Caltrac’s and high rpm doesn’t mix

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kursplat said:
My "new" '74 Duster- or why I need a project like a hole in the head
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I'm just spitballin........but what I was wonderin is, if the sliders are somehow letting the springs extend, instead of lifting the body....and planting the rear axle. Maybe that the sliders are letting the springs "just straighten out" if you will. If that makes any sense. At any rate, "SOMETHING" is keeping the body from rising......and the axle from planting the tires. It's just not happening.
 
RustyRatRod said:
I'm just spitballin........but what I was wonderin is, if the sliders are somehow letting the springs extend, instead of lifting the body....and planting the rear axle. Maybe that the sliders are letting the springs "just straighten out" if you will. If that makes any sense. At any rate, "SOMETHING" is keeping the body from rising......and the axle from planting the tires. It's just not happening.
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the shackles do the same thing when they swing. the sliders are just smoother and eliminate the side to side lever affect of the shackles
 
kursplat said:
the shackles do the same thing when they swing. the sliders are just smoother and eliminate the side to side lever affect of the shackles
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I get that. But if you notice from the pictures, the sliders don't allow the springs to hang down as far as the shackles.......whether that has anything to do with it, I don't know.

I do know this. I KNOW there are LOTS of Mopar cars using the leaf spring rear suspension and running fast. There are also lots of Mopars using Caltracs and running fast........and planting the tires a LOT harder than this car. He's got "something" going on and I don't see a lot of other people coming in here trying to discuss it, so that's what I am doing. Throwing ideas out.
 
I’ve tuned Caltracs and it’s a *****. But once you figure out what your car wants they will work. I watched the video in slow mo a few times and it’s hard to tell but if I were tuning that car I would loosen up the front on rebound as much as I could, tighten up the compression some, and put more preload in to the Caltracs. I think the rear is still loading, and unloading the leafs. Loosen up the compression on the rear shocks and tighten the rebound. But that’s really a guess from a hard to see quick video.
 
Try the lower hole on the front spring mount bracket. It will lower the IC. The rear ride height will increase which might make the IC change a wash, but worth a shot. You may need lower ride height rear springs. I would also loosen the rear shock extension a lot. The car has no separation on leave. The front end doesn't appear to have much travel either. Needs 5" or more of front travel. Caltrac Abody cars have to be one of the most unforgiving suspensions ever. The 20" front spring segment makes the IC WAY TOO SHORT, which is the root cause of the issues people have. Nobody in their right mind would build a 20" ladder bar or have their 4 link intersect at 20" for the same reasons.
 
skrews said:
Try the lower hole on the front spring mount bracket. It will lower the IC. The rear ride height will increase which might make the IC change a wash, but worth a shot. You may need lower ride height rear springs. I would also loosen the rear shock extension a lot. The car has no separation on leave. The front end doesn't appear to have much travel either. Needs 5" or more of front travel. Caltrac Abody cars have to be one of the most unforgiving suspensions ever. The 20" front spring segment makes the IC WAY TOO SHORT, which is the root cause of the issues people have. Nobody in their right mind would build a 20" ladder bar or have their 4 link intersect at 20" for the same reasons.
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It's funny though, that 20" front segment works like a charm with an SS spring equipped car.
 
skrews said:
Try the lower hole on the front spring mount bracket. It will lower the IC. The rear ride height will increase which might make the IC change a wash, but worth a shot. You may need lower ride height rear springs. I would also loosen the rear shock extension a lot. The car has no separation on leave. The front end doesn't appear to have much travel either. Needs 5" or more of front travel. Caltrac Abody cars have to be one of the most unforgiving suspensions ever. The 20" front spring segment makes the IC WAY TOO SHORT, which is the root cause of the issues people have. Nobody in their right mind would build a 20" ladder bar or have their 4 link intersect at 20" for the same reasons.
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I agree with loosening the rebound but
Won’t that allow the tire to be hit harder?
 
RustyRatRod said:
I get that. But if you notice from the pictures, the sliders don't allow the springs to hang down as far as the shackles.......whether that has anything to do with it, I don't know.

I do know this. I KNOW there are LOTS of Mopar cars using the leaf spring rear suspension and running fast. There are also lots of Mopars using Caltracs and running fast........and planting the tires a LOT harder than this car. He's got "something" going on and I don't see a lot of other people coming in here trying to discuss it, so that's what I am doing. Throwing ideas out.
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I agree lots of people using the Caltrac
System and going fast
But not many people hit the tire with a lot rpm most people are using the foot brake
And if they are using a transbrake they are leaving at most 3500
I’m leaving at 5000rpm with not a ton of power
 
yellow rose said:
A ladder bar won’t fix it. A 32 inch IC that’s what, 12 inches up isn’t that much better than what you have.


If you can’t get what you have to work, get a 4 link.


FWIW, you need WAY more bump in the shocks, probably need to slow the extension way down, put some air in the tires and see if you can use the shocks to control the hit AND keep the tire from bouncing back every time it gets hit.

What you are seeing is the tire getting hit, then bouncing back, then getting hit again and repeating.

Once you tame the back end down, you’ll probably need to go back up front and and tune it. Probably more travel, a bit slower to keep it from shocking the tires.
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My 68 fastback has the same set up on it , and it didnt do the bouncing thing, only had 10'' wide drag radials on , virtually no front end lift , it went straight and didnt bounce at all , altho it was slipping the tires. Knew a guy with ladder bars , his duster would run low 9`s w/ ladder bars , and threy didnt change the front spring segment length either----------??
 
famous bob said:
My 68 fastback has the same set up on it , and it didnt do the bouncing thing, only had 10'' wide drag radials on , virtually no front end lift , it went straight and didnt bounce at all , altho it was slipping the tires. Knew a guy with ladder bars , his duster would run low 9`s w/ ladder bars , and threy didnt change the front spring segment length either----------??
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I’m not done trying to get it to work
But if anyone can point me to someone that is using the Caltracs that are leaving at or above 5000 rpm I’m very interested in watching their car leave
If I drop this two-step to say 3500 it leaves great .
I will post a video of a lower rpm launch
Trust me I want and need this to work
If you guys watch brad watt’s demon leave
You can see it has very little to no front travel and the car seems to separate as soon as he lets go of the transbrake .
His car is very fast but he is only leaving at 3500.
About the only thing I haven’t done yet is adjust the rebound on the soft side
And the reason I haven’t is because of how hard it is hitting the tire now
But this Friday I will loosen the rebound a ton and tighten the front and see what I end up with
 
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This is with a 3500 transbrake launch
Looking back doesn’t seem to be separating much even though it did work
 
Verify pinion angle looks to me that the axle is wrapping and unloading. Could have thrown off angle with your lowering blocks. I’m assuming you’ve mad several hits with various tire pressures with same results.
 
67/6barracuda said:
Verify pinion angle looks to me that the axle is wrapping and unloading. Could have thrown off angle with your lowering blocks. I’m assuming you’ve mad several hits with various tire pressures with same results.
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Yes,I’ve been from 12-16 lbs
14 seems to work the best
I do Need to look at the pinion angle
I haven’t look at it since I finished the car
A couple years ago
 
o1heavy said:
I agree lots of people using the Caltrac
System and going fast
But not many people hit the tire with a lot rpm most people are using the foot brake
And if they are using a transbrake they are leaving at most 3500
I’m leaving at 5000rpm with not a ton of power
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why the need for the rpm? Its very unlikely it will make the car any faster. Very unlikely.
I had a 9 sec(3350 pound) S/S spring car. 28 by 10 tire.
No clamps on the leafs, moved the RPM around on the 2 step until i found the sweet spot(4100) and the car would hook anywhere.
Off the foot or brake, the 60 foot and ET were virtually identical. Only issue i had was car occasionally got out of hand regards wheelstands.
Dont give up, your issues are fixable.
 
My Dart has the same set up only with Viking DA's, the fronts were sent to Afterworks and revalved for no prep surfaces. I had it out a couple weeks ago and it was doing the same thing although not as violent, probably because I was foot braking leaving at 2000. After I tightened the rebound two clicks on both ends of the car and it left clean. My buddy was in the water box behind me and he said the car just left, no squatting or raising. It went 1.40 60' on that pass, with some more tuning it should be in the .30's.
 
B3422w5 said:
why the need for the rpm? Its very unlikely it will make the car any faster. Very unlikely.
I had a 9 sec(3350 pound) S/S spring car. 28 by 10 tire.
No clamps on the leafs, moved the RPM around on the 2 step until i found the sweet spot(4100) and the car would hook anywhere.
Off the foot or brake, the 60 foot and ET were virtually identical. Only issue i had was car occasionally got out of hand regards wheelstands.
Dont give up, your issues are fixable.
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The car is actually faster when I “run at the converter “
But with the 5000 two step the car will cut a killer light
I use the car in a 7.0 index pretty much every weekend unless I break it
The class is setup on a 4ths pro tree
And if you can’t cut a .0teen light you will be a duck
 
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justinp61 said:
My Dart has the same set up only with Viking DA's, the fronts were sent to Afterworks and revalved for no prep surfaces. I had it out a couple weeks ago and it was doing the same thing although not as violent, probably because I was foot braking leaving at 2000. After I tightened the rebound two clicks on both ends of the car and it left clean. My buddy was in the water box behind me and he said the car just left, no squatting or raising. It went 1.40 60' on that pass, with some more tuning it should be in the .30's.
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Two clicks from what setting? How close are you to being at max rebound on that shock?
 
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