There have been a lot of threads here on CF over the years from C3 owners expressing dissatisfaction with the excessively laid-back angle of their seatbacks and how best to remedy this situation. I had the same complaint when I purchased our new '77: driving the car, I was leaned back so far I was staring at the sun visors. No bueno.

I did some research here on the forum, but quickly made my first mistake: when I went to back out the two large Phillips head adjusters on the driver's-side seat bottom, it broke the tiny spot welds retaining the (formerly) captive nuts located underneath the seat frame that the adjusters thread into. Bollocks!

I went ahead and shimmed the adjuster screws with some chrome spacers I had left over from one of my Harley projects (and had to shim the seatback locking gizmo a similar amount with an assortment of washers so the seatback would still lock in place).

Driving the car, this small change in seatback angle made all the difference in driving comfort, so I knew I was on the right track, but the combination of hardware I used to achieve all this was a little too redneck for my taste. I wanted something less Bubba, something simple, strong and elegant that would also hopefully be nearly invisible cosmetically.

I found these bad boys while sniffing around on Amazon and purchased a set as an experiment:





Link:

These things worked perfect!

I do NOT recommend backing out the large Phillips head adjusters located on the seat bottom. You don't need to, and you run the risk of breaking the spot welds on the captive nuts these adjusters thread into. Leave them alone (feel free to polish them, however...)

(I also don't recommend shimming underneath the rear of the seat tracks to change the angle of the seat. Can't believe how many times I've read someone recommend this. )

Instead, shim the rubber bumpers located on both sides of the bottom of the seatback. How many shims? It's a guess, really. I ended up using five per side, giving me a total of 5/8" "lift." So far I'm happy with the subsequent change in the seatback angle, but if I wanted to reduce the angle further, or increase it again, I could easily and quickly add or subtract a rubber washer or two to the stack. Doing so doesn't take a screwdriver; I used a smear of anti-seize on the bumper bolts and they now thread in and out like butter. I can now install or remove the adjusters easily by hand – the rubber bumper, along with the stack of rubber washers, gives you a ton of purchase.

The rubber shims compress (and conform) just the slightest bit when you tighten them down, sort of acting like a stack of flexible lock washers. As such, the stack very effectively mechanically joins the rubber bumper and its bolt to the bottom of the seatback. The finished assemblage is very stout and robust.

I also used some of these rubber shims to adjust the locking mechanism so the seatback would still lock in place. Again, because of the size and composition of the shims, you end up with a very robust mechanical structure, if that makes sense.

Here are some pics:

I don't recommend messing with these things.


Instead, back the bumpers out of the bottom of the seatbacks...




...and install a stack of rubber shims like this:



The ID on the rubber shims is 1/4", the OD on the bolts is 5/16", but as the shims are rubber and have a little give to them, you can easily screw them down onto the bolts (or screw the bolts into the shims). You can also see from this photo that even though I've commandeered 5/8" of bolt shank, there's still plenty of shank remaining to thread back into the seatback frame to insure a strong, robust mechanical connection.






Simple and strong, and easily adjustable via adding or subtracting shims to further raise or lower the seatback angle. You can see that the shim on the far right, at the bottom of the stack, has conformed slightly to the seatback base, helping insure solid mechanical contact of the bumper assembly to the base. Stacked and slightly compressed in this manner, the rubber shims are actually load-bearing and a key component of the strength and integrity of the overall structure.


I only used three shims per side on the seatback locking mounting assembly, instead of five; this took up a little slack in the locking mechanism so the seatback now doesn't have excessive fore-aft "play" in it when it's in the locked position:



In the above pic you can again see that the shims are large and load-bearing, contributing to the mechanical strength and integrity of the overall structure. Bulletproof, in other words.


I originally bought 25 of these rubber shims, for $6.99, not knowing if they would work to my satisfaction, and liked them so much I bought another 25. In retrospect, I should have bought a 50-pack for $8.99.



All in all a pretty slick solution, especially if you have a black interior. If not, they would still work fine from a mechanical standpoint, they just wouldn't be as inconspicuous.

This was an oddly-satisfying little project.

All of the above pics are clickable.

RPO Joe

 

Great write-up!!!’

 

Nice post but the metal bumper on the bottom is supposed to have a rubber cover.
Bumper

 

Thanks!


From the verbiage at your link, it looks like they're meant to be used as washers, not covers: Hard to tell in my pic, but there are indeed plastic washers UNDER my seatback bottom adjusters:


RPO Joe

 

great

 

Having to deal with Bubba's seat repair shenanigans also makes you go "what were you thinking?"(G rated version) when it comes not doing it right.
Bubba's idea was to use 1/2 inch pipe about 3/4 long to place under the rear seat frames with longer cheap hardware store bolts. All of this broke the welds on the seat frames which has to be rewelded and painted. Since the Corvette vendors offer all rear seat hardware I rebuilt the seats back to stock and am pleased with the results.

I do like your idea for seat back. Nice write up!

 

You are correct

 

A while ago I replaced the upper, rubber coated, bumpers on our '78 because the rubber had disintegrated. Of course, when I did, it pushed the seat back forward a little, as the bumpers were now thicker.
I find the angle of the seat is ideal for me (I'm 6'2") and I didn't want it more upright so decided to adjust the lower bumpers. I discovered that a "lock nut" had been fitted to stop them turning in the weld nut. Otherwise, they were as fitted, with the washer etc. I have seen mention of this additional nut in a couple of publications, but I don't see it in my AIM, (That said, my 1978 AIM pages for the seats show the pre 77 seats and are marked "Cancelled"!) I was able to release the lock nut easily and with a bit of measurement I was able to screw the bumpers down just enough to achieve the same angle as I had had.
I hadn't considered using the top bumpers as adjusters, although I was surprised by just how much thread there was to screw into the base of the seat back, so they are probably more suitable to use, with the addition of the rubber washers.
Yours is a neat little "fix" and even on my Oyster seats, the bumpers are coated in black rubber and are not visible unless the seat is tilted forward, so no worries about the black rubber washers!

 

I've concluded that the bumpers on the seat bottom are just that: bumpers. I don't believe GM ever intended these things to be adjusted.


The reason for all that thread – way, way more than is needed to simply secure the bumpers into the bottom of the seat back – is to allow adjustment of the seat back. What's missing from the factory, however, is a way to lock the adjusters as you experiment with different angles of the seatback. The rubber washers/shims provide an inexpensive and easily adjustable solution.


Thanks. I'm pleased to have stumbled into these rubber washers and glad to hear they can be used with interior colors other than black.

RPO Joe

 

Thanks so much. Been looking for a solution for the same issue.

 

Nice thread and nice solution to adjusting the seat back position.
Thanks for sharing!