Technical Straight axle set up question

I'm rebuilding the front suspension on my car, a 1933 Plymouth. Previous owner installed his spring hangers himself; not in the original locations on the car.

It's running a Mopar wavy axle and parallel leaf springs.

I've got new custom springs from Eaton and a set of original front spring perches. I'm going to use aftermarket rear hangers.

So, probably a basic question:

Should the springs run 100% parallel to each other? Same as a rearend?

 

Parallel how?
Not all parallel leaf set ups are “parallel”

 

Not sure what you mean? Think about old Chevy or Mopar front end setups (think the 1930s) or '50s era pickup trucks.

Parallel as in twin leaf springs running equidistant from each other supporting a single axle.

 

Way, I did mine.

 

47/55.5 gm trucks have parallel leaves. The springs are not parallel when viewed from the top

do you have pics

 

I can take a pic of the existing set up, but it's what's making me ask this question.

Have you set up a front end like this before? Do you have advice?

What's the reasoning for the GM truck design?

 

Yes I have. I also have a Plymouth axle set up in my parts pile.
The gm frame tapers from rear to front. It’s just how they designed it. The springs match that taper.
One way to check is measure the spring u bolt mounts in the axle.
If you measure the rear 2 holes and the front 2 holes are closer (side to side) the springs shouldn’t mount completely parallel as viewed from above.
You can also measure your frame width. If it’s narrower in the front that the rear, it MIGHT not have springs parallel as viewed from the top

 

Also measure the spring mount width on the frame. Compare front to rear.
Same with the frame rails at spring mounts
Also can mount the springs in the axle and check the width front to rear

 

On that car the springs will run in line with the frame rails and may or may not be perfectly parallel but it doesn't matter as most early frames with parallel front or rear springs had frames that tapered a bit front to rear. If you were putting an aftermarket straight axle under a later model = 55 Chev you might be more concerned with having the springs perfectly parallel just to simplify installation.

 

Parallel leaf springs, whether front or rear are usually not parallel. They usually taper toward the front. It stabilizes things. Helps to keep the leaf springs from wanting to roll over during a turn.

The hole pattern on the spring perch on the axle should tell you whether it's designed to have the springs parallel or not.

 

Connect the front of the springs to the front perches. Be sure the "front" of the both springs are the same length, from the spring eye to the "center bolt" a lot of times the center bolt isn't at the center point on the leaf spring length. The position of the center bolt locates where the axle mounts. Most of the time, a shorter front section and a longer rear section are correct. Mount the axle onto the springs. Mount the rear springs to the rear spring mounts. Some front parallel leaf spring set ups have the shackles at the front of the spring, and other front leaf spring set ups have the shackles at the rear of the springs. Set your shackle position up the way they were designed from what ever vehicle they came off of.

"Parallel" leaf springs simply mean the springs run length wise along the frame, as compared to transverse springs that mount across the frame from one side to the other. It is a directional statement rather then a perfect image statement.

 

From motor-car.net. Frame from a 1933 Plymouth PD. It looks to me as if the front springs are set closer at the front than the rear.

 

Early Chebbies had front perches the moved the springs out away from the frame rails so the springs were not as tapered to the front as the rails were .