Technical Transverse spring preload/setup question

I am in the process of building a traditional t-roadster chassis - first time building one. I am going to use a speedway medium arch spring on the back axle. Speedway says this spring measures 38" eye to eye, don't know if that's unloaded or loaded. My shackles are 1.5" bolt center to bolt center - this gives me 41" overall width with the shackles parallel to the ground. My question is how far apart do the perches on the axle need to be in order for this spring to work correctly? I have searched and have found as many different answers as there are search results. Hopefully someone can give me a definitive, no shit answer.

 

I don't know the answer, but it got me to thinking(dangerous after this many beers!!)...Is the set up the same for front and rear transverse springs?

In other words, are the spring shackles supposed to be at the same angle, say 45 degrees?

 

I think they are, however the front springs are quite a bit different than the rear springs are, they have a much shallower arch and aren't able to stretch out as much as the rear spring can - when compressed. Keeping this in mind one would assume the rear spring perches should probably be spaced out quite a bit further (in proportion to the spring's eye to eye width) than the front spring perches.

Perhaps I will just call Speedway and ask them. They claim to have "knowledgeable techs"....let's put them to the test.

Here's a pic of a rear spring arrangement on a roadster project that I recently acquired in a trade deal. I have already disassembled and liquidated this car. The rear spring setup on it was obviously incorrect. It was completely bound up and wouldn't allow any movement of the rear suspension whatsoever.

 

According to the speedway catalog, 41" is where they should be. That is according to the drawing and explaination of method B for figuring spring length on p23 of the 2012 catalog I have sitting on my desk anyways. That is for the front axle. oops just reread your post

 

Hmmm. I do not have this spring in my possession yet - the description says the eye to eye dimension is 38". I just assumed that was in the unloaded state. Perhaps that is not the case. If it is the case and they state the perches should be 41" apart, then there is no way in hell that would work.

Thanks for that info.

 

IF the main leaf had reverse eyes and the next leaf were shortened, looks like it would have worked OK.

 

Possibly - but I really think those perches needed to be spread out at least 3 more inches, maybe 4. The picture really doesn't explain it - you'd have to see how it performed when you jacked it up and relieved it, then let it back down under its own weight. The perches were clearly too close together.

 

If you get the rear speedway kit shackles and spring perches it gives different perch measurements for the total weight over the axle.Pretty sure that 38" eye to eye is unloaded.For reference a stock Model A is around 50" eye to eye on the perch which would be around 47" loaded in the spring eyes.

 

Yes, but a stock Model A has a full arch spring - which will stretch out even further than the medium arch spring will - hence the wider perch mounts. I guess I'll just have to figure this out on my own once the spring gets here. I may rig it up in my press and compress it and take some measurements. Hopefully I can do this without getting maimed.

 

Wouldn't it be nice if a company that sells hot rod parts for the last 50 years could give a customer some vital info about the parts they sell. It's not just Speedway, it's most of them....even some of the big name speed shops.

 

The problem is that there's just no more craftsmen around like there used to be. Used to be that every business that catered to this sort of market employed craftsmen...not milquetoast couch potatoes that are just earning a paycheck by answering phones and bullshitting other milquetoast-ish left-handed wannabes that call and ask dumb questions. Just thinking about it makes my head hurt.

 

Got my spring today, it's definitely 38" in the unloaded state. 41" to the center of the outside shackle bolts with the shackles parallel to the ground. After many hours of thought, checking and experimenting, I think I have settled on a 43" spread for my spring perches. This will require the spring to be spread out 2" in order to make the hookup. Just thought I'd post this here incase anyone else is pondering the same conundrum. I'll update the thread again once I have this all installed with weight on the wheels.

 

Mechanic58- meant to responde to this sooner so my apologies. I'm using the speedway medium arch non-reversed eye spring and have my axle mounted spring perches at 43 3/4" eye to eye on my model a coupe. I would however like to move the perches to 44" or 44 1/4" eye to eye. Shackles are close to 45 but I would like to see them lay out a couple more degrees since this is locating the rear side to side. Hope this helps.

 

Thanks for that information. I am assuming you're running an all steel coupe body - I suspect your car is probably quite a bit heavier than mine is going to be. I may not need that much of a spread. I am fixing to start working on this as we speak.

 

can you install the spring in the frame and let the weight of the frame and body rest on the rear housing or better a long 2X6 and see how far the spring streaches out to. then measure eye to eye.

 

This is basically what I did - sorta. My frame isn't built yet, which is for a reason. I looked at lots of 'plans' but none really suited me. I really like the stance of Speedway's Tribute T and that's what I'm going for. I have searched high and low for some specs on that frame and I just can't find anything beyond the wheelbase measurement - which is 106". So I have my axles laid out in a jig at 106" and I'm going from there. I'm getting very close though to having the frame mocked up.

 

I make my frames during mock up with 2x4s and let everyone around me laugh. But, i can have a fully built car with measurements before i cut any frame rails. If you make this mock up frame well you can get some weight on it and figure your spring width. Just be creative and it is fun!

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This is exactly what I'm doing....

 

The weights of the cars listed in the Speedway catalog are not correct.




Ago

 

Surprise, surprise...lol.

I am actually weighing every piece of this car as I assemble it and keeping a log. By the time its finished I will know the exact weight of it.

 

I found when building the spring setup on my '27 that 4" wider worked well I am running adjustable perches out back so I fine tuned the shackle angle. But remember Ford used the rear spring with tension as the locator side to side!

 

I went with 5" wider than the eye-to-eye measurement on my unloaded spring. I feel like its going to work well. It was a little hairy getting it hooked up, but I got it figured out.

 

From 1909-1941 Ford used the installed tension of the spring as a substitute for a Panhard rod to obviate side sway. In 1942-48 the springs were bushed with large rubber bushings and not under tension to soften the ride to compete with other makers dual rear spring suspensions. The Panhard rods were then used front and rear from 1942-48.

 

FENDERS has the solution. Your second leaf, the one above the main leaf, is just too long, period.

 

The magic 45* angle of shackles is NOT, I repeat NOT, the angle of the shackles when mounted and not under load of the car. When assembled the shackles will be laying straight and when the weight of the car is put on it the shackles drop to between 30 and 45 degrees. This allows the suspension to also keep sidesway to a minimum.
This high and medium arch stuff was dreamed up by somebody at Speedway or in dreamland. How much simpler is it to say Model T or Model A spring design. Model A eye to eye on perches would be 49 1/2". Model T is 48".
The Model A roadster spring, once upon a time THE spring to find, is I suppose a medium arch spring like the T?, but has wider width leaves. From looking at modern builds it seems most are using any A spring they find and simply deleting leaves for height, softness of ride. The A roadster spring needed no mods for that purpose.

 

So - this "medium arch" speedway spring that I have - WHAT is it? A model T or a model A spring? Or is it something different all together?

Either way I am certain I have it set up properly - when installed and not under a load - my shackles are parallel to the ground. They only assume the magic 30-45* angle once the weight of the car is applied.

 

I am reviving this thread to get some feedback on the rear spring setup on my channeled 32 roadster.
The rear rides very harsh on local streets but is passable on the highway if nice and smooth. The car is very light in the rear of course.
We used a SoCal rear spring designed for the 32 chassis Here is their blurb on the spring.
"Engineered specifically for use with the SO-CAL Step-Boxed™ 32 chassis—though they can be used on most early hot rod chassis, this rear spring—exclusive to SO-CAL—was engineered after the 40 Ford spring in that it is straight and not curved like a stock 32 spring."
http://www.est1946.com/so-calrearspring.aspx

I have done measurements and they are in line with other info here. 41 inches approx between eyes under load and shackles at around 45 degrees. You can push down on the rear of the car and it is very stiff and no real movement.
It was suggested that the spring shackles be lengthened? I am also wondering if the ride would improve if we removed the second spring leaf (above the bottom spring)which was also suggested in this thread. I want just a nice smooth ride. Some of our highways here are particularly bad and riding in the roadster on my last trip nearly shook my teeth out.
We did change out the shackle bushings with softer rubber and all that happened there was that the RHS has already shagged out after only 700kms.

 

I made a spring calibration rig. I have two fixtures that I can put spring in and a load cell and hydraulic rams. I have done springs for all my friends. You can load the spring and determine the spring rate and the deflection for a given load. The guys come over and run the springs and when they are installed, everything is as wanted. They don't have to guess as to ride heigth or spring stiffness. Works great.

 

You did not mention the shocks. Have you tried the car bounce without the shocks? If the shocks are some heavy duty type, they could be aggravating the ride.

I would not remove the longest leaf next to the main leaf JMO. If the spring is still way too stiff with the test without shocks, then I'd keep trying to remove certain leaves to get it soft, then get proper soft shocks, (and not gas charged either)

 

Using SoCal shocks that are supposed to be for this set up. The next bit of advice I have had is that the spring perch fittings on the rear are actually front ones(40mm between the eyes) and should be 50mm.