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Lord of Lords
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Discussion Starter · #1 ·
Hello everybody, I've been lurking for a while here and this is my first post. I spent most of the day yesterday searching and reading but couldn't find anything definative. I know that ladder bars should be the easiest thing to tune but for some reason I still think I have something wrong. I know the car should be able to hold whatever I throw at it, but it hoooks leaves then blows the tires off as soon as the front tires come down. Here are the details of the car

1970 Chevelle
True 10.5" slick 29.5-10.5-15
3200lbs race weight with fuel and driver
52.5% nose weight
VariShock Double Adj on all 4 corners.

Corner weights
890 LF 810 RF
755 LR 755 RR

I used the adjuster in the bars to get the rear weights even, but can't get the quarter panels to be the right height, the LR is .65" lower than the RR

Shock Settings are
1up 4down front
3up 6down rear
Front and rear shocks are within the installed height alston calls for from eye to eye.

Ladder bar has 5 holes and is in the middle hole at ride height the bar is 1.2* downhill even on both sides.

Motor combo is Blown Injected SBC on a soft tune, should be able to hold, have gone best of 1.35 60' and 5.48 @ 132. Have been 165 in the 1/4 on same tune but no ET cuz of traction.

I took everything apart and tried to adjust everything to 'neutral' but not sure if I succeded. The driveshaft is pointing 1.8* downhill towards the rear end, the rear end is 2.2* pointing down. The car ran this weekend dead straight, and left evenly but it looked like the car was just getting pushed up in the air the front end came up and lifted the wheels about 10" or so, it didn't look like the car was really seperating in the rear, I can try to get videos up later in the week.

The problem when it does not hook is the car will launch, pick the wheels up, then as soon as the wheels touch down the rears break loose
hope I provided enough info, hopefully someone can provide some feedback.
 

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You need to post pictures of the car and ladder bar set up and the video or we will be shooting in the dark video should be of the left rear quarter panel and 45* angleseeing the front and rear tires going away from the camera


it sounds like you in to high a hole withthe front and you have set the preload wrong the adjuster on the ladder bar is not for static weight adjustment
 

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Lord of Lords
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Discussion Starter · #3 ·
What kind of pictures do you need? pictures sitting still, what pictures of the ladder bars also? just from under the car at ride height?

This is on slicks


This pic is when the car was on radials



This is thie most recent pic from this last weekend
 

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Are the weights you posted with the car sitting on level ground with the car level, anti roll disconnected if equipped with one, full of fuel, tires set and drivers weight in it with no preload in the chassis? No preload like the top bolt is out of the passenger side ladder bar.
 

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Lord of Lords
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Discussion Starter · #5 ·
The weights are with fuel and driver in the car at ride height. Tire pressures are all set, 40psi front 11psi rear. I do not have an anti roll bar, and never took the bolt out of the passenger side top. For the most part the car sits pretty level measuring at the rocker panel.


I also replied with some pictures earlier but it said something about having to have a moderator approve the post, not sure what that is all about.
 

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You should not need a anti roll bar with a ladder bar the rear end housing is the anti roll bar

This is what bothers meVVVVVVVVVVVV


"I used the adjuster in the bars to get the rear weights even, but can't get the quarter panels to be the right height, the LR is .65" lower than the RR "
 

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firm the shocks up an lower air in tires a 1/2 lb at a time till she hooks. If your not seperating in the rear it might not be the ladderbars.
 

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Set your ladder bars to the bottom hole in the front. You have enough power, what you are doing now does not lift enough front weight, hits the shock stops and blows the tires. My Chevelle only went up on the bars when I had a high to mid 12 sec SB in it. Adjust all the shocks in the middle to start. Be ready for it to launch. Go up one hole at a time till it stops hooking, back down one and fine tune with the shocks.
 

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Like Jeff I didn't like the, I adjusted the bars to get rear weight set. I like the car level at race weight with no preload unless the car needs it to go straight. Are the tires real good and is the track prepped well? The chassis has to consistantly hook initially for anything good to happen.
 

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EFI/N2O JUNKIE
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Move the front of those bars down.
Why do you want 4 degrees pinion down-angle?
Rotate your ladder bar adjusters and get the pinion pointed up. Try to get it around zero (with the driveshaft going 1.8 down that is what you will be left with). My car worked much better after I fixed that problem.
Does the car leave straight the way it is right now? If so, don't add any more preload to the bars, leave that alone.
If you adjust the ladder bar adjusters (provided you have them) make sure you re-center the rear in the car if you are using a diagonal link!
 

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MEASURING REAR

The last reply states to recenter rear with diag link. What is the best procedure, at race weight and measure from what point on rear to what piont of frame or is it done with mounts on rear and mounts on crossmenber, can the car be raised off ground and if so where is the best place for stands to be locates (tires off makes it much easier). would it make a difference if mounts on rear are at different locations (not even side to side ?) just curious about that last sentance?
 

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A diagnal link does not change when changing holes, if everything is square like it should be, you measure across like any square, front to rear on oposing sides it should be the same
 

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EFI/N2O JUNKIE
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Man, I know I am going to hear shit about this, but here is how I did it:

Put the car on level ground, use a straightedge and put it on the outer lip of the wheelwell on each side. Measure the distance from the rim to the straightedge and get the two sides the same.

Yeah, I know, the quarter panels are probably not perfect side to side....... It has worked for me, but I haven't been too fast either. Goes 100% straight @ 9.2 @ 146+.

The CORRECT way would be to measure off the frame somewhere. A lot of people will find the exact center of their car and put marks front to back so you only need to do it once.

That can be done on a lift, but good luck trying to do it on your back with the car on jack stands!

Take a look at the car from the back, you will see if the rear appears to be moved over towards one side or the other by where the rear tires sit inside the wheelwells.
 

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the rear being centered in the the car has nothing to do with the traction problem he is having. it sounds like he has a travel problem like over extending the rear shocks not sure what he has for the rear shock wise that is. on a ladder bar setup you should need no more then 1-2* pinion angle. there are alot of variables that still need to be aware of before you can decide what changes need to be done. front end travel, spring rate on the rear shocks, is front end tied down with limiters? it goes on and on. it sounds to me like he really needs to work on his rear shocks such as tighten up the compression
 

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Lord of Lords
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Discussion Starter · #16 ·
Mike centering your car that way is not correct, centering the tires to the body/frame could mean your ladder bars are not paralell in relation to eachother. The correct way to center the rear end is to mark the centerline of the ladder bar crossmenber, and measure form a point wide out on the rear end to that centerline mark (I usualy make a small dot to measure to) Having the rear end centered is going to allow the force on the bars to lift up evenly projected through the front mounting points on the ladder bars. I know this doesn't really affect the traction much, but it will affect how the car launches if the rear isn't centered properly. I used to center based on the distance from the tires to the wheel lip edge, but found that I was off by as much as 1/4"

As for springs I am running 9" 500lb front springs on a 4.25" travel shock, and 12" 165lb springs on a 5.15" travel rears. I do have a general idea of how the shocks work upon launch from watching some racepak data on a car that had shock sensors and video intergration to the software.

Now the general concensus seems to be lower the ladder bars to one hole down, that sounds great and all but without an explanation or understanding on 'why' I want to learn how changing holes relates to what the car does not just make wholesale changes without understanding their effects.
 

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you should never align any of the powertrain off body points only the factory frame points. but the real correct way is to align the driveshaft with the engine which we use 2 diferent ways of doing this we use a bar that goes thru the block mains straight into a bushing in the pinion's place or measure the distance between the u-joint its kinda hard to explain the u-joint but you turn the cross to look like a plus sign and measure on each side of the pinion the distance from the shaft to the cross . so lets say you have a larger gap on the driver side then the passngr you would move the rear end to the passngr side of the car or vise versa this will line up your driveline. if this is incorrect the more power you put to it the worst the effects are because the driveline is trying to align itself under power
 

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Man ask five people get five answers, LMAO If the crossmember is in it square and the brackets are on it right, then you should be able to measure in a criss-cross and come up with the same measurements this tells you the ladder bars are square I line my stuff up with plumb bobs on the rear axle and the lower ball joints thru the grease zert, once again in a criss cross. However I have had great luck lately with a lazer alignement machine to adjust setback and thrust, you can't line one up with a tube in a stock front end car because the drive trains are offset to start with. You line up the wheel base other wise it will drive you down the track sideways like a old Nova with a broken leaf spring pin dog tracking
 

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EFI/N2O JUNKIE
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See, I knew I was centering the rear incorrectly!
But, the car works perfectly and I won't be changing it.
I only mentioned that it needs to be checked because if you have ladder bars with adjusters in the lower bars and rotate them to get the pinion angle correct (4 degrees down is not correct) the body is going to move in relationship to the rear due to the diagonal link. Just how perfect does the centering have to be? How fast is the car in question?

Maybe I'm just a lucky SOB, but I've made 1000+ passes with my car in the last few years with no problems. Have left the line and drove past the 60ft clocks on the rear tires so obviously it is going straight.
 

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when you lower the front of the ladder bar it make the ladder bar apply the power slower and longer , versus raising it will make it hit harder and faster

i had ladder bars in my car for 10 years and when i went from a sbc bbc i lowered the bar to the bottom hole

i also had 7 inch travel shocks in the rear so when the shock seperated at the hit it would not top them out and upset the chassis

i also ran 95lb shocks with 3 inches of spring preload in the shock so it would hit the tire easier and had the rebound set tight so it would not fall off the tire to fast

also had the front end set very loose as to get as much weight transfer as i could as fast as i could to keep the rear planted
car would run 1.21 at bakersfield lacr and carlsbad

the seven inch travel shock theroy came from a conversation with jerry bickel when i attended his chassis class


i also ran my ladderbar set up with no preload and 2 degrees of down pinion

should also talk to mike at chassiworks i think you have their shocks ? he also has some good advice


i now have a 4 link set up so i am sure i will be fucking lost...


good to see you back out there i am hoping to be out at the wchra later this year..
 
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