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Author Topic:   REAR CONTROL ARMS
JML
Member
posted May 18, 2002 11:11 PM
I race a metric chassis street stock with a 9 inch rear. Our rules read "stock type locating arms. Optional Radius Rods and Heim Ends allowed. Lower locating arms must be stock length center of bolt to center of bolt for type of frame. Frame and rear end locating arm mounts must be stock, unaltered. After market locating arms must mount in stock location." (No panard bar).

I have stock upper control arms shortened to 10.5 inches boxed with rubber bushings. Lowers are stock length boxed with polyurethane bushings. Some guys are running adjustable uppers with heim joints. I understand that with all polyurethane bushings I may encounter a suspension bind. Is this true? Has anyone else used heims on the uppers and how?

Thanks

snowman
Member
posted May 19, 2002 02:00 AM
JML, For a race car, the stock metric 4 link is a piece of junk.......Look at the design.......The 2 upper links, they are attached at the chassis and angled to the housing.......for the arms to rotate upward without binding, They would need to seperate from each other as they rotated on thier respective arcs..........But they can not,because they are attached to the rear end housing.........So,as they move,they are placed in a bind.........

The only reason this system works at all is, because of the compliance in the bushings and arms,and, the degrees of rotation is small.

So, if you take out all the compliance, It will bind............

At the local tracks, the hime joints are illegal.......So, I have not personally experimented with them.......However, I would think that a carefull guy (being aware of the potential binding ) may be able to use them to an advantage..........

A lot of guys use the solid lowers and keep 2 stock bushings in the uppers.....Seems to be a fair compromise.........

Good luck,

Snowman



bbchs
Member
posted May 19, 2002 07:36 PM
SEE ABOVE, Snowman's got it. If I might add, when building our I-stock, I spoke with Jeff Anderson, multi-time I-stock champ. He indicated he left the original rubber bushings in his car as long as they are not coming apart. I did so in ours and the car works very well. SLEEPY


istock59
Member
posted May 20, 2002 07:32 AM
I use urethane in the lowers, and stock rubber in the uppers for the exact same reason that snowman talks about.


WesternAuto17
Member
posted May 20, 2002 08:53 AM
Would rubber on the housing uppers with eurathane on the frame-end of the upper control arms suffice to prevent binding?


snowman
Member
posted May 21, 2002 01:16 PM
Thanks Sleepy, I was just thinking of you yesterday,I hadn't seen you on the forum lately. I hope all is well with you and your family. Glad you're back.

Chuck, I would say that's your problem. On my car I run the solid bushings on all the lowers. Stock bushings on the chassis end of the uppers. On the rear end housing,9 in, I make the upper brackets out of 1/8 X 2in flatstock and a piece of 1/2 in.ID tap tube.
So,in effect, I have 2 stock bushings and the rest are solid.

If you take out all the compliance, It will bind...........

WesternAuto 17, I think You should be OK

Good Luck Guys

Snowman

widebody
Member
posted May 21, 2002 01:31 PM
What about using Heim joints and rods for the upper links? Wouldnt these eliminate the bind?
Widebody


snowman
Member
posted May 21, 2002 11:20 PM
Widebody, I know from your previous posts that you are a pretty sharp guy. You may be able to figure something out.........
As I mentioned earlier, these kind of mods are illegal (and obvious) around here. So, I haven't made any effort to utilize them.

I think perhaps I have failed to explain the bind very well.........Let me try again.....

Imagine we are standing behind the car and looking at the rear end. Now,if we disconect the upper arms from the rear end housing..........As we move the arms upward ......... the left arm does not move straight up, it moves upward,forward,and to the left.........The right would, of course, move up,forward and right........Two opposing arms wanting to move the rear end two different directions..........What I am geting at is, it is a bind consisting of opposing arcs, not a bushing bind.

They are in a bind with any movement,and it only gets worse........

Our race cars are even worse in this respect,as we lower the cars.......more than stock.........

Solid rods with rod ends would make the problem worse..........

Having said that, let me say again that a carefull guy may be able to figure something out.........For every scenario that I can think of using them, I see a problem, a more overwhelming reason not to use them.......But thats just me, and there are those who feel that I am "challenged" in that area.......lol

Good Luck,
Snowman


widebody
Member
posted May 22, 2002 12:26 PM
First thanks for the kind words. I was tring to get some thought going, and was running late, I should have added some more ideas.. I realize using heims and Rods dont eliminate the bind, And I agree that a controlled bind can be dealt with in many
ways. I fell a bit UNsharp these days becase as sharp as you'll may think I am I cant find(dont have) that asnwers I seek. I agree with all that your saying, The whole issue of bind/ compliance and so forth is an old issue.
HERES WHAT I SHOULD HAVE SAID YESTERDAY. (This is a bit long)
This is my current delema that keeps me awake at night. My rules are very simular to what these guys are saying. My rules differ in that I can run adjustable uppers. The biggest problem is NO PANHARD BAR. Ive spent many hours under the car tring to come up with that "compromise". Are rules are a bit looser in that although were suposed to use stock mounting, by running a 9", the need for fabricated upper mounts, allows me a bit of freedom with "STOCK" the mounting location, (Grey area apears from the west).
Heres where Im at: as of 1:00 AM this morning. I have used longer upper arms and decreased the angle (laterally) towards the frame rail. I did this by moving the diff mount outwards(away) from the center. My THEORY(another grey cloud), I need to check actuall movement tonight,(about fell asleep under the car as it was) Is that by lessing the angle Im lessing the bind, and by using longer rods, im lessing the angle changes per movement under compression. I know I am sacrificing lateral stability. I am setting the car for a drastic amount of rear steer(Lower Right arm is 20* up) and going to run heavier springs to limit spring movement to under 3".
My other ideas that are really really pushing the limits of grey areas in our rules, is to use the 2 stock upper mounts on the frame and fabriacate 2 longer upper links and mount those on a central piviot on the top of the diff.Look here http://www.yager.net/motorsports/rearsusp.jpg
this was from an old cadilac suspesion.
This is my rendition using heims and rods. http://www.yager.net/motorsports/uppercenterd.jpg.. Overlook the lack of artistic ability, and it was the best picture I could find.

My other option if they cry about the mount not being a "stock" mount on the diff is to cross one upper and tie it into the other arm or mount. http://www.yager.net/motorsports/uppercrossover.jpg

FLAME AWAY, I just bought a new pair of 2 layer driving pants.
Only kiding, please point out obvious disregrds for the laws of physics and mechanical principles.
I realize some guys here wont be able to have such a loose reading of thier rules.
Widebody


snowman
Member
posted May 22, 2002 11:08 PM
Widebody, No flaming.........Not my style.

My apologies for over-explaining the bind.....Obviously, you are very familiar with the issues on this stock 4 bar.....I just misunderstood your post.......It was a long day........I couldn't remember if your forte was chassis,engines or both......But, I did remember that you were sharp and very helpful on the forum......I salute you for that........

You seem to have a handle on the mechanical principles.......No broken laws that I can see..........As I was reading through your post, I seen some things that I thought would be a problem for you.....But, in every case, your next sentence acknowedged the problem......and your solution for the problem.........

Since You are aware of all the problems.....and the solution........and the effects of each solution.......I really don't think I can offer anything helpfull......

I will share a few thoughts.......the direction I am thinking in....Not in any way to dispute or disrespect the direction that You are going.........By the rules,I simply cannot go that way..........

I am not overly concerned about the bind issue........using the 2 stock bushings seems to work OK.........Of course, in my case, everybody else is in the same boat........ If they weren't, then I might change my thinking in a hurry.......

I am more concerned with the arm angles in the verticle plane......increasing anti-squat while controlling roll steer and brake hop........How far can I go ??? I really don't know.......I hope to define the limits this season.....

As far as lateral location.........I think that the stock angles are inadequate........it moves quite a bit.....So, I would be concerned about decreasing them...........I have had the thought of placing an angled brace from one to the other.......As You mentioned.......My though was to have one of the arms cut off just past the mounting point......and have the other attached to the housing.......To make it appear to be stock........(except for the angle brace).........But in reality....it would function as a 3-link.....with the angled brace serving as the panhard...........In my paticular case......this would leave the gray area by a mile........Then some jerk would call me a cheater...........lol.......The nerve of some people..........

I don't know what you can get away with........But, I wish you the best of luck.

Snowman

o5racer
Member
posted May 23, 2002 10:51 PM
I know im new on this board but i would like to add some input on this. I think the wishbone idea is a good one. if you were to slot out the holes on the frame for the upper trailing arms and rotate the bushings untill they were straight of as close as possible, instead of angled and then mount them both to one single pivot on top of the rearend housing that would eliminate most or all of the bind. also if you used hiems they would be able to pivot side to side as well as up and down.
tried a setup like that last year. i tood a stock lower arm, bent it over to the side and rewelded it. i mounted it in place of the right upper arm and made a bracket to hook the back end of the arm to the rear bushing on the left upper arm(confused yet?). by putting the pivot on the left it put more bite in the left tire to tighten the car up. it drove better and worked pretty good but it is too much load for one stock bushing. after about three nights the bushing was falling apart. i dont think there is any way to use a stock bushing for the rear pivot. with the triangulated four link(stock) all the bushings pull or push in a straight line. the way i had it mounted it was pulling the bushing to the side and it just couldnt hold up.
rear steer isnt that bad sometimes. my car last year i had the left lower mounted at 25 deg. up and the right lower at 5 deg up. i also ran about 56 percent rear weight. the extra rear steer helped it drive right around the bottom and the angle in the left lower gave it alot of lift(2-3 inches). the thing i didnt like though was that when in the middle or on the top side of the track the rearend wanted to walk out to the wall. i put it back stock this year. 10 deg on the lefr and 5 on the right.


widebody
Member
posted May 24, 2002 02:21 PM
Thanks, o5racer and snowman;
I bought a bunch of heims and tubes and will be experimenting this weekend with a couple of the designs, the wishbone idea and the more triangular looking idea.. Well see how it goes.

Question for o5racer; You said you had 25* arm angle on the left side lower, I thought to create a loose roll steer condition, you angled the right lower up, and as it compressed under roll it would lentghen resulting in a longer right side WB and causing the car to steer.
were you creating a loose or a tight steer condition, and how much stagger did you normally run with that setup. Just tring to paint a picture of what you were describing. I was unclear on that part.
Your description of the arm fabrication made sense, I did read it a few times to be sure!!

Heres a new topic: You mentioned you crossed you left upper over to the right upper, for increase bite, In that case the left upper would be tring to extend or pull away from the left arm. Was this a problem with the arms, or did they appear to be holding up in that manner? I was thinking of fabrication them in reverse for the only fact that it would than be working in compression on the other arm, and would appear to be a stronger design. But if the arms hold up in the way you had fabricated them, that seems like the better choice. Thanks for the conversation, I know its a busy time of the year.. widebody

o5racer
Member
posted May 24, 2002 10:04 PM
by angling the left lower up it let the left rear pull ahead as the car rolled to the right. this created a loose rollsteer. for roll steer it had the same affect as angling the right up. as the right compreses it pivots back and as the left drops it pulls ahead. in my case though the left lower also pushed up on the chassis as it rolled ahead.

i run 255/70/15 all the way around. same brand same size.

the arms on my setup didnt hold up to well because by bracket was not designed very well. it was just a quick "lets see what happens if we do this" type thing. i only had it on for 3 nights. like i said i dont think a standard rubber bushing would hold up for a single upper pivot. the reason was because it was side loading the bushing and trying to pull the sleve out the side. a single ball joint ot a large hiem would last longer for this.

as for the wishbone try to picture it like this.. the left bar is the pullbar and the longer right bar is the panhard bar. more angle on the pullbar creates more lift on the chassis, pushing down on the rearend. the right bar or panhard bar mounts on the housing on the left and on the right side of the frame. as the car turns left the frame pulls on the bar. by adjusting the front mounting hieght of the bars seperatley you could tune the handling of the car. drop the right mount to add more angle and tighten it up or raise it up to take angle out.

widebody
Member
posted May 25, 2002 08:21 AM
I see, I wasnt thinking about the LR droping that much, but I see if you had a heavy enough LR spring it would lift when rolling over on the RR. I run soft springs in the rear, I see @2" of compression of the LR and 3-4 on the RR. Ill have to try it your way one night to see, how much of a difference the LR loading in that manner feels. Out of curiosity what springs do you run and how much travel do you see from them on a typical night. COOL .. Widebody


wam24u
Member
posted May 26, 2002 10:48 PM
Hey widebody how bout you drop me an email.
o5racer@yahoo.com


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