Technical 1937 Dodge Rear Leaf Spring Upgrade

1937 Dodge D5 4 door sedan.

Old on top. New on bottom.

Old is 7 leaf. New is 8 leaf (850 lb rate).

The new made springs are for the 40s/50s Chrysler (heavier car) and others. All the measurements are the same. Sole difference is the rear spring eye is not threaded for the old steel Cee Shackles rather using the more modern Rubber bushings and shackles. The Cee Shackles were used on the 37 and many models before 1942ish in part due to a cross member just aft of the fuel tank.

I am lead to believe that a leaf spring rides best flat or with 1 to 2 inches of arch. Passenger side was flat, drivers side inverted. Time to replace. 86 years is a good run.

Doing a lot of research, it seems this particular spring length/rate was used Mid 30s clear up to late 60s on Mopars, and clear up to date on other items like trucks, trailers, other make cars, etc.

(Freshly installed, the new springs are giving me about 2+ a little inches of arch, so, even with normal settling, should be perfect for a long time.)

 

Better view. 86 road years is a lot of flexing and the old springs have quite a set. Spring shops say that spring rate does not change with age but Arch will.

You might have them rearched (Factory arch should be 8.5 inches for MOPARS using this spring) but finding a shop that can...and given the low price of brand new springs...plus the upgrade to one additional leaf...and the ability to convert from those hard to service threaded bushings.....

 

The new part number. Available from lots of places, shop around for the best price. These were under $400 the pair shipped. NOS springs are still available with the threaded eye but its getting darn near impossible to find a matched pair.

 

The old shackles. These were righty tighty on both sides, others may or may not be so I try the socket in both directions and don't round off the head, they can be in the frame sleeve pretty darn tight.

I thought these would be the last of Ma Chryslers righty loosie stuff, but, thankfully it was all normal thread. Heavens know if she stashed anymore backassward threaded parts in there but I think I got them all swaped out now.

 

The new shackles and bushings, Boomerang style/heavy duty courtesy of the OffRoad types.

The old Cee Shackles measure 4 inches CTC. The new Boomerang Shackles (allow clearance of the aft cross member) are sold at 4 inches CTC but actually measure 4.5 inches CTC. Not a problem, thats only 1/4 inch lift out back. New grade 8 hardware, including grade 8 locking nuts were acquired. Some triming and reshaping of the inner shackle arm was required to ensure cross member clearance through out full stroke. Finally, a few washers are acquired to ensure the spring is aligned to prevent bind and breakage. (I used 3/8 thick shackles for strength since I knew I'd be trimming a bit. Not shown, a 2.25 in steel sleeve was used on the center bolt establishing a 2.9 in width across the shackles arms with the bushings compressed)

The bushings shown are rubber, 7/8" outer, 1/2" inner and of a length needed for 1 3/4" wide springs. (EG just a bit longer so they smush up and lock tight in the eye/sleeve and around the bolts.) I did not smooth out the old threads in the frame sleeve as rubber bushing do NOT rotate in the hole....they twist a bit with the shackles turning on the bolt. And those threads are really more round bottom and shallow, shouldn't be any problem at all.

Short leg goes up (Frame bushing) and large Vee faces the rear bumper to maximize clearance and stroke.

 

New and old ride height. (Factory ride height restored!) Remember to leave all the bolts (including the axle u-bolts) slightly loose until you have weight on wheels. Jounce the rear end several times then torque the front eye bolts, snug up the rear shackle bolts to compress the bushings. Finally, tighten down the axle U-bolts.....then go ride.

 

Test ride went amazing. Nimble and stable to 80 mph. And noise plus squeaks, klunks all gone. With the pinion angle restored, all the vibes are gone too. Amazing.

 

When we bought Ol Bessy home she was hotrod low front and rear. (Top photo).
Now she sits like a Grand Lady, stock height out back and just 1 in low out front. (Bottom photo)

 

Old thread, I know, but I'm replacing the shackles in my '37 PT50, and I ran into the righty-loosie situation with the new shackles. The ones on the truck were farmyard replacement rigged, so I don't have them to reference. Does the righty-loosie go into the shackle hanger, or does it go into the leaf eye? Thank you!