Hot Rods Tranverse Springs Tech Info.

You can lower your ride by the way you step your chassis and by using a front axle with a greater drop in it, but once these two choices have been set the only other possibility to tweak the ride height is usually by playing with the springs.
The choices are;

• reversing the spring eyes on the main leaf.
• Removing or adding leaves from the spring set.
• Resetting the arch in the spring.
• Playing with the length of the shackles.
• With a mono leaf spring, by repositioning spacers if they exist.

However each needs to be done knowing the consequences of doing such modifications.

 

I quite unexpectedly found myself modelling the movement of a Model A front spring for a somewhat unconventional situation. I need a front spring which will carry about 16% of the total sprung mass of the car, provide a pitch frequency of around 1Hz, and add very little to no roll stiffness to the system. The bare main leaf of a stock Model A spring should give me around the 70lb/in* or so I need: so far so good.

I had initially thought that I'd need to devise a pivoting mounting to give the spring zero roll stiffness. Then I thought about reversing the idea I had above; getting the roll centre and shackle instant centre as close as possible to the same point, at least at 0° of roll. That would allow me to bolt the spring to a crossmember in the conventional way. Of course the instant centres will diverge as roll increases, and that would cause a slight deflection of the spring, so it isn't quite zero roll stiffness except at 0° of roll.

Modelling the spring at 1° increments of roll about a roll centre which is on the ground at 0° of roll reveals that the spring deflects slightly over ⅝" at the maximum of 6° of roll. That represents a wheel movement of 3" up on one side and 3" down on the other, and translates into a maximum wheel rate in roll of a mere 8lb/in.

(*Actually it's around 40lb/in I need at the axle, but as this is a mutation of a "suicide" front end there is a motion ratio at play. That rate is well within the meagre capabilities of a pair of Armstrong lever-arm dampers like the ones on my Morris Minor. I'd thought to interconnect them, but not interconnecting them might just give a useful bit of warp damping.)

 

I believe that not enough respect is given to the mounting of a transverse spring when it is out of the stock scenario it was designed for, which includes stock position but rake or stance change.
I've seen hot rod front springs particularly that have almost been wrenched into position required to connect shackles or mate with cross member or obtain a desired degree of castor.

 

https://www.jalopyjournal.com/forum/threads/transverse-spring-hanger-repair.1114374/

 

All great information, thanks for posting seabeemc.

 

Everybody wants to use a transverse spring, even where they were not previously used.
There is just something about running a transverse spring up front...

 

Any metal that constantly flexes will eventually develop metal fatigue to the point of breaking.

 

Great !
So now we can’t have any kind of springs that are made from steel...........

 

That's a high arch trailer spring.
Lots wrong with that set up, it fits better in a catagory of what not to do.

 

Well springs do get fatigued, weak, broken and need replaced. It takes a long time and lots of use and cycles but eventually every single one will fail.

 

Metal fatigue is something which has only recently been understood adequately. Well within living memory it was still a bit of a mystery. For that reason our world is full of stuff designed without an adequate understanding of metal fatigue, including a lot of the hardware we like.

Some materials have a critical stress below which fatigue cannot happen. Most aluminium alloys don't, but most steels do. In theory it is perfectly possible to design a spring which will last forever, i.e. for an infinite number of cycles – provided it is never stressed beyond its intended limit.

This knowledge informs the design of a lot of engine parts. Compare the size and proportions of a modern crankshaft to those of a c.1935 crankshaft.

 

Mike Eaton from Eaton spring told me shackles should be more vertical in the front and controlled with a panhard bar?

 

That echoes what I said in post 86, paragraph 4, above.

 

My 46 Mercury front shackles are vertical with the full weight of the car on the ground. What happens to the front end geometry if I use longer shackles to bring the front end of the car down?

 

If there is a lateral locating device other than the shackles themselves (i.e. Panhard bar etc.) there shouldn't be a problem – provided there is enough clearance for everything throughout all the necessary movements.

 

If it's a spring in front set up, with no obstructions (aka perch bolts) for the shackles to crash into / well that's how Henry set them up isn't it?

If it's a spring over set up, you need to be sure the shackles don't crash into the perch bolts as the spring works. Again how Henry set them up.

 

Sadly, too many transverse spring setups accidentally end up as you say, but not thru design of the builder.
That is why I said previously that many folks do not take setting up a transverse spring serious enough.
The shackles should sit pretty close to 45 degrees which reflects a good choice of spring characteristics when it comes to arc height relative to the weight being carried in proportion with the main leaf length.

 

those bushes don't go with those shackles - those shackles should only be used with a tube type bush not the type you have in.

 

My idea is to install a complete 46-48 front suspension under a Model A frame and use a Panhard bar. In order to keep the wheelbase right, I'll have to move the front crossmember about 4 inches forward. Take a look at the picture of Dana Barlow's front end in post #31. There appears to be plenty of room under the frame for the axle. As you said, longer shackles shouldn't be a problem if I install a Panhard bar.

 

That stuff came right out the same package. Take it up with the manufacture and their tech Dept. Maybe you can educate them I could not. Their absolute best solution was to not tighten the nuts.

 

I don't see how the spring perch holds up when it's set up like the one in the upper pic. I also think that a trailer spring would jar your teeth loose. I've seen several spring brackets welded out front like that but it looks like over time it would develop stress cracks .

 

that doesn't surprise me they told you to do that, none of the shackles out there seem like they fit very well. I don't know how they can get something so simple so wrong...

 

There are units that fit and work.
That supplier est 194x can kiss my ass. I buy a lot of parts and refuse to spend a nickel on their stuff.

 

My first thought was this guy is trying to build a Gasser of some sort...

 

It appears as if you went down to your local Tractor Supply Company or someone else who sell trailer springs. IMO if you overload one side of the main spring, (rebound from a pothole, speed bump), there is a distinct possibility that the spring will bend where the squared off end of the second spring lays on top of the main. Also, there is little chance of adjusting the ride with those springs. There has to be a better solution that that.

 

That certainly wasn't my first thought

 

Here is generally what comes to mind when we think of a hot rod front transverse spring setup.
I choose my words carefully as I acknowledge that there are other stock factory versions along the same lines.
I am talking for now about stock configuration.
I'm sure most would agree that the Model A Ford front cross member has been a popular choice for many years.
Other styles can be posted later.
Just an appetiser for now...

 

A variation of the above spring to chassis attachment point is the modified version of the stock metal channel that makes up the cross member by flattening its shape or by removing the crank affect.
Using this method it will obviously lower the ride height of the car, however it will require the chassis rail to be notched out to provide clearance for the spring during upward movements so as not to bottom out on the rails.
This probably the next most common and recognisable version of attachment.

 

The next most recognisable front transverse spring mounting method is what I know as the suicide front end.
The mount point sits forward of the improvised cross member which is usually made from substantial sized round tube/pipe and the attachment plate canter levers from the tube.

Probably, more in the past, but I recall many attempts to make attractive covers to hide the U bolts by using cut down polished finned aluminum valve covers and similar.
In the early days, this style attachment was likely to be found on T buckets.