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| How "flat" should the springs sit? https://slantsix.org/forum/viewtopic.php?t=21105 |
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| Author: | '74 Sport [ Thu Dec 14, 2006 10:33 pm ] |
| Post subject: | How "flat" should the springs sit? |
I just noticed a couple days ago that the leaf springs on Aaron's Dart Sport appear to lie almost completely flat when you get down and look straight up them from the rear. In other words, there isn't really any noticeable arc in them. Is that typical, or are they pretty much worn out? A local brake and spring shop estimated it would cost roughly $150 to have all the springs re-arced. I've been reading in another thread about the ones offered by J.C. Whitney, reasonably priced and shipped to your door for less than that. Any comments are welcome, Jerry |
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| Author: | Brian [ Fri Dec 15, 2006 4:45 am ] |
| Post subject: | |
I have seen the 4 leaf springs on the 73 and up A bodys go flat like you are talking about. There not as strong as the pre 73 5 leaf springs. If I were you I would upgrade to 5 leaf springs or go with the Mopar XHD springs. I think the springs changed for 73 because of cost and lighter weight for fuel economy. |
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| Author: | Dart270 [ Fri Dec 15, 2006 8:42 am ] |
| Post subject: | |
Actually, for best handling, the springs should sit exactly flat, or in some cases with a tiny amount of upward arch. For drag racing traction, upward arch is favored by many. Possibly the best question for you guys is, how do you want it to look/sit. Sometimes if they sit flat at rest and you routinely load the car, it rides too low. Lou |
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| Author: | '74 Sport [ Fri Dec 15, 2006 9:35 am ] |
| Post subject: | |
Actually, Lou, the car has a nice looking stance as it is. Since I've never seen an A-body with "fresh" leaf springs, I guess what I was wondering is if the springs are worn out (lying flat), then replacing them with new springs (upward arch) would jack the rear end up more (how much more is the question). How does one know if the springs are doing their job, considering that there are also shocks in the back helping out? Jerry |
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| Author: | dakight [ Fri Dec 15, 2006 10:01 am ] |
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The shocks do not help support the weight; they merely dampen the motion. The stance of the car would be virtually identical if the shocks were removed. |
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| Author: | SlantSixDan [ Fri Dec 15, 2006 10:47 am ] |
| Post subject: | |
Quote: Actually, for best handling, the springs should sit exactly flat
H'mm. Never heard this before, and most of the A-bodies I've ever owned have not had flat-sitting springs, even the low-miles units. What's the operational theory at work giving best handling with flat-sitting springs?There was a service bulletin from the factory stating that appearance of the springs is not a valid indicator of their condition, and that ride height should be measured to check the springs' condition. That said, my experience is that if you think the springs are sagging/tired, you're almost certainly right. Remember, the newest A-bodies are now 31 years old, and many of them have covered numerous hundreds of thousands of miles...many of us haven't seen an A-body sitting at its intended height and attitude in a long time, if ever. Sure, it's possible to overdo the rear springs' arch and wind up with the car looking like a refugee from teenager ownership in the 1970s, with thoughtful purchase of new springs from a reputable source, or careful and competent work from a local spring shop, the rear of the car can be "unsagged" and brought back up to the correct ride height range without making the car look dumb. I prefer the rear to sit a little higher than the front for improved handling on the highway and maximum leeway in loading with cargo and passengers. Once you have your rear springs reworked, remember to have the front end realigned and the headlamps reaimed! |
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| Author: | DionR [ Fri Dec 15, 2006 12:47 pm ] |
| Post subject: | |
Quote: Quote: Actually, for best handling, the springs should sit exactly flat
H'mm. Never heard this before, and most of the A-bodies I've ever owned have not had flat-sitting springs, even the low-miles units. What's the operational theory at work giving best handling with flat-sitting springs?Keeping the spring flat is kind of like having a panhard bar, without having to install one. 
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| Author: | rock [ Sat Dec 16, 2006 3:09 pm ] |
| Post subject: | My recent experience (last week) validates Lou and Dan.... |
Hi guys, I might as well have moved in a bed I spent so much time under my truck since July on my little oil leak...and spent much time looking at my springs. Passenger side front was so flat it was recurved, and other three "looked" ok with a very slight arch.(2.5 inch wide 4 leaf sets). I had been toying with getting a front set from Springs N Things so upon deciding to get my tranny to rear pinion angles validated, I ordered a set of springs ($354 delivered for a 5 leaf set) and took my vehicle over to a truly fine truck spring and driveline place here. My angles were indeed unmatched, causing my clutch chatter and putting in new front springs took about 40 minutes, AND THEN! The spring wizards said..."actually your front springs weren't too bad, c'mere and watch this arch and flex test on the old set...BUT your rear springs are shot. Step back here to rear and look...the body is tilted to driver side. Now put a good measuring tape from floor across rim up to fender on both sides." Yep, about 2 inches lean to driver side and they "looked" fine to me until the front set was truly matching. So, rock is saving now for the rear set. Moral is if you think you can look at springs and tell, don't delude yourself. you can't. If you think you can re arch, as an act that may be possible but achieving the design ride after re-arch may not be possible. I am now a believer that this here spring stuff is one of the few areas I now prefer to leave to a shop truly equipped to do the work. They only charged me $65 to swap springs and adjust pinion and tranny angles....which would you rather do...guess or pay $65? rock '64d100 |
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| Author: | Eric W [ Sat Dec 16, 2006 8:52 pm ] |
| Post subject: | |
The FSM says the leaf springs are supposed to be flat or have a slight upward arch. Like Lou said, it helps with side to side sway...thus, handling. |
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| Author: | slantfin [ Wed Jan 10, 2007 8:07 am ] |
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I have a series of articles titled 'Muscle car handling 80's style', so it's the latest word from the now long gone MoPerformance Magazine. I somehow ended up with the project car, a 67 fastback, built by Mike Martin as a subject for photos etc. According to Mike, at that time Mopar made a 'road race & circle track spring' that had almost no arch, and was designed to have almost the same spring rate "in all of its operating modes (arched, flat, reverse arched)." With a lot of arch, as one side gets loaded up in a turn, the effective radius arm of the front section of the spring lengthens and causes the car to oversteer (roll-steer or toe-steer). He also mentions that 'super-stock springs' are strictly for drag racing and "will not work for any handling operations."[/i] |
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| Author: | Doc [ Mon Jan 15, 2007 10:01 am ] |
| Post subject: | |
Bingo, it is the small amount of "rear steering" that makes a flat spring important for handling. You need to see a diagram but think about it in terms of a spring being longest, front eye to wheel center when it is perfectly flat. As soon as it archs a little, like being pushed down when going into a turn, the bent spring will pull the rear wheel forward a small amount. That helps steer the rear end into the turn, not away from it, as arched to flat would do. (arched going to flat will cause more oversteer) DD |
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| Author: | '74 Sport [ Mon Jan 15, 2007 11:42 am ] |
| Post subject: | |
And that makes perfect sense to me. So then, the question becomes... What makes the rear end feel spongy. Could worn out 30-year old springs lose their spring rate, yet still be stiff enough to keep the frame up off the axle. In other words, it sounds like our flat-looking springs appear to be situated correctly, and perform as they were designed to do. Yet, riding over a decent bump or dip causes the rear end to squat down pretty good. Are we now talking about the quality and choice of shocks, rather than adequate springs? It would seem that a flat spring is going to be totally ineffective in absorbing bumps, and that may be the whole design concept for this system. Jerry |
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| Author: | slantfin [ Fri Feb 16, 2007 7:32 am ] |
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Did you hear the one about what do you call it when a blonde dyes her hair black? Artificial intelligence. Combine that with the plain English version of the 3 laws of thermodynamics: 1) You can't win. 2)You can't break even. 3) You can't leave the game. Seriously though, I'm guessing that there's a difference between de-arched new springs and played-out flatties. Nothing that a small pile of currency won't solve. What the hell, while you're emptying out your wallet some nice KYB's will take care of the bounce. The nice lady at Springs n Things told me they will arch or de-arch to whatever specs you like. |
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| Author: | Matt Cramer [ Fri Feb 16, 2007 10:38 am ] |
| Post subject: | |
Quote: And that makes perfect sense to me. So then, the question becomes...
Leaf springs can sag over time, but unless you get a crack in one of the leaves or have somehow had a significant amount of metal rust off it, the spring rate will remain unchanged. There isn't really a difference in spring rate between de-arching and sagging. So if the ride height is correct, check to see if you have any of the leaves broken or clamps that have gone missing. The rubber bushings can wear out, too, as can the shocks.What makes the rear end feel spongy. Could worn out 30-year old springs lose their spring rate, yet still be stiff enough to keep the frame up off the axle. In other words, it sounds like our flat-looking springs appear to be situated correctly, and perform as they were designed to do. Yet, riding over a decent bump or dip causes the rear end to squat down pretty good. Are we now talking about the quality and choice of shocks, rather than adequate springs? It would seem that a flat spring is going to be totally ineffective in absorbing bumps, and that may be the whole design concept for this system. Jerry Also, an A-body is pretty lightly sprung by modern car standards. If it isn't actually hitting something or bottoming out, it may just be the suspension is behaving as designed. |
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| Author: | slantfin [ Fri Feb 16, 2007 6:38 pm ] |
| Post subject: | |
So, according to Matt Cramer, my thermodynamic effects don't apply, at least not until oxidation sets in. Sounds like the trick is to get them to sag equally; try to center the toolbox, maybe. |
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