[Tinindian6702]

I took my 67 firebird to the spring shop today. The car has 3-leaf leaf springs installed in what look like mono leaf perches. (Not too deep) The shop wants to replace them with 4-leaf leaf springs. They saqy that they can do it by not installing the rubber isolator pads. They say the are for spacing only and don't do anything. Is that true??? What is their purpose??? Tahnks

[Tinindian6702]

Anybody have an opinion??? Thanks

[getmygoat]

Since they are rubber, and sit between the spring and the body (or rear?), I assume they provide some vibration damping.

How reputable is your spring shop? They are professionals.... Do you trust them? If not, maybe you should find another shop.

[Tinindian6702]

Tahts what i thought. They are reputable i think they have been there for 60 years!

[guccieng]

they are not 'spacers' in the assembly manual, but 'isolators' for noise, vibrations, and harmonics. i have my camaro on the performance side of the spectrum and run no isolators at all; steel on steel. i have no issues with it. if you're looking for performance, the only thing rubber will do is distort and cause unwanted movement. i plan on running the poly isolators on my bird with the same spring setup. the poly acts like more of a spacer than an isolator in that they don't deflect very much.

[HWYSTR455]

That is THE setup, sounds like they know what they're talking about. Using a mono-leaf perch with multi-leaf springs is the only way to go with high-power application, because it's the only way to positively locate (and keep located) the rear. I've seen cars that the track that have actually slipped the rear forward off the pads on a launch.

I my case, I had to use a longer spring pin, and slightly open the perch hole. I do run the lower insulator, but I could have probably gotten away with just a thin shim to take up the space.

If you're at the point of going through this, take whatever extra steps required to move away from using the upper isolator and positively locating the spring to perch. If you can, get rid of the T-bolts and use U-bolts in both locations too.


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[Tinindian6702]

What was the reason for using a longer spring pin and opening the perch hole???

[HWYSTR455]

So the pin passed through the perch hole completely. Once you look at it you'll see what I mean.

[Tinindian6702]

If you are talking about the bolt that goes through the springs in the middle, My spring shop says that he should countersink the bolt into the leafs????

[HWYSTR455]

Countersink the bolt into the leafs? No clue what he is saying, but that center bolt on the leafs locates the spring on the perch. The top of the bolt is actually a 'peg', and fits into the hole in the perch. Here's a pic of some standard leaf spring perches. Note the hole in the center where the 'peg' goes through. Some call the 'peg' a centering pin. Those pins come in different lengths depending on the number of leafs, and also come in different diameters. In my case, the pin I used was slightly larger in diameter than the hole in the perch.

[Tinindian6702]

Just checked, my perches have no hole in the middle!