2nd Gen Firebird Measurement
 

I got the 2" drop rear leaf springs from Detroit Speed. I finally got the car on the ground and it doesn't look much different than stock ride height to me. Maybe it's an optical illusion from the short tires??

Anyway, if a few of you would be so kind as to measure your 2nd Gen's from axle centerline up to fender lip, so I can compare. See attached picture. Mine measures 16"

Thanks in advance!

Eric

Car is still away, but this is the stock ride height as measured from the underbody, out of the 76 assembly manual.

I don't normally measure from the center cap up but understand why your are. The white car is all original low mileage. The blue one seems to sit correct. The white car has a 235/60 the blue car a taller 255/60.... Hopefully these pictures are helpful.

My 70-73 rear measurements from ground to wheel well lip are around 27 1/2 to 28 inch. Those measurements are from TAs with original springs.

For my second gen (1976) I used the Hotchkis Sport Suspension Lowering Leaf Springs Package - 2409C designed to lower 1.5 in. With the OEM rear leaf shackles my wheel center to fender was 14.5 inches. On dips etc. my exhaust was hitting the road a lot. In the pictures my spacing is now 15.25 inches. I raised the car 0.75 inches by fabbing up longer shackles (the difference in the shackles isn’t even obvious and still tucked under. Not like those foot long shackles of the 70-80s LOL.) Running 285 40 18.

Mine seems to match Paul's measurements.

Nice looking car!

45 years of ownership and changes, and still having an awesome time with it. Thanks.

Thanks for all the replies. That tells me a lot.
I need to look into those Hotchkis springs....sounds like they may be better for road courses than what I have now.

Eric

Eric have you looked a Landrum? ..... We used a lot of the springs for drag racing and they worked great. They also made us several pairs of "custom" street/strip springs. I believe their specialty was circle track.

I'm running a five leaf spring assembly that was designated for the 1975 Chevy Nova police suspension option. No special additional curvature, just a stiffer rate.

Distance from axle centerline to wheel opening lip is 15.75"

I measured my rocker panel height last night. I'm right at 8" so that double confirms all the other observations. I have "2" drop" springs and tires that are 2" shorter than stock and I'm only 1/2" lower than stock. Grrrrrr.....

Thanks....everybody was a big help.

Eric

This is for your road race second gen, correct? They are a bit spendy and I don't know your budget, but I'd talk to Global West about their Cat5 leafs.

PTFB has some nice 1.5-2" drop springs, priced better than the other big suspension companies. I have had them on my 72 firebird along with some of their other parts, been in use for 10+ years & sits very nice, lower than my stock other suspension 2nd gens using factory size tires at about 27-27.5" tall.

Eric

Your post got me to go measure my wife's '72 Camaro that still has the original 53 year old leaf springs in the back. 13.5"! My short (25.7") 275/40/17's fill the wheel well as shown in photo below.

I've been contemplating getting new rear springs to alleviate the rear end sag, but have been hesitant on what springs to get to lift the rear .75 - 1" in the rear.

Front springs are 2" drop Eibach coils installed back in 2001.

I talked to PTFB and he thought their GT Pro leaf kit springs would be my best bet and they come with shackles that have two positions to give me easy adjustability if I needed more lift:

https://static.wixstatic.com/media/8...e2413a~mv2.jpg

I might cheap out as I need to replace the 7 year old tires this spring anyway. Currently running 275/40/17's (25.7") and go with 255/50/17's (27.2") to get the .75" that I'm looking for. Fronts are currently 235/45/17's (25.3"), but looking at 245/45 or 225/50/17's this time to gain maybe .25" up front.

Speed bumps and highly crowned rodes are a b!tch....

These are 235/55R17 with what should be, stock height springs on mine.

When I obtained a copy of the AMA specifications for my 1970 2nd Gen they stated this as the factory ride height. These are height dimensions from the rocker panel to the ground in two places. The forward point on the rocker panel is located 36.3 inches from the front wheel centerline and it is supposed to be 6.5 inches off the ground. The rear point is 16.1 inches from the rear wheel centerline and is supposed to be 5.5 inches off the ground.


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Did it indicate the tire size for that? Seems a bit low, but considering that might be the spec with the base F78/14 tires, then correct.

Have you driven it some to settle those new springs?

There's a pretty big discrepancy between the numbers in these two posts. Below is what I found in my 1970 assembly manual. The car they show is a 1st gen but if you look in the bottom right area of the page it says it's for 1970.

https://i.imgur.com/BMVfdBOh.jpg

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?

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

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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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.

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.

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

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