Tire Shake on a ProMod... Rear Spring Question - Yellow Bullet Forums

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Old 09-18-2008, 05:54 PM   #1
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Default Tire Shake on a ProMod... Rear Spring Question

One of the Nitrous ProMods I work on, It is a Jerry Bickle 2006 Chassis, 800" Reher Morrison BBC, 4 speed Liberty with a Clutch, 36" Goodyears, It has been shaking the tires like mad for quite a while. I had to go to their shop to weld up some cracks in a few tubes around the anti roll bar... Well I started looking at how they have their suspension set... They run 145 lbs. of left rear preload but the had the right rear spring seat run up 1-1.250 inch higher and have a 1 inch spacer.. That is correct, the Right rear spring was compressed 2-2.250 inches more than the left.....

With the right spring and shock carrying most of the weight and the suspension adjusted for the left tire to carry 145 lbs. cause the shake problem they are having??? I sure think so.

They were fighting the anti roll bar with the spring trying to get the chassis to set perfectly level and ended up doing the springs that way, I do not know how long they have been like that but it has been for awhile.

I got them started back in the right direction but when I left they only had 3/4 difference left in the springs seats with the right still being more compressed

Thanks for the input
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Old 09-18-2008, 07:19 PM   #2
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Id say it'd defenitely cause some whacko things to go on. They're basically fighting themselves...trying to put weight on the left rear, but then trying to compensate for it, by running the right rear spring up.
Running the spring up or down is NEVER the right way to adjust ride height. Doing this, you lose alot fo your travel in the shock. That could be the problem by itself. One shock has alot more travel than the other, becuase one spring is run way up on the coilover. So while the left side can go "X" inches in compression, the right side can only go "Y" inches in compression, causing the chassis to go crazy. Try getting the springs equal number of turns up off the bottom with the spanner nuts, and then go from there.

Also, where is the tire shake at? Hit of the throttle, or down track a bit? Any shock graphs?

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Old 09-18-2008, 07:37 PM   #3
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It has had tire shake at alot of different points of the run but mostly at the 1-2 gear change and at times after the 2-3 gear change....

The shocks were perfectly level, the chassis was perfectly level,

The left shock would separate just slightly at the hit and then would compress about 3/8 of an inch...the right would not extend or squat at the hit and would compress about 1/4 inch into the run..

This thing has electric shocks and it has the Bickle MONSTER anti roll bar.

I did not know if the anti roll bar would compensate enough for the spring seats being that weird
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Old 09-18-2008, 08:05 PM   #4
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The right rear spring is not compresing as much becuase it is whadded up already before anything at all happens. I would say it should be more of a difference from right to left in shock travel, when the spring is turned up 2" higher than the left side. That alone, tells me theres something going on.

Theres two ways to run a high horsepower car, with tire spin, which pretty much anything over about 1200 horse, your going to have tire spin, and trying to get the thing to dead hook. Being its a Pro Mod, your not going to get it to hook, you want a controlled spin. Therefore, you dont need alot of seperation of the rear shocks to "plant" the tires, because they are going to spin anyways.

What shocks are they running? Ness sweeps? Old style yellow Koni shock box, or the newer Koni/MSD shock box? What are they set at? Graphs would help ALOT, but we may be able to figure out something without them.

My first judgement call would be to get the springs on the same spot on the shock, and also take alittle pre-load out of it, just to see what happens. It seems like maybe with that much left side pre-load, plus weight of the driver and all that, you may be really upsetting the thing. Why does it need pre-load on the left rear corner anyways?

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Old 09-18-2008, 08:16 PM   #5
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Well, I dont have have the shock graphs... I dont wok on the suspension on the car, I just do the upgrades and repairs..

He has the New Koni MSD shocks with Gorilla Valving...

He has a set of Bickle/ Konis that you are not supposed to touch.

This car has been 1.000 60 and has run a best of 4.08 in the 1/8

I got them started on getting every thing reset with the springs being closer to even and will see if it changes anything... I was just wondering if anyone has ever had any experience with the springs being this drastically different, I have never been past 3/4 difference before that I know of...
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Old 09-18-2008, 08:31 PM   #6
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They should stay pretty darn close, if not the same. There's really no need to have one turned way up, unless your compensating for something else. And like I said, by doing this, your eliminating travel out of the shocks.
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Old 09-19-2008, 12:18 AM   #7
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does the car have any front stagger in it?
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Old 09-21-2008, 02:23 AM   #8
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Well he got the springs all straightened out... It did not change 1 single thing!! Still had all the same problems....

Took quite a bit of power out and managed a 1.003 60 and a 2.71 330.. but it did not run well past that!
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Old 09-21-2008, 02:24 AM   #9
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Quote:
Originally Posted by little art View Post
does the car have any front stagger in it?

They have very little stagger Less than a 1/4"
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Old 09-21-2008, 07:44 AM   #10
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i think it needs a stiffer spring. a lot of people think that moving the springup and down changes how the shock acts. well, it does but because its a biproduct of it. it only change the way the shocks because now it is a bind. the two things a spring are supposed to do are 1)maintain ride height by using the proper rate and 2) control oscillation of the shaft going in and out of the shock body. when you have the situation you are in now, it is doing a third thing and that is putting the shock in a bind. put a stiffer spring on it.
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Old 09-21-2008, 12:04 PM   #11
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Quote:
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i think it needs a stiffer spring. a lot of people think that moving the springup and down changes how the shock acts. well, it does but because its a biproduct of it. it only change the way the shocks because now it is a bind. the two things a spring are supposed to do are 1)maintain ride height by using the proper rate and 2) control oscillation of the shaft going in and out of the shock body. when you have the situation you are in now, it is doing a third thing and that is putting the shock in a bind. put a stiffer spring on it.
Well here would be the problem, that would be telling Jerry Bickle the way he sets up His ProMods is wrong....

The springs are now close to the same and the spring seats are only about 1" up and the ride height is where they want it to be.

They have about 300-400 more HP and it is taking quite a bit a work for them to get back to where they can go down the track every pass... they finally made a shake free pass but had to take out around 300 hp to do so.. hopefully they can work the power back up..
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Old 09-21-2008, 12:11 PM   #12
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tha reason i asked is having a lot of negative preload.i staggerad a front end on a promod the other week.we put 2 inches in it.we scaled the car and it went from 20 pounds to 120 pounds on the left rear.tommy mauney told the guy that it was common to have it do that.the car went stright and picked up 2 numbers in the 60 foot.i like to have the springs run up equal as possible.then use the spanner to help get the weights close so you dont have to put so much in the bar.most of the guys i know run around 80-85 pounds negative preload.

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Old 09-21-2008, 01:04 PM   #13
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well, i am not going to say that jerry bickel does not know how to set up a pro mod car but i will tell you that if you look statistically at most of the "fast" pro mod cars, it is going to be a mcamis or vanishing point car. when you look at most of the pro stockers the chassis builders of choice are bickel, jones, haas and ness. just making an observation.
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Old 09-21-2008, 01:34 PM   #14
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Quote:
Originally Posted by little art View Post
tha reason i asked is having a lot of negative preload.i staggerad a front end on a promod the other week.we put 2 inches in it.we scaled the car and it went from 20 pounds to 120 pounds on the left rear.tommy mauney told the guy that it was common to have it do that.the car went stright and picked up 2 numbers in the 60 foot.i like to have the springs run up equal as possible.then use the spanner to help get the weights close so you dont have to put so much in the bar.most of the guys i know run around 80-85 pounds negative preload.

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They were running with 120 left rear this weekend.... all 4 springs with very little stagger and the 4- link is 2 flats long on the right upper, so it dos not have alot of preload. Speculation from several people as to the reason it needs more left preload is because they are running liberty, and it does not have the cushion a lenco gives..

I think that are trying to run there clutch WAY to tight to keep from hurting the clutch... I told them to burn up some discs and see it will solve their problem...
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Old 09-21-2008, 01:39 PM   #15
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Quote:
Originally Posted by barszcz View Post
well, i am not going to say that jerry bickel does not know how to set up a pro mod car but i will tell you that if you look statistically at most of the "fast" pro mod cars, it is going to be a mcamis or vanishing point car. when you look at most of the pro stockers the chassis builders of choice are bickel, jones, haas and ness. just making an observation.
I know what you are saying, but the problem is I dont work on the Suspension, they set everything up the way Jerry Wants it done, although the spring stagger was their idea and they didnt tell jerry about it...

I want them to bolt on a set of Santhuffs but they wont do it, I have a car we can pull them off of and give it a try but Jerry doesnt like them... Why Jerry doesnt like them is probably because there is no way for him to make a killing off of them!

I was surprised that the extremely offset springs was not causing anything weird to happen...
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