How do you tell if the stock spring is wore out. I have a '77 Gymkhana with back tires doing the duck squat / \

Up on the lift everything looks original and untouched (42k miles). Well, except for the new brakes I just installed. Looks like the leaf spacers have done some moving around....

 

Hi CB,
The camber adjustment really doesn't have anything to do with the rear spring.
It's the strut rod eccentrics at the mount at the differential case that determines the camber.

At normal ride height the half shafts should be about parallel with the ground and the rear spring should show very little if any arch.

Regards,
Alan

Happy Thanksgiving.

 

Thank you Allen. I read that the stock strut rods are prone to loosing adjustment...just didn't think they would both go out equally. After looking now at a rear end diagram I can see how the spring doesn't really come into play.
Thanks again.

Looks like I'm gonna have to cut on my front springs so this thing don't look like a parade float going down the street....sigh.

 

Hi CB,
Do you know the specifications of the front springs.
Are they the original springs?
Are they seated properly in both the upper frame pocket and in the lower a-arm?
Regards,
Alan

 

Worn leaf springs (steel ones like in your 1977) sag when they get old and worn out.

You've got some pretty good advice in the first reply.

There should be some visible arch to the leaf spring. Not a whole lot, but some is pretty much required for it to operate correctly. Put a yard stick across. The ends should touch the spring, and there should be some space (1/4" to maybe as much as 3/4") between the middle of the yardstick and the center of the spring. If the yardstick touches in the middle with the ends not touching the leaf, that's a problem.The half shafts should also be level or very close to level. If they aren't level, the diff end should be slightly higher than the wheel end.

Check the bushings on the strut rods. Those are rubber, and they wear out/deteriorate by getting soft or in extreme cases eroding. With the rear on ramps, you can crawl under and try to move the ends of the strut rods relative to the bolts through those bushings. If you can move them with your hands, they are probably weak/worn. Polyurethane busings are available for those strut rods, and may be easier to find than good quality OE replacements. Worn strut bushings will usually manifest as excessive negative camber when parked/stopped, and can cause handling issues and/or wobbles and shakes when driving. In more extreme driving, worn strut rod bushings can cause corner entry oversteer (because you lose some negative camber and you also get some toe out when the bushings compress more than they should).

While you're checking things out, check the wheel bearings as well. If the wheel bearings are worn, the trailing arm bushings are almost always toast as well, and fresh (new or rebuilt) trailing arms with fresh bearings and fresh bushings are the way to go for those issues.

 

This is a Gymkhana optioned car so from what I read they are 550lb. up front Allen. And to be honest I never thought to look if they are seated properly(will do) and,.also, I imagine they are still the originals. Although the car has only 42k miles I believe it must have sat outside for quite a while as everything on the suspension is pretty much covered in light rust buildup and it shows that nothing has really ever been taken apart IMHO. Surprisingly, all the rubber bushings look really good under the car.
I've looked at pics of other Gymkhana c3's and just don't like the (higher) ride height they provide, plus I read that ride quality is harsher so I will probably just replace the springs with lighter ones rather than cut on these originals.

Do you know if there is a good thread here on the forum where it shows different ride height/spring combos that could possibly spare me from having to do this swap multiple times on this small block car?

Thank you for your help and consideration....I enjoy all your posts whenever I come across them. You are a great asset to the forum.

 

Hi CB,
You might begin by measuring the ride height at all 4 wheel wells which will give you an idea what the car is now.
You measure from the ground to the center of the fender wheel arch at each wheel.
The current tires/wheels on the car affect this measurement, but it should give you something to begin with.
Do you have the Assembly Instruction Manual for your 77? The ride heigh dimensions should be in it.
On 68-72 cars the dimension is a hair less than 28", and will likely be close to that on your 77.
Regards,
Alan

 

Wow...great write up/response RacerX, thank you! Now I've got something to go by(good ole yard stick).

 

Yes, Allen, I have the AIM book and I just checked sheet A-14 "trim heights" page 20....doesn't show the dimension we are discussing. However, I went out and measured the car and am getting 26 3/4ins So that's an inch and a quarter off from the number you gave me....if the camber was removed and tires straightened up I believe it would then be right on spec @ 28. I don't want it any higher than that ...I like the look at the current height very much.

Which brings me to my final question here....I've read great things about going with the fiberglass mono in the back. I believe I will probably rip everything out in the back so I can give a nice clean restored look. Again, if you have a link you could provide for the best detailed thread dealing with mono spring weights/ride height it would be much appreciated!

Thanks for any consideration...

 

Hi CB,
I don't really know anything about the fiberglass rear springs so can't help you with the changes required to switch from the steel leaf spring you presently have to the fiberglass version.
Sorry.
Regards,
Alan

 

The fiberglass spring is a great upgrade. It saves 40 to 50 pounds over the steel springs (I think you have the 7 leaf spring if you have the "gymkhana package", and the weight savings is about 42 pounds IIRC).

From my memory, I think it's a direct swap. You might need longer end link bolts where it attaches to the trailing arms. I don't specifically remember. I know longer bolts are available to lower the rear on these cars. I just can't remember the spring curvature differences between the fiberglass spring and the steel springs.

That brings me to the one piece of advice. The end link bolts that attach the spring to the trailing arm are used to set ride height. If you're keeping the same spring, or replacing it with an exact replacement, count exposed threads and when you put it back together, put the nuts on the same number of exposed threads. If you're changing to a different spring, measure your ride height (wheel arch to ground or wheel arch to rim lip) and match that dimension after you change the spring. If you tighten the nuts "snug" and put the cotter pins in, your car will very likely be jacked way up in the back. Don't ask me how I know this.

Loosening the nut lowers the ride height on that corner. Tightening the nut raises that corner. If you have access to scales and can measure weights at each wheel, you can even square the weight on the chassis after you have the ride height set about right. That's a bit more advanced than I want to get into at this point, but if you want to do that, let me know (on this thread, or private message me).

Disclaimer: about "from my memory." My memory on C3's is many, many years (a few decades) old. Some things I definitely have strong memories of because it was the first full out race car I ever crewed for. But I'm digging way, way back in my memory here.

 

Another thing that will affect the rear camber is the side yokes in the diff. With the rear raised up, grab the tire at 12 and 6 o'clock and push in the top and pull the bottom, may have to put some power into it. Watch for the diff side yoke sliding in and out of the diff.

 

Thank you '75...that was one of the first things I did with the car, wanting to see if I got sold an expensive repair right off the bat(trailing arm problems). All is goodintite.

 

Sorry for high jacking an old thread but I wonder if my leaf spring is too worn? By the description I guess it is close to completely flat.
I would appreciate any input.


Cheers Chris