Technical Model A rear spring questions (updated with final pic)

I think you have some very practical ideas on how to fix his problems without a large outlay of cash or total re-engineering.

To me getting the existing main leaf shortened is the better option. It fits the arch and curve of the other leafs and its ride height is a known factor. There have been two methods of determining how much to cut mentioned here. One by Chappy and one by me. I don't think I would start removing leafs until after I felt what it rode like after it was driven with the spring travel freed up.

If he shortens the hairpin bracket on the rear I would suggest bending the lower bar up. If you look just forward of the X you drew, the upper bar rides fairly close to a cross member. Leaving the upper bar straight would gain a little additional clearance there. I would be tempted to add another gusset to the hairpins close to the ends after bending one of the bars. In that case I wouldn't drill my new hole until after I added the gusset.

 

I do too, as long as the rear will be replaced in the future; BUT, bend the upper hairpin leg at its joint up front, keeping a straight 'leg' for compressive integrity.
The upper bracket can be shortened 1" safely. Main leaf may be re-rolled 1" in per side.

 

F&J has the right idea, but change to a standard eye spring might give enough clearance over the batwing.

 

Curb Height factor...that'll raise it up.

 

I would too, but in a pic that Chappy put up last week on cobra51addict's thread...I swear I see what looked like the former builder ran a 4.5 grinding wheel on the front underside of the main leaf edge, making crude notches?? Maybe Chappy can verify if the main leaf was notched, or not.

I had missed that, and you are correct...good catch.

Sure, it's fairly easy to try it first, then do a static bounce test with no shocks on. If it feels like a brick with no shocks, then comes the long task of messing with leaf removal quite a bit, then more bounce tests.

 

F&J,
Thanks, I like this idea...
I hadn't considered cutting the hairpin bracket... dont know why I didnt lol... to close to the problem i guess.
I am assuming that heating and bending the hairpin won't cause any strength issues in the metal.
Out to the garage to take some measurements
Thanks again...
Chappy

 

Looks to me that if you put the proper length spring in the car it will clear all brackets. I would be shooting for less than 45 degree angle on the shackles. Then tune the spring for desired ride and ride height.

 

The plot thickens....
It was late when I got the spring removed from the rear so I didnt look at it close untill this morning.
A few things I noticed.
1. It appears that the main leaf may have been shortened at some point... ther is evidence of "vice" markets on the eyes and the second leaf appears to have been cut shorter...
2. I am not convinced that the upper half of the spring is moving at all, no evidence of grease or slide marks on those springs (possibly painted together after assembly)
See pics
Chappy

 

Those little grip marks are common on spring eyes. Might be original from Ford.

 

Your observations look correct, that spring is about 3-4 inches too long. If you choose to make a new main leaf I would suggest not reversing the eyes of the spring because then you can make a tool to spread the spring to install properly.

 

The spring can't move because the shackles are hitting. You might as well have an 'I' beam in its place.

 

That was the reason I suggested adding a gusset between the ends of the legs. Another way would be to pie cut the gusset half way along the lower leg and make the bend in the middle of the gusset and reweld the gusset to the lower tube. I think as long as the two legs of the hairpin don't become parallel there won't be a problem. Engineers?

If the shackles can't move outward upon compression, the leafs can't move against each other. Its almost like using a 2x4 for a spring.

 

Chappy, sorry that my comments on the other thread snow balled into this. I am with others on here new shorter main spring to start, the rust bleeding from the spring pack I another reason to replace, looks like there is excessive wear on the main spring as well as the secondary spring. I also do NOT recommend the reversed main spring, it is done a lot with safety concern but it does make stretching the spring into place very difficult.

Measure the center to center distance of the axle, spring should be 5" shorter eye to eye. when new spring pack is assembled, please take the time to grind sharp edges off the springs, this will help with the spring wear and ride. the leafs need to slide on each other, sharp edges only cause binding and wear.

 

I'm not a Model A guru so help me out here, >> doesn't that spring have reversed eyes? ..and if so, then that is why the 2nd leaf tip was cut off? You can see the former wear mark of that tip once wore the main leaf in post 38. That tip would have been jambed against the eye?

I'm not engineer, but look at the pic in post 36 with the tape measure... those tubes are beefy, and it looks like there is only roughly 9 to 10" of unsupported tubing from the middle reinforcement spreader plate to the rear clevis. I simply can't see those tubes being weakened no matter how he ends up modifying them.

He's got a hobby "driver", not a blown Hemi on slicks..is what I am getting to, as far as low stresses.

 

FWIW. The spring is reversed. I think it was done by re-arching rather than re-rolling the eyes.
I would modify the upper radius rod mount by moving the upper eye forward to provide clearance for the spring. The bottom is fine. Just move the top and tap the radius rod for the new shorter length.
I would put the spring back in the car without the rear axle. Put a beam across the spring eyes and jack the beam up until it supports the car. You can now measure the loaded spread of your spring in the car. I put some steel under the eyes with grease to get an accurate loaded position. I use two floor jacks. You can now figure the required dimension for the mounts. Add 2/3 of the shackle length per side. If the c/c of the shackles is 1.5” add 2” total to the dimension from the spring spread.
I can also measure the spread on a stock A rear if you like.

 

Boy that Andy fella knows how to think

Chappy that looks like a nice car, worth doing right.

There have been some good ideas put down here about making your inherited string of misguided compromises better. Should you pull it together with these ideas - In the end you'll have misguided compromises that are better. Compromises stacked up on top of bad decisions is not a place to start from. Looks like you're going to correct about 6 individual symptoms with 6 different tasks. Then who knows because most changes create 2 for 1 problems.

 

Mr hemi. Thank you! I really appreciate your compliment.

 

With the spring out of the car I can apply my 190lbs of body weight to the top of the full 10 leaf stack and get the eyes to slide out ~3" per side... seems kinda weak to me.

That would involve welding on a new mount, and cutting and tapping the upper rod correct?

Are we still talking about welding on new perches?

As I said, a couple of times, I am not in a position to redo the rear the way I want to. There is a long term plan for this car that involves a different rear (including the suspension). It is just not going to happen in the next 18 months.
I dont have a fab shop and my welding skills are fair but I dont trust them on critical components.

My perch centers are at 47"
The shackles spring mount centers at 0* measure ~44.5"
There is an off the shelf spring designed for 46.5" perch center with 39.75" eye centers
I have been told (on this thread) that the spring eye spread at rest should be about 5" shorter than the shackle spring mount points spread
44.5 - 39.75=4.75"
As I will be gaining actual suspension travel (that I didnt really have before) I will need some amount of increase in the ride height.
If I get this spring without reverse eyes I will gain about .75" of ride height out of the box.
From there I can play with spacers and leaf removal to find the optimum ride height to ride quality point... and that point may resolve the hairpin mount clearance issue without having to do any modification.... to anything.... please see the pic below of the clearance between the hairpin mount and the spring with the shackle between 0* and 45*
So, I can potentially solve all of my issues with a $300 part and some labor, and I can do all the work in my garage.
I cant see this solution and configuration being any "worse" than the original ford design.
This car is a weekend driver... 2 hour radius from the house, no interstate type of thing.
The planned future rebuild is a different story all together.
I will say that if anyone has spare parts, free labor, or cash and checks they want to donate to this rear end solution please feel free to PM me for my shipping address

Please dont think that I am ungrateful for the advice and knowledge dump. I really do appreciate it, but I have a very specific set of boundaries I am working in right now... and I am trying to prevent mission creep on this particular issue. I have had more than one project that a simple system repair turned into a complete rebuild of the car... the old "while I am here I might as well do something with that also" and that turns into, "well, I got it this far apart I might as well just redo it all" and I dont have the space or the checks appeal right now to let that happen.
Having said all that, if someone has a legitimate safety, engineering, or application concern about my plan above please share.
Thanks again for all the info and assistance, I really do appreciate it.
Chappy

 

Thanks for the input, please see my response to Andy's post above.
Chappy

 

You have nailed it. I sure am glad I read this whole thread before I commented because you ended up with all the changes I was going to suggest. The only thing I would add is if you relocate the upper mount and or bend the bar down just be sure you still will have enough thread length on the clevis .

 

I think a friend or a welding shop could fix all the problems in half a day. If you don’t do any mods then I guess it will stay the same until the next rear gets installed.
I will get the stock perch width for you so you will be ready then.
I built a whole car in a carport using a pawn shop stick welder and a gas rig. I would sure look into getting a stick welder.

 

I'm fairly certain that I have read all of the posts so far. As it's been posted that the perch mounts are 27" on center. As I see it, wouldn't it be best to address that issue first? If I had this issue and had limited welding skills here is what I would try first, and it wont cost a dime. Remove the spring from the differential, make a straight line cut on the perch just below the perch "boss" without cutting it off (see my red line on your pic for reference only). Heat the perch at the end of the cut and bend it up and out, this will do two things, one it will move the perch up, and second it will move it outward. Tack weld it in place holding it to the correct width. If this helps resolve your issue (hitting the ladder bar mount and spring hitting the perch mount) the area can easily be prepped and final welded. As I recall, correct me if I'm wrong, but the distance between perch bosses should be 28" to 28-1/4" plus or minus. Any other input on this low impact tactic?

 

Just be forewarned that this $300 part could leave you with more problems, and not be a quick & easy fix.

You have a 10 leaf spring, and you are calculating where the where the ride height, ride quality, and shackle angles "will end up", using a new spring with a different amount of leaves.

As you remove leaves for optimum ride quality, the spring width will get stretch out, changing the shackle angle.

There is not one person here that could guarantee where things will end up by spending $300 on a different spring with or without reversed eyes. I suppose there is a chance it could end up Ok by "pure luck", after messing with the leaf counts and still maintain the 45 degrees. I'm not a person that would ever advise that $300 gamble will definitely work out. There are just too many variables that will come into play.

If it was me, (and not wanting to move those perches),
-I would mount just the spring in the crossmember without the rear end in place.
-Then put blocks under both spring ends with steel for the ends to "glide on", & let the full weight of the car sit on those glides.
-Then do a static bounce test to see how stiff it is now, then start the time consuming process of removing leaves to get the bounce test correct.
-Then with the total weight still on the "final set of leaves", you can now measure "eye to eye" loaded width of the spring pack.
-Now find a local spring shop or blacksmith to shorten the existing main leaf & reroll the eyes to the proper width, to match the existing unmodified perches. (and yes, a blacksmith can also do this easily)

BTW, those eyes were definitely re-rolled. If you look at the old wear marks where those trimmed tips of the 2nd leaf once were, on the "top" side of the main leaf, that proves the spring eyes were re-rolled, rather than having the main leaf "flipped over & reverse arched" back when it was first built as a hotrod. If it was reverse arched, that old tip wear mark would be on the underside of the main leaf.

 

My concern is those spring perches..... those are meant to be used in a "spring behind" capacity. Changing over to a proper "spring over " mount will likely solve part of the issue. The second this would be the eye to eye measurement on the spring. My reverse eye springs for a Model A are 41" eye to eye to 43" eye to eye depending on the spring style....


This utilizes our Spring Over perches and "Hot Rod " spring fyi

 

Matt, he has said several times that he is looking for a no-weld solution. There is no way to change the existing perches without welding with his rear end. His current perches can work with simply narrowing his current spring.

...working on somebody else's mess is usually going to be a compromise if you can't start from scratch.

 

I understand he's looking for a " no weld" solution.... but imho I don't think the current set up is particularly safe or properly engineered.

 

I have a Millermatic 115 gas mig and a stick welder...Its not the equipment, its my ability that concerns me! This isn't an exhaust pipe, body panel or hitch on the tractor. On top of that, welding on this assembly will require a minimum of removing the axles, bearings and seals... more mission creep...
Chappy

 

I would agree with F&J. The spring you have is the devil known, a new spring is a total unknown that will need to be fine tuned also. Do the bounce tests and figure out how much the main leaf, in its new configuration, will have to be shortened. Get standard eyes rolled on it. That will raise the back of the car the diameter of the eye which you said you will need for suspension travel. The standard eye will also get you the needed clearance over the hairpins. If the softer spring causes the rear of the car to sit too low you can get a longer center bolt and make a spacer to go on top of the spring. You would then need longer "U" bolts and spacers between the frame and spring clamp. Another thing you can do to smooth out the spring action would be to get a roll of polypropylene spring liner and place strips of it between the leafs. One other thing I would do is to start with some 80 grit on my DA and kind of polish up the area on the tops of the springs where the leaf above dug in a little. Then I would round the lower edge of the end of the spring above. Anything spent less than the $300 is money towards the new quickchange.

 

Thanks for all the input guys!!!
I spent some time last night taking some measurements and gathering some data.
Below is what I compiled about my existing 10 leaf spring and a new 8 leaf "narrow" spring.

Looks like shortening the existing spring will get me about the same results as buying a new spring.
My question now is about minimum eye to eye distance. I assume that there is a point where the main leaf can be shortened to much to be able to pull it over the shackles. I have seen the measurement of 5 inches tossed around.
My shackles (at 90*) are 44.75" apart. What would be the narrowest eye to eye measurement on the spring that would still allow me to install the spring?
I would hate to go through all the measurements and cutting and then find its to short...lol
Thanks again
Chappy


Sorry about my crude drawing....

 

Here is some info from the posies site !!!
They have 3 different springs available for a model a .
the given measurments are for springs to fit in between perch centers.
STOCK 48.5 -49 inches
NARROW 46.5 inches
ULTRA NARROW 44.5 INCHES
The springs will be 5 inches narrower than those measurments
STOCK 43.5 -44 inches
NARROW 41.5 inches
ULTRA NAROW 39.5 inches
these are your choices for off the shelf springs
measure your perch holes and see what is close anything much different
will require you to have your bottom leaf custom made