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Originally posted by msavoia23:
imakehp, good thought, had not gone that far but may be worth a try if we can get a proper setup.

green1, we have not tried our tires/wheels on another car yet but may end up doing that this weekend. We had the shock off for a bit but don't recall moving/trying much while it was off, will look at that as well.

Robl384, we've been running the same wheels and spacers the last couple years but will absolutely look at those to make sure nothing changed, good thought.

NC3x58, we replaced the heim joints at the end of the 4 link bars that go to the housing and 4 link holes/brackets on the chassis.

Bob, yes we did buy a new yoke earlier in the year. Forgot to list that but was one of the first things we tried.

If you can, double check all of the measurements and adjustments and maybe give Travis a call to make sure it's all within spec.. If something wasn't put back to where it was, the rear end could be out of whack, causing your issue when going down track when the movement of the rear end matters. Up on jacks, it wouldn't be pushing one way or the other because the wheels are off the ground just free wheeling.

Nick, we have had the car there a couple times and Travis has measured and squared everything up right there with us and has not found anything out of line. He has been extremely helpful and has let us borrow parts to test which we are very thankful for, can't beat the customer support over there. Obviously we have not found the issue so I figured I'd post on here to get more ideas that we maybe haven't thought about yet.

I would go back to what was mentioned before, take shock or shocks off and run the suspension all the way through travel to make sure no binding and while at it unbolt driveshaft in each maximum travel distance and check engagement in trans. This could be don’t with shock on and just using weight or straps to pull suspension down and jack to lift it up. Also check for runout on driveshaft for it possibly being out of center for some odd reason.

I would put it up on jack stands and run it to see if you can tell what is vibrating. Can not tell, then remove back wheels and try it again. Then remove drive shaft until it stops.

Lots of good thought on here. My Undercover TD did this when we first ran it. (255" low run mono-shock car.) Turned out to be the rear tires. (Balance was fine...) Was un-drivable! You've tried different tires so not much help. Let us know when you figure it out.

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Checked all steering equipment/columns/etc

Did you include king pins and bushings, and wheel bearings?

That vibration looks and sounds intense! I'm thinking it must be caused by something with a lot of mass. Rear tire/wheel, bent axle/flange, bent wheel studs, wheel/tire eccentric for some reason, bent wheel, tire out of round, etc.

Hope you find it soon. I've chased a problem all season too. It's been a frustrating year!

Topfuel, yes king pins bushings bearings you name it, looked it over here and American did as well.

Matt, thanks, hope you get your situation figured out as well. Been a tough year.

I can’t help above what anyone else has posted but please come back and let us know when you do find out what it is. We’ All too invested now to not know. LOL

I uploaded 3 passes to look at. 2 shaking passes from this year, and a good pass from last year for comparison. I do not have video of any more recent passes, but as you can tell by looking at graphs I posted in the original post, the vibration has gotten worse as the year goes on.

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Pass 1: April 2019 at Stanton. 3rd pass of season, Super Comp style. Few notes: Yes I rolled through the tree a little (thumb and foot were out of coordination a bit). You can see the vibration driving down the track, and if you look closely near the finish line, I take BOTH hands off the steering wheel for a moment, and you see the steering wheel shimmy back and forth pretty quick.

Youtube link: Pass 1



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Pass 2: May 2019 at Martin. 5th pass of season. When I start the burnout, I hesitated while bringing the RPM up because it vibrated/shook and caught me off guard. The vibration becomes pretty noticeable on camera around 300 feet down track.

Youtube link: Pass 2



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Pass 3: Last year, June 2018 at Martin. This was a nice smooth pass for comparison to look at.

Youtube link: Pass 3

Have someone take a video from behind the car while you make a pass. Try to have them zoom as you go down the track. Then look at the video, preferably in slow motion to see if you can pinpoint anything that way. Not sure if you'll see something but you never know

The other option is to point your camera towards the rear of the car and see if you catch anything

The pass labeled "pass 2" at Martin earlier this year I did have a friend behind the car videoing and have watched it over and over on my phone and have not found anything.

Check axle flange runout with an indicator. While you have the rear tires off, secure the rotors with lug nuts and spacers. Have jack stands under the axle tubes and start it up and run it up till it vibrates. Even strap the axles to the jack stands if necessary. This should simulate going down the track. Was backlash in the ring and opinion checked in several spots ? Thinking bent spool possibly ! Pull drive shaft out of it and run it on the stands. Could converter lugs be bent ? If all else fails unbolt it too !

I didn't read all of the thread so sorry if this was already covered. A friend chased a vibration this season and figured out finally that it was in the transmission. By chance he had to change trans, and it was gone. Thinks it is a planitary set.

I'd be looking at the gear set/spool in the rear end. There is a lot of noise coming out of it when you are backing up which doesn't sound right to me. Good luck and keep us posted there is nothing worse when people are trying to help and your never find out what the solution was. Kevin

I am betting on cracked chassis.Something that opens under load and closes when not.

I know you said checked it.Did you try jacking it up in middle to flex as much as possible to simulate down track load? Just throwing it out.

Can you build two plates from axles to ground solid/ bolted down and start moving the front end left right looking for movement in the suspension/car. Appears it’s horizontal movement and not vertical movement?

Keith, those are some good thoughts we will look at. We did have a complete new rear in the car, replaced everything except the rear end housing itself.

Bucky, thanks for reaching out. We have had 3 different transmissions in the car. We were leaning that way initially but I believe we have ruled that out.

Undertaker, we have replaced the entire rear end minus the housing. I think the noise backing up is from the trans. I will definitely update the thread if and when we get it figured out.

Wideopen and stk758, good thoughts. We have had the car jacked up but not in the middle yet. Will give it a shot.

Kyle Curley ( Curley Race Cars ) built us 4 adjustable brackets/stands to accept any axle and any height. We use them for 4 link /torque bar and setting shocks in the shop. Kyle is on DRR but cannot remember his screen handle...

What about heims and 4 link/swing arm? Could be a cracked or stripped tube adapter.