Author Topic: I could use some tips in chassis tuning  (Read 9166 times)

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Offline Moparal

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I could use some tips in chassis tuning
« on: October 31, 2012, 08:50:06 PM »
A member here has been giving me some very good pointers for me to check out, I was having trouble around half track with the car swerving in the 1/8 mile around 100 mph or so and under throttle only.

This a tube chassis mild steel, ladder bar car with strange coilovers in the rear and coil over front with a rack n pinion

14x32  with a dana 456 spool, glide and a b1 511  Launches straight, but acts like a motorcycle on a grooved road out about 200 ft or more. Hooks very good.  Going to re scale the car again, and kinda needing to start from scratch lesson one  lol  Could use some pointers for me to check

I did measure from the chassis to the dana housing on both sides, it is square now.  I had a loose jam nut and got it taken care of.

Offline mopwr2004a

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Re: I could use some tips in chassis tuning
« Reply #1 on: October 31, 2012, 09:19:01 PM »
check for bumpsteer. take and put the car on jackstands under the frame rails. take the front coilovers off and work the front suspension up and down and see what all changes. check the toe, and camber.  if you can get a copy of Dave Morgan's chassis tuning book. his book has good info.

Offline Moparal

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Re: I could use some tips in chassis tuning
« Reply #2 on: October 31, 2012, 09:46:11 PM »
It's not the front end, I'm pretty sure it is correct. I also have heim joints and tower tubes for tie rods.  I have limiters on the front  end also.  The car is going straight and feels fine, I can feel the back end shifting, but you dont need to turn the steering wheel to correct it, just hang on.  Im thinking a shock or spring adjustment, since some weight has changed in areas.

Offline Quicktree

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Re: I could use some tips in chassis tuning
« Reply #3 on: October 31, 2012, 09:50:52 PM »
how much air pressure do you run?
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Offline hustlin hoosier

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Re: I could use some tips in chassis tuning
« Reply #4 on: October 31, 2012, 10:18:28 PM »
AS I POSTED EARLIER  I think Bigtime had it right, we had the same problem . A about 180 yards out or just short of 1/2 track our car went hard left. I t just took off on its own.   When we went to small tires I had raised the back of the car to make it sit level and did not think it would make much difference  ,  Wrong it was not drivable talked to our chassis guy and told him what I had done . He had me lower our lower 4 link bar 1 hole. We were perfect from then on.

Offline Josh

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Re: I could use some tips in chassis tuning
« Reply #5 on: October 31, 2012, 10:47:32 PM »
this is a dragster correct
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Offline Moparal

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Re: I could use some tips in chassis tuning
« Reply #6 on: October 31, 2012, 10:55:57 PM »
I've done 7psi  I usually run 9psi, but I tried 12 to see if maybe it would help the side walls.  H H I'm not sure if a 4 link and ladder bar settings are judge the same.  I didn't change tires either. The car was acting good, then I added a few 100 more hp. I also had some weight changes both in front and the drivers side.  So I am planning on scaling the car on all 4 corners to see if something big has changed.  I wont rule out lowering 1 hole on the ladder, but I need to check the basics before I go jumping on the throttle again to check.

I am curious about rollout tho.  But if 1 tire was that much bigger than the other, it would push one way I think.

The body shell is secured to the chassis in 4 points, then the front cap is a slide pipe into the chassis up front, and the fender bolt on top. and bottom

As I was laying up under the car, checking for loose bolts, bent bars n such. I put my hand on the body pushing on the side. I could see my shocks tilting a little lft and right. Only 4 mounting points for my ladder bars and a  diagonal between the 2. even though it's all mounted to the frame on those points, I see nothing to keep it completely straight with the body in back.  Bolts are tight, but maybe I need to pull them out to see if they are wearing out inside the heim.

The chassis seems stable from front to rearend, but what keeps it stable from side to side. A diagonal doesn't. , or does it?   It's easy enough to drive it in the 5's in the 1/8, im not sure about the 1/4.  This isn't a big swerving problem, I just want to find out what it is to get it right.

On the return road, you can let go of the wheel and it drives straight, it drives straight holding the rpms, just under full throttle and a short time I feel this. It seems to correct itself after it goes for a second or 2.

This is a dart tube chassis Josh

Offline Moparal

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Re: I could use some tips in chassis tuning
« Reply #7 on: October 31, 2012, 11:07:54 PM »
If there is anyone close to the northern part of Alabama/ten  state line willing to come check this out with  me, that understands how to check out this type of car, I am willing to spend some coin on the education.  With the way the car drives now, it can't require much, it's just knowing where to get to where the problem is. 

And if I can get it figured out with the help here online, its all good.  I never ask for something for nothing.

Offline Josh

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Re: I could use some tips in chassis tuning
« Reply #8 on: October 31, 2012, 11:13:10 PM »
When was the last time the car was scaled and when was the last time you checked front tire pressure
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Offline Moparal

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Re: I could use some tips in chassis tuning
« Reply #9 on: October 31, 2012, 11:21:49 PM »
Tire pressure was checked before, during and after the test breakin.  I have moroso frnt runners at 30 psi, new about 20 passes ago, new rears at the same time. Chassis hasn't been scaled in a few years.  My scales are in Louisiana, I was checking local to find some for this weekend, or make the 900 mile round trip to go get them from the other shop

Offline Josh

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Re: I could use some tips in chassis tuning
« Reply #10 on: October 31, 2012, 11:32:03 PM »
Start with the scales
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Offline Bigtime

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Re: I could use some tips in chassis tuning
« Reply #11 on: October 31, 2012, 11:45:23 PM »
scales are only good after you square the car, set the ride heights, set the suspension neutral, align the front end and know what your looking for.

Offline Monte Smith

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Re: I could use some tips in chassis tuning
« Reply #12 on: November 02, 2012, 01:55:17 PM »
How much toe in does it have?..........If the car has the front end, up, against the limiters, while under power, that is where you need to check the toe. Jack it up, until it hits the limiters and measure the toe

Monte

Offline Moparal

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Re: I could use some tips in chassis tuning
« Reply #13 on: November 02, 2012, 08:29:36 PM »
Monte, I'm re checking all that now, and I should have my scales tomorrow, but as of now, it is kinda looking like a week drivers rear spring or the shock.  I am checking caster, camber and toe in on the front also, along with the weight on all 4 corners.  Since it's winter time coming on, I am going to go all through the car.

Offline Moparal

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Re: I could use some tips in chassis tuning
« Reply #14 on: February 11, 2013, 07:46:58 PM »
I finally got to scale my car. 2622 with out me in it. Full of fuel and race ready.   2870 with me in it.  I had a time getting it dialed in, but for the most part it wasn't that far out.  I'm close to making a few passes when the track opens in March.   

1 loose jam nut, LR coil adjuster was loose and backed off a little, reset the tire pressures, and the difference from the last driver to me was 80 lbs, so my cross section was off some. As far as I could tell.  Balance also said 49% back and 51% front.  Cross section now says 48% and I got tired of up n down up n down. The shop floor is cold.