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I recently pulled the differential out of my 1969 L36 .Upon disassembly I noticed that it had a replacement 9 leaf spring. On the 4 bolts that hold the spring on, one of the rear holes had been stripped and a extra long bolt and nut where used in it's place. When looking for new bolts, I see two sizes. 3 1/4 and 3 3/4 . I measured the 3 that I have and they are the 3 1/4 with the WB on the head of the bolt. Would this not signify that it would have been originally a 7 leaf spring? The front sway bar is 15/16. There is nothing on my original option sheet from GM about a F41 suspension. Also the shocks have all been replaced at one time. I didn't think a L36 could be ordered with F41. Does anyone have any ideas what's going on ?
My April '68 L36 coupe was spec'd originally with F41 suspension option.....although OEM dampers were long gone. Its a 4 speed c/r Muncie.....some seem to think its unusual for a 4 speed with 3.08 rear-end....but that was its original spec'
Do you have a rear sway bar? Front bar is too small and nothing on your build sheet.
ever occur to you that your bolts are not original? You said that the spring isn't. And, what if the bolts are not original? Will this somehow affect the way your car drives?
Do you have a rear sway bar? Front bar is too small and nothing on your build sheet.
ever occur to you that your bolts are not original? You said that the spring isn't. And, what if the bolts are not original? Will this somehow affect the way your car drives?
sorry but this is incorrect.
For 1969 F41, the front sway bar is 15/16” diameter.
I recently pulled the differential out of my 1969 L36 .Upon disassembly I noticed that it had a replacement 9 leaf spring. On the 4 bolts that hold the spring on, one of the rear holes had been stripped and a extra long bolt and nut where used in it's place. When looking for new bolts, I see two sizes. 3 1/4 and 3 3/4 . I measured the 3 that I have and they are the 3 1/4 with the WB on the head of the bolt. Would this not signify that it would have been originally a 7 leaf spring? The front sway bar is 15/16. There is nothing on my original option sheet from GM about a F41 suspension. Also the shocks have all been replaced at one time. I didn't think a L36 could be ordered with F41. Does anyone have any ideas what's going on ?
How did you know it was a replacement rear spring?
The rear leaf bolts from the factory were 3 7/32” long and were the same bolt for 7 leaf or 9 leaf.
There was 1 “ of threads.
For service replacement leaf spring bolts in later years they changed the bolt to more of a standard size bolt 3 3/4”.
The original 3 7/32” bolt was also discontinued at some point.
This information above is from Joe Lucia from the NCRS tech forum.
Other ways you can determine if your car came with the F41 is to carefully measure the front coils. They should be .675” if F41 and lastly, the rear shock spindles are different for F41. They are angled as opposed to straight.
the angle gives a bit more room for the fatter F41 shock.
These shock mounts rarely get changed out.
On my 69 L71, the PO put on a composite spring and aftermarket suspension.
Old pictures of my car taken with the body off and the chassis on a lift showed an original 7 leaf spring.
I was pretty certain my car came with the F41 suspension, but knew for sure when I removed the rear shock mount.
My rear shock mounts:
Last edited by Tuna Joe; Mar 10, 2025 at 03:27 AM.
sorry but this is incorrect.
For 1969 F41, the front sway bar is 15/16” diameter.
I stand corrected Sir. I thought the 1 1/8" front bar was a standard Gymkhana thing. As is the rear sway bar.
As per the rear shock studs. These are commonly replaced when strut rod bushings or strut rods need replacement.
Many Big Blocks of that era were ordered with the F41. Close to half?
The wire diameter of your front coils would be your best clue.
Those get changed out much less frequently than either the rear spring or the shock mounts.
The sway bars are the same for all BBs.
Also the above mentioned wire diameter was not correct.
Here are the 3 front coil options for BBs from 68-72
The F41 springs have a .680" wire diameter, and also only 7.0 coils. An EA spring tag if it is still there.
Many Big Blocks of that era were ordered with the F41. Close to half?
The wire diameter of your front coils would be your best clue.
Those get changed out much less frequently than either the rear spring or the shock mounts.
The sway bars are the same for all BBs.
Also the above mentioned wire diameter was not correct.
Here are the 3 front coil options for BBs from 68-72
The F41 springs have a .680" wire diameter, and also only 7.0 coils. An EA spring tag if it is still there.
I was under the impression that only the high HP options were able to get the F41?
So that would be the L71, L89,L88,
Not sure if the 400hp Tri power was able to order the F41.
Are you saying the 390hp/427 could order the F41 option?
Can anyone verify this?
I was under the impression that only the high HP options were able to get the F41?
So that would be the L71, L89,L88,
Not sure if the 400hp Tri power was able to order the F41.
Are you saying the 390hp/427 could order the F41 option?
Can anyone verify this?
For 1969 it appears the F41 suspension was only available with the L71 435hp option.
Ok Thank you to everyone who replied . I think the mystery is solved. The car is a 69 L36 turbo 400, 3:08 rear made March 1 /69 The question was why are the leaf spring bolts the short ones with a 9 leaf spring. The front sway bar is 15/16, the coil spring wire is .618, and the rear shock mounts stamping numbers match my AIM
( there was only one shock mount listed for all of the suspensions) The Aim also only listed one size of leaf spring bolt as well which goes along with what the NCRS judges say. So the short bolts were probably used on both the 7 and 9 leaf springs until someone at GM realized that this was not safe.. I will say now that I do not have the F41 suspension. FYI my rear spring has a part number on it that I see our favorite Corvette sites sell as a replacement. Thanks again to all for helping me figure this out.
So the difference here is the unpublished L88 engine had no OPTION for the F41 suspension - it was mandatory along with the HD brakes and transistorized ignition, radio delete etc.
On the other hand, in the published Corvette brochure the F41 suspension was available as an OPTION but only if you ordered the L71 engine option.
So the difference here is the unpublished L88 engine had no OPTION for the F41 suspension - it was mandatory along with the HD brakes and transistorized ignition, radio delete etc.
On the other hand, in the published Corvette brochure the F41 suspension was available as an OPTION but only if you ordered the L71 engine option.
F41 Suspension Question
