richard M.]

Re: &F40 / &F41 Rear Spring ID

Good eye Gary, I didn't notice that in Ray's photos.

Here are some from a '67 F41 7-leaf I restored. I had to replace the main leaf as it had a bad spot. Eaton's replacement was very good.

Rich

Eaton left, Orig right
P5220052.jpgP5260013.jpgP5260028 - Copy.jpg

[Gary B.]

Re: &F40 / &F41 Rear Spring ID

Richard,

In your photos, I see the expected ~1/8” reduced width for the last 2” or so at the end, and the classic ski jump end with the relatively sharp tip. I don’t see that 1/8” reduced width section on Ray’s spring. But I haven’t closed examined many GM HD springs to know if they all have those features. But the non-45 cut is concerning.

Gary

[Danny P.]

Re: &F40 / &F41 Rear Spring ID

Is there a "known" way to identify if a F40/F41 rear spring?
I have a F40/F41 heavy duty spring and I'm trying to determine if it could be an original, service or aftermarket spring.
The 1965 6th Edition Technical Information & Judging Manual doesn't provide much to help identify it (stampings, part number, date code, manufacture letters/numbers, etc).
Can anyone help?
Here are a few jpegs:
Ray K (#43777)[ATTACH=CONFIG]114601[/ATTACH][ATTACH=CONFIG]114602[/ATTACH][ATTACH=CONFIG]114603[/ATTACH][ATTACH=CONFIG]114604[/ATTACH][ATTACH=CONFIG]114605[/ATTACH]

Ray , there should only be 7 leafs total and no liner between on 7 th and 6th spring and no top spacer , this a photo of my F41
rear spring on my 67 DuntovIMG_3649_InPixio_InPixio.jpg

[Richard M.]

Re: &F40 / &F41 Rear Spring ID

Richard,

In your photos, I see the expected ~1/8” reduced width for the last 2” or so at the end, and the classic ski jump end with the relatively sharp tip. I don’t see that 1/8” reduced width section on Ray’s spring. But I haven’t closed examined many GM HD springs to know if they all have those features. But the non-45 cut is concerning.

Gary

Gary, yes that 65 spring I showed is in fact likely a repro. Its a 37k mile car, but was drag raced most of its life, then restored by my friend. He bought it in the mid 80s.

After I posted the original 67 spring the features you mention are more obvious.

Rich

[Gary B.]

Re: &F40 / &F41 Rear Spring ID

This table is from a Restorer article that Joe Lucia and I wrote about 10 (?) years ago. As one can see, for some years the HD spring had a flat top plate. A 1975 HD spring could easily be converted to a 63-74 HD spring by removing the top plate.

Gary

681B9817-E155-4846-A4AB-D8320D2BA2BD.jpg

[Richard M.]

Re: &F40 / &F41 Rear Spring ID

PS... just remembered this thread from a while ago regarding the top plates.

https://www.forums.ncrs.org/showthread.php?130080-69-L71-rear-leaf-springs

[Gary B.]

Re: &F40 / &F41 Rear Spring ID

This table is from a Restorer article that Joe Lucia and I wrote about 10 (?) years ago. As one can see, for some years the HD spring had a flat top plate. A 1975 HD spring could easily be converted to a 63-74 HD spring by removing the top plate.

Gary

681B9817-E155-4846-A4AB-D8320D2BA2BD.jpg

[Ray K.]

Re: &F40 / &F41 Rear Spring ID

All,
Thanks for the very informative on my &F40/F41 rear spring.

Now the question becomes: what should I do with it?
Ray K

[James W.]

Re: &F40 / &F41 Rear Spring ID

It looks like all the other 6 spring leaves and top plate are correct. I'd buy a replacement bottom (main) leaf spring from Eaton Spring that has the correct 45 degress mitered end cuts. I would also buy a pair of the closer to original (shallower) replacement spring cushion cups from Gary Beaupre.

James

All,
Thanks for the very informative on my &F40/F41 rear spring.

Now the question becomes: what should I do with it?
Ray K

[Richard M.]

Re: &F40 / &F41 Rear Spring ID

Gary, Nice document. Thanks for posting. I'll put that in the DoRD Sticky when I get a chance.

Ray, yours has a different profile on the ends of the angle cuts on the main leaf, so likely a reproduction. The rear spring gets 5 points for Originality, 5 for Condition. 10 Total. At worst case scenario, you'd loose 5 points for NTP. If mine, I'd restore it and use it.

So.... I went back and looked at the judging sheets on that '65 fuelie coupe that had that 7 leaf rear spring I pictured earlier.

It appears that at both the 2010 Florida Regional and the 2010 Charlotte Nationals, the spring did not receive a deduct for originality, other than a 1 point hit for not having the shallow cushion cups. So now I'm confused if it was just an oversight(twice!), or in fact it's a original GM spring. Unsure. My gut tells me it's not original because of the top spacer plate and the non-narrowed leaf ends. But I've not seen any other original '65 F40 springs.

Rich

[Gary B.]

[Joseph W.]

https://www.corvetteforum.com/forums/c3-general/4551521-79-gymkhana-rear-spring-questions-2.html