How much travel do leaf springs need?

[Idaho]

I'm planning to lower a 69 Dart but keep the original suspension. I'd like it to be capable for autocross.

I'd also like to get it as low as I can. Up front I'll use 1" or larger torsion bars, maybe offset bushings if needed for alignment.

I'm not sure how much travel leaf springs require. I'm hoping I can lower the frame to within 4" or less of the axle with some heavier springs and shocks.

Is this reasonable or do the leaf springs require more travel?

 

[Idaho]

The book "Mopar Suspensions" is apparently good and might have this info but sadly its no longer in print.
Anyone have this book, or know of another resource?

 

[67Dart273]

MP's "Chassis" book, the one I have is P5007160

or MP's "Mopar Oval Track Modifications" the one I have is P4529814

should have the same or similar info.

Also I asked this the other day, and don't think anyone came up WHERE can you REALLY get a copy of the mods done to the "Green Brick?" People post links and refer to it, but the ACTUAL article is a no-show.

 

[zhandfull]

I have about 5" to the frame 4" to bump stops with my dearched S.S. springs in my 68 Dart never had a bottoming out problem even with trunk loaded and one rear passenger. I did have to find some shorter than stock shocks. Hope that helps.

 

[dustinmoran91]

they dont really need to much. i would say to find how much you need for your application would be to, lay under the car in a safe spot with a tape measure and have a couple guys rock the car side to side and see how much you need since you want to do autocross and body roll is going to be your biggest factor. stiff springs, lowered ride height, good shocks, and performance sway bars will drop you to probably in the 3-4'' travel range with some room for clearance so you dont ride the bumpstops.

 

[Idaho]

MP's "Chassis" book, the one I have is P5007160

or MP's "Mopar Oval Track Modifications" the one I have is P4529814

should have the same or similar info.

Also I asked this the other day, and don't think anyone came up WHERE can you REALLY get a copy of the mods done to the "Green Brick?" People post links and refer to it, but the ACTUAL article is a no-show.

I'll look for those. Thanks. I've read a bit about the Green Brick as well. Would be nice to know the setup.

I have about 5" to the frame 4" to bump stops with my dearched S.S. springs in my 68 Dart never had a bottoming out problem even with trunk loaded and one rear passenger. I did have to find some shorter than stock shocks. Hope that helps.

That is helpful. Thanks.

they dont really need to much. i would say to find how much you need for your application would be to, lay under the car in a safe spot with a tape measure and have a couple guys rock the car side to side and see how much you need since you want to do autocross and body roll is going to be your biggest factor. stiff springs, lowered ride height, good shocks, and performance sway bars will drop you to probably in the 3-4'' travel range with some room for clearance so you dont ride the bumpstops.

Well that's the ballpark I've been considering, and exactly the mods I'm looking at. Thanks. I read a bit about shock absorbing bump stops - might be useful for getting it down as low as possible, I don't know.

 

[inkjunkie]

Also I asked this the other day, and don't think anyone came up WHERE can you REALLY get a copy of the mods done to the "Green Brick?" People post links and refer to it, but the ACTUAL article is a no-show.

I have all the magazines with the articles on it.........somewhere.......

 

[67Dart273]

I have all the magazines with the articles on it.........somewhere.......

Oh Doug, you shouldn't have said that..............

"Adventures: Dec 2002 of Mopar Action

"tech analysis" Feb 2003 (says part 1)

"powering a quicker brick" March 03

Don't know if there's more or not

Odd that Mopar action would only mention two issues:

http://www.moparaction.com/Tech/archive/one-lap-pix.html

and I managed to find 3 just poking around

I have no idea what this is supposed to be:

http://victorylibrary.com/mopar/re.htm

 

[dustinmoran91]

you might look at hydraulic bump stops, they absorb the impact and slow it down rather than just a sudden slam stop that jars the whole car.

 

[scrappydoo]

When I had my Valiant setup for racing (flat track) about 14 years ago, I rotated the front spring hanger 180 deg. and used 6 leaf springs from a ute and this was all the lowering it needed at the rear.
The added benefit of rotating the spring hanger is it takes most of the self steering out of the rear end.
You will need to use a shim to get the pinion angle correct again.
I used the 1" mopar torsion bars up front with a 20mm sway bar.
This setup handled very well.
Get as much positive caster into the front as you can then as much neg camber once you have the caster dialed in.
Offset on the wheels is important, going wide to get more track isn't a good idea.
And use a race seat with a harness.
HTH.

 

[Idaho]

I'll look for those. Thanks. I've read a bit about the Green Brick as well. Would be nice to know the setup.



That is helpful. Thanks.



Well that's the ballpark I've been considering, and exactly the mods I'm looking at. Thanks. I read a bit about shock absorbing bump stops - might be useful for getting it down as low as possible, I don't know.

you might look at hydraulic bump stops, they absorb the impact and slow it down rather than just a sudden slam stop that jars the whole car.

Ever seen them in use? Seems the offroad guys like them. Could be interesting.

 

[273]

If your gonna have only 4-3.5" ground clearance your only gonna have minimal amount of wheel travel, probably 3-2.5" axle to bump stop will do.

 

[C130 Chief]

There's no real fixed amount of travel. It's more important (for handling) to have the springs flat, or nearly so, and not have the axle hit the bumpstop in a corner (bad). Don't go too nuts lowering, beyond a certain point the hassles outweigh the gains. Generally, if you're lowering the car you'll want the springs to be stiffer to keep from hitting the stops.

Also if you're serious about autocross download an SCCA rulebook. It's really easy to make a modification that will put you into a class which you'll not be competitive. I learned this the hard way with my last TR-6.

 

[Idaho]

If your gonna have only 4-3.5" ground clearance your only gonna have minimal amount of wheel travel, probably 3-2.5" axle to bump stop will do.

I'd like to go that low but I think the factory front suspension will be a limiting factor. I don't mind a stance with slight front incline, but don't like the look of cars going up hill on the level

My plan for the front so far... big torsion bars, use the adjustment to lower as much as possible, offset bushings to optimize alignment, maybe upgrade the front sway bar, reinforce the k member, upgrade shocks. Not sure yet how low that will let me go but all the really low cars I've seen are not on the factory suspension.

 

[Idaho]

There's no real fixed amount of travel. It's more important (for handling) to have the springs flat, or nearly so, and not have the axle hit the bumpstop in a corner (bad). Don't go too nuts lowering, beyond a certain point the hassles outweigh the gains. Generally, if you're lowering the car you'll want the springs to be stiffer to keep from hitting the stops.

Also if you're serious about autocross download an SCCA rulebook. It's really easy to make a modification that will put you into a class which you'll not be competitive. I learned this the hard way with my last TR-6.

Sounds like you have some background in racing. I've seen your cautionary note about the rules on other threads and appreciate the wisdom. At this point, I have no major competitive aspiration, just a desire to drive the car in a fun way legally, and my vision for the car will take precedence over competing to win. If I get more serious, I'd consider building another car for it.

I suppose hitting a bump stop may introduce a jarring force that could cause loss of traction?

For lowering, I just want to acheive what I can without replacing a lot of parts. I know the factory setup with some tweaking can perform well enough for my intentions.

Any suggestions for a flat stiff spring? I have springs from a 73 340 Duster, a 74 318 Dart Sport, a 73 /6 Duster, and the 69 /6 Dart. Would de-arching and adding a leaf make sense? I'll buy something if I need it. Part of my goal is to get the most bang for the buck since I also want to save for retirement some day.

 

[dustinmoran91]

Never seen them personally used, but i saw them on extreme 4x4 and they were cool. The axle contacts it and slowed the travel down very gently instead of a sudden stop. Their pricey but they can help if you need them. I would get it all together and drive it before buying them. Even then id only buy them if you actually hit the stops.

 

[Idaho]

I have about 5" to the frame 4" to bump stops with my dearched S.S. springs in my 68 Dart never had a bottoming out problem even with trunk loaded and one rear passenger. I did have to find some shorter than stock shocks. Hope that helps.

Forgot to mention, very nice clean looking Dart. What year? Can't see any fender reflectors.

dustinmoran91 Never seen them personally used, but i saw them on extreme 4x4 and they were cool. The axle contacts it and slowed the travel down very gently instead of a sudden stop. Their pricey but they can help if you need them. I would get it all together and drive it before buying them. Even then id only buy them if you actually hit the stops.

Makes sense. I suspect I won't need them.

 

[zhandfull]

Forgot to mention, very nice clean looking Dart. What year? Can't see any fender reflectors.

Thanks 1968

 

[Idaho]

When I had my Valiant setup for racing (flat track) about 14 years ago, I rotated the front spring hanger 180 deg. and used 6 leaf springs from a ute and this was all the lowering it needed at the rear.
The added benefit of rotating the spring hanger is it takes most of the self steering out of the rear end.
You will need to use a shim to get the pinion angle correct again.
I used the 1" mopar torsion bars up front with a 20mm sway bar.
This setup handled very well.
Get as much positive caster into the front as you can then as much neg camber once you have the caster dialed in.
Offset on the wheels is important, going wide to get more track isn't a good idea.
And use a race seat with a harness.
HTH.

Thanks for the interesting tips. I plan to use a shortened 8.8 diff so I'll have to adjust the pinion angle regardless. I'm guessing "self steering" results from leaf spring movement when the shackle twists? Could you comment further?

 

[BigBlockMopar]

Depending a bit on the current state of the leafsprings, the axle-snubber in the center will hit the body at about 3-3.5" drop. Don't think you can remove the snubber as then the driveshaft will hit and rub the tunnel. Especially during accelerating.
I've got most of my cars lowered 3" in the rear purely for estethics, but on some cars I always feel the axle-snubber hit the body on the larger bumps in the road.

A driveshaft-tunnel modification is in order to clear that issue.

 

[scrappydoo]

The steering effect is caused by the angle of the leaf spring. The standard leaf spring angle causes the rear end to steer to the inside of a turn during cornering, considered a safe characteristic by car manufacturers.
Making the leaf spring sit level with the road surface reduces the self steering and it also lowers the wheel rate of the spring.
You can also add a watts link to the rear end for extra stability.

 

[Idaho]

Depending a bit on the current state of the leafsprings, the axle-snubber in the center will hit the body at about 3-3.5" drop. Don't think you can remove the snubber as then the driveshaft will hit and rub the tunnel. Especially during accelerating.
I've got most of my cars lowered 3" in the rear purely for estethics, but on some cars I always feel the axle-snubber hit the body on the larger bumps in the road.

A driveshaft-tunnel modification is in order to clear that issue.

Interesting. I'll take that into consideration. Thanks.

The steering effect is caused by the angle of the leaf spring. The standard leaf spring angle causes the rear end to steer to the inside of a turn during cornering, considered a safe characteristic by car manufacturers.
Making the leaf spring sit level with the road surface reduces the self steering and it also lowers the wheel rate of the spring.
You can also add a watts link to the rear end for extra stability.

I had to do a little research.

Spring rate is the amount of force it takes to compress a spring 1-inch. Wheel rate is the spring rate actually measured at the wheel. Both are expressed in lb/in.

Seems one would need to boost spring rate to compensate for levelling the spring and even more to avoid the bump stops on a lowered car. I wonder if supplemental air bags might be helpful and provide some adjustability.

Watt's linkage consists of a chain of three rods, two longer and equal length ones on the outside ends of the chain, connected by a short rod in the middle. The outer endpoints of the long rods are fixed in place relative to each other, and otherwise the three rods are free to pivot around the joints where they meet. Thus, counting the fixed-length connection between the outer endpoints as another bar, Watt's linkage is an example of a four-bar linkage.

A picture is worth a thousand words in this case.
http://en.wikipedia.org/wiki/Watt's_linkage

 

[Idaho]

What's that creaky sound? Oh thats, the wheels in my brain trying to turn...

Properly engineered and designed, air springs are doing for suspensions what EFI engine-management systems and overdrive trannies have done for the drivetrain. Yes, there's a learning curve; yes, the sophisticated high-end systems are pricey-but they're yet another step forward in making it possible to truly build a car that you can race on Sunday, drive to work on Monday, and cruise the parking lot on Friday night.

Read more: http://www.hotrod.com/howto/hrdp_0701_air_suspension/viewall.html#ixzz24ym4vZns

Seems the right air shock could work. Not sure that exists though.

 

[scrappydoo]

The change in wheel rate is minor, so I wouldn't worry about it too much.
Adding air bags isn't necessary. Besides you're going from a 4 leaf to a 6 leaf spring.

If you can't get 6 leaf springs easily then get a reputable spring resetter company to add an extra leaf to your 4 leaf spring.
You'll also need a decent set of dampers to keep the stronger springs under control.
I use Koni's on all my cars, expensive but worth it imo.

 

[Idaho]

Sounds like good old KISS type advice (keep it simple stupid)
Any particular model of Koni shock you like? I suppose I'll have to measure for the right length.

...and used 6 leaf springs from a ute and this was all the lowering it needed at the rear.

ute = sport utility vehicle?