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This topic was originally posted in this forum: Modified Tech Talk
Author Topic:   Bouncing?
JAW
Member
posted April 25, 2004 09:01 AM     Click Here to See the Profile for JAW   Click Here to Email JAW     
We have a new Bob Pierce car 4bar Zlink,real nice by the way,but are problem is when the driver is going down the straights the car in the back is bouncing.
Car must weigh 2700lbs
LF 800 RF 950
LR 225 RR 250
Yes I am trying to get ahold of Bob but any help would be great.
Thanks


Xtreme12x
Member
posted April 25, 2004 12:48 PM     Click Here to See the Profile for Xtreme12x   Click Here to Email Xtreme12x     
too much pullbar angle.....


JAW
Member
posted April 25, 2004 01:12 PM     Click Here to See the Profile for JAW   Click Here to Email JAW     
? Too much angle will make the back bounce?
Can you explain more?


Xtreme12x
Member
posted April 25, 2004 02:57 PM     Click Here to See the Profile for Xtreme12x   Click Here to Email Xtreme12x     
called wheel hop...
take angle out... it shocks the rearend and in turns it hops


Ego Racing
Member
posted April 25, 2004 03:30 PM     Click Here to See the Profile for Ego Racing   Click Here to Email Ego Racing     
Are you runnign a top 90/10 shock?


JAW
Member
posted April 25, 2004 03:58 PM     Click Here to See the Profile for JAW   Click Here to Email JAW     
Yes 90/10 on top with quickcar biscuit rod.


Elwood
Member
posted April 26, 2004 09:03 AM     Click Here to See the Profile for Elwood   Click Here to Email Elwood     
too much preload has it hookin up too quick and too much. I had the same problem cept mine was at the end of the straight. Take out angle and soften pull bar pre load. Do angle first then if that dont help it 100% then go to preload. I got rid of my quick pull bar acted like a solid rod too much for me, I could never get it right.


NJantz
Member
posted April 26, 2004 09:40 AM     Click Here to See the Profile for NJantz     
Is the axle housing hitting the frame rail?


Road52
Member
posted April 26, 2004 10:21 AM     Click Here to See the Profile for Road52   Click Here to Email Road52     
Have the Qwikcar bisquit rod as well and I haven't satisfied myself yet on the proper pre-load on it. With the car up on blocks and ramps (tires on blocks, not the frame) high enough for me to slide under it, the bar feels like its loose where it connects to the front long tube rod. Took it out and went through every jam nut and connection and was satisfied that it was tight and right and put it back in car, adjusted pinion angle and it still feels shaky loose!! Is this normal? The old D&M rubber bar didn't feel like that...it was tight with load on car. Pullbar is 38" long with 20 degree downhill angle. 4 bar on both sides.


Dman
Member
posted April 26, 2004 11:46 AM     Click Here to See the Profile for Dman     
If your car is a short link 4 bar, 20 degrees is probably too much especially if you are running light rear % and excessive bar angles on the 4 bar.The car jumps up quickly when you get on the throttle and basically goes rigid on the bars and bounces on the rear tires.Give up some of the angles and calm the car down.You want the car to rise slowly when you get on the gas and not drop too quickly when you get off the throttle to enter.Smoother is faster. Dman


2nd2none
Member
posted April 26, 2004 09:10 PM     Click Here to See the Profile for 2nd2none   Click Here to Email 2nd2none     
I agree with Dman, the car is probably up on the bars which will make it bounce because there is no spring or shock controlling it......its a solid, rigid suspension.


Road52
Member
posted April 27, 2004 05:37 PM     Click Here to See the Profile for Road52   Click Here to Email Road52     
Thanks for the replys guys. First experience with a 4 bar. Both lower arms are 15" and level to negative 1 degree. Both uppers are 17" and run uphill at 15 degrees. 2500 with driver & 58% rear percentage(with about 23 gallons of alky). 53.5% left. Started at 90# LR bite. COE & Shocks are parallel in all aspects. What different angles/lengths should we try?
Thanks again,
RW


S_motors1
Member
posted April 27, 2004 05:39 PM     Click Here to See the Profile for S_motors1   Click Here to Email S_motors1     
is the track tacky or dry when this happens, if its tacky then, slowing the transfer of the rearend down is good, but if the track is dry and slick the faster it transfers the better to a certain extent. the faster it transfers on a dry slick track the straighter you can keep your car,and the straighter you keep your car the faster you get through the corner.


hamer36
Member
posted April 27, 2004 05:58 PM     Click Here to See the Profile for hamer36   Click Here to Email hamer36     
When you buy a new pierce you get a setup sheet. How are you so far from the base setup? You can't change pullbar angle because there is only 1 hole.


JAW
Member
posted April 27, 2004 08:42 PM     Click Here to See the Profile for JAW   Click Here to Email JAW     
Well there was a few things he did and I built a nother pull bar mount because some of the rules are different from IMCA,UMP,etc.
One of the big things is that we can't run the lift bar and we run with 10"rims and RC3 Hoosiers that are 12" across the face so this car is different to Bob and Brent R.
So any help from any one is good.
I did get a hold of Bob and like some of you said take angle out of the pull bar and we made ashock change as well.
Thanks from all the info and help.
JAW.


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