chuckabtjr

Could someone tell me the length of the sway bar link for the 2010 base FE1 front. Is it the 11.?" inch one? Thanks

jdbaugh1

iTrader: (1)

Yes, assuming the GM engineers optimized the geometry from the factory the 11.8" end link is the correct unit for your car. However, there are other members on this site that will tell you to go with the shorter 9.86" end link which is for the FE5 sway bar which has different end geometry. But the only justification for doing so is people have been doing it for years and they think it works better. Using the wrong end links may result in a more rigid front suspension which some people may think is an improvement. Long story short, either end-link will "work" but the longer end link is the end link that was paired with your sway bar from the factory. If the shorter end link was an improvement in every way it makes no sense to me that they wouldn't just install it that way from the factory. Less material makes a cheaper part and also having two different length configurations makes manufacturing across the different trim levels more expensive. It is possible that GM chose to go with a different end link length just because they wanted to waste some money or just for ***** and giggles but I like to think they did it on purpose and for a reason. Until I see something other than anecdotes I will continue to believe the 11.8" end link is the correct choice for your application.

exninja

iTrader: (1)

https://www.cobaltss.net/forums/susp...5/#post7668528

There are pictures of the differences. The end result would be that your FE1 bar would be rotated at rest. The bar works by putting torsion into the bar when the struts are compressed at different lengths. The end result of having the shorter endlink is that your moment arm would reduce slightly creating a larger torsion moment, but I doubt you'd even notice that. You could have a clearance issue with whatever the reason is of that bend in the middle of the bar, but someone likely would have mentioned it if it were an issue. Regardless, if you have the choice, just get the correct endlinks.

This was more for JD's benefit. Doesn't really answer why they used the different lengths, though. The answer for the endlinks is because the sway bars are different, but I don't know why they changed the angle of the sway bars. My guess is to change the moment arm and get a "stiffer" bar without having to make the bar thicker.

jdbaugh1

iTrader: (1)

I thought about this too which made sense when considering one end of the sway bar. However when you consider both sides have the same moment arm lentgth I don't think the stiffening mechanism is because of the shorter moment arm but because of the angle of the moment arm with respect to the force vector from the end link which results in more force being absorbed by the sway bar bushings and less force being transmitted through the bar via torsion. This would make the sway bar function more like having stiffer springs up front (more force to fixed frame) and less like a sway bar. (less force transmitted across to other side as torque) I may be thinking wrong though. What do you think?

exninja

iTrader: (1)

I would have to think about that. My first reaction is no, there would just be more horizontal loads in the bushing. The rotated FE1 bar would behave very similarly to the FE5 bar. But I'll have to draw it out during lunch or something.

exninja

iTrader: (1)

OK, I got it. The bushing (bearing) loads wouldn't change much at all. Those loads depend on the bar's rotational stiffness. It's that rotational stiffness that keeps the bar from moving freely (because it's "fixed" on the other side).

The FE1 bar with shorter endlinks would behave very similarly to the FE5 bar with the same endlinks. The holes would be off by a small amount forward.

jdbaugh1

iTrader: (1)

I'd have to look at the different sway bars installed with their respective end links but I am working under the assumption that when the car is at rest the sway bar end links are transmitting their force close to 90 degrees to rotational axis of the sway bar. At 90 degrees the arm of the sway bar is a pure torque arm with zero force transmitted axially through the arm. When you install a shorter end link you rotate the sway bar arm so that the end links are applying force at a different angle further away from 90 degrees. The more you rotate the bar by dropping the suspension height or going to shorter end links the further you rotate the sway bar thus changing the angle that the end links apply force respective to the rotating axis of the sway bar. This reduces the force perpendicular to sway bar arm and increases the axial force on the arm which causes a reduction in torque being transmitted through the shaft. This change in torque is progressive all the way to the other extreme where the end link would be 180 degrees or straight in line with the sway bar arm at which point NO torque is being transmitted with the sway bar arm being loaded 100% axially and 0% perpendicular.

Edit: Also have to consider the other end isn't fixed, it is mounted to a spring. If torque is being transmitted through the sway bar it can compress the spring on the other side. If the sway bar is rotated in a way that reduces the torque through the sway bar it will also reduce the load it can transmit to the spring on the other side.

exninja

iTrader: (1)

Remember that the endlinks are inputting a motion, NOT a force. The force is from the rotational stiffness of the torsion bar, which does depend on the angle of the bar. There would only be a direct force from the strut when the endlink maxes out wrt the torsion bar arm, which I don't think is possible.

That's also why the sway bar uses end links. If it were connected straight to the strut, then yes the bearing loads would be nuts. Two pin joints take that away.

jdbaugh1

iTrader: (1)

See my above edit about how the force is partially from the rotational stiffness of the bar but also the compression state of the spring on the other side. It's a live system that connects the two suspensions on either side of the car. The rotational stiffness of the bar only dictates how much flex is allowed between each side.

exninja

iTrader: (1)

That's not really that important here. The cause of torque in the bar is differential motion on the two sides. If I want to find the force on the endlinks, all I need is the angle the two ends have moved wrt each other. I don't really care what they're attached to.

EDIT: further thinking, that angle DOES affect the fore/aft load on the strut/strut mount. Probably not very significant compared to the other fore/aft loads on the strut, but I wouldn't know.

jdbaugh1

iTrader: (1)

My argument was properly functioning suspension vs. less properly functioning suspension. I'm not trying to identify the difference in force between the two end links, I'm trying to point out how it affects the function of the sway bar which is to transmit force from one side of the car to the other with its stiffness dictating how much it will transmit before deflecting from torsion. When you change the angle of the end link input force with respect to the rotating axis, you change how much of that force is resulting in torsion on the bar. The further you move away from the stock position, the less torque you are inputting into the bar for any given amount of force from the end link. This would mean less force is being transmitted through the bar to the suspension on the other side effectively changing the way the sway bar functions.

exninja

iTrader: (1)

That is true, but the stock FE1 sway bar would act almost identical to the FE5 bar in that respect (with a slight difference due to the fore/aft location of the hole). You can pretend the bend in the arm of the FE5 sway bar is straight and for all intents and purposes would behave just like the FE1 bar in the same situation (neglecting the thickness change).

That being said, and thinking further, you're right, the "axial" force does go up in the torsion bar arm. I figured it out again. Let's just say we're both right, but I'm not going to draw it out here.

It's a complicated system. I make free body diagrams for a living, and I had to think about this.

exninja

iTrader: (1)

I edited my previous post here.

jdbaugh1

iTrader: (1)

I'm just glad we you see the point I was trying to make. I was sitting here drawing free body diagrams and playing with a paperclip trying to verify I was thinking right because up to this point people just acted like I was a contrarian suggesting the right length end link for the sway bar. I don't know how much it affects things but I still don't think throwing on a shorter end links in combination with lowering springs and an FE1 bar is the best idea like has been promoted on this site time and time again. Thanks for hearing me out.

exninja

iTrader: (1)

It's still weird (and even more so after this) that they shortened the FE5 link and bent the arm of the bar. I guess they traded axial/shear/bending/bearing forces with a thickness change and just came up with a compromise rather than thickening it further.

jdbaugh1

iTrader: (1)

And I had it in my mind for some reason that the FE5 sway bar was formed differently on the ends so they could use the shorter, more rigid end links with the stiffer bar. I don't know why I think that though and it could be a false memory. Been a while since I had the two sway bars side by side.

exninja

iTrader: (1)

It is, check out the photo in the post I linked. But that bend doesn't really change anything. What's important is the angle of the strut motion to the line from the end of the sway bar/endlink joint to the axis of the torsion bar, and how far away that is from perpendicular.

Also seems like if you have lowering springs on an FE5 suspension you'd want the FE1/3 endlink so that it evens out a bit. Lowering springs with FE5 endlink and an FE1/3 bar would be awful.

ECaulk

iTrader: (6)

Read through half of it, not in an mech engineering mindset right now, but you have to remember that the resting distance between the swaybar and the strut will change with ride height. The position of the control arm changes with decreased ride height.

Maybe if I get unlazy (unlikely though as I have more **** for work to read in my free time) I'll draw it up. IIRC originally it was from a discussion John Powell had with one of the GM suspension engineers.

jdbaugh1

iTrader: (1)

Yeah the photo you posted in the link is my photo from when I first brought this up when someone asked which end links they should be using. If you read through that thread you will also see that I got blasted for arriving at the same conclusion I bolded in your above comment.

exninja

iTrader: (1)

LOL I didn't even realize that. I take a gander.

exninja

iTrader: (1)

OK read through. The response of "you didn't do testing so your picture is wrong" was worthless. You're right, it may work fine, but there is no really good reason for it. You will put more wear into the bushings and potentially lose the mount (one bolt vs two). Better to get the proper sway bar and endlinks.

I don't see anything wrong with the pictures. They are exaggerated, but unless you change the strut length that's what would happen.

jdbaugh1

iTrader: (1)

Yes they are exaggerated on purpose to show the effect more clearly. I have no idea on the actual dimensions I just threw something together quick because no one seemed to understand the point I was trying to make while simultaneously saying I was wrong. I have to admit I feel kind of vindicated now that you agree with me. So thanks for that.

exninja

iTrader: (1)

JD drew it up just fine in that thread I linked earlier. I saw that happening the whole time, but my epiphany came later when i realized that there is in fact a change in force because of it. Basically, the torque is dependent on the angle of twist in the bar. That puts a tangential force in the joint of the bar and the endlink. Because the joint is pinned, the angle of the endlink determines the axial force in the endlink. The further from perpendicular, the greater the axial force (because the tangential force doesn't change). When the axial force in the endlink is greater than the tangential force, there is a similar axial force in the arm of the torsion bar. That axial force has to be reacted in the swaybar bushings.

I'll bet right now that's why all of our swaybar bushings are crap and need to be replaced.

jdbaugh1

iTrader: (1)

You said it more correctly than me but that is exactly what I was trying to say in my original comment.

exninja

iTrader: (1)

Yeah, i was stuck on the tangential force. I wasn't figuring out the load in the endlink correctly at first. I figured it out at 12:43PM. I know you get it, I was thinking Eric might want another explanation.