31 Model A rear spring
 

I have a question concerning the rear spring on a Model A, vs the rear springs on a normal/newer rear leaf spring car. On the regular leaf spring car, if you take the weight off the rear axle, you can disconnect the rear springs from the body/shackles, and remove the axle and springs without issue. Why is it so dangerous to do that with the Model A. If you take the weight off the rear axle, why can't you disconnect the spring from the body, and remove the axle with the spring attached. I have read articles on the subject, but still confused. Thanks..TommyJ..

Re: 31 Model A rear spring
 

The spring exerts force and and travel in 2 directions, Ends,- eyes come together and down for lift. The together at the eyes is not visible when the axle housings are in place. The ends are static. You need the spreader.

Re: 31 Model A rear spring
 

Tommy - you can do this, but it's unadvisable. The Model A spring is under tremendous pressure when attached to the shackles. It is not slack (or nearly so) when at rest like many modern cars, that's why you have to use a spring spreader to install it. What holds the leaves together is a single bolt through the center of the leaves. The leaves at rest have curvatures much tighter than when assembled, and when you compress the leaves the energy to flatten them is stored in the leaf. If this (maybe 90+ year old) bolt breaks, then all that stored energy in the spring is released catastrophically. That is why you constrain the leaves with C-clamps and chain when you disassemble the spring on the bench. I've had that center bolt break on me when releasing it during disassembly of a spring, and it's frightening when you hear the BANG and everything jumps.

When in the car, not only is this spring contained within the channeled crossmember, the spring leaves are constrained by the two U-bolts that hold the spring assembly within the cross member.

So - it's not that you cannot remove the axle assembly with spring attached, rather it's a safety issue that you should not lest that single bolt fail. Body parts are slim protection against that much energy released at once. Use the spring spreader, spread the eyes to release tension on the shackles, remove the shackles and then drop the axle assembly with the spring extended on the spreader. If you need to work on the spring then release the tension using the spreader, and only then remove the spring from the frame.

We really don't want to read about you here as a "what not to do"...

Re: 31 Model A rear spring
 

to do the job safely, calls for a Model A spring expander. even then... it is a task best accomplished with a full understanding of what you are doing, what can go wrong, the consequences of such... and a lot of well thought out attention to detail!!


uh-huh ~

Re: 31 Model A rear spring
 

Copy..Got it. Thanks

Copy..so the pressure isn't off the spring with the weight off the axle. That make sense. Thanks.

Re: 31 Model A rear spring
 

http://www.santaanitaas.org/wp-conte...ear-Spring.pdf

Tom Endy

Re: 31 Model A rear spring
 

Thanks Tom..That is great..

Re: 31 Model A rear spring
 

Tom, as always, says it best.

Re: 31 Model A rear spring
 

The front & rear springs are stretched when installed. So regardless of the weight acting on those springs, you should use a spring spreader to safely remove them.

Re: 31 Model A rear spring
 

The A also only has one spring streched out to support the cars weight where as a newer car has two springs with only one end in a shackle so there not streched or compressed to install (only after the cars weight is put on them)

Re: 31 Model A rear spring
 

A good time to restore the spring. That old center bolt is an unknown.

Re: 31 Model A rear spring
 

I painted my springs (the rubbing surfaces) with graphite paint when I rebuilt the springs. Haven't finished the car enough to know if it makes a difference, but the leaves sure did slide together nicely when I assembled the springs. Some of the leaves were rust-pitted but I tried to smooth those out with a flap wheel without reducing the thickness.

Re: 31 Model A rear spring
 

Thanks for all the info. I don't plan on rebuilding the spring at this time, but you know how that goes! TommyJ

Re: 31 Model A rear spring
 

The reason why the Model A springs are under tension is, as Phil Brown said, the springs on a modern car are attached to the frame at one end. That anchors the spring and keeps the axle in place. The springs on a Model A are not anchored but have shackles at both ends. So the tension keeps the axle more or less in the center of the car. A track bar will anchor the rear end to eliminate any side movement, however slight, in the rear end.

Re: 31 Model A rear spring
 

Please advise: Rear spring bolt fractured!

My 30 coupe is getting an overdrive. I am in the planning stage.
The rear spring bolt is missing the bottom half. I can feel the fractured upper half in the hole and feel the nut end on top of the channeled cross member

What should I do in dropping the rear axle. As I let the axle down all but the last leaf should loosen and fall out and since nothing is retaining the spring it should be ok, correct?

Diastole in the Smokies

Re: 31 Model A rear spring
 

Here is a picture

Re: 31 Model A rear spring
 

Two things:

I had to rebuild my Mitchell due to my mistake. I took the whole thing out at once but could not get it back in. I had to take the rear spring off, install it separately and then axle. But while it was out of the car I had at least one 6" clamp on it. going back in I had two more added and a chain-probably should have done that in the beginning. Either way I had to put it in separately and then the axle. Still hate dealing with that thing.

Diastole: with a broken bolt that means there is nothing holding that spring pack together. So I think you have one option: Release the tension very slowly by raising the body off of the axle or dropping the axle. Making sure that the spring can't fly off in any direction. Do this by clamping the spring pack together, lower, add a clamp/chain, lower and add a clamp etc., etc. I am sure someone smarter than me will chime in with a better idea. My 2 cents worth.

Mike

Re: 31 Model A rear spring
 

You'll still need a "spring spreader" for the main leaf and and when re-assembling.

Re: 31 Model A rear spring
 

I’d try to push the broken bolt upwards from the bottom, then install either a new one or a length of 3/8” all thread from the top to contain it. Do this with the two brackets still on. Then use the spreader, remove the spring shackles, drop the axle out of the way, remove the spreader, remove the brackets and remove the spring. You may have to gradually lengthen the all thread as the leaves separate.

BTW, if you’ve never used a spring spreader, you will be surprised at how much oomph it takes to expand it to push the spring. That’s how much energy you are containing from escaping.

The nut should be on the bottom of the spring, and it gets the threads of the bolt peened over after trimming to length. The square bolt head fits into the square hole in the crossmember to center the spring.

Re: 31 Model A rear spring
 

You need the spreader. Check to see if your local club has one they loan.

Charlie Stephens

Re: 31 Model A rear spring
 

You should be able to take the four nuts on the u-bolts off completely and then lower the rear differential slowly (with the cars frame on jack stands)and it should release the pressure on the upper leaves. You will have to have a spring spreader as mentioned in removal of the lower leaf. If I had my rear spring out I would definitely refurb it with disassembly, re arch and graphite paint. I just did my front and rear and am very satisfied with the results. There are a few videos you can watch on YouTube as to how, it’s not rocket science and it would be very hard to over do it in the rearching imo. Rumor has it that the allies dropped two model a rear springs from aircraft during WW2, one over Hiroshima and one over Nagasaki. :). Seriously they are dangerous but once you understand the pressure and how it releases it’s easier to deal with it.

Re: 31 Model A rear spring
 

All correct except there is no defense for "spring squirm." I.e. spring pack moves laterally (front to back) when it is removed from the restraint of the rear cross channel.

I would clamp it with two large C-clamps and catch as many spring leaves as the cross channel/spring will allow as the load/frame is lifted.

Once removed - use a spring spreader in any of the patterns with the c-clamps in place.

Joe K

Re: 31 Model A rear spring
 

If you have a spreader use it before releasing any spring fasteners. Why wait till it is loose or out?