Working on 33/34 frame. I'm looking for some info on rear springs. If I could find a chart or something that told the arch of various springs when mounted in the shackles - I'd be in a much better spot if that exists. If I could find info of the above cross referenced to the required perch distance that corresponded to those springs I'd be golden. Then I'd know where the top center sits and where the outer eyes are in relation to axle center line. Trying to set this up (see pic, mocked up at desired ride height) - I think I will need a flatter crossmember but since I can't find the above info, I don't know for sure. Maybe I just need to lower the perches. The C notch isn't a problem. Thanks guys!
I made a rig where I could load springs and check the deflection. With one you can apply the sprung weight and measure the ride height. I have found the 37-40 front springs are very good as to ride height and rate. Most importantly, they are narrow so they will fit between the backing plates of later rears. Most have a spring rate of about 130#/in /side. You can fnd one and measure the arch and if you know the weight you are going to support, you can figure the drop. I made a load cell from a wheel cylinder. It is handy to weigh cars/engines/etc. My roadster weighs 1060 total on the rear and the unsprung weight is 360.
Thanks Andy! Your load cell is the bomb So what's the spec dimensions on that spring ? Loaded eye to eye and loaded arch height? "If I can find one" - I guess that's my problem. I need to start with something. I have one here mounted up in another 34 5 window but zero idea what it's from and it's pretty wide, too wide for this one.
I dunno about the arch height, but my '33 spring perches are 49-inches c-to-c. Not sure if this info helps.....I flattened the shit out of my rear x-member to get the ass end down.
Yea that helps a bunch. probably what I have here on the other one maybe I can get a positive ID on that from your info. Too wide for Elvis ( red one) Arch height available?
I editted my post....49-inches is the perch c-to-c. I can go take more measurements late tonight if you're not in a hurry.
I'm sure they could, but I need to tell them what I want the way they want to have the info spoon fed to them. They will want free eye to eye and free arch, and free eyes to center bolt. This is the problem because I don't know where to start to get where I need to be. Here's how this feels to me if i were getting directions - go down this road and turn left exactly 5.4 miles before the dead end. I guess you'd need to go exactly 10.8 miles out of your way to find out where to turn.
I took some measurements for you. Centers eye to eye unloaded. 34 5/8 Centers eye to eye measured along bottom. 40 3/4. Rough measurement. Arch from bottom of eyes to bottom of center. 10 Width 2 Mount center to center 42 1/4 I should have gotten center thickness and eye diameter. The springs have safety spring doublers and are grooved for grease. The center bolts have grease fittings and you grease them and the grease goes between all the leaves. They ride great.
Thanks Andy ! So the axle mounts are 42-1/2" to 42 1/4" and you spread the spring about 5 inches to mount it- sound right? Am I following here? It's almost flat when loaded ?
I got this from Bass's coupe thread. On that build thread he said this was a 39 spring, in another spring thread a year later he said it needed more leaves to stop bottoming and stiffen it up. Spring Looks almost flat in this pic with axle perches at 42.5
Same car ( thanks Bass) however im at a loss as to how the leaves get taller but the spring gets flatter, and the car gets lower. However I still can't get the perch heights to axel CL relation from these pics.
The picture of the bare chassis is from before the spring had any real weight on it, and before it had "settled". The engine placement in an early Ford is pretty far back, compared to most other (modern) cars. I feel that this is why the rear spring needs to be much heavier than the front spring. Look at the difference between a front spring pack and rear spring pack on an original Model A, '32-34, or any of the later Fords up to '48. Big difference in the thickness of the individual leaves and width of the spring pack. Using the '37-40 front spring in the rear of a hot rod can work pretty well, but they are pretty soft in my opinion compared to an original '28-41 rear spring. On my '29 coupe, the rear spring rode pretty well at first, but the car started sagging in the rear pretty rapidly from the very beginning. It eventually got to the point that the main leaf was basically flat, and was starting to show signs of arching the opposite direction at the ends near the eyes. When I rebuilt/updated the car a few years later, I put a NOS '37-40 front spring on it, but added a bunch of leaves to try to stiffen it up and prevent sagging. There was only a slight difference in ride quality...just the slightest bit stiffer...but that actually made it ride better. It still settled a bit, but not to the extreme that it had before. Honestly, my '29 Roadster rides a little better than my '29 Coupe, and it's got a Model A rear spring. Andy touched on one of the keys to getting a good ride out of a transverse leaf....grease between the leaves. Do that and use a good set of shocks, and you'll be surprised how well a buggy sprung hot rod can ride.
Thanks bass! Later today, after the family festivities, ill make and post a drawing without dimensions and maybe you guys can help me fill in those dimensions.
The spring perches mounting relative to the axle centerline is determined by the pinion angle (3 degrees up) when using 35/6 bones. The spring hanger center line should be parallel to the crossmember/spring mount (non-binding). Rotate the axle to the desired angle and tack weld. I would think each chassis would vary depending on the motor/trans installation.
I believe Posies makes a rear spring "40 front" ( styled after the front spring of a 40) $250? They also make an adjustable spring perch. For both height and angle,I used it before,works great!! This is ideal for pinion changes and height adjustment. Their mini catalogue used to list the spring perch distance dimensions,I'm sure that info is on their website as well. Anytime I had any question their tech guy was very helpful.
What's missing is the arch measurement and in a loaded configuration. 36 bone hangers pretty much lock the perch height to axle center height. However fabbed perches can lower the perch in relation to axel center line and lower the car, and raising the frame crossmember mount also lowers the car. In other words, frame mount further from ground or eye mounts closer to ground lower the ride height, or opposite for raising the cars ride height.
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