Wrong assumption. The fixed length rods force the rear end to try and move in an arc instead of up and down. Even if you weld them at ride height you will force a bind when the ride height changed during driving because the leaf springs and rear end are bolted together. If it was not for the bushings you could rip out weld.
Correct. The front of the leaf spring forms a radius of X inches, which changes as the spring compresses and decompresses. The traction bar forms a different (longer) radius. When the axle moves up and down (on either side) it is trying to move in an arc around 2 center points (with one, the spring, constantly changing), thus the binding. The only way to keep it from binding is for the radii to be the same (always) and the bar parallel to the spring (always), or better yet, always parallel in the horizontal plane (trac bar back welded to the axle centerline and the front to the center of the spring eye bolt. The binding might not be noticeable but it's putting stress on the mounting points and bushings and ultimately limits the suspension travel.
Here's a crude diagram to show the issue (not to scale).
CalTracs avoid this by leaving the bar loose until the car is accelerating, only binding when it is desired. Front-biased springs (like Maier Racing) eliminate this by designing the spring for minimal wrap up so no need for traction bars.
__________________ Plain Jane 65 Coupe - Scary fast (at least that's what my wife says). (SOLD 10/2012)
Feature Car in December 2010 StreetScene (the magazine of the National Street Rod Assoc)
Gee I wonder is this is why shackles essentially allow for pivot/deflection
They do at the back, but the traction bar and the front half of the spring are what forms the radii and the binding. The front bushing is the locating point and the back end is just along for the ride (looking at the spring from an 'axle positioning' perspective).
__________________ Plain Jane 65 Coupe - Scary fast (at least that's what my wife says). (SOLD 10/2012)
Feature Car in December 2010 StreetScene (the magazine of the National Street Rod Assoc)
Wrong assumption. The fixed length rods force the rear end to try and move in an arc instead of up and down.
You are simply dead wrong here. The eyes at the front and rear of the bar form a parallelogram, allowing free, un-binding vertical movement of the suspension. Apparently, you are unfamiliar with the component I am describing.
Traction-Masters™ eliminate leaf spring wrap up.
The dual pivots still allow normal leaf spring up and down movement.
__________________
Amateur restorer. (Well, once in a while I have been paid for it)
You are simply dead wrong here. The eyes at the front and rear of the bar form a parallelogram, allowing free, un-binding vertical movement of the suspension. Apparently, you are unfamiliar with the component I am describing.
Traction-Masters™ eliminate leaf spring wrap up.
The dual pivots still allow normal leaf spring up and down movement.
You are correct when the car is accelerating (forcing the axle to move in an arc of fixed length). However for normal driving and cornering, it will bind since the front half of the spring is not twisting but acting as a fixed (well, actually variable) length arm positioning the axle. In the bottom drawing, the traction bar is clearly longer than the distance from the axle to the front spring bushing. Thus, the axle and the rear traction bar mount will travel in different arcs. When the axle drops down, the leaf spring will pull tight and the trac bar will push. When the axle goes up, the trac bar will pull tight and the leaf spring will push. It's only where the arcs cross that there is no binding.
__________________ Plain Jane 65 Coupe - Scary fast (at least that's what my wife says). (SOLD 10/2012)
Feature Car in December 2010 StreetScene (the magazine of the National Street Rod Assoc)
You are simply dead wrong here. The eyes at the front and rear of the bar form a parallelogram, allowing free, un-binding vertical movement of the suspension. Apparently, you are unfamiliar with the component I am describing.
Traction-Masters™ eliminate leaf spring wrap up.
The dual pivots still allow normal leaf spring up and down movement.
If these were drag cars we could let some of this slide (pun) but these are street cars and in some cases sports cars, and sports cars do not handle correctly with the fixes rod design. With a 4.5 leaf you can eliminate the axle wrap and still allow one side to move with less impact on the other side, and allow the axle range of motion under sever compression and extension.
I am going to add a watts link next year if the budget allows, but when I was doing some investigation with Fay's they are very clear that under ride bars are a bad idea and that peaked my curiosity and I did a bit more digging and found they are not the best option for performance handeling.
Well, it can't be very significant. I always figured the slightly forward location of the forward eye accounts for the difference. After more than 200,000 miles, if all this theoretical "bind" was going to be a problem, it would have showed up by now. I get no wheel hop, and surprisingly, slightly smoother ride than without the bars. I've never needed to replace the bushings, also surprising.
__________________
Amateur restorer. (Well, once in a while I have been paid for it)
Well, it can't be very significant. I always figured the slightly forward location of the forward eye accounts for the difference. After more than 200,000 miles, if all this theoretical "bind" was going to be a problem, it would have showed up by now. I get no wheel hop, and surprisingly, slightly smoother ride than without the bars. I've never needed to replace the bushings, also surprising.
Yeah. It probably isn't that significant for a midly-driven street car, and the bushing probably accomodate most of the length differences.
__________________ Plain Jane 65 Coupe - Scary fast (at least that's what my wife says). (SOLD 10/2012)
Feature Car in December 2010 StreetScene (the magazine of the National Street Rod Assoc)
well i think i am going to run these original springs for the time being until i decide on what to do, but does anyone have any recommendations on what types of bushings to use. i want to use polyurithane but i have been told by some people to run rubber and i have been told by others to use polyurithane. what do you all think?
i'm surprised nobody has made the measurements of the traction master setup and calculated how much bind and what will bind (if any) at full compression/deflection. it seems like the same discussions about them occur over and over again.
I could be wrong, but I thought this was originally GM's innovation?
Quote:
Originally Posted by Al Newman
Ford's solution (sort of) was to stagger the rear shocks. One shock was mounted in front of the rear axle, while the other was mounted aft. I believe that this was done with a unique upper shock mount cavity and possibly different shock spring plates, also. You would most likely have to find a donor car to make the fix, most probably a 69-73 model. A bit of complexity, true, but not so much as ladder bars. How about old style traction masters?
Best,
Al
i want to use polyurithane but i have been told by some people to run rubber and i have been told by others to use polyurithane. what do you all think?
I ran polyurithane for a while and then twisted my rear spings and changed to rubber when I changed my springs. I didn't see much difference.
__________________
Greg
1969 Mach1 428 4-speed 3:89 gears,
31 spline posi "N" case, ported edelbrock heads,
full length headers, 292H Comp cam, 750 holley.
Born July 17, 1969
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