Long post but out of ideas and need HELP with dragster vibration...

Since the 1st pass of this season back in April, we have been fighting a vibration in our dragster. Vibration happens during burnout and then also downtrack during the run. Virtually not raceable and couldn’t go ¼ mile if I wanted to (tried to at Norwalk running SC). Car does not skate around on track, drives straight but very violent vibration.

Best way to describe the vibration is a quick side to side shake that you can feel in your butt and body, but then also in your hands as you get faster down track. Car will also continue to vibrate once motor is clicked off and you are coasting at a high speed.

-245” single shock swingarm (Originally a hardtail 2003 Undercover that was backhalved in spring 2018 by American. Ran all of 2018 with no problems at all.)
-Steel block 12 degree 632 brand new by Sunset in Spring 2018
-Little Bubbas on beadlocks
-High 4.40/Low 4.50 car

So of course we looked at what we changed over the winter. We put the car in the shop at the end of 2018 and ONLY things we changed:
-New transmission CASE (Dedenbear > Reid). All internals were checked and remained the same when we put the Reid case together.
-New tires (new set of Little Bubbas)

We went to Stanton MI in April to test, and the very first pass of the year the car vibrated so hard down track everyone on the starting line could see it. We have been to 4 different tracks since, trying different things each time to no avail. Been to the track a total of 14 times this year and made 20 passes.

Things we have done that didn’t help (in order as I can remember):

-Removed and balanced the new Little Bubba tires
-New front tires, balanced as well
-No cracks in front wheels/spindles
-Checked all steering equipment/columns/etc
-New trans borrowed from a buddy
-New converter
-New rear tires/wheels from a buddies dragster (Hoosiers on beadlocks)
-Checked GRID to make sure ignition was working properly/not missing
-Had shock dyno’d and rebuilt by Penske
-Replaced balancer
-New Meziere Billet Flexplate
-Rear end was completely torn apart and rebuilt
-Checked for brakes dragging
-Spent hours going over chassis with light and magnifying glass looking for cracks
-Pulled motor and checked for cracks in motor plates/tabs
-Brand new driveshaft
-Tried without the wing for the hell of it
-Brought the entire car to American Race Cars and had them look over it. No issues found.
-Swapped MOTOR, put a smaller 555 in it. Same issue.
-Brand new center section and axles
-Built a brand new trans using the old Dedenbear case, same issue
-New front wheels
-Replaced brakes, went from dual to single

May have left some things out? But posted what I can think of now...

Racepak graphs with Lateral G’s showing are posted below.

We are way past stumped and looking for recommendations/thoughts. Thank you in advance.

Just throwing it out to see what sticks.
You said new axles.
Are these one piece axles or a full floater?
If full floater my question is..
Flange run out?

You also said it had no vibe issues in 2018.
Then you fixed it.
Now, I know you have been making yourself insane but the question that remains unanswered is
What changed?
Ask that over and over and over.
Something is not on your list that got changed.

This message has been edited. Last edited by: Dave Koehler,

The lateral g's are pretty aggressive. It has to be a handful. Is there any chance that the rear-end housing got manipulated and has somehow gained toe-in or out?

1 piece Strange axles. Correct, no issues in 2018. We have asked that question over and over. Lost in the final in our last race of 2018, parked it in the shop for the winter, bought new tires, put a new trans in it, and left it there until this spring. Literally nothing else changed which is why we focused so hard on tires or trans early in the year, but no luck..

This is a long shot. When the chassis was inspected, was the seat completely removed and the welds in that area inspected, on top of the lower rails? or the diagonals. The most critical area of stress is at the lower area directly in back of the seat.. Mine cracked and broke in that area. I spent a month of Sundays inspecting. Found nothing.I put a call into Frank Parks. Told me to pull the seat and look. sure enough ..Cracked. I see by the Laterals .
Violent.
When American had it did they string the car or check it for square? Just curious. Like Frank Parks explained to me. Dosent matter whats on the back Suspended or hard. Always keep an eye on this area.

This message has been edited. Last edited by: TD3550,

Mike, it is a handful in terms of vibration but still drives pretty straight. We did check housing and it was dead straight and axles slide in and out easily so I wouldn't think it is bent.

If you are shutting motor off down track and it’s still there then it isn’t motor or torque converter because they are no longer spinning. I would doubt its the transmission too.
I would try putting it on some good and sturdy jack stands and run it up slowly to see if you can feel it to verify it is in back of car then start looking there.

TD3550, yes I actually removed the seat at the track right after a pass because I thought maybe a weld broke and found no issues. Also removed it again later at home, still found no issues. Yes, when it was at American we were there when they did string it and measure it and it all came back perfectly square.

Green1, we were at US 131 earlier in the year and left the front on the ground and set the back up on a warm up stand and ran it up some RPM and did not see or feel any vibration sitting in the car. Had a few guys behind the car visually looking to see if they saw anything out of rotation or wobbly, nothing.

I can see its literally more than a handful to drive. Not knowing.

With the car up on jacks stands and idling in gear do the wheels wobble or out of round? Since you changed tires and driveshaft I would think it is not the issue but I would still like to check it.

Have you looked at the driveshaft or U-joints? ........Howie

Sorry....I missed the new driveshaft.....But still check the joints....

Howie, u joints came with the new driveshaft - no luck. Also replaced heim joints, forgot to mention that in original post.

Whew I know you said you changed tires and used someone else's tires but I am leaning that way. I've been down that road with a tire that was balanced but wouldn't quit shaking. This is good info either way.

Seems like it has to be something rotational....what about the driveshaft bottoming out in the transmission or the rear joint being centered in the rear yoke?

you have tried and changed all components,i wonder if there is some small piece being used in conjunction with major pieces that is causing the issue,ie wheel spacers or something else

What brand brakes..

quote:

-Replaced brakes, went from dual to single

Did the above include new discs?

Just an idea - do you have a chassis dyno in the area that can accommodate the dragster? National Speed shops usually are setup with it sunk in the floor. Testing it there - no body in place, you might either find it or discover that it's not in the drivetrain.

Hey Mike put the car on Jack stands. And run the suspension through its travel. Make sure drive shaft is not bottoming out at trans. Also make sure the yoke is not pulling out of trans. To far.