Comparing Rear Spring Specifications

[Heg87t]

Hey,

Spent a couple of hours last night wrestling with the rear springs in my 87 T. I had the stock replacement Moog Cargo CC627's in the car and with my B-body front spindles the back is just too high. So I put another pair of used springs I had in the back hoping the rear would be lower. Nope, that didn't work. I think they may have been from my Caprice and not my Regal.

Anyway, started looking on the board here and checking the Moog specs to try and find something that will give me a lower rear. I have found that most people are using the 5413's in the back but also found a 5385 being use. The 5385 has 0.33" less free height but 0.5" more install height than the 5413. What is the difference between install height and free height? Which of the two will give me a lower car?

 

[charlief1]

What was the spring rate on both springs and what was the original application. That will tell you what the installed height si suposed to be for what car. You may be looking at a heavier car so the height may be different.

 

[Heg87t]

I don't know the original application for the 5413 or 5385. Installed height on the stock replacement is 8.5".

Here's the full specs:

Spring # Inside Dia Bar Dia Install Height Load rate (lbs) Spring Rate (Lbs/in.) Free Height Type

5413 5.53 0.593 8.50 740.0 167.0 12.93 Pigtail Ends Recommended board replacement should be about 26" at fender
5385 5.57 0.593 9.00 602.3 167.5 12.60 Pigtail Ends Recommended board replacement # 2


I am guessing that the free height is the uninstalled height and the install height is well... the height installed. I would think if the installed height is within a inch or so of the 8.5" stock they would work fine after installation.

I know there is a formula to find spring rate but there probably is one for install height if you weighed your car at the spring perch and used the specs for each spring.

I just hate to throw springs at it until it looks right.

 

[charlief1]

Spring # 5413, 5385
Inside Dia 5.53, 5.57
Bar Dia 0.593, 0.593
Install Height 8.50, 9.00
Load rate (lbs) 740.0, 602.3
Spring Rate (Lbs/in.) 167.0, 167.5
Free Height 12.93, 12.60
Type:
Pigtail Ends Recommended board replacement should be about 26" at fender.
or
Pigtail Ends Recommended board replacement # 2

It's a little easier to read this way. As you can see the inside diameter is almost the same and wire diameter is the same. The installed height is .5 different but the 5413 spring has a higher load rate so it will be lighter. How ever the spring rate is a better way to figure out what you want. It means that for every inch you get X amount of presure pushing back. With the free height on the 5413 spring it will have to compress more before you get the same response. For a firmer ride use the 5385 and your handling should improve some and the height should be a little higher but not by much.

 

[Heg87t]

Thanks Charlie. Looks like they are pretty close to each other.

I have been following another thread: http://www.turbobuick.com/forums/brakes-suspensions-tires-wheels/287435-rear-springs.html that worries me about shorter free height springs.

Now I am wondering if I can find a spring with a free height closer to the stock 14.75" but still lower the car. I don't think I can get the best of both worlds though...

 

[charlief1]

Thanks Charlie. Looks like they are pretty close to each other.

I have been following another thread: http://www.turbobuick.com/forums/brakes-suspensions-tires-wheels/287435-rear-springs.html that worries me about shorter free height springs.

Now I am wondering if I can find a spring with a free height closer to the stock 14.75" but still lower the car. I don't think I can get the best of both worlds though...

To keep the orginal height the answer is no, but there is an alternitive.:biggrin: Ever heard of buckets? You need to do some reading up on suspension designs in some of the dirt track forums. Try doing a search for smilysracing (may be spelled wrong) and see what's available for the metric chasis. Some good ideas.

 

[ijames]

Here's a good link to some Moog spring info: Moog Springs for High Performance Monte Carlo and G bodies Doesn't have the 5385s but you can easily do the math to add it to the table of ride heights. I ran some old sagged springs from an 86 Caprice for a few years since my car is pretty heavy with me and my trunk-o-junk (4060 lbs going down the track the last time I weighed it and I bet it was 4100 the last time I raced). They picked the rear up about 1-1.5" over the cargo coils. Rode well but never hooked at the track. Finally pulled them and went to the 5391s from an early 80s wagon and the ride height came back to about stock, the ride quality was good, and it hooked way better.