violent shake middle of pass

[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  

[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

[wideopen231]

I have had shake at 1000 feet  twice.One was number 5 and 6 hanging out block,could not see track onn that one. The other was tire/balance. I had goddyear replace them and the shake was gone.

 Think 140 bad try it little over 200. Even worst was when helmet rotated downward and over eyes at half track.Lights out at 195 will get your attention quick.

[JrFuel Hayden]

So how big was your helmet ?   Or did you not cinch it up ?   
Good thing you didn't crash your head/ brain would have been beat-up inside that extra roomy helmet.

Jon

[StigO]

Had some unpredictable tireshake before and after bend two set of axels i change to stiffer axels and problem disappeared.

[wideopen231]

So how big was your helmet ?   Or did you not cinch it up ?   
Good thing you didn't crash your head/ brain would have been beat-up inside that extra roomy helmet.

Jon

Cinched but was either worn inside,one size to big and angle of head made it show problem or my head not as big as everyone says it is. Now you all are LYAO

Not to mention crash would have scuffed my paint!!

[wideopen231]

well axles are one thing I went overkill it anything on .Parks even asked why the____ I bought 40 splines,have 3 complete  centers for them was answer.

[LaneM]

wow  all you guys just gave me awhole lot more to think about and look at..I did notice it has loosened one front motor plate bolt..I am fixing to pull the motor and trans out next week and recert a soon to expire flexplate and seatbelts so now I will for certain go over everything to make sure I have no cracks anywhere that thought now is going to cause me some loss of sleep til this is checked out Im still hoping for something tire related to cause the shake but this is a new ride with new bugs and I am new to passing the 10 second mark from my old door car to this..thanks for all the advice everyone.

[LaneM]

so now after reading your posts I had to go out and do a quick check for broken parts..well jon you called some issues..what I just found now without getting to  deep into it was a broken weld on cross brace at the nose(where my ballast sits) then both left and right rear engine frame weld tabs are snapped off which also as I can see from the paint marks has let the engine and tranny slide about 1/4 inch forward in the frame..well I certainly have some issues..like I had mentioned this is a new ride that I had gotton from the guy who built her who claimed to have only made 3 passes with her..his best claimed time was 7.29 in quarter in florida..I have made 9 passes but only stayed in throttle the full quarter most of the way 1 time which ran a 8.68  ....my history in car was 2 full quarters out of 6 passes for licensing which I just stayed in throttle hard til 1/8 so as to do the 9.99 for license(ran a 9.40 and 9.20 something)then when I went back I did three full runs..first I had bad shake(oh I had shake durning license full passes also)so I got out of it at 1/8th..2nd pass had a car next to me so I ran him down..it was ok but my attention was on him not the car..3rd pass was solo again and at 1/8 so violent it deployed chute so I of course was out of it then..so..this is a whole new experience..long side from story is the guy I got this from said he belieaves this motor is around 1200 horse..I don't know haven't seen dynos just know it pulls non stop..Im running 32 nossels with a 95 pill still rich and timing at 38.(Was told from mike at alky diggers these nossels were likely what I need here already went from 100 pill to 95..was running 35 nossels and 110 pill with 36 timing..so long and short of this is with this motor(548,dragon slayer crank,jw 14.5 pistons,hellfire rings,dart pro 1 345s milled to 380s,neil chance 5500 stall..running 390gears)came from florida to salt lake city..is this set up going to need awhole lot more support like I am just starting my list of broken parts..lol..wondering what I need to do on the frame and mounts this winter wondering if the rear engine frame tabs were just crappy weld from start and they were easily broke which now in turns lets everything bounce around and cause other things now to start to break. love the ideas,thanks again

[JrFuel Hayden]

Well Lane I'm glad you looked for and found some broken stuff. Now the question is what has caused the motor to come loose in the chassis. Maybe just not tighten the bolt enough when installed, but I suspect something else.  Now that you have moved to Salt Lake City, you might want to call Neil & Parks Racecars, in KS, Frank and Scott Parks started in SLC, 785-654-3440. I'm sure they could give you some advice and a contact in SLC to help you get your chassis right.
Now about your racecar set-up, one of the biggest things to keep in mind, is if you raced your car in FL [ about sea level] and then ran the same tune-up in Salt Lake [ 4400' above sea level]. There for allot less air at that elevation, so she'll be rich. BTW, you changing your main pill from .100 to .095 just made it richer. THe pill controls the fuel going back to the tank, ie .095 = more fuel into the motor. If you want more advice on your fuel tune-up you could call Don Enriquez at Hilborn, 949-360-0909, he can help you no matter what fuel system you are running. You could also call Spud Miller at FIE, too.
 We have raced there twice, 2013, 2014 [runner-up] in the JrFuel Heritage, and I put one size smaller nozzles [ #12 from #14 Hilborn], changed the powerglide 1'st gear from 1.68 to 1.76, and the 11" wide wheels instead of the 12", moved the timing to 42° from 32° and maybe the biggest change, a much looser converter. Because of the 6600 DA any motor will make less HP, so that's why the changes I just listed, like 10 mph slower thru the lights than Bakersfield. I would also like to try a 5.14, or 5.34 rear gears too   [instead of my 4.88], because I'm down 300 rpm thru the lights. I'm not sure how much looser the converter is because I never ran the SLC converter at any other track, but my guess is 500-600 rpm. I just called A-1, 360-574-9966, and told them I needed one for 4400 to 6600'. I think I'll go even looser for 2015 SLC. You see the converter is a big deal on performance, you want to have the converter let your motor run in the RPM range it's making good power.
We run a 406ci SBC on injected alky, so I don't know what converter advice to give you on your 548ci. But the best is to run your motor on a dyno so you could send the dyno sheet to A-1. If no dyno sheets, call Allan or Adam at A-1 anyway, see what they recommend, they may also be able to change your current converter. But if you plan on racing any other tracks you may want two converters, one for SLC, and another for the lower elevation tracks. If I could legally run your motor in our 1435 lb car [ with driver], we would be running 6.60-6.70's.
So, have fun, I know you'll have a blast once you get your combo straighten-out.
Say, how about coming to Bakersfield Oct 16-19 for the NHRA Museum Hot Rod Reunion, and look us up, an all orange JrFuel car.
Anyway all this you can work on AFTER you get your chassis program worked out. 
Feel free to call me anytime, 805-444-4489, SoCal
Jon Hansen

[LaneM]

thanks jon you have gave me more to think about I will have to give those guys a call and another builder..dave mott from Utah chassisperhaps he has advice.thanks a lot for your input it helps me with other things to look at..since I didn't build the car or know more history then what the former owner had gave me perhaps I just took on someone elses headache..well I will work on it I know it will be a fun ride when bugs are worked out.I'd love to go to Bakersfield but sadly I am dealing with some medical stuff on the 16th but I really hope to make it march.thanks again,Lane

[masracingtd1167]

Hi Lane You have gotten some very good suggestions and I have only one thing to add . It sounds like the car has done this from the very beginning and that makes me wonder if something happened on the trip from Florida to Utah ! If the car was not supported very well it could have cracked something on the ride out here . Don't get discouraged and just take your time and check everything 3 times . There are some really good chassis guy's on here who can help you . Bill