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 Post subject: car leaving right
 Post Posted: Sun May 29, 2011 9:54 pm 
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i have a 70 chevelle i race in nhra s/st that intermittantly goes to the right. it seems to do this only when using the throttle stop which is set to come on at .1 sec out. the car is back halved with ladder bars ,14.5 32 tires, bbc glide. best of 9.40 off the stop. the housing is sqare, all the mounts are in the same plane, no bind or flex. ive preloaded the r rear 2 flats, tried less rebound damping on the r rear and more compression.the frequency is less but it still happens occasionally. my guess is the stop coming on where it does unloads the tire. has anyone tried to move the housing forward slightly on the pass. side by turning the rod end in a half to full turn? ideas?


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 Post subject: Re: car leaving right
 Post Posted: Sun May 29, 2011 11:23 pm 
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Have you scaled the car to see what the coner weights are?

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 Post subject: Re: car leaving right
 Post Posted: Mon May 30, 2011 7:38 am 
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A few things come to mind for me. But as of right now I don't have enough info to give anything except a few things to look at.

Could be a bad case of bump steer and coming down on the right tire first making it dart some times. But I doubt this is the case. It would be more consistent I would think.

or,... You need more preload. When your off enough to make this kind off difference you need more the 2 flats. Give it 2 more flats, if you make a move to the left then you know you went too far. This is what I think you need more then any think with what you've told us. You may want to increase your delay until after your wheels are back on the ground. This may be upsetting the chassis as well.

A few questions for you.

What are the 4 corner weights?
How high are you pulling the wheels?
How far are you carrying them?
What method did you use to see if the rear end is square with the chassis?

Don

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 Post subject: Re: car leaving right
 Post Posted: Mon May 30, 2011 8:07 am 
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want-a-be wrote:
You may want to increase your delay until after your wheels are back on the ground. This may be upsetting the chassis as well.


Don


I was thinking this same thing. If he increases the time the engine is on until the fronts touch back down it's not likely be as violent a chassis change as there is now.


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 Post subject: Re: car leaving right
 Post Posted: Mon May 30, 2011 9:49 am 
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how long is it one the stop??? If the chassis does not have time to relax and then come off the stop you may be upsetting the separation of the chassis...
Most throttle stops come on just after the release of the brake so they get a "lite" then on for a bit then off...

How old are the tires and if it's hard on one tire it may be shot..Ever swap them from side to side???

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 Post subject: Re: car leaving right
 Post Posted: Tue May 31, 2011 10:44 pm 
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first of all thanks foir the responses.i havent scaled the car but i plan to. of all the chassis and alignment tools i have i still havent bought scales.the housing was squared by using a centerline from the front and rear suspension brackets.all the brackets were also checked to make sure they formed a 90 deg line in reference to the centerline.the mounts and brackets were also checked for level and in the same plane as each other. all within .060.the springs have the same free length, the spring platforms are set the same length .the preload was set on a level surface with my weight in the car and right now is 2 flats past a free bolt.when the car leaves the stop comes on immediatly[.1sec after the trans break is released]it usually pulls the tires a few inches before the stop comes on and kills it. also, the car goes right as soon as the brake is released so its not a bump steer problem although thats been checked as well. obviously i need more force on the right rear but i dont want to upset the car when the brakes come on with excessive preload.i know it needs scaled but what do you think about moving the right side of the housing forward by a half torn to help counteract the tenancy?


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 Post subject: Re: car leaving right
 Post Posted: Wed Jun 01, 2011 4:56 am 
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If you move the rear you won't like what happens when you hit the brakes on the top end.. O:)

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 Post subject: Re: car leaving right
 Post Posted: Wed Jun 01, 2011 7:50 am 
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I agree with the others that you need to get a video of what the car is doing. I had a chassis guy tell me that buying a good camcorder with frame-by-frame playback capability was one of the best chassis tuning tools he had purchased. The fact that it does it intermittently would keep me from changing the set up much. I have had a similar problem with my car making a left and had made some ridiculous chassis adjustments trying to correct it. I had something like 150 lbs more on the LR than the RR. When the clutch started flaking I went back and looked at my logfiles and found it had been doing some strange stuff on the launch. After I put the new clutch in it I put the base set up back in the chassis and it started leaving perfect. The point I want to make here is unloading the chassis during the launch will make a car do some weird things so it could be the throttle stop is unloading it. The stop coming on .1 second into the run has to be while the car is on the back wheels pretty hard.

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 Post subject: Re: car leaving right
 Post Posted: Sun Jun 05, 2011 9:51 am 
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heres the results of scaling the car lf 826 rf 802 lr 805 rr 721. checked suspension for bindind and made sure the shocks were moving freely. bouncing the car front and rear changes the weights as much as 20 lbs after it settles. loooks like the right rear was way light.after half a turn of preload i got an average of lf 869 rf 758 lr 758 rr 773. did i go a little far? i thought the right rear should have a little more weight. to bad the car isnt a light tube chassis car or i would move weight around instead of adding preload


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 Post subject: Re: car leaving right
 Post Posted: Sun Jun 05, 2011 10:51 am 
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Last time my Camaro was scaled it was 600lr and 613rr and it ran straight that way. We didn't touch it.

From what I understand, the rr should have a little more than the lr.

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 Post subject: Re: car leaving right
 Post Posted: Wed Jun 22, 2011 6:35 pm 
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the car is leaving fine after the ladder bar preload adjustment. what i hate is the way it leans with the extra preload. would i be better off to move some weight around in the car until i have the rear weight equalized with driver and return the preload to zero?


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 Post subject: Re: car leaving right
 Post Posted: Wed Jun 22, 2011 7:02 pm 
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Did you scale the car to see how much more is in the right rear now?

You do realize that you can jack the left front with spring spacers to put more weight on the right rear don't you? Hell, I've even changed air pressure as little as 2 lbs on one front tire to put some bite in the opposite side rear tire and it works too!

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 Post subject: Re: car leaving right
 Post Posted: Sat Jun 25, 2011 7:27 pm 
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the scaling results are a few posts back in this topic. i know you can add some length to the right font spring or left rear i just thought it might work better moving the weight . i have ballast tubes with lead shot in the rear that are centered. i could offset them to the right with a little work. or i could add a spacer under the right front


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 Post subject: Re: car leaving right
 Post Posted: Sat Jun 25, 2011 7:40 pm 
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When you use the 4 link to apply preload you then have a different geometry 4 link on one side of the car compared to the other.


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 Post subject: Re: car leaving right
 Post Posted: Sat Jun 25, 2011 8:13 pm 
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gnicholson wrote:
the scaling results are a few posts back in this topic. i know you can add some length to the right font spring or left rear i just thought it might work better moving the weight . i have ballast tubes with lead shot in the rear that are centered. i could offset them to the right with a little work. or i could add a spacer under the right front


If you want to make it stop turning right then you need weight on the right rear, which means that if you're going to mess with the front then stiffening the LEFT front spring will put weight on the RIGHT rear tire. ;-)

If the front springs are stockers or a reasonable facsimile thereof you could just use those twist in coil spring blocks to jack the left front. If one doesn't do it then put a second one in. This is a cheap and easy fix just to prove to yourself that it will work. http://www.summitracing.com/search/Bran ... toview=SKU


Moving weight around is an option but if using the above spring boosters will work and make the car sit closer to level then why bother.

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