With a parallel leaf spring set up can you increase the wheelbase bij just moving te axle back on the parallel leaf springs or would that affect the springs travel or load to much ? On my 33 Plymouth chassis I'm looking for a 4 inch longer wheelbase.( rear body will be custom) Ik can cut the frame and ad the 4 inch or just move the axle back. I have no experience with parallel setups and the search did not help.
The rear axle perches locate on the spring perch bolt that holds the spring together. You can move the whole leaf spring assembly back 4 inches by either relocating it on the frame or lengthening the frame but you can’t just move the axle back 4” on the leaf pack.
I have seen "axle relocation plates that put the axle offset off the center , I can fabricate them but don't know if 4 inch is to much ? Something like this :
From an engineering standpoint, it won’t work the way the factory intended, but actually could work. You will loose suspension travel if you don’t extend the rear spring shackles. That could raise the rear up. Best option is to leave the spring section alone and add inches ahead of the front shackle.
I moved the rear axle center line back 2” on the Comet. I could have done it by redrilling the spring plate but I decided to order new leaf springs. I ordered a pair of stock length springs but had the spring shop punch the center holes 2” farther to the rear from stock. I also had them reverse roll the front eye to lower the car. I fabricated new spring plates that incorporated the lower shock mount in the stock location. Original rear shackles were retained, the car rides great and I have more tire clearance in the wheel opening.
how hard would it be to move the front spring hangers back, and lengthen the frame just ahead of the rear shackles? it might help to post some pics because most of us are not familiar with that chassis...
It would not be a problem but here in the Netherlands we are not allowed to cut and weld a chassis( we can do if we do it invisible ) tech inspection is a pain over here
Then you could use the relocation block shown above. One issue I see, would the rear still be an acceptable distance from the “curve” in the frame?
just musing here, what is the hole offset from center of spring? could the springs be turned front to rear? (2" offset would move hole 4").. if eyes are same..
Thoughts....to use what you have, and seeing as "rear body will be custom", lengthening the rear rails and moving things back makes things easiest. If you aren't allowed to weld the extended rails on, how about fabricating some extensions that can be bolted on to the existing rails. If done properly, it should/could/might work and look just fine....
Per the rules on chassis mods in the Netherlands I can see that you have to be careful as to how you do the mods so they will pass inspection. If I were to use the flat plates that you fabricated I would put a proper U bolt around the plate and the spring on the far side of the pin from the axle to make sure it stays in place. If you are changing rear axles you could fabricate extended spring pads similar to these that are intended for 47/54 Chevrolet trucks to center the rear axle. They obviously would have to be long enough to move the axle back but you could also adjust the ride height with how thick they were between the axle and spring and not have to add lowering blocks.
'33 Plymouth springs are quite long and also skinny. I am pretty sure the spring bolt is not in the center. Sedan springs are different than coupe springs. Coupes have the eyes reversed from sedans and sedans have more leaves. Only disadvantage of turning the spring around front to rear is you will have more spring wrap up when spinning tires and less wrap up on hard braking. Not sure what you are building but if it is a sedan spring and you are building a lighter than stock car, cut a leaf or 2 off just behind the axle pad so you have more leaves in front of the axle than behind. Works like traction bars and softens the ride at the same time. I used sedan springs in my '33 coupe and reversed the main leaf eyes and removed 1 leaf plus have 2" lowering blocks. Measure your spring and see where the center bolt is. Dave
What ever distance you move the front brackets, you need to move the rear brackets the same amount in order to keep the spring functioning correctly. 4" is a long way to move an axle without moving the center bolt on the leaf spring. However, you could drill or punch a new center bolt location on the main spring back the full 4" (which may cause issues with the other springs). I would also then be concerned that the axle is going to hit the frame as the suspension moves up and down. Shifting an axle back in a frame hump 4" might put the axle pretty close to the back edge of the axle hump on the frame. I've moved the holes in the spring perches 2" before, resulting in moving the rear axle on the springs 2" without issues, but 4" is really pushing it IMO. You can probably order new leaf springs with the correct front and rear segment lengths to meet your needs, but the axle hump on the frame could still be an issue. Another possibility would be to move the spring mounting points on the frame to where they need to be (the hump may still be a problem). Gene
Looks like you have lots of good options. Custom springs, or flipped around backwards for a different offset are pretty easy options. As others have said 4" is a lot to do with just the perches, but it it is bolted in properly with attention given to the centering bolt it should be doable. Do you have any pictures of the chassis? Spring perches are usually pretty easy to move weather they are riveted or welded on too. Just pop them off and re attach them where you want them. Then it's all factory parts with no funky engineering and replacement parts are that much easier to get.
I’m gonna take the body off the chassis in a few.weeks when my other car is finished. Then i can see what my best options are. Thanks for all suggestions
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