Mono-Leaf question

[Zandoz]

I did not want to hijack the other thread with a mono-leaf discussion, so here I am, and here is what I have...

• The configuration will be spring over axle
• 48" king pin width 5" drop tube axle
• 31" Speedway monoleaf spring, with a 3-5/8" underside height unloaded
• Speedway stainless adjustable spring perches
• Speedway standard (no shock mount pin) shackles
• Speedway stainless under axle shock mounts
• Generic 4-1/4" travel 3-way adjustable gas shocks
• Combined engine and transmission weight apx 450 lbs

Here is the issue...I have no certain idea what height frame spring perch I'll need, because I have no idea how much the mono-leaf is likely to deflect under load.

A year or so ago I chatted with someone who gave me some info to make a guesstimate, and I used that to do my cad drawing...but I have since lost my notes. According to the CAD file, I used 5/8" as the amount of deflection under load. To me it seems like there would be more deflection.

This is another one of those "I'll seal with it later" issues that are now becoming critical, as I get close to commissioning my frame.

 

[T-Test]

I did not want to hijack the other thread with a mono-leaf discussion, so here I am, and here is what I have...

• The configuration will be spring over axle
• 48" king pin width 5" drop tube axle
• 31" Speedway monoleaf spring, with a 3-5/8" underside height unloaded
• Speedway stainless adjustable spring perches
• Speedway standard (no shock mount pin) shackles
• Speedway stainless under axle shock mounts
• Generic 4-1/4" travel 3-way adjustable gas shocks
• Combined engine and transmission weight apx 450 lbs

Here is the issue...I have no certain idea what height frame spring perch I'll need, because I have no idea how much the mono-leaf is likely to deflect under load.

A year or so ago I chatted with someone who gave me some info to make a guesstimate, and I used that to do my cad drawing...but I have since lost my notes. According to the CAD file, I used 5/8" as the amount of deflection under load. To me it seems like there would be more deflection.

This is another one of those "I'll seal with it later" issues that are now becoming critical, as I get close to commissioning my frame.

First off, why are you using a spring over the axle? This limits you ability to lower or raise the frame except at the perch, by making it[perch] higher or lower. Secondly, a mono spring is good and is just as effective a leaf spring and is rated for weight just as the leaf springs are. There are also steel mono springs, just maybe not the length for a T-Bucket. The only drawback I see to using a mono spring is if it breaks-- and they do-- you will lose all control of the car.

Whomever builds the frame[commissioned] has to know all the pertinent info in order to do it right. Or use traditional setup ways and configurations. Still may not be correct.

Just because it is/looks good in a CAD file, doesn't mean it will work. JMHO Back to the drawing board--again.

 

[409T]

I have a steel mono spring that came from CCR, and am very happy with it. As to whether or not they will break, I suppose common sense dictates that anything will break if flexed long enough, but I don't think it is going to happen in my life time. Nevertheless, even if it does break you needn't loose control of the car. Ted Brown used to make a bracket to prevent this, CCR may still. If not, you can learn about them and fab your own.

 

[RESINATOR]

The license plate bracket is that safety bracket, but nowadays we use shocks on all the chassis we build which would be a backup if something were to break.
Jeff, please e-mail me when you get a moment. My son will be interning down your way over the summer and I need some neighborhood advice.

 

[Zandoz]

First off, why are you using a spring over the axle? This limits you ability to lower or raise the frame except at the perch, by making it[perch] higher or lower. Secondly, a mono spring is good and is just as effective a leaf spring and is rated for weight just as the leaf springs are. There are also steel mono springs, just maybe not the length for a T-Bucket. The only drawback I see to using a mono spring is if it breaks-- and they do-- you will lose all control of the car.

Whomever builds the frame[commissioned] has to know all the pertinent info in order to do it right. Or use traditional setup ways and configurations. Still may not be correct.

Just because it is/looks good in a CAD file, doesn't mean it will work. JMHO Back to the drawing board--again.

The reason for using the spring over configuration is that it makes for a shorter wheelbase. My target is the wheelbase of the late 50s Tweedy Pie T...adjusted for my stretched body...92". Plus I am trying to keep the overall length to the minimum, to enable it to fit in a shed for winter storage.

I do not understand the issue with a mono-leaf. I had no problem finding one the length I needed. Adjusting ride height is accomplished by adding/removing shims. Breaking should be less likely due to there being 100+ lbs less weight than a vehicle with small block V8.

I have a problem with the premise that a mono-leaf breaking would mean a total loss of control. The axle will remain located via the 4-bars, panhard bar, the triangulation effect of the shock geometry, and finally in a spring over configuration the perch landing on the axle itself. When it comes to component failure, I'm far more worried about the 4-bar set-up failing, resulting in loss of axle location in a way that would absolutely result in serious control issues.

Yup, there is nothing that can substitute for reality...but CAD work can definitely point out a lot of issues...and sometimes lead to new ideas. I've been playing with CAD systems for over 25 years...for everything from furniture to model railroads to 3 whole homes and several remodels. With so much of this project being non-standard, I'd not even consider tackling this project without having a CAD system.

Right now, the question is how I get a guestimation of the deflection of the mono-leaf under the load of the vehicle, so I can get a height for the perch that will allow for at least a couple of shims for ride height tuning. Even a figure for the deflection of a mono-leaf under the weight of a small block car would give me more info than I have now.

 

[Zandoz]

I have a steel mono spring that came from CCR, and am very happy with it. As to whether or not they will break, I suppose common sense dictates that anything will break if flexed long enough, but I don't think it is going to happen in my life time. Nevertheless, even if it does break you needn't loose control of the car. Ted Brown used to make a bracket to prevent this, CCR may still. If not, you can learn about them and fab your own.

The mono-leaf I have is a forged steel Speedway unit.

 

[Zandoz]

The license plate bracket is that safety bracket, but nowadays we use shocks on all the chassis we build which would be a backup if something were to break.
Jeff, please e-mail me when you get a moment. My son will be interning down your way over the summer and I need some neighborhood advice.

View attachment 11202

I need to be ordering one of those license plate bracket spring plates soon. I've not found a way to order from the web site. Am I missing something, or do I have to place orders over the phone?

 

[2old2fast]

Deflection would directly corrolate to the spring rate, I would think , is that info not available ? You don't need a panard w/ a cross spring.. Why in the world would you worry about the 4-bar ?????
dave

 

[2old2fast]

Just thinking out loud ... the front of a T may be marginally heavier than the rear.... in any case , it's generally accepted that the rear coil-over rates are between 150-175 # per inch..so -2springs = 300-350# ... o I would think that's about where your front spring would be ???? So , approx 1000# on the front- 300 # spring = 3+ inches of "drop"
dave

 

[Zandoz]

Deflection would directly corrolate to the spring rate, I would think , is that info not available ? You don't need a panard w/ a cross spring.. Why in the world would you worry about the 4-bar ?????
dave

The spring rate is not known for sure. Speedway refuses to give a figure, and the figure I was working with was given to me by someone based on a spring from another source...and that figure was lost with my notes. Also, in addition to the drivetrain weight which I have a good figure for, I have no clue on the rest of the weight bearing on the spring.

Everything I've found indicates that with a 4-bar set-up a panhard bar or other lateral locating device is a must. It's not a major configuration issue, so I'm playing it safe. At one point I laid out a Watts link for the front lateral location, but rejected it on a "bang for the buck" basis.

To me, the typical off-the shelf bracketry for mounting the frame ends of the bars is a weak link...not very heavy material, and all the mounting welds in a single plain on the top or bottom of the frame rail. I've got 2 sets of brackets, and I'm not really happy with either...but I'm going to go with the flow and use one of the sets.

 

[Zandoz]

Just thinking out loud ... the front of a T may be marginally heavier than the rear.... in any case , it's generally accepted that the rear coil-over rates are between 150-175 # per inch..so -2springs = 300-350# ... o I would think that's about where your front spring would be ???? So , approx 1000# on the front- 300 # spring = 3+ inches of "drop"
dave

Standing free on the top of a table, the distance from the top of the table to the bottom of the center of the spring is 3-5/8" or so. A 3"+ drop would only leave 5/8" of compression before starting to reverse the spring <shrug>

 

[2old2fast]

If you make your perch for 3" drop , the worst you'd have to do is put in a spacer ........welding the brackets to the top & bottom of the frame rail should NOT be a problem........ And you still don't need a panard w/ a cross spring ...
dave

 

[Zandoz]

If you make your perch for 3" drop , the worst you'd have to do is put in a spacer ........welding the brackets to the top & bottom of the frame rail should NOT be a problem........ And you still don't need a panard w/ a cross spring ...
dave

I did a bit of playing with a 3" drop. That would put the top of the spring around 7/8" below the centerline of the front crossmember, with the crossmember at the height I'm shooting for. <shrug>

The bracketry I have is something like this...

I'm used to the much heavier bracketry used on off-road vehicles. But I'm going to set aside my paranoia and just go with the conventional. Besides I have more than enough unconventional in my planned R&P steering and especially the rear suspension set up...LOL

 

[Zandoz]

Well, I did a little more research. The spring rate for an example of a 6-leaf spring for a 48" axle is 450 lbs. What I dont know is if that 450 figure is for both sides of the leaf combined, or is it for each side of the spring?

With the short wheelbase and light weight engine, I'm guestimating a total weight of around 1500 lbs. But I have no feeling for how much of that is unsprung weight to be removed from the equation.

 

[2old2fast]

I would think that unless listed otherwise , 450#/inch is for the whole spring
dave

 

[Zandoz]

OK....the following numbers are pulled out of my ____. (fill in the blank)

I will assume that my little short wheelbase light engined bucket will weigh around 1500 lbs...with 2/3s of that, or 1000 lbs up front.

80 pounds of that will be the wheels and tires, and another say 200 lbs for the axle, spindles, brakes,etc. That leaves 720 lbs.

Assuming we want a minimum of 2"s of up-travel in the suspension, and there is only 3.625" of spring arch, it seems to me that those 720 lbs of weight would compress the spring 1.625"s...roughly a 443 lb spring rate.

But all of this assumes a lot of weights and their distribution...and that the entire arch of the spring can be used for suspension travel (which I doubt).

 

[RESINATOR]

Zandoz, orders need to be placed over the phone.

 

[T-Test]

There is just too much over thinking in this build for me. Wayyyy over my head when it comes to calculus.

 

[choppinczech]

The mono spring I'd bought from Speedway turned out to be 1/2" longer than advertised.

Doesn't sound like much, but it put my shackles at wrong angle.

I ended up getting one from these guys.

 

[choppinczech]

Sorry