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Leaf spring

2K views 23 replies 6 participants last post by  Bob37pont 
#1 · (Edited)
I have a 1937 Pontiac Deluxe 6 4 dr sedan. It is eguipped with a mid 70's Camaro rear axle.
The axle is mounted on a 1 1/2" block above what I believe are Camaro leaf springs. The springs are mounted to the stock rear shackle, and I believe the front eye mount has been moved on the frame. With the weight on the wheels the rear shackle moves all the way back up to contact the frame rails. 70 psi in air shocks keeps it from constantly riding on the frame.
When I jack the car up to remove a tire, the axle drops 9-10 " and the rear shackle is then vertical.
My thought is these springs are too long and too weak.
How do I go about measuring for a replacement spring?
I can get the eye to eye distance with the rear shackle vertical and the approximate distance the down axle should sit in relation to a straight line between those measurements, as well as the axle center from that same straight line. I know the spring will need more arch than what I can get from these measurements.



I have sent this info request to Eaton Detroit springs, waiting for their reply. Their measurement form has you measure a spring removed from the vehicle.
I just heard from Eaton Detroit, they want me to disassemble a spring following their measurement chart. Not sure this will give me the correct spring.
I guess the question is, how much arch do you allow for movement to get the rear axle height correct?
Does anyone have a mid 70's Camaro? If you do could you measure the leaf spring distance eye to eye in a straight line, and also along the arch? Also how many leafs? Thanks.
I guess I need a rear axle weight for my car, and then find a similar weight rated car with a close spring size.
Probably time to head for the junkyard......
 
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#2 ·
I had about the same problem with the '39 and enough blocks to put the U-bolt ends to close to the ground. What I did was to switch to air bag rear suspension so when people climb in the back it's just a push of the button to level the ride again. Other times I used a local truck spring shop to re-arch the springs and they were spot on. Might consider adding a leaf if necessary.
 
#3 ·
Don't you need to go with a 4-link to use airbags?
I'll have to ask around for a local spring shop.
If I get these springs stiffened & re-arched to where the rear shackle is off the frame the body will be raised up a bunch!
This is how the rear shackle sits now, I put the rubber in the frame to keep it from squealing!
 

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#7 ·
The Posies stuff is neat, also $$! I'd have to call to see if the '37 Chev stuff will work on my Pontiac. I like that it incorporates a 3" drop, wonder if that is with the axle above the spring.
I had seen these sliders earlier, might be an easy fix without raising the car.
There are some Camaro springs of different weights listed on the speedway site as well, I'll have to take some measurements and do the weight calculation Eric mentioned.

Yes, I went with triangle 4 bar. Could not get the car down with leafs and it's still a bit high with bags but couldn't go lower without cutting into the back seat. Step one would be to find a local spring shop. Where I lived in Fla we had an excellent one that worked springs with ease.
Working on finding one.

Shackle angle in the photo doesn't look that bad, looks more like the use of possibly the original frame bushing hole combined with the short Camaro shackle is a lot of your problem.
Have you considered just making a longer shackle?? You can buy longer shackle kits too, been used since forever to raise cars for bigger tire clearance.

If you decide you are going to replace the spring, the very FIRST thing t=you need to do is go to somewhere they have a vehicle scale, like a truckstop or Agriseed/Farm lot and weigh the car....weigh just the front tires on the scale, the whole car, and just the rear tires so you know the weight on each axle and the total weight.
Can't choose a new spring without knowing how much weight it carries so you can use the spring rate to calculate how far it will flatten out.

Stock 70's Camaro/Firebird is typically 4 or 5 leaves depending on standard or sport/Z28/Trans Am and very close to 160(standard) to 175 lbs/in.
The pics are deceiving, the spring eye is laying on the rubber pad on the frame rail.
The slider Rip mentioned looks like a decent option, I really don't want to raise the car.
I have an truck scale available locally, plan to weigh the car as you described. Speedway also lists some Camaro springs with different weight ratings, up to 225#.
What's the formula for calculating the spring rate with the axle weight?
I'm going to measure my springs length from front to the centering button to see if they will match what Speedway lists.
 
#6 ·
Shackle angle in the photo doesn't look that bad, looks more like the use of possibly the original frame bushing hole combined with the short Camaro shackle is a lot of your problem.
Have you considered just making a longer shackle?? You can buy longer shackle kits too, been used since forever to raise cars for bigger tire clearance.

If you decide you are going to replace the spring, the very FIRST thing t=you need to do is go to somewhere they have a vehicle scale, like a truckstop or Agriseed/Farm lot and weigh the car....weigh just the front tires on the scale, the whole car, and just the rear tires so you know the weight on each axle and the total weight.
Can't choose a new spring without knowing how much weight it carries so you can use the spring rate to calculate how far it will flatten out.

Stock 70's Camaro/Firebird is typically 4 or 5 leaves depending on standard or sport/Z28/Trans Am and very close to 160(standard) to 175 lbs/in.
 
#11 ·
add a leaf

WE have 36 an 37 Pontiac's. I have never had the 37 project up on the hoist. the 36 has springs that are narrower and more leaves than the camaro parts on the racks. some 4 X4 forums tell what bone yard springs will swap. I reversed the arch (reversed eyes) in my Model T front main leaf using a Hf tubing bender. chalk the shape then gradually work along the spring enough times. I don't know id the camaro springs would fit thru a HF tubing roller to do it faster. The 36 is stock straight 8, the 37 had a SBC and chevy pickup rear with the Pontiac wheel lug pattern
 
#12 ·
WE have 36 an 37 Pontiac's. I have never had the 37 project up on the hoist. the 36 has springs that are narrower and more leaves than the camaro parts on the racks. some 4 X4 forums tell what bone yard springs will swap. I reversed the arch (reversed eyes) in my Model T front main leaf using a Hf tubing bender. chalk the shape then gradually work along the spring enough times. I don't know id the camaro springs would fit thru a HF tubing roller to do it faster. The 36 is stock straight 8, the 37 had a SBC and chevy pickup rear with the Pontiac wheel lug pattern
Adding a leaf along with the sliders may be the answer.
Next question where does one get a single leaf to add, a pair of junkyard to disassemble?
 
#13 ·
This afternoon I pulled a wheel to get some better pics & info. The wheel/axle drops 6" when the car is jacked up until it is off the ground.
Measuring the spring eye to center pin confirms they are Camaro, 24" from the front, 30" from the rear. Speedway offers a good selection in different weight ratings.
I still have to get the car weighed so I can calculate the correct spring rate.
It's apparent to me the front spring eye mount has been replaced, while the rear shackle is mounted in the stock frame hole.
The pics show the spring both weighted and hanging free, I did let the air out of the air shocks.
When there is weight on the axle the leaf spring is almost flat, with the rear shackle pushed back tight against the frame.
I normally run the air shocks ~ 75 lbs, this gives me about 1/2" clearance between the rear eye and the frame. Sliders might allow the spring to move a bit more.
I'm tempted to get the sliders and install them with the current springs to see how that works.
All of the speedway listed springs are described as having 6 1/2" true arch. Does this mean that is how the spring sits unloaded?
Once I get the weight I can better figure out what weight spring I need. From what Eric mentioned standard Camaro springs were either 160 or 175, I betting these are 160.
First pics show the spring loaded, axle on a jack stand.
 

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#15 ·
first thing I have to comment on is the very last picture.....holy unsafe, Batman - no u-bolts around the axle tube!. The way the spring is clamped in the perch with just regular bolts is a very poor way to do it. Even when the factory started to cheap out and do this in the 1970's on Camaro/firebird and Nova they always used 1 u-bolt per side and just 2 regular bolts.

Second thing is that rear shackle angle when spring is unloaded....it should not be vertical like that, it should be straining forward almost to the point of the spring eye touching the frame(the reverse of what your dealing with when it is loaded).
My guess is the use of the convenient original bushing hole in the frame created this problem....correct use of that original frame hole would have meant the front spring hanger would have to be moved forward 3" or so, and that would mess up wheel centering in the wheel well. Correct fix here with the Camaro spring is to correctly locate a new rear bushing mount hole. Slider might be the easiest way to fix that.
The standard Camaro leaf pack is well known for going flat and sagging out, so they probably do need replaced...but to fit and function as they should you really need to do something about that rear shackle location problem.
 
#20 ·
Magic Number!

Got the car on a certified CAT scale at the local truckstop.....
She's a not-so-svelte 3,720 pounds! :eek:

Landrum lists a 225# spring rate for vehicles weighing 3000 to 3500#.
And a 250# spring rate for vehicles weighing 3600 to 3800#.
These springs with the "A" suffix have a 5" arch.
I checked under the car and with the air shocks at 75# I raise up about 1.5 to 2".
I called Landrum to get the spec on static compression for the weight, but the owner/tech guy is on vacation. :( I'll call him next week.
My thought is the lighter spring rate might get me closer to my stance without excessive lowering blocks, and still give me a compliant ride.
 
#21 ·
More weights

I went back to the CAT scale and weighed both axles with the car set pretty much centered (by eye) on the wheelbase.
Front axle: 1660 lbs.
Rear axle: 1820 lbs.
Total weight using the 2 pads of the scale: 3480 lbs
Total weight using a single pad of the same scale: 3720 lbs
I've not been able to contact the owner/tech at Landrum, I'll try again Monday.
I'm thinking the 3000 to 3500 spring will be right, But I want his opinion.
I've not been able to find a rate calculation for leaf springs based on vehicle weight, as opposed to measuring the springs themselves.
 
#22 ·
So I keep leaving voicemail at Landrum Springs with no call back....
Called tech support at Summit and was told that generally the 'racing' spring for a specific weight is a bit softer than a 'street' spring. Given my axle weights he felt the 225# rated spring would give me a more compliant ride on my Pontiac.
Springs & shackle sets ordered, as well as a set of U-bolts! :)
 
#23 ·
Springs arrived Thursday afternoon, busy schedule kept me tied up until today ( I'm retired, I don't know how that happened!).
Took about 4 1/2 hours, surprisingly no bolts were stuck in place.
As I got the u-bolts ready I realized,after drilling the 7/16" holes to 1/2", the brake line runs tight across the axle, with a welded hold down tab right in the center.
Pretty sure this assembly was not designed for u-bolts.
Quick trip to ACE for grade 8 1/2" bolts and everything went together smoothly.
I ended up gaining 1" of ride height with the 1 1/2" lowering blocks in place.
Put about 40#'s in the air shocks and gained another 1/2", the stance looks good. It's now 2 1/2" higher in the rear that the front, measured at the running boards.
The suspension now has some travel and a smoother ride.
Additional bonus I don't have the jack the car 12" in the air to remove a wheel, the springs don't sag with the weight of the axle!
 
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