Transverse leaf spring question

[mike100]

Here's what the shims look like when not installed above the spring bushing. my car was slammed and the two aluminum shims are shown here going along for the ride (at least they didn't toss them).

[WVZR-1]

I checked two springs I have here, a '91 removed at 16K from a ZR-1 with the "green ink" and a code of FHA with the molded pad as in Mike's image. I have another from a '93 that is assembled with the riveted on metal reinforcement and the 1 1/4" square pedestal cushion like I believe all '92+ cars are assembled with and they both have the same FHA code. That tells me the spring rate is the same and if there are differences in any of the publicized specifications then the assembly procedure at the control arm ends is responsible for that variance.

Mike - What are the actual codes stamped/molded/branded in your two springs?

The code can be checked from underneath easily, it should be maybe 2 - 4" inboard of the control arm contact area.

[mike100]

I'm away from my car until the end of the week, but I do remember the stamped code matching from one spring to the other when Erik(YZpilot) and I swapped.

[secondchance]

WVZR-1,

'91 @ C is 177mm and a '94 @ C is 192mm"
Am I understanding correct that end of spring rubber pad (90-91) vs. later cars w/ puck results in later cars sitting 15mm (about 9/16") taller?

[WVZR-1]

Originally Posted by secondchance

WVZR-1,

'91 @ C is 177mm and a '94 @ C is 192mm"
Am I understanding correct that end of spring rubber pad (90-91) vs. later cars w/ puck results in later cars sitting 15mm (about 9/16") taller?

The description of the measuring point matches for C in both charts. The balance of the datum reference points change from '91 to '94 so the comparisons can't be compared.

The math substantiates your deduction. If though the '92+ spring is assembled with the "puck" then that would seem to negate that thought because the '92 FSM mentions the 177mm @ C.

There's no doubt that it's somewhat confusing.

[secondchance]

Yes. It is very confusing.

[USAZR1]

Originally Posted by mike100

when you cut the bushings and/or remove the shims, you effectively lower the spring rate so you might be better off with the early spring. Another way to put it is you reduce the spring preload so the car sits lower. you probably don't approach the stock tension until you are near the bumpstops. Doing the lowering wedges makes the car softer imo.

You might consider taking out one or both bushing shims as that will get you some drop without having to remove the spring 100% (it is easier and about 2/3rds the work). The ZR-1 (early cars at least) has two shims presumably due to the weight of the LT5, whereas the coupe/vert came with just a single shim or no shim.

Sorry for bumping this thread back to the top but I haven't heard the results of Yun's changes and what changes he settled on with his car. I want to lower our 94 1.5"-2" without having to install coilovers. Have talked with Vette Brakes & Products about one of their adjustable front springs like Jeff Moore has on his 91 ZR-1. Only possible downside I can see with one is the 900-1K spring rate but the ability to adjust the ride as easily as a C5 is a bonus.

Mike,can you post a photo of the bushing shims you're referring to in the above post?

[secondchance]

Originally Posted by USAZR1

Sorry for bumping this thread back to the top but I haven't heard the results of Yun's changes and what changes he settled on with his car. I want to lower our 94 1.5"-2" without having to install coilovers. Have talked with Vette Brakes & Products about one of their adjustable front springs like Jeff Flint has on his 91 ZR-1. Only possible downside I can see with one is the 900-1K spring rate but the ability to adjust the ride as easily as a C5 is a bonus.

Mike,can you post a photo of the bushing shims you're referring to in the above post?

I will be installing a pair from 91, front with shaved wedges, after engine is reinstalled.

[mike100]

the two shims are actually shown in the last photo I posted. they are riding under the bracket and sandwiched together. They are supposed to be on top of the spring- at least the PO didn't throw them out. they are just flat aluminum stock- You could make replacements easily. On the previous page, one is also shown next to the blue floorjack wheel on that pic.

[Hib Halverson]

Originally Posted by WVZR-1

It's an interesting read but then you need to consider the source. Halverson - oh well! He publishes what he's paid to publish.

Actually, I was not paid for that article on the CAC web site. I decided what was published and am responsible for it's accuracy.

"WVZR-1", if you're aware of any incorrect information in that article, so I can correct any mistakes, please post the errors and your documentation to support them.

But even if I was paid for it–let me ask you "WVZR-1"–in your opinion, how would that impact the credibility of the content?

It still doesn't negate the possible + to the increased spring rate. Halverson's #'s for his suspension parts are numbers he was supplied with from production specifications, you don't think there were manufacturing tolerances?

There were, indeed, "manufacturing tolerances". In fact, the tolerances were so large that, during the earlier C4 years, frustrated with chronic differences in trim heights of cars with the same springs, GM finally divided each spring into three "groups". Then it developed the spring shims one finds on the front and rear spring mounts.

The spring suppliers were required to categorize each spring which met the initial specifications into three groups. Some were right at the specified spring rate, some were a bit below and some were a tiny bit above. The spring group determined the number of shims (ft.) or the location of the shims (rr). This system allowed the assembly plant to have all the cars much closer in trim height and was used for the rest of the C4 production.

Obviously, in the front, the ideal sitch is a car with 2 shims because pulling the shims out lowers the car by about 1/2-in.. In the rear a car with 2 shims above the rear spring is desireable because if you move the shims to below the spring you lower it in the rear by about 1/2-in.