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Front-end design: What does a strut rod do?

 
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Old 01-05-2003, 12:27 AM
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Front-end design: What does a strut rod do?

[updated:LAST EDITED ON 05-Jan-03 AT 01:29 AM (EST)]Ok, so one thing the strut-rod does is to take the rotational load of braking. So the metal of the strut-rod must be spring metal like the torsion bar - designed to resist shear loads forever. That means that the strut-rod probably bends a little when the brakes are on hard. That would tend to pull the A-arms foreward and inward, adding to the toe-in. That seems like a very good thing.

Another thing the strut-rods might do is to help transfer lateral loads during turns. If you take a sharp left turn, or are carrying a load and making a left turn, or are braking in a left turn, there is a large load on the right side of the front suspension. (Visa-versa for the other side, of course.) The angled strut rod on the right side would be exactly in the right place to help keep things in place in this situation.

So my IFS needs the strut-rods to be mounted to handle both shear and tension loads (the shear loads in a vertical plane), and it needs to be mounted with the front ends right on the axis of the A-arms. That's the kind of information that will help me install it properly. Thanks to all.

The other point I need to explore is how to mount the cross-member. I'll need to properly box the frame, and then either bolt or weld it in place. If I bolt it in place, I need to understand what forces it is going to be subjected to. Bolts should not be used in heavy shear applications. I'll be looking at either fabricating locating dowels or find some other method of addressing the shear forces.

Remember that I'm a computer hack, not an engineer. I'm just speculating. But with your help, I think I'm on the right track.

Good night, all.

 
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Old 01-05-2003, 01:24 AM
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Front-end design: What does a strut rod do?

<<<Bolts should not be used in heavy shear applications. I'll be looking at either fabricating locating dowels or find some other method of addressing the shear forces.>>>

Paul

There is much more in your post that I could use an explanation for eventually. Can we start with the above. How is a locating dowel going to be different than a shouldered bolt in a heavy sheer application?

This should be a real informative thread before it's through.

Dewayne

 
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Old 01-05-2003, 08:43 AM
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Front-end design: What does a strut rod do?

Carl

While I do think you have made up your mind on this subject, you have the right to as you have definitely read plenty of opinions on the subject in your internet travels. There is definitely some evidence to support the opinion. If you have, you aren't alone. Whether you have or not, its time to take a look at John's PICs and suggest improvements if you can. A number of the IFS threads have ended with guys getting mad. There's no value in that. There are forum members who are welders, engineers etc that can offer insight if they don't get chastied for it. There really isn't a huge problem with that here. I can't believe the way the "experts" on HAMB treat people. I won't be back there after I saw the way a fellow 48-60 poster was treated after asking an innocent question.




Dewayne
I dont believe that I am qualified to offer suspension engineering suggestions. Things that I thought were taken for granted now leave me confused. Im an EE by training and a car buff by choice and after 45 or so years I do feel qualified in certain areas.

As far as HAMB, there are more than one over there from here, including the guy who took a ribbing. Its a different type of forum that takes getting used to. And do an intro before posting questions!
The RRT is another choice that is a bit tamer.

Engineers said the Titanic was sink proof and the Challenger was perfection.
I go for second and third opinions when I go to the doctors; I like to do the same when my family jewels are on the line.


 
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Old 01-05-2003, 09:08 AM
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Front-end design: What does a strut rod do?

Carl

You are probably like most of us here. You know a little about a lot of things, and everything about nothing. I come here to learn and share. We have tried to discuss different IFS systems here and it usually doesn't end with much deep thought. We need to get past the generalization that MII is just not going to work because F100s are heavier than Mustangs. I am tired of hearing that and I don't even have one. A few thousand people are probably driving F100s around with MII. I can't cite a single failure in an F100. It may not be an ideal IFS, but apparently it can work.

At least three guys on the forum are doing the Gibbons clip now or soon. I plan on learning something about suspension principles while I am here. After Paul's last post, I am certain he is knowledgeable and I await my next lesson.

'fenders
 
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Old 01-05-2003, 10:53 AM
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Front-end design: What does a strut rod do?


Dewayne writes;How is a locating dowel going to be different than a shouldered bolt in a heavy sheer application?

Dewayne,

A shouldered bolt might be sufficient. I'll have to look into it. We'll need to estimate the potential shear forces and then use the right size bolt. We'll also have to properly prepare the frame and crossmember and then properly size and align the holes so that the bolt fits tight in the holes.

Examples of the use of dowels that bear shear loads include the dowels that 'locate' the bellhousing to the engine block and the dowel that 'locates' the flywheel to the crank. Those aren't locating dowels like the locating dowels used to locate a head on a block. The dowels on the bellhousing flange and the end of a crankshaft are there to bear shear loads.

I have first-hand experience with the crank dowel thing. I bought a Chevy S-10 that had an 'engine knock'. When I pulled the engine off the automatic transmission I discovered that somebody had left the crank dowel off during a transmission swap. The flexplate was shifting back and forth and knocking on the flywheel bolts.

Properly preparing the frame for a locating bolt or dowel will include welding some reinforcing material around the hole that will be used to bear the shear forces. Then the hole will want to be drilled slightly undersized to the bolt shank or the dowel's diameter, and after the crossmember is trial fitted, the holes in the frame and crossmember will want to be carefully reamed to fit the bolt. If I did all that, I would feel pretty good about having addressed the shear factors. BTW, I'm talking about the vertical surface on the inside of the boxed frame where the frame and crossmember join.

When I first heard about the idea of bolting the Gibbon's crossmember on instead of welding, I was not sure if I liked the idea. I have changed my mind. Welding effects the metal welded and leaves residual stress. Properly bolting something on would be fine as long as you do it right.

All criticizisms and arguments will be cheerfully entertained.

Carl, hang in there with us as we flog this issue.

 
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Old 01-05-2003, 12:51 PM
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Front-end design: What does a strut rod do?


BTW, I'm trying to get an idea of the amount of shear forces that need to be allowed for. I'm using this type of information to get a ballpark idea of what the forces are. I'm rusty with my Physics, so if somebody out there is a little sharper with this stuff, I'd appreciate it if you'd help me with my calculations.

A 4000 lb truck travelling at 60 MPH can come to a stop in 160 feet.

60MPH times 5280 ft divided by 3600 sec/hr is 88ft/sec.

4000lbs times 88ft/sec divided by 160 feet is 2200lb/sec? This is where I'm fuzzy. If this really is the force applied then I need to multiply this times the distance from the center of the mass to the point where the bolts or dowels are located to calculate the shear forces. And I might need to know the surface area of the holes that the bolts/dowels are inserted through. The last part could be tricky, the hole is round.

 
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Old 01-05-2003, 01:40 PM
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Front-end design: What does a strut rod do?

Paul and everyone,

While we wait for a Physics major to stop by, I thought i would post this for 'rage. Feel free to use it for a screensaver if you like. 1 5/16 inch diameter spring steel torque strut. Feel the strength jumping out of your monitor.

It's not too late Joe, you said you haven't welded yet!

'fenders



https://www.ford-trucks.com/user_gallery/sizeimage.php?&photoid=12095&.jpg

https://www.ford-trucks.com/user_gallery/sizeimage.php?&photoid=12096&.jpg
 
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Old 01-05-2003, 03:01 PM
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Front-end design: What does a strut rod do?

>I'm rusty with my Physics, so if somebody out there is a
>little sharper with this stuff, I'd appreciate it if you'd
>help me with my calculations.
>
>A 4000 lb truck travelling at 60 MPH can come to a stop in
>160 feet.
>
>60MPH times 5280 ft divided by 3600 sec/hr is 88ft/sec.
>
>4000lbs times 88ft/sec divided by 160 feet is 2200lb/sec?


Hmmm. I used to teach dynamics in college but it's been quite a while. I'm probably rustier than you, John. Maybe I should take a shower in my grit blast cabinet?

Let's see if I can get through it without the usual result - making a fool of myself.

Converting to SI units:
Truck mass = M = 4000 lb / (2.2 lb/kg) = 1820 kg
Initial position = Xo = -160 feet = -49 m
Initial velocity = Vo = 60 MPH = 88 ft/sec = 27 m/s

Equation for position under constant acceleration (or deceleration):
X = Xo + VoT + aT^2/2
Equation for velocity under constant acceleration (or deceleration):
V = Vo + aT

when the truck comes to a stop:
X = 0 = -49 m + 27 m/s * T + a * T^2 / 2
and
V = 0 = 27 m/s + a * T
Solving these two simultaneously:
a = (-27 m/s) / T
49 m = (27 m/s) * T + (-27 m/s) / T * T^2 / 2
49 m = (27 m/s) * T + (-27 m/s) * T / 2
49 m = (27 m/s - 27 m/s / 2) * T
T = 49 m / (13.5 m/s) = 3.63 s
a = -27 m/s / T = (-27 m/s) / (3.63 s) = -7.44 m/s^2

Now to the loads on the truck wheels:

F = Ma
F = 1820 kg * (-7.44 m/s^2) = 13550 kg m /s^2 = 13550 N
13550 N / (4.448 N / lb) = 3050 lbs

Assuming the rear brakes don't do squat and the braking force is evenly distributed between the front two wheels, each wheel sees about 1500 lbs backwards on the tread during this stop.

Note that I rounded some of the numbers to a couple significant figures.

I'll also note for comparison that the maximum dynamic forces from the vehicle weight bouncing along are very roughly 3 times the static weight of the vehicle. If we say the front of the truck weighs 3000 lbs then the static load on each wheel is about 1500 lbs upward on the tread. The maximum dynamic load is going to be about 4500 lbs upward on each front wheel - three times the braking load.

John, you can multiply the vertical loads above by two or three based on whatever size engine (or engines) you are putting in and their increased weight.

>This is where I'm fuzzy. If this really is the force applied
>then I need to multiply this times the distance from the
>center of the mass to the point where the bolts or dowels
>are located to calculate the shear forces. And I might need
>to know the surface area of the holes that the bolts/dowels
>are inserted through. The last part could be tricky, the
>hole is round.

To really do the analysis you need to do a free body diagram and compute the static forces and moments. I'd be happy (sorta) to do this but I need accurate dimensions of ALL the components and their relative spacing. Getting enough info for this kind of analysis is going to be a challenge.

George

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See my 1956 F-250 in progress at www.clubfte.com/users/earl/index.html
 
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Old 01-05-2003, 03:21 PM
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Front-end design: What does a strut rod do?

John

Thanks for emailing the PICs offline. That made it easier. I like the mods you propose. One in particular is the brace on the back, designed to add back some of the strut rod function. If you make it a real brace that heads back more than 2 inches on the frame, I think this mod is worth as much as all the other bracing combined. I don't think you have missed anything. There is just so much bracing you can do in one small spot. Since I guess you aren't open to welding in a big beefy chunk of Volare torsion bar, I guess this will do.

Have there been any control arm issues you are aware of? I haven't seen one of those that impressed me since the days of 4000 pound LTDs.
It looks like the weak spot on my Volare. I may box the lower. I don't like MII arms either. You have heard this one from me before.

I have already conceded and gusseted up my Volare so I guess it's time to find a weak spot on the Bat clip geometry. Bolt on quick disconnect IFS? I don't know John. Maybe they use big hood pins or DZUZ (sp?) fasteners?

Seriously though, I am hopeful I will learn how to calculate required bolt sizes when this is over.

'fenders


 
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Old 01-05-2003, 09:21 PM
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Front-end design: What does a strut rod do?

Wwwhhooaaaaa!!!!!!!!!!!!! Ok, you guys have just blown over my head and below my knees. I slept through physics class. Has it occurred to anyone just how soft the rivets are that hold these jalopies together?!? George if anyone should know after drilling every single one of them out. And now we're calculating shear loads and figuring for dowel pins?!? I didn't know that I was building a space shuttle here. I though I was just revamping a 50-year-old pickup truck. 1st point: I had to pinch the frame rails to get this thing in. This wasn't due to a problem or a defect. It was designed to be a snug fit and this is the accepted method of installation. The interference fit alone plus the 1/2" and 3/8" bolt on either side would be enough for me to keep that bugger under there. I added 3 more 3/8" bolts per side on top of that just for piece of mind. All bolts are in equally sized holes. I.E. 3/8" bolt in a 3/8" hole. 2nd point: I have not and will not box my frame. The art of frame boxing in my opinion is useful only when you have done major surgery to the rails themselves such as chopping the bottom half of them out to hack in a Volare clip or lopping the front third off to graft on a Camaro or LTD clip. Even the MII warrants boxing due to the frame rail becoming a structural part of the crossmember after the spring perches are welded on diagonally fron the rest of the crossmember. The only other case may be if you're building a lovely trailer queen that will spend more time with the hood propped up at the World of Wheels than out on the interstate and you're concerned about them being pretty. None of that becomes an issue with the Gibbon unit. It surrounds and bolts (or welds) to the frame. It doesn't compromise the frame's original structural integrity at all. The only place where it may be weakened at all is in the area where it must be trimmed for steering gear clearance. This is even a moot point as far as I'm concerned as this area is supported by the new IFS crossmember. The steel that this crossmember is built out of is all 3/16" and 1/4". The frame stock is 1/8". Ample reinforcement in my book for a little sliver cut out of the upper and lower flanges. I'm not going to lose any sleep over whether or not it will fall out of there. The only thing that might knock it loose is an impact. An impact of the magnitude that will ensure that I'm either in the morgue or a long term hospital resident. In either case, I won't care much about the truck anymore anyway. Lastly, are we forgetting about the entire purpose of this post? THE STRUT RODS!! THe strut rods will take the majority of the stress of braking and turning away from the rest of the suspension. We've already established that. If anything in the Gibbon kit is critical to safety, it's the strut rod mounts. After installing mine, I'm not worried about that either.
 
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Old 01-05-2003, 09:59 PM
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Front-end design: What does a strut rod do?

[updated:LAST EDITED ON 05-Jan-03 AT 11:11&nbsp;PM (EST)]"Lastly, are we forgetting about the entire purpose of this post? THE STRUT RODS!! ............. After installing mine, I'm not worried about that either."

Your IFS integrity is not really being questioned here. You don't check back often enough rage, I got bored and called in the big guns. Hold on, we are going to learn something here. Nobody is suggesting you should lose sleep over your install. Maybe at the end of this you will decide to weld in your clip. Maybe not. No harm will be done. If someone finds a flaw in a Volare or a Gibbon's IFS along the way, then we will know how it feels to be Niolon. Sound good? Great!!!

Joe or Paul, can you post a PIC of the Gibbons to this forum? Don't worry Joe, we'll make them speak English after the numbers stop flying.

'fenders
 
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Old 01-05-2003, 11:07 PM
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Front-end design: What does a strut rod do?

It's past my bedtime and after all that typing on the 9" post, I'm bushed. I'll get one up tomorrow after work if Paul doesn't beat me to it.
 
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Old 01-06-2003, 09:58 AM
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Front-end design: What does a strut rod do?


Dewayne,

I can take a picture of the parts and I can post a copy of a picture from a magazine article. I'll work on that today.

 
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Old 01-06-2003, 05:48 PM
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Front-end design: What does a strut rod do?

Thanks Paul and take your time. I am interested for future projects. I regard the Volare as a permanent installation (Sorry masochist John) My next step from here would be to chop her off at the firewall. Last resort if my Dodge adventure doesn't pan out.
I have applied for admission to MIT so I can continue reading George's posts .

Just kidding, I know I asked you to contribute. My low comprehension is not your fault. I intend to research some definitions so we can continue on. I think we need to wait for the PICs so you have a clear idea what we are asking before you go to so much trouble. Thanks for doing it. It was above and beyond the call of duty.

'fenders
 
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Old 01-06-2003, 06:36 PM
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Front-end design: What does a strut rod do?


Ok, so I went out and bought a Physics book to get the lexicon of Statics and Dynamics figured out. I also bought the book "High Performance Handling Handbook" by Don Alexander. Once I know what to ask, I'll be back with some questions on that subject.

Meanwhile I'll dig out the Gibbons/Cordoba stuff, lay it out to get an idea of everything that's there, and plan my installation.

John, I'll have you and the MII in mind as well, while I bone up on IFS design.

 

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