Spring or frame problem?

[EZLIFE]

Why does the left rear of my car sag? Do I need to replace the spring?
The front of my ’31 coupe is level, but the left rear sags down about 1 inch. (Measured at the fenders and bumper). I will soon be pulling the rear end out to install a Mitchell Overdrive and wondering if I will be able to tell what might be causing the tilt? Looking for ideas on what to measure or look for as I remove the rear end.

[Chuck Sea/Tac]

Shackle wear, the spring center bolt not in place, broken leaf, or worn out springs, are some common causes. I added a metal shim on one side next to the center bolt, for a short term repair.

[Conaway2]

Could be the spring or frame. I doubt you’ll need to replace a spring. While you have the rear end out, it’s a great time to take an extra day or two and drop the rear spring to refurbish it and check the spring shackles and bushings - especially if the spring appears to be very dry and rusty.

Check to see that the rear spring is centered in the rear crossmember of the frame. The square head of the spring bolt (goes through the center of the. Spring leaves) fits into a square hole in the cross member. Sometimes the spring has shifted away from center, causing a sag.

Or, the frame may be sagging. This usually happens on the driver side near the rear motor mount and is fairly common on Model A’s. Straightening the frame is not difficult and can be done with the body on the car…..but that’s a different discussion. Search this forum for posts on how to do this.

You will need a spring spreader to safely remove the rear axle. Once it’s off, you can slowly remove the rear spring by loosening the nuts on the two U-bolts. It’s a very good idea to wrap a couple of chains around the spring as well as you can when you lower the spring from the frame. The spring bolt is often very rusty or sometime broken. Use a good penetrating oil on the spring bolt nut before you try to remove it. It may break if it’s corroded and the spring leaves will go flying, as they’re tightly compressed. I like to keep the spring compressed with chains or C-clamps while removing the spring bolt and replace it with a length of threaded rod and nuts and slowly remove tension on the spring.

Wire-brush each leaf and grind down the ridges near the end of each leaf where the leaf on top has gouged a ridge over time. I paint each leaf with rust-Oleum black enamel and then lube each leaf with a moly-graphite grease. Others will have other suggestions for a lube. Some A owners also add strips of teflon tape between the leaves before re-assembly.

Reassemble everything with the threaded rod holding the leaves in line. As you tighten things up, you’ll be able to reinstall the two clamps on the rear spring. I use C-clamps again as the leaves are compressed. This can be a tedious job, as the leaves will want to slip around as you tighten the nuts on the threaded rod. Once everything is compressed, re-install the center spring bolt, and you’re almost ready to re-install it.

Replace the bushings at each end of the spring - the old ones can usually be removed with a hammer and punch - do the same with the bushings in the spring perches on the end of each axle housing. If the bushings are stuck, you can cut a slot in them with a hacksaw - this usually works. New bushings will need to be reamed. Most vendors sell a drill bit for this - I believe it 1/2”. Install new forged shackles and grease fittings on each end if you can find them. Then whenever you’re ready to reinstall the rear axle the spring is all set to go.

A freshly re-conditioned spring will make the ride softer and you won’t be hearing squeaks.

Good luck -
Jim

[Big hammer]

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I left the spring on the axle when I put the overdrive in, slide the rear end out, c-clamps on the spring, stood the drive shaft up with the spring on the floor. Much easier to install for me with it standing on the spring ! When you reinstall the spring the center spring bolt head needs to fit a hole in the frame, draw the u-bolts nuts up evenly you could tighten the right side up more if needed to level your car. I didn’t need the extra heavy duty spring spreader