[Steve C.]

I presume the AMA specs were with a factory tire. The distance was from the bottom of the rocker panel

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[jhein]

Originally Posted by Steve C.

I presume the AMA specs were with a factory tire. The distance was from the bottom of the rocker panel

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I wonder if the AMA spec is measured from the pinch weld seam?

[Elarson]

Originally Posted by yahooskidoo

Have you driven it some to settle those new springs?

Yup. Tightened all the bolts with the weight of the car on them. Drove around the neighborhood a few times.

I'd expect maybe a half inch of settling but these things are definitely not a 2" drop.

Eric

[Steve C.]

My information came from the Pontiac Historic Services in 1991 along with a copy of the factory order form for my specific car.

Listed as AMA Specifications- Passenger Car.
Pontiac Firebird, 1970
Date issued 2-5-70.

The dimensions are listed in the section for car and body dimensions and there is also a diagram of the measuring points. Listed in the section for height are the specific dimensions for rocker panel to ground. They are measured at specific points on the rocker panel at a specific distance listed from the front wheel center line and the rear wheel centerline. No other specifics given and there is no diagram with a cross section view of the rocker panel.

Of interest...

The Cowl Height is listed at 35.3 inches to the ground. It looks like it's measured at the base of the windshield The Deck Height is listed at 38.1 inches to the ground. It looks like it's measured at the base of the rear window.


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[JLMounce]

Originally Posted by Elarson

Yup. Tightened all the bolts with the weight of the car on them. Drove around the neighborhood a few times.

I'd expect maybe a half inch of settling but these things are definitely not a 2" drop.

Eric

The Hotchkis leafs I run in my 69 never settled. I put the car on the ground, torqued the bushings and it's sat were it's sat since.

Part of the problem is homologated parts. Different cars and option packages had different springs within the same model, not to state different models like the firebird to the camaro. I'm not as versed on 2nd gen's but Pontiac was playing around with getting the windshield out of the wind. They had a tendency to put the ass on the ground a bit further than it's cousin. Heck, they dimpled the 69 axle tubes to make extra room for that.

Point being, if the part is a single sku part based off of a typical spring found on a camaro, it's entirely possible what should be a 2" drop doesn't materialize.

This is one of the reasons I recommend the cat 5 leafs for this car. They are reverse eye which already allows the car to be lowered while keeping a better arc on the springs. This theoretically allows the spring to be able to lower the car further before there's risk of hyperextension. The spherical front eye bearing will keep the inside tire from lifting in the corners as well.

All that said, have you thought about simply running lowering blocks? For an inch or so, I wouldn't worry about the use of those on track.

[Elarson]

Originally Posted by JLMounce

All that said, have you thought about simply running lowering blocks? For an inch or so, I wouldn't worry about the use of those on track.

Hmmm....interesting idea. That would open up the option of adjusting the ride height with different blocks.

Eric

[JLMounce]

Originally Posted by Elarson

Hmmm....interesting idea. That would open up the option of adjusting the ride height with different blocks.

Eric

Pretty common to do this. You can corner weight the car with these as well.

[Elarson]

Thanks for everyone's ideas and info. I have a plan. I'm a little gun-shy to just order new springs, since I got burned by the Detroit Speed springs that weren't as advertised.

Plan A) install 1" lowering blocks and do the Herb Adams modification to the front spring mount which should drop the car by about another 3/8". (I didn't do this the first time around because I thought it would be too much with the advertised 2" drop). Going to raise the front by 1/2" and then see how things look and check ground clearances. If that's not enough, then...

Plan B) take out the lowering blocks, buy the Hotchkis springs that 76TA462 described in post #5 and see how that works out.


Thanks again,
Eric

[Elarson]

Update: I did the Herb Adams mod to the front mount and put in the lowering blocks. It's still not low enough and I don't like how far the springs are out of the axle brackets. Road courses will put lots of side load on those.

So it's time for Plan B...Hotchkis springs. I had a good talk with John Hotchkis yesterday and he was pretty interested in my project. He's going to sell me the springs only; since I have all the other parts from the 2409c kit.

After doing a lot of research, I see the problem. The Detroit Speed springs have an extra leaf and are just too stiff. The Hotchkis springs are progressive.... they compress a bit before all leaves are engaged. Also, Hotchkis has different springs for 70-73 vs 74-81. Detroit Speed has a one size fits all. I have no clue what's the difference.

30 day wait for the new springs so it's on to other tasks.

Eric