Z28cross-fire

I recently got around to making my own set of solid aluminum LCAs.

6061 Aluminum
Spherical rod ends, carbon steel with steel race
Rubber rod end boot
1/2"-20 tap, left and right hand
Knurled since the rod is round without a spot for a wrench.

Tell me what you guys think, and what could be done better/changed.

//<86TA>\\

iTrader: (14)

1/2" rod ends may be a little on the weak side, most aftermarket arms use 3/4 ends with reducers. They may work just fine though

FueledSoul

iTrader: (18)

Agree with above... 3/4" minimal...

scooter

iTrader: (11)

Those taps couldnt have been cheap, you can buy the aluminum stock already drilled and tapped LH/RH for 3/4" pretty cheaply from Coleman and the ends are hex so you can put a wrench on them

Z28cross-fire

The left hand tap was the expensive one, otherwise the right hand taps were pretty cheap. As for the tubing, I got 2 sets out of the rod I bought for a third the price Coleman wants for the already tapped ones. Plus I can tap as many as I want now in the future, it seemed more practical.

As for the size, there's nothing saying I can't drill a 3/4 hole for them and re-tap those too. Has anyone tried 1/2" before? Did it snap, or something happen? I will have to update this when I get them on the car, and see how they fair.

Thanks for the input so far guys, keep it coming!

gregsz-28

iTrader: (1)

I think even a .5" rod end is stronger then the car it is bolted to.

//<86TA>\\

iTrader: (14)

in reality, the lca bolts are only 1/2", 12mm actually, so they are just as strong as the lca bolts, but the loading is different, double vs single shear.

Z28cross-fire

That is what I was thinking. It's going on a stock car. But that got me thinking as to what these could hold up to on a non-stock car.

Let's say my car weights 4500 lbs (it's not, but for sake of argument). I raced a couple times this summer and my fastest 60' was 2.134 seconds (this is real, not just for sake of argument). The rod I have is 6061 aluminum, and is for sure strong enough against bending. So let's look at the rod ends. Made of carbon steel, and going by wikipedia the low grade carbon steel is 55 KSI. The tap size/threading I used has a tensile area of 0.1599, found here, or calculated here.

car = 4500 lbs = 2041.166 kg
time = 2.134 seconds;
velocity = 60ft/2.134s = 28.116 ft/s = 8.5698 m/s
acceleration = velocity/time = 4.0158 m/s^2
rod ends = 0.1599 * 55,000lbs tensile yield = 8794.5lbs = 39119.885 Newtons

F = ma = (2041.166 kg)*(4.0158 m/s^2) = 8196.914 Newtons

So basically, yes the 1/2-20 taps are strong enough with the rod ends I am using. If anyone else wants to do the math and make sure I didn't make a mistake it'd be appreciated. Also, I calculated the fastest 60' with that weight and assuming the rods would break right at their yield. Is 0.9769 seconds a fast 60' time? I don't mean for this to start a flame war. I just found it interesting calculating what these can hold up to, especially since they're going on my car.

scooter

iTrader: (11)

Even with your calculations I think you are horribly underestimating the loads that the LCA's are experiencing.

Z28cross-fire

I know what loads are put on the LCA, the math above is just an ideal case. So does anyone know someone, or have themselves, made/put 1/2" tapped LCAs on?

Guest

What about impact loads? Those are going to be higher. Also you have to take into account where the load is coming from, and where its being resisted at. Your math above is a gross oversimplification of whats going on in reality.

Not sure how you figure that. The LCA bolt itself does not know if its in a rod end, or a sleeve for a rubber bushing. If you're talking about the rod end itself where it goes into the tube it cant see shear forces in use, because the ends are free to rotate. Only way they could experience shear is if they were fixed in place.

howy03

iTrader: (2)

nice job! go for the panhard bar and sell them as a set..If u made an extra set find some one with a 3rd gen that drags or autocross and let them put a set thru the paces for u.

Z28cross-fire

@madmax

Yea I know its simplified, hence why I said ideal, and nothing is ideal in the real world. Impact loads are obviously different. Launching on a solid hook is definitely going to take huge hit versus going from a 20 mph roll.

@howy03

I did make a second set actually. And I will be making the panhard soon. The panhard will be a lot thicker diameter rod and probably better rod ends. It's not quite as short as the LCAs so I fear more of a chance of bending/breaking.

Stephen

iTrader: (12)

The knurled is a good idea. I woulda machined the very center, into a hex for a open end wrench to fit. Did you make spacer bushing to fit between the rod ends & the LCA mounts, or are they just really wide/thick?

You gonna make more & sell? (just asking...i already have some solid LCAs)

Guest

I was more referring to if this thing was street driven and you hit a pothole or other similar problem while doing 60+. Its not going to be pretty.

Twin_Turbo

iTrader: (25)

1/2 way too small, at least 5/8 and if used rigorously I'd use 3/4

Z28cross-fire

Does anyone have an answer to my question?
@madmax, I thought about potholes/train tracks/etc after I posted. It raises a good point, and we will have to see.

@Stephen, if people would like to buy my other set, or if there's more than one person wanting some despite people thinking they are too weak, I would be willing to make more.

83 Crossfire TA

iTrader: (2)

First... your math doesn't have much to do with the actual loading that they experience. Any alloy steel that they should be made out of would be much stronger than that (anyone care to look up some actual numbers for typical rod ends?), and then the fact is that unless you do something stupid the LCA's will not be in tension, but in compression most of the time (at least under acceleration.

In the end the forces on them are not nearly what you expect them to be, and much smaller LCA's will live on our sliding link TA rear suspension then a typical 3 or 4 link. Most setups, unless they significantly change geometry or how the suspension works (like replacing the front sliding link on the TA with a pivot or other solid link) don't really use the LCA's for much but locating the axle, so you shouldn't be able to break even much undersized LCA's unless you hit something or go airborne.

Even if they're not strong enough, usually the mode of failure on them is to either wear out or to stretch the pocket around the ball out, so you'll get some warning (clunking) before catastrophic failure.

All that said, I don't see much of a point in really messing with them to start with... but that's a completely different issue.

89_RS

The 6000 and 7000 series of aluminum alloys have close to or better yield strengths as SAE 1020 mild steel.

6061-T6 aluminum yields at 40kpsi (ultimate is 50kpsi), 7075-T6 aluminum yields at 73kpsi (ultimate is 83kpsi), and SAE 1020 mild steel yields at 51kpsi (ultimate is 61kpsi). All values were found on matweb.com.

If these guys are sized right, then he's ok. But hes not given enough info on the rod ends. You can buy a $4 1/2" rod end from AED and its only rated for 5kpsi or you can spend almost $100 for a 1/2" rod end at AED and it be rated for 33kpsi.

DeanJ

I had spherical joints in my rear control arms and panhard bar and they were very noisey. I swaped them out for UMI Roto Joints, and I love them. Very firm and almost as quiet as stock. The sphericals were the good teflon lined ones too. Those carbon ones are going to make lots of noise. I wouldn't use joints with 1/2" shanks here. Use 3/4" and never worry about it. My

customblackbird

iTrader: (15)

They look nice, I have to agree with 83 crossfire TA on that the LCAs dont really see much of a load and are mostly for centering the rear end. The tq arm is wat really takes the brunt of the tq. And we all know what the panhard bar does. LCAs basically compress under acceleration and stretch under deceleration. Am I ok with your 1/2" rod ends... i think you should be fine depending on the road conditions and how u drive/how much power you have(too much traction with slicks).

Just wondering how much you made the LCAs for? how much u have invested in them? I made a DOM steel 1.25" LCA with mild steel rod ends and 3/4" rods for less than 40$ each. I also made a shorty tq arm with sliding mount and 3/4" rod ends for less than 70$.

I personally wouldnt use 1/2" rod ends tho on my car which is why i went with 3/4". Id rather be on the safe side with the suspension being too strong than one day break something.

88 350 tpi formula

iTrader: (9)

Ive seen the stock bolts bend and get beat up on a friends car (my old car) it doesnt take more than a few good hard launches and thats it! I will give that he has a tunnel mount tq arm but it has a slide joint and he went up to bigger bolts

83 Crossfire TA

iTrader: (2)

I'd be really surprised if he bent them without something being wrong or the car being in an accident.

3rdgenmaro

iTrader: (9)

But Aluminum fatigues.

customblackbird

iTrader: (15)

I agree! I slid into a curb at 45mph after my *** end swung out. I snapped my rear axle like a twig and destroyed both front and rear passenger rims, bent up my hotpart 1/4" steel strut bearing caps and I bent a LCA pretty bad from the rim pushing into it... yet the 1/2" LCA bolts are completely fine. The 1/2" bolts are strong.

perhaps the bolts he was using wasnt grade 8? perhaps less than a grade 5... like hardware store bolts that have a low grade?

89_RS

So does steel, or for that matter any material known to man has a fatigue life.

I don't know what the fatigue rates are for steel or aluminum. Seeing as how he's using soild bar, I think fatigue isn't going to be much of a worry.

Unless you have the rates, try not to point out the blatantly stupid obvious things like that and then make it sound as if another material won't fatigue. Makes you look stupid.

88 350 tpi formula

iTrader: (9)

nope he just hooks that hard. hes managed to snap other parts since then as well. had to go with bigger ends on the tq arm, but you know every car is not the same. tq, traction all play big parts. heck aluminum drive shafts are not good with slicks people break those in 12's but I know of one stock 4th gen thats been in the 9's with his. KOTS he pulled the car there too high and came dn on his oilpan but thats another story my point is smashing your car into a curb has little if anything to do with the bolts and i would guess you had stock arms or ones with bushings to take the abuse

88 350 tpi formula

iTrader: (9)

guess you cant read "stock" oh well carry on

customblackbird

iTrader: (15)

Front aarms where stock peices with poly bushings. rear LCAs where DOM tubing, double rod end, offset UMI LCAs. same goes for the panhard bar.

Im saying the shear force of the impact from the curb would be much more than hooking the car at the track, the impact was sudden with no give like a launch.

Z28cross-fire

customblackbird, mine where around the same price as yours if you just count cost of parts. Cost of tools that I now have to use over and over is in addition.

Hitting a curb is different than hooking on a good launch, apples and oranges. I'm not making them to survive through a crash. Driving in street conditions is good enough for me with these. Drag racing especially with radials will be a different story.

I have already driven with them on, although not much, but they have been holding up well. It is a noticeable increase in stiffness and noise on acceleration and hitting bumps, respectively.

White'89

iTrader: (8)

I don't think you will have any issues what so ever. But then again stress testing will be the ultimatum. I believe as long as you are using a rod end that goes deep enough into the tube paired with metric threading you should have no issues.

Even though I personally love aluminum I have to say it has that one BIG con. Unlike steel which bends, when aluminum fails...it breaks.