Technical Setting up a transverse rear spring suspension

I'm curious on how to set up something like this, a transverse rear leaf spring suspension.
What I am wondering is how do you determine the final ride height of something like this when you are setting it up.
This is the rear suspension kit with the winters QC that Speedway offers for their Tribute T.
I could conceivably use their spring and brackets on my Winters QC and make a crossmember for the kick up part of my frame......
I know how I set up my ride height for the coil overs I have designed and built for, however I have been considering the transverse spring instead......
Just not sure how I would set it up for my ride height if I decided to switch over.
Anyone have any solid info on how it's done ?

 

Excellent question! How DO you determine ride height if the weight of the finished car hasn't been determined yet? And who's ever seen the spring rate of a buggy spring identified in print? Gary

 

The rate on a leaf spring is linear. Meaning... if it compresses 1" for 200lbs... it will compress 2" for 400lbs.
The hard part is guessing the weight in the rear or front.

That's why some guys take a couple out or add a few.

Additionally the hangers should ride at 45 Deg at static position.

Sent from my iPhone using The H.A.M.B. mobile app

 

Honestly, the quickest and easiest way I have found on a bare chassis is to pare it down to just the main leaf for mock up purposes.

 

Just to throw another question out there if I may,

I have always been intrigued as too why most rear transverse springs have more leaves than the front springs....?

 

Yup.

 

Would be like setting up a front end, use only the main leaf with shackles at 45 degrees? You need to determine where you want the chassis to be at ride height and the height your rear cross member needs to be in relation to chassis. Plus pinion angle needs to be also correct at set up stage. The same principles apply to the rear as to the front in relation to shackle set up.


As you'd be aware the ladder bars would taper towards the car centreline and rear of the transmission. A longer arc is better than a short arc. Also consider suspension travel, length of shocks and whether or not a frame 'C' notch is necessary? Consider your spring design as well, reverse eye or standard. What is the load and rate of the spring?



Free Arch is how much arch is in a leaf spring when there is no load on it. To check free arch draw a line through the center of the spring eyes, then measure from that line to the top of the main plate (the leaf with the eyes) next to the center bolt. (C). This measurement can be positive or negative. You can measure free arch by placing the spring upside down on the eyes on a floor and measuring upward is unacceptable. Leaf thickness, different eye sizes, distorted eyes, twisted eyes, uneven floor, and etc. can and will lead to an inaccurate measurement.

The most popular method used to measure the length of a leaf spring is eye to eye. As a spring flexes up and down the eye to eye length changes. A 48-inch spring that has a 6-inch arch will measure 46-3/4 inches eye to eye. With a 3-inch arch the eye-to-eye measurement is 47-3/4 inches. This would assist with placing brackets on your rear end housing and centralising things in relation to the frame.

The correct way to measure a spring is to measure as though the spring was flat. Following the curve of the spring, measure from the center of the front eye back to the center bolt (A), then measure from the center bolt back to the center of the other eye (B), again following the curve of the spring. The measurement at 'C' would be the loaded height (Ride height) with shackles at 45 degrees. Until I read the article I knew nothing about the rationale of stepping the leaves and how critical it was as well.


http://www.hotrodhotline.com/md/html/spring_basics.php

There are quite a few threads on the HAMB in relation to setting up rear ladder bars correctly and reinforcing OEM wishbones if used.
.



The ladder bars need to point up or be horizontal to be geometrically correct and give you anti-squat with the correct amount of pinion angle at ride height. Pointing them down will cause the car to squat under load which will in turn can cause the rear tyres to easily unload. The pinion will point down. The front pivot point needs to correspond horizontally with centreline of housing at ride height.

With anti-squat built in and bars pointing up at the front up, the wheels have a tendency to turn the axle in the opposite direction. This motion causes the bars to push the car up. With them pointing down the opposite occurs and the rear drops.



I plagerised a few other threads and used Dr. Google. I'm sure others will have something more to contribute but for me I'd start with selecting the right spring (Load capacity and rating) and brackets for the specific vehicle and weight. Measure twice and cut once and always remember the 7 x 'P's, Proper planning and preparation prevent piss poor performance.

 

There are so many varaibles I wondered the same thing...even asked here on the HAMB. I tac welded the rear crossmember in, tac'ed the shackle mounts in at 45 inches [I think] for my stock model A spring and the car sat too low.......tires wanted to hit the wheel wells as in my avatar photo. I put several leaves back in the spring and tried again. I put a pair of air shocks in to approximate desired height..let the air out and let the car sit on the springs to settle..
I still have my desired 45 degree shackle angle but I'm gonna have to raise the crossmember up 2 inches in the frame rails. No sweat. Just slice a few tac welds and reposition.
So, basically, having never done this before and getting conflicting info here,I went by trial and error.

 

This is true.
However the explanation makes ZERO sense to anyone that's never set it up. There are 2 ways to wrap your head around this concept. 1st is blind faith in what a poster has said and hope that all the work doesn't come out wrong.

Second is to have all the components, measure, guess, estimate, re check, simulated weight, get it together, finish the car, make adjustments to achieve final results. At that point dismantle everything and check it to see that using the main leaf alone does in fact get pretty damn close.

Also when adjusting final ride heights it's much easier to shim up and retain the ride quantity than is it come down.

You won't, because you can't convey or apply that conventional leaf spring knowledge to a spring that's mounted in tension. It's not the same as pick up truck springs. With a pick up truck, the spring eyes are always pushing against bolts, add more weight and the push is harder.

 

Every car is going to be different, Hell not all springs are the same either, age and arch make a lot of difference, then you have leaf thickness to deal with as well.

On my A sedan with the gutted body the stock suspension settles right at 1 7/8". Sometimes it is easier to start with a complete car. But even at that if I decide to dearch the spring or reverse it that will all change and it will be pioneering allover again. The way I set them up is take my main leaf and set my mounts, that is not going to change much unless you change the main leaf, then build the rest of the suspension. Sometimes you end up moving the cross member as @Rocky suggested and you almost always end up juggling leaves.

 

Who wrote those ladder bar Tq loads? It's wrong. The rear axle, as viewed from the side, loading forward, the action of the rear axle is up, or clockwise from the driver's side. All rear axles under load, again going forward, looking from the rear, the reaction is counter clockwise. It states that the ladder bar wants to pull the car down under load, also wrong. Lift occurs at the mounting point by simple leverage. Yes, it has to lift the weight of the car or more accurate, fight the weight, which then plants the tires. In our hot rod street builds all of that is simple academics and won't be noticed in anything less than a fire breathing racer with slicks. As you bump down the road the ladder bar will indeed articulate the axle some. How much depends on spring rate and total travel, both bump and drop out.

blue one, I know that's outside the basis of or your question, sorry...

 

I'm so confused
When I looked at setting the ride height for my coil overs I used their recommendation of 13" as the compressed ride height of the shocks.
Unloaded in the open position they are 14 .5 "
After that you can use the shocks adjustment or change coil spring rate.
This transverse spring thing is like learning Greek

 

Don't over think it. That is what's kicking your ass right now.

You know that it is going to smush some when you get weight on it. Try to allow for some smushing, if it smushes too much or not enough then just back up and regroup. Easy peezy

 

Larry I'm liking you more all the time even though you bad mouth me.

You should have listened to me right away.

Put an A or a T spring back there. You will need one to clear the quick change and every time you look at it you will be glad you did.

Gary

 

Between , amount of leafs , leaf springs material , and differences in car weight ect ect it's all a bit of a Hail Mary , for me anyway .. I like to measure off of knowns , for instance say I know a 40 spring with 7 leafs and perches mounted 48" has an arch of x" in a 32 coupe so I use that as a baseline it gets me close but may have to tune it at a spring shop rearching ect I have had some springs settle 1" over 2 months and ones not move on a virtually identical setup

That's my experiance but I'm no scientist

 

I'm still on the fence with this change Gary.
And I don't really bad mouth you
Heck I agree with you 95% of the time and I think we would get along just fine for the most part

 

I have run a transverse rear spring on my Roadster for 45 years. It is a stock Model A rear spring. Upon installation I used every other leaf, beveled at the end for smooth movement. After about 2-3 weeks the shackles were up against the mounts. Went and had 1.5 inches taken off each end and reinstalled. 2 months later the shackles were straight down. Had another 1/2 taken off each end. Been good since then. Like was said before just use the main leaf for a good guesstimate of ride height.

 

It's been printed before (can't find it) but could someone post the distance of shackle eyelets of rear spring brackets on "T", "A", Etc.? I believe this measurement go's hand in hand with Blue Ones questions.......................................

 

Stock dimension for 35-41 Ford is 48.5", works well with an A- spring.

 

I doubt I'll understand your last para, but for the sake of example, let's say I want to build a car with 3" of rear travel with a buggy spring. I'm also going to put in an 1" snubber just to save my kidneys, so on the frame table I'd like 4" between the top of the axle just under the frame rails where they intersect. And then let's say the back of the car is going to weigh 1200lbs when done (including the diff, wheels and all the other sprung and unsprung weight. So.. the advice offered above is to just use the main leaf (of any old spring?) and hope for the best later when trying to adjust things? No way to determine what spring rate or design / load rate should be in advance IVO sprung / unsprung weights? And even if we could take a good guess at that rate, I've never seen these rates ever published in the catalogs that sell them to hot rodders. Sign me frustrated and one who should probably prefer torsion bars or coilovers! Gary

 

using the main spring on its own is a good starting point but you will need to make a block of some material to simulate the actual thickness of the spring. I did this by cutting a 4x4 block of wood on the band saw to allow the main spring to be bolted into the frame at the right location for the fully assembled spring pack. The block extended only as far as the mounting U bolts allowing the main leaf to flex as it would with the fully assembled car while only having the chassis bearing on it. This worked well on both the A frames I've done.

 

Larry
I'm sure we would get along fine too. Just kidding you. I love your build "for the most part" Wish I had your skills. I'm just a hammer, hack saw and buzz box guy.
The change will please your eye but be hell on your butt. You make the decision. I chose my eye and don't regret it until the second hour.

Gary

 

Here is the best place to start and figuring & thinking from





Go back up and notice the shackles are horizontal?
That means the spring is in tension and pulling on the shackles enough to suspend the weight that's there right now. How much tension ???? IDK but it's a bunch and I don't think there's any easy way to measure it if any way at all. You following so far ?

Ok let's call this visual above the starting point. At this point (with lots of pre-load tension) is where what you want to call and know as "spring rate" would begin to apply it. All You want to know if you add 100 lbs how much it moves right? At least I'm pretty sure that's what you want to know. Ok well that info or movement is not anything like any manufacturer publishes as "spring rate" because they can't account for the pre loaded tension. (See below for more) The formula for calculating spring rate of any standard leaf spring are all over Google, but this isn't standard. Are you still following so far ?

Your ride height....
If you can get a some working dimension from the stock set up above you can begin.
Does your frame have a Z? Subtract from above
The stock set up has a spring over with a specific dimension from the hanger to axle centerline......
Is yours spring behind set up? And where are the hangers in relation to axle CL?
Subtract that difference from above.
Taking The above two relationships and altering them are what sets your ride height.


Springs in tension ---
So the above example shows the shackles in horizontal.
That means the pulling force from the spring is greater than the weight.
As weight is added the spring flattens and the eye to eye measurement must increase. There will be no movement (zero) until the weight begins to exceed the amount of preload tension. (Also Standard spring rate CAN NOT APPLY here) As that weight increases each shackle will progressively move toward vertical. When the shackles reach 45* , that is a visual clue (THE EASY CHECK) that the pulling force of the spring and the weight being applied by the vehicle are equal and balanced. That balance also maintains the axle location side to side, a side benefit.
As more weight is is added to the vehicle and the spring must continue to flatten the shackles will go past 45* and begin approaching 90* vertical. At this condition you've lost the side benefit and the axle is free to wag because the spring is no longer pulling on the shackles it's hanging from them. As more weight is added the shackles will rotate towards until they bottom on the hangers, that is the end of suspension action and the spring becomes effectively solid.

 

Did you get it figured out Larry?

 

One old main leaf, some 2x4x and duct tape? Then un-fuck it later... Gary

 

Not yet. Doing a lot of thinking and figuring but the answer may be to stick with my original design
If I ever want to drive this thing I have to stop making changes

 

You just ain't getting it yet are you?
I know I can help you get to where you want to go even if you don't understand how you get there. So where do you want to go?

Generally it's not an Un-fuck type of thing.
All you can do is come close then adjust from there. It's like spotting in a rifle scope, You just can't do it with one bullet. If time and patience and making decisions for adjustments aren't in your bag of tricks take it to a pro and let them fuck with it. The worst and biggest fuck up adjustment would require getting a new main leaf if you took out to many leafs because it rides too hard, that lets the spring flatten and now the spring is too long.

 

Where's a shot of the ass end of your car?
I'll tell you what you should do

 

I'll post a picture tomorrow when I can find one.