Lower Front Shock Mount

[DMC7492]

Hi guys,
I like the look of the lower shock mount in the first picture. But the book shows it like picture two and in the first picture.

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Can anybody come up with a good reason not to mount it like picture 1?

[Bob_n_Cincy]

Hi guys,
I like the look of the lower shock mount in the first picture. But the book shows it like picture two and in the first picture.

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Can anybody come up with a good reason not to mount it like picture 1?

The rule of thumb that I use in case like this. "use the CAD drawing, they have been reviewed by the engineers"
Hey look, the LCA rear bushing is mounted correctly in this picture.
Bob

http://thefactoryfiveforum.com/attachment.php?attachmentid=30500&d=1403564311

[Frank818]

What does "the lower bolts for the stamped steel arm should be in opposite locations than shown above"?

FFR is inconsistent on the shock mount orientation, I just realized that after reading this thread.

See the next 3 pix from FFR Manual 1F:

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So what is it? Let's check Wayne's build and see what he did, that might be another indication.

[Jaime]

I looks like the shock mount hole is directly between the two bolt holes, so either orientation should give the same suspension geometry. I feel better with it "pointing in" so force line goes through the center of the weld than "pointing out" where the force line doesn't intersect the weld.

[apexanimal]

^that's my inclination as well

[Frank818]

I looks like the shock mount hole is directly between the two bolt holes, so either orientation should give the same suspension geometry. I feel better with it "pointing in" so force line goes through the center of the weld than "pointing out" where the force line doesn't intersect the weld.

Well exactly! That's exactly how I logically thought about it. With a lot of force, if the mount points towards the spindle (outwards), I could see the bracket tips/lips fail. I mean a lot of force. But if it flows through the force line when mounted towards the shock, then all the force goes at the bottom of the bracket and not trying to bend the lips.

Besides the manual is very clear with the picture and saying "note the orientation of the shock bracket in the picture".

[DMC7492]

Well exactly! That's exactly how I logically thought about it. With a lot of force, if the mount points towards the spindle (outwards), I could see the bracket tips/lips fail. I mean a lot of force. But if it flows through the force line when mounted towards the shock, then all the force goes at the bottom of the bracket and not trying to bend the lips.

Besides the manual is very clear with the picture and saying "note the orientation of the shock bracket in the picture".

I received my kit two weeks ago, this picture is not there. It is a half page of blankness. So I TOOK IT TO THE STREETS JERRY! Oops sorry,got that from Sienfeld.

But I agree the engineering drawings should be followed, they know what they are doing right?
Common sense sometimes alters engineering...

[RM1SepEx]

welcome to the FFR build manual, you will find many more inconsistencies

[Frank818]

Which version of the manual you got on paper?

I think I will mail the techs to get that sorted out once and for all, with the engineering explanation of why it should be installed on the side it should.

[Frank818]

The rule of thumb that I use in case like this. "use the CAD drawing, they have been reviewed by the engineers"
Hey look, the LCA rear bushing is mounted correctly in this picture.
Bob

http://thefactoryfiveforum.com/attachment.php?attachmentid=30500&d=1403564311

Bob, your picture differs from mine, I see the CAD screenshot with the opposite shock mount orientation.

Page 69 of the 1F manual has this:

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Which version of the manual you took your CAD drawing pic from?

[Bob_n_Cincy]

Bob, your picture differs from mine, I see the CAD screenshot with the opposite shock mount orientation.

Page 69 of the 1F manual has this:

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Which version of the manual you took your CAD drawing pic from?

Frank
My picture is out of manual 1I (latest greatest)
Also notice the 2 spot welds on the strut bracket, that is new.
Bob

[Frank818]

This is becoming very interesting. :) That CAD picture has not been updated in the 1I UPDATE REVISION, it's probably only in the 1I FULL version.

That's it, I'm sending all this to the techs and get it cleared out.

[Frank818]

I got a response from FFR tech.

The difference lies in the type of arm you are using and that FFR took most of the pix using the alu arm, which confuses us.

The bracket pointing towards the spindle is the correct orientation for the ALUMINUM CONTROL ARMS.

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The bracket pointing towards the shock (follows the logical force line, if you will) is the correct orientation for the STEEL CONTROL ARMS.

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So I have to reverse mines. :)

[K3LAG]

So the remaining question is, does it really matter which way it is?

Larry

[Frank818]

Larry, that is the new question, yes.

I have asked FFR with my original question to explain the reason behind the orientation but I didn't get an answer on that part.

I will leave that to everyone's feeling. After all, Wayne installed the bracket on the "wrong" side, so that is probably not a big deal.

In my case, if nothing unexpected happens, it's a 15mins-less fix for which if I don't do it, I know myself enough that it'll be wandering in my head like a ghost in a haunted house every time I will drive the car.

[K3LAG]

Mine, with aluminum arms, are also mounted backwards. That being said, they 'look' like they are the right way given all the angles and such and intuitively it seems like this is the way they belong. It would be fairly easy to change them, but I'm not inclined to unless there is a reason.

Larry

[Frank818]

I hear yeah Larry and I am very sad to still not understand the true reason behind this design. I do not question it, I would just like to understand, that's how I am as well. My job requires me to understand what my clients really need, so it's part of me to do something for me or others that I understand the true meaning of and not go blind. Unfortunately, I failed to get an answer here. Since it's an easy fix for me, I will join Bob's club by simply agreeing that the latest 1i manual's CAD drawing certainly has been approved by engineers (and now has been confirmed by a tech), so that there must be a valid reason behind. After all, isn't that what we do for most of the chassis bars, floor, mount points, etc. anyway? :)

[DMC7492]

Okay I think I have a logical conclusion,I read some where there were some builders are using JB weld under the bracket so it sits flush and distributes the load.
The steel lower arm is relatively flat. The shock bracket is wider where the tabs are welded on and the aluminum arm profile is more of an H shape. Also wider towards the center of the car and tapers towards the ball joint.
To get the bracket to sit flat in the aluminum arm if if is turned around it sits better,on the steel control arm, it really doesn't matter and no JB weld is needed.
I contoured the welds as to match the profile of the lower control arm and they sit perfectly flat. Therefore mounting them so the load is inline with the metal tabs and the welds. End of story...makes sense...
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[Frank818]

That makes sense, yes. If that's the reason why, it's strange that FFR says to flip it around on the alu arms, cuz the tabs really don't keep the same angle which I can't understand why it wouldn't change any load distribution, flex, and other stuff an engineer could tell us (we got engineers on this forum?). I'll check out if mines fit better once flipped, if yes I will follow your idea!

BTW I see you are using the 35mm bolt (shorter one) where the long bolt (40mm) should be used. I tried that and I couldn't tighten the shorter nut enough, the bolt's threads were not long enough to go through the nut. How does it look on yours from underneath?

[Jaime]

(we got engineers on this forum?)Engineer here. Of course, a joint like this requires actual finite element analysis to find its true weak points, but if we guess at the failure modes, we can get some estimates of performance.

There are three readily apparent failure points - the through bolts, the mounting tabs, and the cross bolt. The through bolts can only reasonably fail in tension and their yield strength is well documented at about 30000 pounds force for the pair. The mounting tab's most likely tension failure mode is for the cross hole to elongate and tear off. That requires around 4500 pounds force assuming cold rolled steel. The cross bolt can fail in either tension or compression at about 17000 pounds force.

This joint is almost exclusively in compression. The only time it's in tension is when the front wheels are off the ground and then the only tension force is gravity, so it will never be more than a few hundred pounds. The most likely compression failure mode is cross bolt shear failure, or perhaps a more complex collapse of the welded mount piece. I couldn't imagine that being less than the 17000 pound that would shear the cross bolt.

I would say that this piece is more than strong enough, given that it is likely not the first failure point. With a 350 pound per inch spring, whatever would shear that bolt off would compress the spring 20 inches - which is obviously past the point where the spring would bind. I would love to see a shock dyno graph of the Konis that are provided with the kit to get an idea of how much load they are capable of transmitting.

Of course, this analysis only holds true if my gut feeling of the failure mode is correct.

[Frank818]

I love those explanations, it shows what's really going on in the real world behind the parts and based on physics laws.

Reading the above, it means no matter the orientation you install the bracket, it will not change anything in flex, load distribution and stuff like that?

[Jaime]

It will very slightly change the suspension geometry. With the tabs pointing in, the shock will be a degree or so closer to vertical.

I mounted mine the way that they recommend for the steel arms - but I have aluminum. I did have to clearance a bit to make them fit nice. I can't see how it's possible for the tab to be stronger like this:

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Than like this:

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[Frank818]

I don't think the suspension needs to have a different geometry whether it's steel arms or alu arms. 1-deg is probably nothing for a car that is not an F1 or something. If we assume 1-deg difference is the same as 0-deg difference, then flipping the tabs around may just be for better fitment on the alu arms (knowing that the strength is enough no matter its orientation). Which makes sense, it prevents builders from modifying the bracket or alu arms.

[Jaime]

Don't forget that the mounting point on the aluminum arms is fixed - you drill through the bosses that are already there. But people with the steel arms drill their own holes based on Factory Five's measurements. I would assume that the measurements provided put the shock in the same position even with the mount reversed. So, flipping the mount on the arms really does locate the hole slightly inboard of where it was intended. Personally I like this. It will raise the effective spring rate and reduce the force transmitted through the shock. Both are very small amounts, but they are in the right direction.

[Frank818]

Definition: by "flipping the mount" we mean having it like this ? :

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[Jaime]

I'm taking that direction as the one recommended by FF for the aluminum arms, so flipping would be the other way.

[AZPete]

The main reason I have for mounting it the way FFR recommends is so whenever I post a front end photo someone doesn't say, "Hey, you need to reverse it!" :)

[DMC7492]

I leveled the lower control arm in the drill press then drilled and tapped the holes in the drill press to ensure the holes are true and perpendicular to the base of the bracket.
The bolts on the bottom will be trimmed down, as the nuts donot seat properly on the bottom and I do not want to remove any metal from the control arm. They will be torqued to spec with Lottie.