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Rear spring shackle replacement

Another discovery that may explain what's going on, though certainly not to me...

To summarize, My '66 Fastback rubs the inner fender lip, on the left rear tire, when I hit a dip in the road. It happens most of the time but more so with two riders and a full tank of gas... (Tires: P225/70R14 (R), P215/70R14 (F)).

The car does seem to lean to the left and best I can determine there's about a 9/16" drop to that side (ground to ww lip).

I think it's unlikely to be weak springs because they're new; replaced with Springs from NPD, OE Rate 110, part #5560-23, "Special, GT Competition / Special Handling".

I thought changing the spring shackle on the left side with one 1" longer would correct the lean/rub; it helped but didn't eliminate.

Now, all that to ask this...

I just realized that somewhere along the way someone shortened the right spring shackle; presumably to adjust the lean (full size left/shortened right). I've noticed since replacing the left shackle that instead of just raising the car by 1", the shackle rotated to the rear (almost hitting the valance). It seems to me that most of the expected lift was negated by that rotation. If that's the case, could the shortened shackle have the opposite effect with its limited extension when rotated, and actually result in more height on that side? Hard to put into words but I wonder if shortening that right side shackle actually resulted in more height to that side than what a stock shackle would provide?

Maybe just wishful thinking but I think I'll add the other 1" longer shackle to the right side to see if it evens things out. If so, I may just go back to stock length and see if I can put 215's in the back without rubbing...

Any thoughts?
 
Sounds to me like one of your leaf springs is shot, and everything else is a band-aide to correct that flaw. Those tire sizes are well within the design parameters of the Mustang for 1966 (I've run exactly those two sizes without issues), so there has to be another problem.
 
"Midlife" said:
Sounds to me like one of your leaf springs is shot, and everything else is a band-aide to correct that flaw. Those tire sizes are well within the design parameters of the Mustang for 1966 (I've run exactly those two sizes without issues), so there has to be another problem.
Click to expand...

What do you think, swap springs to the other side and see if it reverses the lean/rub?
 
First, get a good set of stock shackles and find out what the car sits like...or use the longer ones........then fix the issue.
 
"stump" said:
What do you think, swap springs to the other side and see if it reverses the lean/rub?
Click to expand...

First, I agree with AZPete: go back to as stock as you can and go from there. It may be that you bought a bad leaf spring, they may be mis-matched, or not centered on the alignment pin. Something is not right. Just because you were told these were "performance" springs, in reality you know nothing about their origin, right?

If I were you, I'd spring for the $250 and buy a new set of leaf springs if you can't find anything obvious.
 
"Midlife" said:
First, I agree with AZPete: go back to as stock as you can and go from there.
If I were you, I'd spring for the $250 and buy a new set of leaf springs if you can't find anything obvious.
Click to expand...

Makes sense to me.

Since everything in question came from NPD, should I try another source? Any recommendations?
 
NPD has an excellent reputation.

Wait a sec! Didn't your body man screw up your car? Could they have swapped out one leaf or some other component?
 
"Midlife" said:
Wait a sec! Didn't your body man screw up your car? Could they have swapped out one leaf or some other component?
Click to expand...

Original guy did but most was corrected later... Certainly possible he screwed something up early in the rebuild.

I really can't judge since this is what he started with...


66Mustangfastback049.jpg
 
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My near-term plan...

Replace the right (shortened) shackle with another +1" (since I have another one here), and see how it sits with two equal size. I'd go back to two stock type, but since the one was shortened I don't have a second one.

If it still leans to the left I'll reverse the springs to see if the lean follows the spring. If so, I'll order another set of springs and chock it up to bad luck...

Should I go with the same type/part #?
 
Another thing to look at....

Park it on a level floor and lift it off the ground...no wheels touching. Support it from the front frame rails and the rear frame rails just in front of the rear axle. This leaves the rear portion of the frame rails free of any pressure except body weight. Check the rear frame rails for being parallel...

A 1/4" in one place can really screw things up 2' away.
 
"AzPete" said:
Another thing to look at....

Park it on a level floor and lift it off the ground...no wheels touching. Support it from the front frame rails and the rear frame rails just in front of the rear axle. This leaves the rear portion of the frame rails free of any pressure except body weight. Check the rear frame rails for being parallel...

A 1/4" in one place can really screw things up 2' away.
Click to expand...

This is some of the measuring I did last night, however, only the rear was off the floor...

As for a tolerance, with my eyes it would have to be (+/-) 1/16" at least...

I measured in 4 different places on each side:

1. End of Subframe connector (it is square and close to the front spring mount) (L) 13-13/16" (R) 13-5/8"
2. Center of front spring mounting bolt (L/R) 17-1/4"
3. Wheel well opening (centered on wheel center cap) (L) 34-13/16" (R) 35" Not a good measurement as the inside fender lip differed between the two.
4. Frame rail behind shackle (between shackle and valance) (L) 28" (R) 28-1/16"

I'll do so again with all four wheels up, after I replace the short shackle...
 
Yes, again because the front springs can and will effect how the rear sits for level. I chased a rear spring problem on my first 66 until I found out one front spring had slipped from the proper location.....
 
"stump" said:
My near-term plan...

Replace the right (shortened) shackle with another +1" (since I have another one here), and see how it sits with two equal size.
Click to expand...

Well, I executed my near-term plan and am happy to say it helped. somehow, that shortened shackle contributed to a lower left rear side... Go figure... It sits level, or as level as I could hope, and when I took it for a ride over the same old dips, I only had a slight rub when hitting the worse of them at 60+ mph...
I had ordered the stock length shackles and since they'll be here in time for the long weekend I may just try them on and see what happens...

Thanks for all the help!
 
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