69 L71 rear leaf springs

[Richard M.]

Re: 69 L71 rear leaf springs

Patrick, Thanks for the info. I was informed years ago that only F41 used the unique spindles. It appears I was misinformed.

Rich

[Mark F.]

Re: 69 L71 rear leaf springs

Mark, Correct. The center bolt passes through that flat plate so the head still needs to be low enough to fit in the diiferential center locator hole. In rebuilding that original F41 spring, I acquired a repro center bolt. It's head was significantly taller than the original I removed. The original head depth was apx 0.248". Repro bolt apx 0.373". Checking it for clearance, it could have been disastrous if I used it. I ground the head to fit the space properly before reassembling the spring and attaching to the differential.
[ATTACH=CONFIG]112227[/ATTACH]Rich

Thanks, Rich,

It's been so long, I wasn't remembering that detail.

I DO remember what a pain in the butt that job was getting it back in and secured at the ends of the springs while laying on a concrete floor (no lift and no helper)!

[Joseph W.]

[Lawrence S.]

Re: 69 L71 rear leaf springs

I recently restored my rear end on my 67 BB Coupe. Upon reassembly used Zip correct head mark spring to differential bolts and noticed they were too long. If I would had continued to torque them up likely would had cracked the differential. I measured the originals vs. the repos and clearly the repos are longer. I cleaned up my original bolts with Evap O Rust and re-used them. I know this has already been mentioned in this thread just another heads up.
I also re-used my original center leaf spring bolt for the exact reason Joseph mentioned earlier, repro head too long and would had been a terrible issue likely if not caught.
My original trailing arms had the "x" on the spindle, and unfortunately were just too trashed to re-use so I bought new correct 67 trailing arms from Bair sand installed those.
My original leaf spring did not have a top plate, but was just a F40 suspension. I was able to buy a nice used restored original from a Jimmy Gregg and am very happy with the ride height and ride.
Joseph sounds like your car will be very nice when complete. Good luck with it.
Lawrence

[Joseph W.]

Re: 69 L71 rear leaf springs

Thank you Lawrence!
you didn’t happen to measure what your original 4 bolt lengths were?
I have nothing to reference to as the PO installed a composite spring.
I think I read they were 3 5/16” long?

C06E0953-2CB8-4440-B5B0-64ADAC7E2895zz.jpg
she’s coming along….

[Lawrence S.]

Re: 69 L71 rear leaf springs

Joseph,

Here you go.

[Richard M.]

Re: 69 L71 rear leaf springs

Here .....

... beginning at paragraph 3 of the post, is a detailed description from a few years ago regarding the bolt length measurements I made on a '67 F41 original rear spring. Sorry for the hen-scratching notes info but it may help to see what I went through. Bottom line is this, best to make accurate measurements. Leaf thickness & liner thickness play a big role in bolt length. I used original leaves, but the liners were thinner than the originals and required shorter than original bolts.

Note in my description that the forward blind holes in the diff case are NOT threaded to their deepest end. There is about 0.2" unthreaded at the end of the blind holes, and if your bolt is just slightly too long, you could put it in a bind and not achieve proper ride-weighted torque. Of course if the bolt is extremely long, broken diff case.

Rich
PS Joseph I took the liberty to rotate your photos in your posts.

[Joseph W.]

Re: 69 L71 rear leaf springs

Here .....

... beginning at paragraph 3 of the post, is a detailed description from a few years ago regarding the bolt length measurements I made on a '67 F41 original rear spring. Sorry for the hen-scratching notes info but it may help to see what I went through. Bottom line is this, best to make accurate measurements. Leaf thickness & liner thickness play a big role in bolt length. I used original leaves, but the liners were thinner than the originals and required shorter than original bolts.

Note in my description that the forward blind holes in the diff case are NOT threaded to their deepest end. There is about 0.2" unthreaded at the end of the blind holes, and if your bolt is just slightly too long, you could put it in a bind and not achieve proper ride-weighted torque. Of course if the bolt is extremely long, broken diff case.

Rich
PS Joseph I took the liberty to rotate your photos in your posts.

Thank you Rich!
somehow I missed your post when doing my research..
Very helpful.
I feel dumb asking, but how did you cut the end of your bolts? Band saw? Dremel tool? Hacksaw? And then prior to cutting, you screw on the thread chaser/cleaner so you can then unwind it to clean the threads?
thank you

[Richard M.]

Re: 69 L71 rear leaf springs

Thank you Rich!
somehow I missed your post when doing my research..
Very helpful.
I feel dumb asking, but how did you cut the end of your bolts? Band saw? Dremel tool? Hacksaw? And then prior to cutting, you screw on the thread chaser/cleaner so you can then unwind it to clean the threads?
thank you

Joseph,

That post was buried in a long build-thread I did then and I used the Advanced search to find it using my user name, and results filtered by "Posts", not "Threads".

I recall I used my Sawzall to cut them then bevelled the ends on a grinder. Then I chased the threads.

Rich

[Joe L.]

Re: 69 L71 rear leaf springs

All------


As far as I can determine, GM #3833486 bolts were used for retaining the rear spring to the differential for all 1963-74 Corvettes regardless of whether equipped with 7 or 9 leaf rear spring. According to GM, this bolt was 9/16-12 X 3-7/32" with 1" of thread length. It was material grade GM-280M (SAE 5)

However, the 3833486 bolt was discontinued in March 1988 and replaced by GM #9428598. This bolt did not have the same specs as the original. Instead, it was 9/16-12 X 3-3/4" with a thread length of 1-3/8". It was material grade GM-300M (SAE 8).

It may very well be that this is the bolt that is actually reproduced and that's what creates problems. If one is using an absolutely original spring with original thickness liners (or, even thinner liners), this bolt is going to be too long and could well cause problems.

When using any non-original spring (e.g. reproduction, aftermarket replacement, etc.), one needs to carefully calculate the bolt length required and adjust the length of the bolts used.

By the way, I believe that the GM #3833486 bolt, given it's rather unusual length and thread length, was a special bolt specifically designed to be used with the 1963-74 springs which likely had a standardized center thickness dimension. I highly doubt that the 3833486 bolt had any other GM applications. The replacement GM #9428598 bolt, on the other hand, was more of a "standard spec" bolt and probably had many applications. I think it was a poor replacement for the 3833486.

[Joseph W.]

Re: 69 L71 rear leaf springs

Another update to this thread……
I finally got around to installing the F41 7 leaf spring, F41 rear shocks, and the F41 rear shock mount on my 69.
When I removed the lower shock mount, imagine my surprise when I realized it was a F41 mount!
Just one more piece of the puzzle to confirm validity of a L71.

Unfortunately , when completed, the cars rear sits extremely high up. Ive taken to calling it “stink bug”.

Did GM make different length bolts at the ends of the leafs?. Talking about the long bolts that go thru the bushings and cups.
I plan on removing this spring and replacing it with my other 7 leaf spring.
sorry for the rotated pic…
anyone see any issues with my install? I find it weird that the shock spindle is what appears to be completely extended. Makes me wonder if the car would sit even higher if not for the shock.
0A85FD92-2C5E-44CF-A5CD-59CDF0D816CC.jpgEE5030A4-B246-476E-86CC-ECBB7530D969.jpgEE5030A4-B246-476E-86CC-ECBB7530D969.jpg
Interesting that although the numbers are the same, quite a few differences with the mount.

[Mark F.]

Re: 69 L71 rear leaf springs

rotated...
F41 Spring 0A85FD92-2C5E-44CF-A5CD-59CDF0D816CC.jpg

[Joe L.]

Re: 69 L71 rear leaf springs

[ATTACH=CONFIG]113540[/ATTACH][ATTACH=CONFIG]113541[/ATTACH][ATTACH=CONFIG]113541[/ATTACH]
Interesting that although the numbers are the same, quite a few differences with the mount.

Joseph------

You need to normalize the suspension by rolling the car with wheels on the ground. With the suspension normalized the spring should appear virtually "flat" with, perhaps, just a very little center high arch.

GM did use different length spring end bolts but not until about 1975 when bumper height became critical due to federal regs.

Original F-41 shock mount shafts usually had the GM part numbers embossed on the unmachined portion of the mount. Later GM replacements and all "reproductions" do not.

[Joseph W.]

Re: 69 L71 rear leaf springs

Joseph------

You need to normalize the suspension by rolling the car with wheels on the ground. With the suspension normalized the spring should appear virtually "flat" with, perhaps, just a very little center high arch.

GM did use different length spring end bolts but not until about 1975 when bumper height became critical due to federal regs.

Original F-41 shock mount shafts usually had the GM part numbers embossed on the unmachined portion of the mount. Later GM replacements and all "reproductions" do not.

Mark-thanks for rotating the picture....not sure why it does that when I post it...

Joe Lucia,

on the other side of those shock mounts the GM part number is on it.
There were subtle casting differences and marks between the 2 mounts.

[Joseph W.]

Re: 69 L71 rear leaf springs

.
62A80D4A-F631-4571-B272-8CB2C66E2BC4.jpg62A80D4A-F631-4571-B272-8CB2C66E2BC4.jpg
These are the marks absent on my originals