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Ron Earp View Drop Down
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Direct Link To This Post Topic: Front Suspension Alignment
    Posted: 25-December-2010 at 1:43PM
Question on the front suspension:

As some of you know this car has an upper arm that is anchored with two pivot points and a lower arm that has one pivot point inboard and a tension rod that located it on the outboard side. I've attached a couple of pictures.

With the upper and lower arm attached to the upright, the spring in place, shock mounted it appears that the caster angle of the upright is more or less about zero. But, when I try to put the tension rod in place it is quite clear it forces the lower arm BACK to the rear of the car resulting in a negative caster angle. Not only that, it seems to put a lot of stress on the inboard pivot point so that I think that bushing, even though hard polygraphite stuff, would be deformed.

The rod is a stock tension rod and locates on two holes in the lower arm. It attaches to the front frame via a large hole in the frame and two large bushings get located on the rod and will sandwich the frame amongst themselves. So, the rod can pivot up and down with the lower arm, a bit I suppose but it is certainly imperfect.

I have both stock rubber and aftermarket poly bushings. Both of them seem to push the rod too far aft and thus create a negative caster angle. Is there something I am not understanding about this suspension design that I'd want a negative caster angle? Does a rear steer application use negative caster to reduce steering forces maybe? With a negative caster angle the center centering of the wheel would suck and the car would always feel darty, although the steering effort owould be very light.  I generally run 5-7 degrees positive caster for my race cars and dual purpose cars. Good stability and steering effort is fine.

The first picture attempts to show how the rod attaches to the frame. The second picture shows where the rod is lying on top of the lower arm because the bolts don't line up with the holes. One has to pull the arm back about 1/2" to get the holes to engage (the same for both sides, the frame seems square by my cross measurements).







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Direct Link To This Post Posted: 25-December-2010 at 2:10PM
Do you have the front nut tight?
When you tighten the front nut squishing the bushings it will move the arm forward and possibly line up the holes.
 
Many might disagree but I will NEVER use Poly bushings in that part of the application.
The T-Bird 89-97 uses the same set up and NO ONE on the SC site will use them as they get deformed and the pressure makes them "wear out" fast. They do not flex enough to make the suspension work well either.
 
Do you have the inner sleeve for that bushing?
It is imperative you have the correct length sleeve in there!
Wrong size sleeve and it will over tighten the bushing not letting it move enough or too loose and the front end will walk around!
 
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Direct Link To This Post Posted: 25-December-2010 at 2:18PM
Doesn't this design help the car track in a straight line? The only example that comes to mind is a shopping cart. Maybe not the best example but the front wheels of a cart are sloped toward the rear so as you push it the wheels straighten up on their own. Wouldn't that work kinda the same on a car? That way even if you let go of the steering wheel, the wheels will want to stay pointing straight ahead.
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Direct Link To This Post Posted: 25-December-2010 at 2:36PM
Originally posted by cowboyupdjcarl cowboyupdjcarl wrote:

Do you have the front nut tight?
When you tighten the front nut squishing the bushings it will move the arm forward and possibly line up the holes.


I don't think it will, or doesn't seem to.  I've messed around with both the rubber and hard bushings in there with the sleeves and it doesn't seem possible to pull it far enough forward to account for how much I have to move it back to accommodate the arm in the holes.

Now, the suspension is at full droop and the car not at ride height. I notice the upper arm is canted back to the rear a bit, which would tend to pull the upright to the rear when the car is on the suspension.

Positive caster results when the wheel trails the king pin inclination angle, like a shopping cart as you say, but to get king pin angle out in front of the wheel the upper arm has to be a little bit behind the lower arm.  This is as good a reference as any:

http://www.facebook.com/topic.php?uid=105240981155&topic=14363

Not sure what is happening but I'm going to make it have positive caster. The right part in that front mount would be a ball and socket joint, a lot like a ball joint actually. I might look into doing something like that with a threaded sleeve to adjust it.

Actually, what I need to fab up is a rod with a heim joint on the end that collects to the lower arm and a ball joint on the front. That way it'll articulate properly.



Edited by Ron Earp - 25-December-2010 at 2:41PM
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Direct Link To This Post Posted: 25-December-2010 at 3:49PM
Ron, I noticed the exact same thing when assembling my 73 front suspension. I still haven't put exhaust on mine so I don't have enough road miles to see how it affects the steering/handling. I'm running poly bushings but will probably change those particular ones back to rubber soon just due to the reading I have done on them. I don't think it will change the location of the bolts any though. Mine were/are a good 1/2" off.
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Direct Link To This Post Posted: 25-December-2010 at 4:38PM
My money is on the fact it could have everything to do with the lack of weight on the front suspension.
I too think I may be going with rubber for those mounts, but I think I have to find better strut rods. I sandblasted and painted mine but I'm not overly comfortable with the pitting where the old bushings sat on the rod. 
 
 
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Direct Link To This Post Posted: 26-December-2010 at 4:48AM
Originally posted by stanman stanman wrote:

Doesn't this design help the car track in a straight line? The only example that comes to mind is a shopping cart. Maybe not the best example but the front wheels of a cart are sloped toward the rear so as you push it the wheels straighten up on their own. Wouldn't that work kinda the same on a car? That way even if you let go of the steering wheel, the wheels will want to stay pointing straight ahead.
 
 
NOPE!
Just the opposite!
You want the lower to be FORWARD of the upper(POSITIVE CASTER ANGLE) to get the car to track down the road straight and the wheel to "auto center" itself.
 
When the top is forward(NEGATIVE CASTER ANGLE)... shopping cart style it makes for EASY turning but VERY unstable at speed. Think about the shopping cart running down the road at high speed and the wheels FLIP FLOP WOBBLE!
The shopping cart set up was used on OLD BIG MANUAL steering cars so you could actually turn the wheels.
 
 
 
Now back to our regularly scheduled thread...
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Direct Link To This Post Posted: 26-December-2010 at 4:54AM
Originally posted by Ron Earp Ron Earp wrote:

 
Actually, what I need to fab up is a rod with a heim joint on the end that collects to the lower arm and a ball joint on the front. That way it'll articulate properly.
 
 
THAT is a GREAT idea for a track car! Should be VERY do-able and EASY to fab up!!
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Direct Link To This Post Posted: 26-December-2010 at 7:38AM
From my experience, getting the strut rods to line up with the lower control arm is often a matter of jacking one part relative to the other to get the proper length. Since it is difficult to fasten the front bushing nut, you need to adjust the suspension to line up the two bolt mount to the lower control arm.

Try sticking a jack underneath the lower arm and raise it up to see if that helps. Often times when I am installing strut rods and sway bars I have a small floor jack to help me install.
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Direct Link To This Post Posted: 26-December-2010 at 8:37AM
Here is a question for you guys. This is a little part of our coil spring thread where we are trying to figure out my lean and what the heck I have for arms on it. On the pass. side where the arm we cant figure out is the wheel is further back in the well. As in the gap in the front of the tire to the fendser is wider than the back of the wheel. Is this adjustable by the strut rod?

Thanks,
Jesse
 
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Direct Link To This Post Posted: 26-December-2010 at 9:08AM
Not really adjustable  so to speak. The rod is a set length. On mine it just worked out that it didn't quite fall back into place when I changed all the bushings so I had to give my lower control arm some love with a ratchet strap to get it to align. Going to take it all back apart when it warms up a little and try to figure out what is causing it.
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Direct Link To This Post Posted: 26-December-2010 at 8:07PM
Now that lower strut can be a pain.. especially with the coils in. I did mine before the coils.

This is where the strength of this design comes from though. I am just guessing this is how it works. I did redo my car too so I have had it apart and to together but really don't know. It's how I would design it anyway.
Think of it as a triangle, the strut is the hypotenuse, that is a set length. The distance from the pivot point of the LCA (lower control arm) to the connection of the strut on the LCA is a leg, also a set length. The distance from pivot point of the LCA to the pivot point (big rubber bushing) of the strut on the frame is another leg, also a set length. So we have one solid, set angle triangle. You suspension is in it's most un-compressed form as of now, hitting the bump stop. So I know it doesn't make sense that the suspension would need to be compressed in order to get those bolts in on the strut or else the strut would bind before the UCA would hit that stop, but see the thing is, the rubber in all the bushing allows "play" almost everywhere, especially in the strut to frame mount which is not only an angle "play" but a distance "play".  Back to the triangle. So take this ridged triangle and put that on an angle creating a pyramid with the extra leg being the travel in the suspension and you have an adjustment that will change the "what used to be hypotenuse" of the first triangle. So lets say, right now, with the suspension uncompressed, you are "stretching" that strut which is actually compressing the outside strut bushing. when the car is at its stock ride height there is least force on either of the bushing but when you hit a backwards force on that LCA (pothole) things all "give" a bit, including the "length" of that strut.  

Bottom line is... find a way to compress that spring and play with the LCA until you get those bolts in.  You are going to scratch the paint if you are trying to GET it done, so just pry it around, bash it, what ever you got to do, but if you want show car status then take your time. Take things apart if needed. It will pay off in a show worthy result.

Sorry, I know that was probably lengthy and overly complex for no reason.  I just started typing and couldn't find a place to stop. Hope it makes sense.

Good luck! you sure are movin on the project. Looks great.
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Direct Link To This Post Posted: 27-December-2010 at 4:04AM
I have poly bushings in the control arms in both my cars and rubber on the lower rod. I know for a fact I just bolted it together (you'll have to force the lower control arm back a bit). I do remember fighting it to get together, however. Crank down the front nut and send it to the alignment shop once you have it assembled and ready for the street. These wheels don't sit totally square in the front wheel opening anyway

.  A BFPB (Big F!#$@ing  pry bar) and floor jack got mine in position. I too, had thoughts like you when I put mine together, but, it seems fine.



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Direct Link To This Post Posted: 27-December-2010 at 4:35AM
i'd pull the springs out and play with the range of motion, watching how the caster is affected with ride height 
 
i noticed on my frame that the drivers side has taken a hit and the bottom edge under the strut is bent backwards maybe 1/2"- 3/4" and may need to be pulled at the body shop... it's not unusual and it's the only way to correct a non-adjustable setting.
 
on my old 73 i recall using an an additional washer behing the nuts in an attempt to compress the rubber bushings a little more because they didn't seem to be compressed much if at all, and hopefully pull the strut a little farther forward
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Direct Link To This Post Posted: 27-December-2010 at 6:29AM
From experince, I have waited till I had the full {or close to} weight on the front end.
-Insert inner rod bushing on.
-Insert rod into the front pocket.
-Attach the rods to the LCA, bolt some-what loosely.
-Once the front end is lowered down with weight on suspension, the rods should roll forward some what. With the suspension at full drop, the rod isn't going to be long enough {My understanding, but remember, I am fuzzy. It's been 5+ years since I had my front end off the car. 
-Insert outer bushing and washer, and tighted nut.
-Tighten LCA to rod nuts.
 
Myself, I have not run into the problem, that I can honestly recall.
 
On the topic of poly versus rubber, the 71-73 mustang uses a similar design.
There is a guy on Fordmuscle and TorinoCobra that has a very nice 71-73 Mustang, and he was in Hot Rod's Drag Week a few years back. Snapped a strut rod and it really did a hell of a number.
 
Myself, if I was a betting man, and really abuse my car {Yeah...like I don't Geek as is...}
I would take the strut rod, get a small diameter DOM tube, fish mouth the ends, burn the DOM tub to the strut rod to bulk it up , and replace the threaded area with a pivot kit like the road racing mustang crowd already have.
But that's just me.
While I am at it, put in a set of coil overs.
But, as I said before, I have a street car, nothing more. Wink
 
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Direct Link To This Post Posted: 27-December-2010 at 6:45AM
Originally posted by Eliteman76 Eliteman76 wrote:

I would take the strut rod, get a small diameter DOM tube, fish mouth the ends, burn the DOM tub to the strut rod to bulk it up , and replace the threaded area with a pivot kit like the road racing mustang crowd already have. Wink 
 
click on the pics to enlarge
 
 
looks like a go for adjustability


Edited by Rockatansky - 27-December-2010 at 6:47AM
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Direct Link To This Post Posted: 27-December-2010 at 12:31PM
Nice. Now, change the LCA mount plate, get some 3/8" thick plate and mill accordingly.

Once again, having issue loading the image.  Geek
  


Edited by Eliteman76 - 27-December-2010 at 12:34PM
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Direct Link To This Post Posted: 28-December-2010 at 3:42AM
 dont use poly on the strut rods . i have seen too many bad storys and even disclaimers . you should be able to adjust that rod to drop in especially with rubber bushings.
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Direct Link To This Post Posted: 28-December-2010 at 6:01AM
Ding Ding, man, the 68-70 strut rods almost look {sigh} like they are a bolt in...
 
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Direct Link To This Post Posted: 28-December-2010 at 6:54AM
How far off are they?
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