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Author Topic: Mult-Leaf Springs or Single for 1967 L30M20? - That is the question.  (Read 951 times)
67rs327
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« on: January 22, 2014, 09:17:39 PM »

So my '67 rs L30/M20 had the rear leaf springs changed over to multi's. After a wonderful discussion with the orig. owner last week (cant believe I located him - more to come on that!) he confirmed that he had made this change at the suggestion of his mechanic after one broke and "almost put me  in the ditch"  Smiley
I'm planning on overhauling the rear - so the time would be right to either re-install the multi's or go back to the singles? - Seems GM realized pretty quick there  were issues with the single leaf application.  Comments? The car will be driven.  Thanks - Chris
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1967rs L30/M20 Bolero Red - LOS 11A.
Chris - New Hampshire.
ban617
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« Reply #1 on: January 22, 2014, 09:30:04 PM »

 I would leave multi leaf springs in it .... Does it still have the mono spring perches?
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hotrod68
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« Reply #2 on: January 22, 2014, 09:52:28 PM »

  Single-leaf springs are fine as long as they aren't subjected to wheel hop. Many high-horsepower cars have run single-leafs with no problem--some drag racers actually prefer them over multi-leafs. The '67s didn't have staggered shocks which compounded the problem with the single-leaf springs. Without traction bars the single-leafs would literally bend into an S-shape then snap back, causing violent wheel hop. After enough abuse they would break. The problem wasn't with the single-leaf springs themselves, but with the lack of any traction control to stop the windup on hard acceleration from a standing start. Some '67s had a traction arm that was supposed to help, but the only real solution was slapper-type traction bars or ladder bars. Hope this helps and good luck!

 
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HotRod'68  1968 SS350 coupe undergoing frame-off resto/rod. 386/350/4.11s
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KurtS
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« Reply #3 on: January 23, 2014, 03:37:32 PM »

Monoleafs are inherently superior to a multileaf.
But there were some design issues in the rear suspension that forced them to switch to multis for higher hp engines.
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Kurt S
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67rs327
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« Reply #4 on: February 10, 2014, 10:13:26 AM »

Sorry for the late reply but thanks to all for the feedback. Looking closer at the perches-they are defiantly the original single leaf set up (recess is only 1" deep) I'm sure this is contributing to the vibration the orig. owner stated developed after his mechanic made the change over to multis. There's really nothing holding the bottom 2 or 3 leafs from sliding side to side except for the outboard strapping on either end. Anyone have a spare set from '68? I don't think there were any multi. leaf configurations in '67. Thanks-Chris
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1967rs L30/M20 Bolero Red - LOS 11A.
Chris - New Hampshire.
TRLAND
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« Reply #5 on: February 10, 2014, 11:30:18 AM »

Monoleafs are inherently superior to a multileaf.
But there were some design issues in the rear suspension that forced them to switch to multis for higher hp engines.

Kurt, Can you elaborate on monoleafs superiority? For a car not subjected to wheel hop what are the advantages to not going to multi leaf?
Thanks, Mike
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Mike in Northern Illinois
1967 RS 327
KurtS
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« Reply #6 on: February 11, 2014, 12:04:58 AM »

Mono has no friction between the leafs. It only flexes, no friction. Rides better too. Anytime a design can be a mono, they use it. Cheaper too.

But the axle isn't well located in an F-body and the monos can deflect too much with hp. Install a radius rod or some aftermarket bars and monos should work OK with hp.
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Kurt S
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Fred Mertz
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« Reply #7 on: February 11, 2014, 11:11:19 PM »

Aren't most Cal-Trac systems done on single leaf springs?  Or is it that Cal-Tracs work better on single leaf spring cars.
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69Z28-RS
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« Reply #8 on: February 11, 2014, 11:41:32 PM »

Mono has no friction between the leafs. It only flexes, no friction. Rides better too. Anytime a design can be a mono, they use it. Cheaper too.

But the axle isn't well located in an F-body and the monos can deflect too much with hp. Install a radius rod or some aftermarket bars and monos should work OK with hp.

From a design perspective, which involves modeling and simulation of the components of the system, one desires the spring to provide *only* a spring constant, and the shock to provide the damping action.   That allows fine tuning of the components for the best combination of ride and handling.  Because of the friction between the sliding springs of a multileaf spring, the spring also contributes to the damping (in spite of the efforts to reduce that friction thru use of the plastic slides).  The frictional component of the spring adversely affects the design of the total 'spring mass damping system'.   The multiple leaves are a 'fix' for a different problem which popped up, or to support larger masses,  or other issues.   Ideally, the designer desires the spring constant, K, to be 'constant' thru the full range of operation as he does the damping action.
http://www.acs.psu.edu/drussell/Demos/SHO/damp.html
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Gary W.  /  69Z28-RS, 72 B 720 cowl console rosewood all tint
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« Reply #9 on: February 12, 2014, 08:02:56 AM »

Thanks Kurt and Gary for the explanations.  It's not as simple as "more is better".
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Mike in Northern Illinois
1967 RS 327
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