[Bl1tzw1ng]

Originally Posted by Z Code 400

Will,

Thanks. I have some real challenges replacing springs with headers, but there are some ways around that. I think cutting the existing springs would be a good choice to start with as it doesn't cost anything and the results are immediate.

Who makes blocks for the rear???...Robert

Before I swapped to a different rear suspension, I couldn't find f body specific lowering blocks. You could just get the width and length dimensions and order some from Summit or the like. I think I picked up some Afco ones for maybe $15? Don't forget to get some longer u bolts. I used 4 u bolts instead of u bolts and t bolts so I don't know if stock length t bolts would still work.

I would suggest removing the rear spring pads completely and fabbing up some plates for the rearend mounts though. I had used 1/4 steel cut to fit inside the perch with the centering hole in them. I then mounted the plates with bolts to the perch. I could be wrong on that theory but the combination of the block and the rubber pads made me uneasy because of potential movement and just too much play for my liking.

[Z Code 400]

Jay,

Thanks for those tips. I'm putting them all down in my notebook...Robert

[Bl1tzw1ng]

Here's some info on the Herb Adams mod that was mentioned earlier:
http://www.nastyz28.com/forum/showthread.php?t=64395

I am looking for the lowering block one but haven't come across it yet.

[Bl1tzw1ng]

Ok just found it:

http://www.nastyz28.com/forum/showthread.php?t=120329&page=2&highlight=lowering+ %2Aplate

[Z Code 400]

Very cool....

Thanks....

[Z Code 400]

According to the information I have found on the stock springs for a 1975 Trans Am, the spring has a square/tangential end configuration, 4.090" inside diameter, 0.672 wire diameter, 11.50" loaded height, 1942 lbs load rating, 294 lbs. spring rate and 18.11" free OAL.

One thing I remember about Herb Adam's articles is he advised against progressive rate springs and heavy spring rates. So, in my mind, a spring with a 10.00" loaded height would be about correct to give me a 1.50" drop and a slight increase in rate.

The Moog #6440 spring features 4.080" inside diameter, 0.725 wire diameter, 10.00" loaded height, 2730 lbs load rating, 463 lb spring rate and 15.875 free OAL.

Any thoughts?????

[Skip Fix]

MOOG CS 5662 or CS 5664 work pretty good.

[Z Code 400]

Hey, Thanks, Skip...

Herb Adams seems to feel that lighter springs allow the tire to better follow the road contours, making the car more stable at speed. he likes the 350 lbs Trans Am/Z-28 springs for this application. I was shocked when I called around yesterday that most springs for a second generation car are 700-800 lbs.

I have driven a few of these Firebirds with the heavy springs and notice a tendency to 'sidestep' over surface irregularities in hard turns...something I want to avoid on my car.

Ever notice this????

[Z Code 400]

Originally Posted by Skip Fix

MOOG CS 5662 or CS 5664 work pretty good.

#5662 I.D. 4.085 - wire 0.740 -Loaded OAL 10.750 - 706 lbs/inch - 13.149 Free OAL - 2370lbs

#5664 I.D. 4.085 - wire 0.760 -Loaded OAL 10.750 -767 lbs/inch - 13.184 Free OAL - 2618lbs

I'm thinking the Moog #5606 might be close to what Herb was doing with the second generation cars. It is actually a G-Body Monte Carlo SS spring, but quite a bit more stout than the stock Firebird/Camaro springs:

#5606 I.D. 4.085 - wire 0.690 - Loaded OAL 11.000 - 420lbs/inch - 14.637 Free OAL - 2142lbs

Compare this to the stock front spring, according to the Moog catalog, on a 1975 Firebird without A/C:

#5384 4.090" inside diameter, 0.672 wire diameter, 11.50" loaded height, 1942 lbs load rating, 294 lbs. spring rate and 18.11" free OAL.

And the front spring for the 1975 Firebird with A/C:

#5376 4.090" inside diameter, 0.671 wire diameter, 12.00" loaded height, 1886 lbs load rating, 319 lbs. spring rate and 17.92" free OAL.

Another interesting spring is one designed for the S-10 truck:

#5658 I.D. 4.085 - wire 0.690 - 10.750 Loaded OAL -579lbs/inch - 13.176 Free OAL - 1968 lbs load rating...still a bit more lbs/inch than I would like to see up front, especially with 125-135 lbs/inch springs in the rear.

Still thinking this one through....Robert

[amcmike]

pro-tour79 is also working on bolt-on a bolt on slider kit. There are benefits to using sliders as opposed to shackles, but they will also by design, drop the rear some. So with the Herb Adams mod and sliders, you might not have to use lowering blocks at all.

[Z Code 400]

Mike,

That's not a bad idea. This car handles so good and is so neutral, that I hate to screw with the spring rates too much. The steel suspension bushings up front will minimize deflection and I am already running Koni adjustables at all four corners, so I would be open to checking out this slider arrangement before swapping in lowering blocks....Robert

[Z Code 400]

After some research, I discovered that the Moog 5658 is used extensively in Buick GN and Monte Carlo SS vehicles to lower the front end roughly 1.250" to 1.500" overal; right where I am aiming for without going up to a 600-700lbs/inch spring rate like the Eibach's, Hotchkis and Global West's all have...Robert

[Z Code 400]

This afternoon, I mocked up the front suspension without springs and took some measurements.

With the 255/60/15 on a 15"X8" wheel with 4.00" backspacing, I adjusted the ride height to 28.0" from shop floor to fender lip. This also gave a 15.0" measurement from centerline of spindle to fender lip and 2.00" from top of tire to fender lip. However, in this condition, I only have 1/2" from factory rubber bump stop and the frame.

The distance from the upper spring seat to the lower spring seat is right at 11.00" so a spring that yields 11.00" loaded would be about correct...Robert

[Z Code 400]

Ok,

Here are a few photos where I want the car to sit. This is with 28.0" between the shop floor and the front fender lip, 15.00" between the centerline of the spindle and the fender lip, 11.00" between the upper and lower spring seats and 1/2" between the lower control arm snubber and the frame.

Doesn't look that low, does it???? Don't focus on the distance between the sway bar and the snubber, look farther back at the distance between the snubber and the frame. I can get my index finger in that space and nothing more.

using the formula (spring rate divided by 1800) and the measurements that I took, it would seem that an 11.00" loaded height spring would fit the bill. I looked at several Moog springs and came up with the following close matches:

#6450 4.080 I.D. / 0.703" Wire Diameter / 406 lbs/inch = 11.500" loaded height

#5006 4.080 I.D./ 0.687" Wire Diameter / 355 lbs/inch = 11.810" loaded height

# 586 4.080 I.D. / 0.718" Wire Diameter / 432 lbs/inch = 11.900" loaded height

Decisions, decisions, decisions...Robert

[Skip Fix]

I like a stiffer front spring personally. Reduces brake dive on hard braking that unloads the rear allowing brake lock up intermittently.

My preference 1 1/4" TA-Formula front bar. 700 lb front springs. stock rear springs 5/8 rear bar. Stiffer rear bar would pick up the inside rear tire loosing traction in a tight turn or angled driveway. Bilsteins all around.

Some spring shops can "de arch" your springs and not change the rate but lower it.

[Z Code 400]

Wow!!!!!

700lbs/inch is a lot of spring up front......Do you have any ride height measurements when you used that Diesel S-10 spring?????

[Skip Fix]

I sat perfect in a iron headed 383 4speed/scattershield Camaro, and the have tighter wheelwell than Firebirds.

[Z Code 400]

Wish you had a bumpstop measurement....:-)

[pro-tour79]

Originally Posted by Z Code 400

Wow!!!!!

700lbs/inch is a lot of spring up front......Do you have any ride height measurements when you used that Diesel S-10 spring?????

what are the basis for "700lbs/inch is a lot of spring up front"?

[Z Code 400]

Originally Posted by pro-tour79

what are the basis for "700lbs/inch is a lot of spring up front"?

Riding in a car with that much up front.....I felt that 580 lbs/inch was plenty, almost overkill in a second gen....Robert