anyone make their own control arms?

[exline]

I am curious if anyone has made their own upper or lower control arms for a custom suspension?
I have made custom crossmembers for the c4 corvette suspension and some others and it has worked out well. but never made my own control arms. I have been studying up on suspension geometry for a while now and want to try something on a project car but i need to be able to make my own upper control arm to do it.
I am a welder and fabricator by trade so i am sure i will be able to handle the welding part. i am just not completely sure what size tube or wall thickness i should use for the arms. some places are using from 1 1/4 - 1 1/2 diameter tube with a wall thickness from 1/8 - 1/4 in mild steel. there are some chrome moly ones but i dont have much experience welding that so i want to stay with mild steel.
i know i could just buy a set of arms or have a shop custom make them possibly but i really just want to do it myself.

thanks for any advice, kenny

[bobadame]

I don't have a lot of experience doing this. I've built suspension components for a little circle track car and a few small formula cars. I suppose that the upper arm doesn't need to be nearly as strong as the lower arm which is usually longer and carries the weight of the car through the spring. The outer, upper arm is in tension during cornering and has to be strong enough to resist the torque caused by braking. The inner, upper arm is in compression during the same turn but has a lighter load because much of the weight of the car shifts to the outside during the turn. Other than that there isn't much load on the uppers until you smack something.

[broberts5]

I am a welder/fabricator by trade too. I have built many custom front suspensions utilizing one inch DOM tubing with a 1/8 wall. I have also used the same in chrome-moly. Never had any problems at all.

[exline]

would you think it would be overkill to use 1 1/4 dia, 3/16 wall dom for the uppers on a street car , about 3300 lbs?
Is there any advantage as far as strength, in tig welding them over using a mig? or would you say that its the same and use what ever process you were better at?
I have the geometry figured out for them i just want to be sure they hold up well. I figure some one had to have a little experience doing their own.

I have done a lot of rear suspension fabrication like ladder bars and frame rails and nothing has ever broken so the front A arm should not be a problem. it should see less stress than a set of ladder bars.

thanks guys for the advice

[oldgoaly]

Kenny, bring it along to the EMMR, if you want I'll bring the magnaflux set up. Have to wait til it gets dark to see with black light. Maybe Rick Mullin will bring his posters for the 70's.....:lol: Kirk too, Can't leave out BillG oh this could be fun..... tt

[bobadame]

How are you going to use the car?

[exline]

I hope to make it to emmr again this year.
I will be using the car for regular driving on the street. and maybe a few passes at the drag strip.
i want to update my dodge dart suspension from the old steering box and torrsion bar set up .to a rack n pinion with coil over springs to make room for a bigger motor and headers. also hope to get a little better handeling.
I plan to use the C4 corvette lower control arms and spindles. the upper arms are too long and will about hit the motor so they need to be shorter. I know that gets into changing geometry but i think i have it figured out. i have seen similar set ups with different upper arms work. Also the aluminum C4 stuff is lighter!

[scranm]

check these guys out. i used to work for them about 10yrs ago. they have every part you need for making a-arms. http://www.ubmachine.com/2010catalog.pdf
i've helped make thousands of those things.

[anders nørgaard]

...I have done a lot of rear suspension fabrication like ladder bars and frame rails and nothing has ever broken so the front A arm should not be a problem. it should see less stress than a set of ladder bars.

thanks guys for the advice


Just remember... when you go from accelerating to decellerating (brake)... MOST of the load is being transferred to the front suspension :eek: ;) And most cars go a lot faster from 100 to zero than from zero to 100 m/h.

[exline]

good point about braking. all of that weight goes forward when the brakes get pushed and it all goes through the control arms , so a little overkill here would be ok. i always figure its better to be a little strong and heavy than not strong enough,especially on a street car where a couple pounds arent going to hurt anything.

scranm that link to ubmachine was pretty nice. i wasnt aware of anyplace making most of those parts for purchase. that saves me a lot of fabricating if i can buy some parts all ready cut.thanks!

[Rick (madera)]

check these guys out. i used to work for them about 10yrs ago. they have every part you need for making a-arms. http://www.ubmachine.com/2010catalog.pdf
i've helped make thousands of those things.
they seem to have good prices also. thanks

[bobadame]

The weight transfer load goes into the lower arms when braking. The upper arm doesn't see that load. The only loads it sees are torque caused by braking and cornering loads which are straight tension and compression. The lower arm sees those loads as well but it also carries the weight of the car, and the extra load caused by the springs compressing into them. The point I'm trying to make is that if you make your upper arms as strong as the lower arms, they are heavier than they really need to be. You want to keep the unsprung weight as light as possible.

[exline]

I will be using C4 lower arms and making the upper arms.
I want to get something together to try in the car before i paint it ,incase i end up changing something that involves welding on the car . i dont want to go burning off fresh paint. I wish i had a high tech program on the computer to figure the geometry out but i dont. i have drawn it all out by hand .

I wish i could use the C4 upper arm but its just too long and it would hit the exhaust on the motor. even if i custom build the headers i dont think i can get them to clear. so i need a shorter upper arm .

thanks for all of the good advice so far.

[bobadame]

You can mock this up pretty easy without a computer. Block the frame up at normal ride height and remove the tire and spring. Place a jack under the disc and work the corner up and down starting with the disc at normal ride height. Record the camber change and bump steer values. Now remove the top arm and rig up a temporary arm using all thread rod and turnbuckles. Try different lengths and angles until you achieve the change you are looking for. Then build the new arms using those values and place the new mounts where they need to be.

Oh, I just re-read your last post and I see that you are not necessarily wanting to change the handling of the car. This is going to be tough to do. Shortening the top arm will increase camber gain in bump and roll maybe dramatically.

[bumbler]

Here is a link to a suspension design calculator which may help you with your design
http://www.racingaspirations.com

Lots of good info and ideas which are not limited to the suspension design calculator

Bruce

[Jim Stabe]

Bob makes good points but you should also consider bump steer (if you you haven't already). You didn't mention what steering rack you are using but if you are using the Corvette rack, the track width of your car needs to be the same as in the Vette. The inner pivots for the rack need to fall in the plane defined by the inner pivots of the A arms, the outer tie rod ends will be OK since you are using the Vette spindles. What happens often is that someone will hang A arms on a frame that is either wider or narrower than the original car and then use the same R&P by shortening or lengthening the tie rods and get massive bump steer.

[bzunker]

Kenny. Here is a web site devoted to "scratch-build" cars with a ton of design information and sources. Just check out the forums for what ever you are looking for. I realize the site is for "sports cars" but the information works for everything.

http://www.locostusa.com/

Enjoy. Bob Zunker

[exline]

I have experienced bump steer before in my first suspension project that i changed it from rear steer to front steer. i learned real fast! went into a turn and the car kept turning as it leaned into the turn. i got a couple books and figured out the problem, also learned about ackerman on that project. so i think i got the bump steer under control.I may need to go to a different rack , i havent checked that yet.

now the roll center change will be something new to me. i have been trying to study up on suspension to make sure its right. i have to use a shorter upper arm so that will change the roll center. I am working on understanding all of that now.

thanks, kenny