Car Bounces after 60 ft. What is causing this??

-
SpareParts said:
IMO you have some other problems going on. Look around the front end for a bind. the car dumps to one side almost instantly, bumper doesn't come close to staying level.
Click to expand...
Everything in the front suspension/steering is new including the gearbox. Bushings are poly with lots of grease. Torsion bars are cranked up pretty tight though, and I think they need to come back down.
 
Darter6 said:
I had a 63 Fury drag car that was green,got the nickname Frog because it would hop like that. Went to taller front tires and loosened the T-bars(Big block with slant 6 bars) solved my problem. Maybe? just a thought..
Click to expand...
Sounds like a good idea. I thought it would be better to have the car level after getting taller back tires, but cranking up on the t bars looks like it was not the way to do that....Will loosen the t bars.
 
The rear tires are acting like springs of their own....the taller tire has affected your spring rate. A couple of things to help you - add more air to stiffen your tire "spring", shift some weight or add ballast to the rear.
 
i don't run leafs but from the video it looks like his shock are at full extension before the car even leaves and when the weight comes up in the front it is not rocking back because it has no where to go. Thus the tire is trying to pick up the car from a bad leverage point because of the poor transfer of mass to help it plant the tires and move forward not up. This equates to loss of power, tire slip, and your tires loading and unloading. My unprofessional opinion is it is all in the leafs, pinion angle, and shock on the rear. The tires and their pressure will have littler to do with your issue... to much air tires spin... to little air you get great first bite until the unload.
 
Launching at a lower rpm will only make it hit harder as the lower rpm you launch at the higher the converter will flash hitting the tires harder making things worse, My suggestion from what I see going on is the front of the car is way to tight and needs to be loosened up and maybe remove the upper control arm limiter snubbers so there is some upward travel then go to the rear and tighten up the rear shocks lower the tire pressure to 6.5 lbs. depending on your converter stall if you have a trans brake I would launch it around 3400 rpm and the car should hook and leave with the wheels in the air, If it's still spinning the tires as bad as it is then I'd look at some new slicks ! I know how to make a car leave give it a try I'm sure that should put you in the right direction good luck . Nice car by the way !
 
Steve, I agree with your front end assessment, but even if his "tail end" is light, the 6.5lbs kinda makes me cringe? Not sure of the track conditions in the vid, but the car looks to wash out a little down track. I don't want to see him put her in the fence on the big end...

Maybe I missed some info, Calvert shocks here with bars? or only the shocks with stock springs?
 
Some 90/10 front shocks would also be a good idea and hold the car in the burnout box a bit longer as the tires hardly had any smoke coming off them, Tires look wore out to me 6.5 to 7 lbs is fine it doesn't get squirly, The track doesn't look very good either .
 
my 2cents from what others have said. I have to agree that this is in the front, no weight transfer. lower it down like was mentioned to the bump stops, also loosen the front shocks. put them on 90/10 or the 3/4 the way loose if adjustable. 10lbs (your hotrod is no lite weight) in your slicks is as little as you should go, it's drifting around down track meaning there isn't enough air.
 
I don't think the front end needs to be loosened. I think when he is coming up on the foot break the front end has already lost its travel because he has extended to much. I bet if he took his brake distribution valve off and put a proportioning valve on, moved his brake bias to the bigger rear tires say 70 /30 to keep the front settled more off the foot break he could rotate his weight better. At the end of the day until the car can keep the rear tire loaded it will keep doing what its doing. In my novice opinion the shock and leafs in the rear are the issue not the front.
 
The front end is what I was referring to before I saw the video. Valiant Steve is on the right track. Check the total front end travel and free up the rebound (extension). Lower the T bars back down. also come back up 3 or 4 pounds in rear tires. If you look in the video it is the tire that is bouncing, so tightening up the rear shocks will not effect it. most of these problems all start at the front end.:thumleft: Hope this helps.
 
I have seen this same problem. If you look at the rear tire on the initial hit, it is compressing the sidewall to much. So what happens after the initial hit, is the tire rebounds and unloads the rear suspension. I would go up in air pressure. Also you may want to consider adding a inner tube if not using one already. The sidewall is basically too soft. On my friends 93 vert with a 26x8.5 Hoosier tire we run 14psi with a tube. That car at 3340lbs race weight will 60 foot in the low 1.30's and have had a best of 1.28 on the 60ft with this set up. When we looked at the video on his car with 12 psi, you could see the rim mash the sidewall almost all the way down to the track on the initial hit. Going to about 14 psi really solved the load/unload of the rear suspension. You may have to play around with air pressure to find the sweet spot for your combo. Also verify pinion angle, and you have to know that your instant center is set correctly before you get too caught up in other chassis adjustments.
 
This is a 10.00 car With Caltracs , You need front suspension travel and more air in the rear tires . these 9X30 had 17 psi.



[ame]http://youtu.be/ssRAHemsB6U[/ame]
 
I agree that the front end needs more travel.......but what i saw, in the first video is that the car is trying to "roll over". What i mean, is that the Left front lifts and so is the Left rear.

In my mind, that means that the Right rear spring and Shock need to be stiffer. this would stop or control better the squat that is happening on the Rear passenger side. That in turn, make the front lift straight or straighter then it does.

Probably help out the wash out happening down track.

I agree on more tire pressure as well.

I'm no chassis guy! just what i see and understand.
 
rockinrobin I run a Phoenix 29.5x11.5 w tire and run 13.25 lbs of air in them also sitiffen your rear shocks all the way tight. Lower your front end to normal ride height. I don't know about running 6.5lbs.
 

Attachments

  • IMG_20140607_191237_116.jpg
    30 KB · Views: 225
looking way back when I was foot braking with leaf springs I couldn't bring the rpm's up very high as it preloaded the suspension..... always had to bring it up off idle and stomp to get up on the tire. Even if you lower the front suspension, you can see when you bring up the rpms, the left front is already pulling up significantly. Do you have a side profile shot of the car? It actually appeared to me that the front suspension was down quite a bit as it looked as if there was quite a bit of + camber that is usually the result of someone lowering the t-bars.

.....If it's a "race car" you'd absolutely love ladder bars on that ride.
 
The majority of opinion seems to be that I need more front end travel, lower launch RPM and higher rear tire pressure.
1. front lowered to just barely on the bump stops. that brought it down about 2" from where it was. Gives it about 6" of travel. (.80 torsion bars)
2. Will try launching at much lower rpm.
3. Will try about 14 lbs in rear tires to start with.
Problem now is I can't get to the track until Dec. 6th :-(
 
Problem solved!
1. lowered front end all the way down to the bump stops.
2. Raised rear tire pressure to 13 lbs.
3. launch at lower rpm.
[ame]http://youtu.be/jZMMNR2xIg4[/ame]
Did ya hear me miss the 1st to 2nd shift on that run??
60 ft. are now a consistent 1.42-1.45
1/8th mile is consistent at 6.50 @ 107mph.
Now to get to a 1/4 mile track to see how that goes......
 
Looks so much better compared to the first video. Congrats! definitely moving in the right direction. :thumbrig:
 
looked good, but you're wearing you motor out doing a burn-out in 2nd gear at 6000rpm. put it in 2nd and hit the throttle then as soon as the slicks start spinning hit 3rd gear and go to no more them 5000rpm until you see the tires smoke. let off the brake and power out a little and go to the line. that's all you need to do.
 
BINGO... that video didn't look right. follow BOB's recommendation and your 60's should come down and that front will come up even more. Then you can start moving that launch RPM up till yours 60s start to fall off.

now lets get into engine specs and rear gear size. What are you shifting at and what RPM is it crossing the 1/4 stripe?
 
bOb shingler said:
looked good, but you're wearing you motor out doing a burn-out in 2nd gear at 6000rpm. put it in 2nd and hit the throttle then as soon as the slicks start spinning hit 3rd gear and go to no more them 5000rpm until you see the tires smoke. let off the brake and power out a little and go to the line. that's all you need to do.
Click to expand...
Bob;
Thanks for the burnout advice, will shift into 3rd next time and do a lost shorter burnout.
 
You must log in or register to reply here.
-

Back
Top