Leaf spring theory question

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smokinnjokin

smokinnjokin

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I was thinking about this the other day, looking at the way the rear suspension pivots.
Is it true that a spacer between the rear leaf front mount plate and the frame where it bolts with 4 bolts (increasing the wheelbase distance by the thickness of the spacer) would do all of the following:

1) Move the front and rear mount points of the rear springs together, effectively changing the angle of the rear shackle to be further towards the rear of the car
2) possibly increase ride height slightly due to increased pressure on ends of spring?
3) pull slip yoke out of trans by thickness of the spacers
4) by shifting the pivot point back by thickness of spacer, the arc of the rear suspension travel would change

Am I understanding this correctly?
 
I don't see no2 and no4 at all

Moving the spring anchor(s) would move weight of the car off the springs but that far is likely not going to be barely measurable
 
Since the rear mount is on a hanger, 2 would be false. 1, 3 & 4 would probably be true, but by a trivial amount. Not sure what the point is.
 
Centering the wheel in the opening with larger diameter tires. Was reading about the spacer blocks and contemplating the multiple ramifications. Does anyone know of a vendor that sells 1/2" aluminum spacer blocks?
 
Your local neighborhood ( or internet) metal supplier, and a drill. I know no help!
 
Dana67Dart said:
Your local neighborhood ( or internet) metal supplier, and a drill. I know no help!
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I walked right into that one. Been meaning to buy a proper drill press for a long, long time. Been keeping my eye on the local ads to get a quality used one instead of harbor freight.
 
Slight variation of a cal trac front spring mount setup?
 
Probably more due to the fact that I have the car riding like 5" over stock height, which has affected a bunch of other things. Best part about having an old car like this, screwing around with everything.
 
I have a b-body with the rearend moved back an inch, with super stock springs and hangers, hanger holes modified from mopar supplied location. All i know is what i see on my car.
1. Yes, more rear shackle angle. Not a problem in my experience.
2. Ride height was modified by lowering the drilled hole in the hangers, in an attempt to reduce rearend lift at launch, altering the theoretical instant center.
3. One inch longer driveshaft.
4. I dont know about arc of travel. I DO know (noticed just the other day) that when jacking up the front of the car, the rearend RISES, contrary to expectations. ( i would have thought that weight transfer would cause the rear of the car to settle) I think that is a function of the super stock springs
 
On number one I don't see where it's really going to change the angle of your rear shackle. Because the shackle only moves so far back depending on its length of course and your not moving where it mounts.
 
Commando66 said:
By moving the axle back 1/2”, have you considered the shocks binding or bending?
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That's a good point, but the upper shock mount brackets are pretty flexible, I imagine they can handle flexing a couple degrees back... Considering the shock angle is changed even more by a super stock spring swap and I don't recall hearing about anyone have shock issues.
 
smokinnjokin said:
Centering the wheel in the opening with larger diameter tires. Was reading about the spacer blocks and contemplating the multiple ramifications. Does anyone know of a vendor that sells 1/2" aluminum spacer blocks?
Click to expand...

Gonna throw rear shackle angle off, pull driveshaft out 1/2'' (same as spacer), take a little weight off rear wheels , if ur on the ragged edge of traction = bad.
 
famous bob said:
Gonna throw rear shackle angle off, pull driveshaft out 1/2'' (same as spacer), take a little weight off rear wheels , if ur on the ragged edge of traction = bad.
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I don't see it really affecting shackle angle since the shackle is ever-changing as the car goes down the road from bouncing or from acceleration or deceleration.
How is it taking weight off the rear tires if anything you have just added the additional weight of the spacer to the total weight of the car. What the spacer has done is make the distance between the front wheels and the back wheels greater which should make it handle better. A longer wheelbase always handles better than a shorter wheelbase.
I could see where that driveshaft being out an extra half an inch might cause a vibration. You just have to drive it and see.

Jmho. That as you know I highly value.
 
I have weighed the consequences and am going to install spacers. Now i just need to find/make them.
 
smokinnjokin said:
I have weighed the consequences and am going to install spacers. Now i just need to find/make them.
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When you do this it would be a good time for you to check to make sure that your frame is square. As in the mount is the same distance on the left side as it is the right side from front to rear. This is where you can adjust for any dog tracking of the car. So say one side is differant from the other side may need to add an eighth of an inch more to make things Square. Just something to check since you'll already be there.
 
Jadaharabi said:
How is it taking weight off the rear tires if anything you have just added the additional weight of the spacer to the total weight of the car.
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Look at how you calculate the reaction forces of a bridge. By moving the rear tires back, the location of the CG of the car remains the same, but the length from the rear tire to the CG is increased, which reduces the reaction load at that point. Won't be by much, and will depend on total weight of the vehicle versus the weight of the suspension components relocated (which will pull the CG along with them to an extent).

One thing no one else has mentioned: larger turning radius.

The arc swing of the rear end though should be the same. It is defined by the length of the front spring section. If you got longer springs, it would change the swing arc. With a spacer, no change.
 
Jadaharabi said:
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I don't see it really affecting shackle angle since the shackle is ever-changing as the car goes down the road from bouncing or from acceleration or deceleration.
How is it taking weight off the rear tires if anything you have just added the additional weight of the spacer to the total weight of the car. What the spacer has done is make the distance between the front wheels and the back wheels greater which should make it handle better. A longer wheelbase always handles better than a shorter wheelbase.
I could see where that driveshaft being out an extra half an inch might cause a vibration. You just have to drive it and see.

Jmho. That as you know I highly value.
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It affects the shackle angle, cause you have moved the whole spring rearward, but you haven't moved the chassis pivot point, so more slant of the shackle. It sure hasnt caused any problem for me.
I did some very rough calculations, and i got around ten pounds less weight on the rear wheels from the wheelbase change. Certainly not enough to concern me, since i quadrupled that weight change by moving the battery to the trunk.
Condidering how goofy (and tire size restrictive) the original location is, i would do the change again in a heartbeat.
 
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smokinnjokin said:
I have weighed the consequences and am going to install spacers. Now i just need to find/make them.
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You can use 1/2'' , would check to see if its square to the body , like posted above ^aluminum since they will be sandwiched tight -------
 
33IMP said:
It affects the shackle angle, cause you have moved the whole spring rearward, but you haven't moved the chassis pivot point, so more slant of the shackle. It sure hasnt caused any problem for me.
I did some very rough calculations, and i got around ten pounds less weight on the rear wheels from the wheelbase change. Certainly not enough to concern me, since i quadrupled that weight change by moving the battery to the trunk.
Condidering how goofy (and tire size restrictive) the original location is, i would do the change again in a heartbeat.
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Agreed , but if u never get enough traction to start with , with the battery already in the trunk and 14-16'' tires, (bad track , and tires back in the day not what they are now)
 
famous bob said:
Agreed , but if u never get enough traction to start with , with the battery already in the trunk and 14-16'' tires, (bad track , and tires back in the day not what they are now)
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I have traction for DAYS with 275’s, caltracs and 3.23 suregrip. Beer math says 340ish crank hp, 260ish rear wheels. It hooks and goes with barely a chirp just mashing the gas in D. 6 sec 0-60 without launching.
 
smokinnjokin said:
I have traction for DAYS with 275’s, caltracs and 3.23 suregrip. Beer math says 340ish crank hp, 260ish rear wheels. It hooks and goes with barely a chirp just mashing the gas in D. 6 sec 0-60 without launching.
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750ISH H.P. . WITH YESTERDAYS TIRES , ONLY A LEAF SPRING SUSPESION , BAD TRACK , 3646 LBS. CAR , GEARING NOT SO MUCH !-----excuse caps-
 
Some people might think it is backwards putting good rear suspension on such a mild motor, but i would choose it again any day of the week. The car drives so well, tracks straight and it is especially noticeable on freeway on-ramps, full-throttle acceleration while doing a high-g turn feels very stable, massive improvement from stock 1967 suspension. It helps that I have tubular subframe connectors also.
 
famous bob said:
View attachment 1715714381

There is an acceptable angle for the rear shackles , moving the rear end back , could throw that angle to far back , depends on how it is now .
Too far back and the shackle can lock in a rearward flat position when the spring flattens out on launch , or in the forward position when the car is jacked up while in the air. We used to have to take a breaker bar of some sort to snap the shackles back into position on this ------
but, we ran 002-003 springs on it , the wheels farther back because the front half is shorter----had to shorten the drive shaft ----------
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^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
big correction , ''my bad'' , the rear wheels were farther forward , 2'' , compared to stock B body springs /put more weight on the rear of the car.
Dont know what the hell I was thinking !!
 
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