Drag Racing Discussions > Front Engine Dragsters

violent shake middle of pass

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LaneM:
so I am working out new ride bugs and my biggest one now is super violent shake at about 800 to  1000 feet out. Now I'm crusin around 140 here so it is a huge issue to deal with. Im looking for possible causes,I have thought perhaps to launch harder(currently 4500 on a 5400 convertor..548 injected alky) thinking maybe im breaking traction mid track so if I leave harder more power sooner..thought  and have messed with air pressures I am running hoosiers at 8.5 psi now..I am not spinning at launch so I could go up..other thoughts include balance of wheels which I am wanting to check this out I think this is a huge part..it was so violent last pass it deployed the chute for me..lol..well I am open for thoughts sad part is racing this season is done for me due to weather however I would like to test ideas in vegas this winter so let me know what you guys got,thanks a lot fellow rail heads :o 

BK:
 Always balance tires. M/T recommends bubble balance and it works fine. Put the tire on upside down to let the offset hang on the balancer. I think Harbor Freight has balancers. I've tried spinning them and all I did will chase them with a ton of weight.  If you have tubes in your tires make sure one is not in backwards. You may be able to spot it looking for a depression in the sidewall across from the stem.

dreracecar:
Has the problem--
existed from the beginning?
in both lanes?
with other tires?(might ask to borrow another set)
Anybody else expirenceing vibration at that point?

There is no possible way that (with your combo) should be getting into "shake" at that point of the track. Shake theory is the tire hooking and un-hooking trying to move weight(the car) and there are plenty of reasons it does that but usualy within the first 100' of the run, At the point on which you are having problems and that speed, you are way-way past that point

Check your tire balence, If you dont find anything wrong with that, inspect the tire

slingshot383:
Check or an out of round tire, bent axle housing, cracked weld to an upright in the front of the chassis.

JrFuel Hayden:
Lane, I agree with Bruce, the vibrations you are having at 800'-1000' is not tire shake. Tire shake can happen before the shift when the tires are hooking and unhooking. Of course check your tire balance, Hoosier, GoodYear balance tires with a bubble balancer, but I have had my local tire store use a slow speed spin balancer with good success. And we run 7.0's @ 188mph.
If you have a tire store spin balance your wheels and tires, check for any run-out, side to side, and up and down. You could have a bent wheel or a ply separation in your tire. I would also call Hoosier to ask them if they have any ideas about your problem, and to confirm you are running the right tire on your dragster. If you went shopping for a slick based on the dia and width you thought you needed, but you might have ended up with a tire designed for a door car that weighs twice your race car.
Raising your launch may help your ET, but not likely to change your 800' vibration. Also I don't know the size tires you are running, and the weight of your car, but we run 31x12x15 light weight GoodYear slicks on our JrFueler running 5 3/4 to 6 1/4 lbs of tire pressure on 12" wide wheels. With your 8 1/2 tire pressure I wonder if you are not getting any sidewall flex. I always check my computer for driveshaft/ tire speed, and I will lower the pressure if I'm looking for more tire speed [ so that it's not pulling the engine RPM down below it's HP power range], and increase pressure if I'm looking for more traction, ie less tire speed.
Now on a real important issue, if you are having "super violent shake" you need to go over every inch of your car. The vibration may have caused welds to crack, motor plate to crack, bellcrank support to break/crack, like we had before we installed more support from the rear motor plate and to rearend because we had flex in the chassis. We even installed a rear Powerglide mount because we found the motor/ trans was moving around. Now you may not need to do that because our real tire shake didn't start until we started making over 800 HP, and started running .100 to .103 sixty foot times. 
Now you may find some cracked/ broken chassis parts, which could be causing your vibrations or the vibrations could cause the chassis issues. SO again please check your complete race car. Tire shake from our rear slicks did cause the steering mounts to crack in the FRONT of the car, also caused our plastic windshield to split.

Good Luck finding your problem, and let us know what you find.
Feel free to call me anytime, 805-444-4489
Jon, Hayden Wheels, and pres of Jr Fuel Dragster Association

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